<p>The problem is that sea level is increasing faster than ever in last couple thousand years. It is currently rising at <a href="https://climate.nasa.gov/vital-signs/sea-level/" rel="noreferrer">3.2 mm/year according to satellite data</a>:</p>

<p><a href="https://i.sstatic.net/XufIa.png" rel="noreferrer"><img src="https://i.sstatic.net/XufIa.png" alt="enter image description here"></a></p>

<p>The curve you showed is not a straight line, it is rising at an increasing rate.</p>

<p>And the trend is expected to continue: The <a href="https://www.ipcc.ch/site/assets/uploads/sites/2/2018/11/SR15_Chapter3_Low_Res-1.pdf" rel="noreferrer">last IPCC report (2018)</a> on the subject say:</p>

<blockquote>
  <p>Projections vary in the range 0.26–0.77 m and 0.35–0.93 m for 1.5°C
  and 2°C respectively for the 17–84% confidence interval (0.20–0.99 m
  and 0.24–1.17 m for the 5–95% confidence interval).</p>
</blockquote>

<p>And projected sea level incrase for year 2100 are summarized in table 3.1:</p>

<p><a href="https://i.sstatic.net/EhMbd.png" rel="noreferrer"><img src="https://i.sstatic.net/EhMbd.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-01-28T03:37:16.800Z
2019-01-28T03:37:16.800Z
Pedro
<p>Sea level rise from thermal expansion is a very slow process: oceans are 3.7 km deep on average, and water has a very large <a href="https://en.wikipedia.org/wiki/Heat_capacity" rel="noreferrer">specific heat capacity</a>.</p>

<p>Here's a related diagram from the <a href="https://web.archive.org/web/20080510080424/https://www.ipcc.ch/pdf/climate-changes-2001/synthesis-syr/english/summary-policymakers.pdf" rel="noreferrer">IPCC Third Assessment Report</a> (page 17):
<a href="https://i.sstatic.net/TTwjJ.jpg" rel="noreferrer"><img src="https://i.sstatic.net/TTwjJ.jpg" alt="sea level rise after emissions are reduced"></a></p>

<p>Climate change didn't have much impact on the sea level, <em>yet</em>.</p>

CC BY-SA 4.0
2019-01-28T13:56:28.570Z
Downvoter: Constructive criticism is welcome!
Eric Duminil
CC BY-SA 4.0
2019-01-28T14:30:01.060Z
Quick question: in the chart, when $CO_2$ emissions drop to very low levels, why does $CO_2$ stabilization (presumably $CO_2$ levels) not decrease?
Underminer
CC BY-SA 4.0
2019-01-28T16:22:39.493Z
@Underminer For the same reason that if you stop putting water into the bath tub the water level in it doesn't go down. For the $\text{CO}_2$ level to go down you need a $\text{CO}_2$ sink.
Camilo Rada
CC BY-SA 4.0
2019-01-29T13:41:17.887Z
I'll not downvote, but cannot upvote because this answer is tangential to the question in this current form. Maybe you cam imporove it if you compare it with the most important factors in sea rising, like ice caps melting and explaining why natural processes takes ages, literally
jean
CC BY-SA 4.0
2019-01-29T14:28:32.603Z
@jean: There's a curve for "sea-level rise due to ice melting" on the diagram, and it appears to be really flat in the beginning. So it seems to fit well with the "not clear that something unusual is going on" argument in the original question. Also, the simple fact that oceans have a very large volume and can absorb a lot of heat is a good explanation why the process takes many centuries. If you want a more detailed explanation, the IPCC summary for policymakers is linked.
Eric Duminil
CC BY-SA 4.0
2019-01-29T15:25:40.423Z
@EricDuminil The link is a good start but as a good practice you can copy the main parts and elaborate about it. Also note while the papaer is still correct it dates back to 2001
jean
CC BY-SA 4.0
2019-01-29T15:32:32.887Z
@jean To each his own. I think the diagram is the most important part of the answer, along with the small explanation of ocean's heat capacity. Finally, laws of thermodynamics didn't change much since 2001. ;)
Eric Duminil
CC BY-SA 4.0
2019-01-29T16:01:19.697Z
@EricDuminil I'm just trying to help. While the dynamics don't chance much over two decades our understand of it increases. Anyway refer to it https://earthscience.stackexchange.com/help/how-to-answer
jean
CC BY-SA 4.0
2019-01-29T16:11:01.237Z
@jean: The most relevant part from the link is the diagram, which answers the question pretty well IMHO. The diagram is uploaded to imgur. The linked pdf is an archive on the [wayback machine](https://archive.org/web/) so it's probably not going anywhere soon. Which part of "How To Answer" do you think could help my answer, exactly?
Eric Duminil
CC BY-SA 4.0
2019-01-29T18:47:25.897Z
@immibis Yes, that happen and is known as $\text{CO}_2$ fertilization. But the effect is rather small compared with the main $\text{CO}_2$ sinks and sources.
Camilo Rada
CC BY-SA 4.0
2019-01-28T09:37:10.633Z
2019-01-28T10:26:33.240Z
2019-01-28T10:26:33.240Z
Eric Duminil
<p>I think <a href="https://xkcd.com/1732/" rel="noreferrer">this XKCD</a> says it all:</p>

<p><a href="https://i.sstatic.net/lWHMb.png" rel="noreferrer"><img src="https://i.sstatic.net/lWHMb.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-01-30T14:35:56.323Z
I really love this graph. I had seen it before and it really makes the point completely clear
arkaia
CC BY-SA 4.0
2019-01-30T15:23:01.927Z
@arkaia Yeah, it's so vivid.
Tim B
CC BY-SA 4.0
2019-01-30T20:37:53.037Z
That graph is very compelling!  But then I looked at it a second and third time and noticed something.  Is the solid part the part where we have recordings of temperatures, and the dashed part where we're making projections either forward or back in time?
bob
CC BY-SA 4.0
2019-01-31T09:33:28.903Z
@bob I believe so. Solid is where we have direct measurements. Dotted into the past is where we work out past temperatures based on other evidence (ice cores, tree rings, etc) and dotted into the future are estimates at the time this was made (2016)
Tim B
CC BY-SA 4.0
2019-01-31T16:06:42.980Z
That's a lot of extrapolation!  I imagine small changes to the past values could greatly change the overall story.
bob
CC BY-SA 4.0
2019-01-31T16:55:24.540Z
@bob The past is neither extrapolation nor projections. It's real figures derived from real data - just not by direct measurement of temperature as we don't have those records.
Tim B
CC BY-SA 4.0
2019-01-31T17:46:52.840Z
Fare enough, extrapolation is a bit of an overstatement with regard to the past data as I know we have a lot of different data points from the past.  But with regard to temperature it does still represent an extrapolation, just one that agrees with a number of other data sets.  Basically much of what we know from the far past has to be extrapolated, and we aim for agreement between the different extrapolated measurements (e.g. temperature, atmosphere, etc.).  Is that accurate?  Not a scientist, so I may be off base here.
bob
CC BY-SA 4.0
2019-01-31T19:18:35.483Z
@bob Extrapolated means taking a trend and extending it beyond the known points. i.e. if you have 1, 2, 3 then you can interpolate 1.5 as half way between 1 and 2 and extrapolate 4, 5 as coming after 3. Extrapolation can go wrong fast (interpolation can also go wrong, but generally not as badly). For historical data we neither interpolate nor extrapolate. We use indirect methods using temperature proxies and combine the results from those proxies. - https://www.theguardian.com/environment/2012/mar/07/past-climate-temperature-proxies
Tim B
CC BY-SA 4.0
2023-04-15T05:25:37.233Z
There have been documented 'Meltwater pulses' of rapid sea level rise in very short periods of time in the past. This chart conveniently ignores all three that have occurred since the chart begins, again rather conveniently, at the lowest sea levels in at least the last 4 million years.
Michael C
CC BY-SA 4.0
2023-04-15T05:29:19.327Z
@TimB Even the chart itself admits (in a note between 15,500 BCE and 16,000 BCE) that localized spikes are very likely and not reflected by the interpolated average presented. If you want folks to take you seriously, at least acknowledge what has been documented rather convincingly regarding at least three Meltwater pulse events since the last glacial maximum.
Michael C
CC BY-SA 4.0
2023-04-24T11:28:28.040Z
@MichaelC Yes, sea levels have risen before.

And when they did we didn't have millions of humans living in or depending on the soon-to-be-flooded land.

So maybe we should try not to raise them again, hmm?
Tim B
CC BY-SA 4.0
2023-04-25T05:06:22.520Z
@TimB "We" didn't raise them the last three Meltwater pulses. Natural processes that we still don't fully understand did. As I say in my answer, this isn't an "Earth" problem, it is a "human" problem. As I also say in my answer, the current trend needs to be considered and acted upon if it can be shown that we have the capability to slow the rate at which sea level is rising. Otherwise in a couple of centuries most coastal *cities* will be under water. There will still be plenty of arable land to live on, it will just require mass migrations (like the last ice age did).
Michael C
CC BY-SA 4.0
2019-01-30T14:29:37.980Z
2019-01-30T14:29:37.980Z
Tim B
<p>In addition to other answers...</p>

<p>This curve isn't a good comparison to the "natural" state of the Earth, because it starts in 1880. The <a href="https://en.wikipedia.org/wiki/Industrial_Revolution" rel="noreferrer">Industrial Revolution</a> had been in full swing for some time by then, and by that point it had been fuelled by coal for around a century. Every factory was powered by coal, every house was heated by coal or coal gas, and every light used coal gas.</p>

<p>Even then, the Earth's temperature and sea level graphs didn't change too dramatically. By the mid-20th century though, climate models fitted to past data <a href="https://en.wikipedia.org/wiki/Global_cooling" rel="noreferrer">were extrapolating to a mini Ice Age</a>. No big deal - the climate cycles like that, <a href="https://en.wikipedia.org/wiki/Milankovitch_cycles" rel="noreferrer">as the historical climate record shows</a>.</p>

<p>Except the climate didn't behave that way. Instead of following the natural cycles that have been observed over hundreds of years, the temperature escalated as the graph shows. So climate scientists had to improve their models to cover dramatic differences to "normal" climate behaviour, modelling climate events which normally would only be seen in a disaster <a href="https://www.skepticalscience.com/volcanoes-and-global-warming.htm" rel="noreferrer">such as massive volcanic eruptions</a>.</p>

<p>The result is that <a href="https://en.wikipedia.org/wiki/History_of_climate_change_science" rel="noreferrer">with all this work, they can predict</a> a lot of the causes and effects of rising global temperatures due to fossil fuel usage (amongst other things). Your friend needs to not just look at the graph of what the Earth is currently doing, but also consider what climate scientists even as far as the 1970s who looked at the historical record were expecting the Earth to do, which assumed not burning stuff.</p>

<p>Even then, the Earth will survive. The idea of "saving the Earth" is nonsense - the Earth will survive. Many species will go extinct, but that's happened a lot in the past too. Many major cities (and some entire countries) will be lost too, which is more of an issue for humans. The question is whether your friend is prepared to accept humans having control over whether this happens or not.</p>

CC BY-SA 4.0
2019-01-28T16:30:31.673Z
Not a bad answer but it could do with some actual data...
Jan Doggen
CC BY-SA 4.0
2019-01-28T16:45:15.337Z
"natural cycles that have been observed over hundreds of years"?
BЈовић
CC BY-SA 4.0
2019-01-28T16:45:28.297Z
@JanDoggen Added a few links.  I doubt they'd convince a hardcore climate-change denier, but then we already know that they hold that position through faith and not evidence.
Graham
CC BY-SA 4.0
2019-01-28T16:46:23.247Z
@BЈовић Added links.
Graham
CC BY-SA 4.0
2019-01-28T16:50:05.667Z
No, I was wondering, you said "over hundreds of years". I don't think that people for example measured temperatures for hundreds of years, and then wrote it somewhere. Or, am I wrong?
BЈовић
CC BY-SA 4.0
2019-01-28T17:02:28.170Z
@BЈовић I meant "cycles over hundred of years have been observed".  Although we've got directly-measured records starting in the 1850s, so that's 160 years of solid observations.  We've got a number of older records as well, from ships' captains and from various gentleman scientists, which are not global records but give us documentation for specific locations (or journeys). The oldest records apparently go back to the 1650s.  https://www.earthmagazine.org/article/earliest-instrumental-temperature-record-recovered
Graham
CC BY-SA 4.0
2019-01-30T14:30:23.413Z
The earth might *not* survive: https://en.wikipedia.org/wiki/Runaway_greenhouse_effect
Martin Schröder
CC BY-SA 4.0
2019-01-30T14:49:31.340Z
@MartinSchröder The Earth will still be there.  Creatures on it, less so... :)  Hansen's hypothesis isn't really fact-based anyway.  Yes, if we burned an order of magnitude more fuel than exists on Earth, then things would go wrong - but that's got a "magic happens" step of where this fuel comes from.  Assuming a Coal Fairy doesn't exist, the Earth isn't really going to turn into Venus.  TBH though, I think it'd stop being a good place to live well before that anyway, and "civilisation" would already have either collapsed or left the planet; either way the human problem goes away.
Graham
CC BY-SA 4.0
2019-01-30T16:23:02.377Z
[Figure 7: World Coal Consumption 1860-2007](https://www.resilience.org/stories/2009-04-20/peak-people-interrelationship-between-population-growth-and-energy-resources/)
Keith McClary
CC BY-SA 4.0
2023-04-15T05:47:29.943Z
@Graham The problem remains, though, that the margin of error for the accuracy of those measurements is often less than the total amount of the changes we're supposedly documenting between then and now. Sediment and fossil records, on the other hand, when combined with study of tectonic plate movements can give us a much better measure of maximum and minimum sea levels at various times over the past millions of years, even if they're less definitive as to exactly how long ago those minimums and maximums were.
Michael C
CC BY-SA 4.0
2023-04-23T09:30:28.253Z
No clear warming signal would have occurred from the Industrial Revolution - coal use was just a few nations back then, with coal still dug and shoveled by hand. We made more emissions in the past 5 years than the whole of the 1800's. Too much opinion, not enough answer.
Ken Fabian
CC BY-SA 4.0
2023-04-24T10:58:37.003Z
@KenFabian Which is why, as I said, "*Even then, the Earth's temperature and sea level graphs didn't change too dramatically.*"  Some effect, but not enough to notice.  It took a lot more coal consumption to clearly tip the scales.
Graham
CC BY-SA 4.0
2023-04-25T05:12:30.683Z
The predictions of another ice age 50-60 years ago were inaccurate due to flawed models, not due to emissions that exceeded estimates at that time. It was never a prediction of natural cycles, it was based on human activity. They overestimated the effect of particulates in the air preventing sunlight's energy to reach and heat the ground without taking into account the particulates themselves would absorb heat and have an effect on atmospheric temperatures.
Michael C
CC BY-SA 4.0
2023-04-25T05:23:49.810Z
We're still emerging from the last ice age that peaked 18,000 years ago and have not reached the typical maximum before the next ice age begins. Whatever anthropogenic effect there is will only accelerate the increase in temperature. Interglacial periods during Icehouse Earth climates (such as we've been for the past 2.5M years) have been  on a 41,000 year cycle based on the eccentricities of the Earth's tilt and orbit around the sun. Ice ages do not occur naturally more than once ever 41,000 years.
Michael C
CC BY-SA 4.0
2019-01-28T07:59:56.420Z
2019-01-28T16:44:30.180Z
2019-01-28T16:44:30.180Z
Graham
<p>I just took the sea level elevation rate (mm/yr) graph from <a href="https://earthscience.stackexchange.com/a/16079/981">Camilo Rada's answer</a> and added:</p>

<ul>
<li>A vertical axis at zero (when the curve is at the point, it means the sea level did not change that year).</li>
<li>Red and green colors showing the trend.</li>
</ul>

<p>Hopefully it will speak more to your friend.</p>

<p><a href="https://i.sstatic.net/RssLq.png" rel="noreferrer"><img src="https://i.sstatic.net/RssLq.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-01-31T02:53:30.730Z
@gansub: All of the explanation and the sources are in Camilo's answer at https://earthscience.stackexchange.com/a/16079/981 I did not want to duplicate his/her prose.
Nicolas Raoul
CC BY-SA 4.0
2019-01-31T02:17:12.723Z
2019-01-31T02:17:12.723Z
Nicolas Raoul
<p>Is rapid sea level rise unusual?</p>
<p>Yes.</p>
<p>Is It unprecedented?</p>
<p>No.</p>
<p>That then prompts the question: Is a less than 0.25 meter rise in sea level over the past 140 years or so considered &quot;rapid&quot; in terms of geological time?</p>
<p>There have been three documented <em>meltwater pulse</em> events during which sea level rose dramatically in relatively short periods of time following the most recent glacial period that reached maximum ice around 18,000 years ago.</p>
<p>From the Wikipedia article <a href="https://en.wikipedia.org/wiki/Past_sea_level" rel="nofollow noreferrer">'Past Sea level'</a>:</p>
<blockquote>
<p>Meltwater pulse 1A was a 13.5 m rise over about 290 years centered at 14,200 years ago and Meltwater pulse 1B was a 7.5 m rise over about 160 years centered at 11,000 years ago.</p>
</blockquote>
<p>and</p>
<blockquote>
<p>Meltwater pulse 1C was centered at 8,000 years ago and produced a rise of 6.5 m in less than 140 years, such that sea levels 5000 years ago were around 3m lower than present day, as evidenced in many locations by fossil beaches.</p>
</blockquote>
<p>Pulse 1A was approximately 27X the rate of change since 1880.<br />
Pulse 1B was approximately 26X the rate of change since 1880.<br />
Pulse 1C was approximately 26X the rate of change since 1880.</p>
<p>Compared to rates of change approximately six meters (6,000mm) per 140 years, is a rise of less than 0.25m (250mm) over 135 years considered &quot;rapid&quot;?</p>
<p>Maybe. Maybe not. After all, for the next 5,000 years following Pulse 1C sea level has only risen about 3 meters (3,000mm). This equates to a rate about 1/3 that observed over the past 140 years. So is 3X the rate of the last 5,000 years &quot;rapid&quot;? Or is it only &quot;slightly elevated&quot; when compared to past events which showed roughly 75X the average rate of change of the past 5,000 years?</p>
<p>Should this be cause for concern?</p>
<p>With regard to human culture, absolutely. If current trends continue, in a few centuries many coastal cities will be underwater. That's a serious problem that needs to be considered and acted upon if it can be shown that we have the capability to slow the rate at which sea level is rising.</p>
<p>Does this mean we should base our argument of what is &quot;normal&quot; on selective data that makes things look worse and more anomalous than they actually are?</p>
<p>No, doing that just makes us look like we're a bunch of Chicken Littles crying that the sky is falling when we choose the absolute minimum sea level for the past tens of millions of years, at the height of the most recent ice age 18,000 years ago, as our baseline for what is &quot;normal&quot;.</p>
<p>Just for some very long term context:</p>
<p><a href="https://news.mongabay.com/2008/03/cretaceous-sea-levels-were-550-feet-higher-than-today/" rel="nofollow noreferrer">80 million years ago</a> sea level was 170 meters (550 feet) higher than current levels.</p>
<p><a href="https://www.usgs.gov/media/images/coastline-eastern-us-changesslowly" rel="nofollow noreferrer">Three million years ago</a> sea level was 50 meters (165 feet) higher than current levels.</p>
<p><a href="https://www.e-education.psu.edu/earth107/node/1496" rel="nofollow noreferrer">125,000 years ago</a>, at the most recent warm peak, sea level was 8-10 meters (26-33 feet) higher than current levels.</p>
<p>At its lowest during the last ice age around 18,000 years ago, when roughly one-third of Earth's total land mass was covered in ice, sea level was 122 meters (400 feet) lower than current levels. As far as we can tell, that's the lowest sea level has been for at least 100 million years, and likely for much longer.</p>
<p>Anthropogenic climate change is accelerating the rate at which the Earth is warming. How much of the current rate of change is anthropogenic and how much is due to other factors, such as solar activity variation, irregularities in the Earth's orbit, and plate tectonics is arguable.</p>
<p>It is no less foolish to pretend that without anthropogenic factors the Earth would not be warming at all than it is to pretend none of our current warming is anthropogenic. In the long term the Earth will almost certainly continue a warming trend for the next several tens of thousands of years with or without humans living on its surface. After all, the Earth is still emerging from the last ice age 18,000 years ago.</p>
<p>Unfortunately for humans, our culture and societies also emerged during a time when the Earth has been considerably cooler than is historically typical and we're best adapted to live in a world that is cooler than has historically been the case over the past hundreds of thousands of years. That's not an Earth problem. That's a human problem.</p>

CC BY-SA 4.0
2023-04-15T06:55:13.953Z
2023-04-15T06:55:13.953Z
Michael C
<p>The problem is the <strong>increase</strong> in the <strong>rate</strong> of sea level rise. I pulled out some approximate numbers from the figure you presented:</p>

<p><a href="https://i.sstatic.net/AXhoH.png" rel="noreferrer"><img src="https://i.sstatic.net/AXhoH.png" alt="enter image description here"></a></p>

<p>Can you see now how the sea level is rising much faster today than a century ago?</p>

<p>Sea level rise, as well as climate change are normal things on Earth history. However, most times they happen at a very slow rate, allowing ecosystems and other processes to adapt to the change.</p>

<p>For example, if the climate changes over several hundreds of years, animals and even tree populations can "move" towards the side of their distribution where climate is still good for them. But if the climate changes in 50 years, all the trees can die before they had time to grow in the areas where they could thrive in the new climate.</p>

<p>In the case of sea level rise. The delta of a river for example, stays in equilibrium with the sea level because of the accumulation of sediments carried by the river. If the sea level rises slowly, the sediments can fill the delta and keep it roughly at sea level. But if the see level rises too quick for the sedimentation to keep up, it will be flooded by the sea, killing all the animals and people that live on such fertile environments.</p>

<p>Analogously, coastal infrastructure have a given lifetime. Let's say 50 years. If the sea level doesn't change much over that period (8.5 cm at the 1880-1940 rate), there is no problem. Once the infrastructure gets replaced, the new building will be set a bit higher.
However, in the next 50 years the sea level could rise 50 cm, or even more (it would be 19 cm if we assume the last rate from the figure won't increase any further), and that is a big deal. That could mean that much coastal infrastructure will be flooded, and maybe destroyed during storms.</p>

<p>In places like Bangladesh there are hundred of millions of people that could be displaced due to sea level rise if the rate keeps increasing. People that will also need to find a new home.</p>

<p>Coastal infrastructure loss, coastal erosion and immigration could be some of the worst expressions of <strong>fast</strong> sea level rise. </p>

<p><strong>ADDITION</strong></p>

<p>Given the interest risen by this question I'm adding here some data beyond what is presented by the OP, and brought to my attention by @Bobson in the comments. It comes from the paper <a href="https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2008GL033611" rel="noreferrer">Recent global sea level acceleration started over 200 years ago?</a> and shows a sea level reconstruction going back to 1700, and it shows also the changes in rate over that period. This is summarized in their figure 3:</p>

<p><a href="https://i.sstatic.net/NFD7a.png" rel="noreferrer"><img src="https://i.sstatic.net/NFD7a.png" alt="enter image description here"></a></p>

<p>Here you can clearly see how, with some ups and downs, the rate of sea level rise have been increasing over the last few centuries. And notably the current rate, about 20 years after the end of this plot is already out of the scale, and around <a href="https://climate.nasa.gov/vital-signs/sea-level/" rel="noreferrer">3.2 mm/year</a> as pointed also by other answers.</p>

<p>I would highlight the following from their abstract:</p>

<blockquote>
  <p>Sea level rose by 6 cm during the 19th century and 19 cm in the 20th
  century.Superimposed on the long-term acceleration are quasi-periodic
  fluctuations with a period of about 60 years. If the conditions that
  established the acceleration continue,then sea level will rise 34 cm
  over the 21st century. Longtime constants in oceanic heat content and
  increased ice sheet melting imply  that  the latest
  Intergovernmental Panel on Climate Change (IPCC) estimates of sea
  level are probably too low.</p>
</blockquote>

<p>Regarding to whether this is caused by humans or not, I rather stay out of that argument and point that our best science and models suggest that lowering <span class="math-container">$\text{CO}_2$</span> emissions can make a significant impact in slowing down sea level rise in the upcoming centuries, so <strong>we should ACT NOW, and stop arguing whether it was or not our fault in the first place</strong>.</p>

CC BY-SA 4.0
2019-01-28T00:54:25.963Z
Excellent answer which addresses the most frightening aspect of climate change: the rate.
Gimelist
CC BY-SA 4.0
2019-01-28T14:08:01.713Z
This goes a long way to pointing out the real risk of CC - not so much that the planet becomes uninhabitable, but that changes in its habitability profile wrecks our complex, globalised economic system. This will lead to refugees, famines, the breakdown of international co-operation and a return to a geo-politcal landscape that was last seen in the 1930s. And we all know what happened then.
Oscar Bravo
CC BY-SA 4.0
2019-01-28T15:38:54.020Z
To be clear the sea levels has risen before, 8000 years ago you could walk from France to England. The end of the last glacial advance caused the  Early Holocene Sea Level Rise (60meters) and a lot of settlements were destroyed by that rise. But since then sea level has been very stable, until now. We know what caused that change and its not what is causing the current one.
John
CC BY-SA 4.0
2019-01-28T16:22:27.660Z
this graph of the last 140 years cannot be used to prove anything, considering the earth is 4.5 billion years old, and the fact that the sea level has risen in the past much, much faster than even 4mm per year
user3163495
CC BY-SA 4.0
2019-01-28T16:25:34.790Z
@Gimelist the sea level has risen much, much faster in the past http://www.climatewarmingcentral.com/images/sea_level_rise.jpg
user3163495
CC BY-SA 4.0
2019-01-28T16:27:54.350Z
@user3163495 No doubt about that. The sea level have risen much faster in the past. But you still need to explain why it was stable for thousands of years and now is suddenly rising at a fast pace again.
Camilo Rada
CC BY-SA 4.0
2019-01-28T16:33:54.500Z
@CamiloRada it's been through periods of stable and non-stable for billions of years
user3163495
CC BY-SA 4.0
2019-01-28T16:54:03.690Z
@user3163495 Natural or not, we must worry because it is rising fast. And what you say is true, but every rise and drop have a reason, and the reason behind the current acceleration is not going to disappear overnight. I haven't discuss the reason here, I'm just pointing that the current rate, and acceleration are worrisome.
Camilo Rada
CC BY-SA 4.0
2019-01-28T22:13:12.703Z
Your graphic is quite narrow in time range: https://en.wikipedia.org/wiki/Past_sea_level#/media/File:Post-Glacial_Sea_Level.png. I see rates on that graph somewhere around 2 to 5 times the highest on your graphic. This strikes me as being selective with your data, unless you can explain why the vastly more dramatic changes several millennia ago should just be ignored. Would be interesting to look at even older levels, but this came up pretty readily. So if the OP is trying to prove it's not natural, your answer seems like an easily disproven argument.
jpmc26
CC BY-SA 4.0
2019-01-29T00:02:53.910Z
This is in all senses a terrible fit of the graph. If you're going to draw a line to delineate what you think would have been the tendency was no human action to take place, the minimum you could have done was to pick data going back to at least 100 years prior 1880 (preferably even more) so we could (more confidently) see a trend. This was nothing more than a shameless cherry-picking of the data. This tells us more about the poster than about a global warming trend.
devoured elysium
CC BY-SA 4.0
2019-01-29T06:14:44.767Z
@jpmc26 The "vastly more dramatic changes" were due to the continental ice sheets melting. It is flat for the last five millennia until recently.
Keith McClary
CC BY-SA 4.0
2019-01-29T06:22:44.797Z
@KeithMcClary Yes, but the point is that those clearly didn't melt due to industrial carbon. The point is that merely showing a graph of recent flatness is insufficient to prove any claims about the human cause. Just plopping out a graph is basically the correlation-does-not-imply-causation flaw. More evidence is needed.
jpmc26
CC BY-SA 4.0
2019-01-29T14:02:04.783Z
@devouredelysium - It's perfectly reasonable to add more data to the same graph that the original poster used, but you're right that more data can emphasize a trend.  So here's 1700-2002: http://www.justfacts.com/images/globalwarming/sea_level_since_1700.png
Bobson
CC BY-SA 4.0
2019-01-29T17:59:07.783Z
@jpmc26 I don't see that Camilo is explicitly making any claim about causation, he is just talking about observed SLR rates. He doesn't really answer the question IMO, so you should write your own answer based on your scientific logic and theory.
Keith McClary
CC BY-SA 4.0
2019-01-29T18:36:58.587Z
@jpmc26 Neither the question, nor the answer deal with the causation of sea level rise. However, you seem obsessed in reducing the discussion to whether humans caused it or not. The question was asking was in unusual of the current sea level rise in the context of the last couple centuries, and the answer is THE RATE, that is now much faster than any time in the written history, what caused it is secondary, we should ask instead if there anything we can do to slow down the rise and if we are prepared to face the challengers of the sea level rise that WILL happen.
Camilo Rada
CC BY-SA 4.0
2019-01-29T18:43:12.147Z
@devouredelysium I never said any of those trends have anything to do with humans. I was explaining that the plot shows how sea level is rising at an increasing rate. The rate at the begin is slower than at the end, that's it. I don't know why you, jpmc26 and so many people focus only on causation. If you are in a sinking ship: would you spend your time figuring out if it was sabotage or "natural"? Or you will try to figure out if there anything you can do to keep the ship afloat longer? Our best science say that we CAN do something to slowdown sea level rise in the upcoming centuries.
Camilo Rada
CC BY-SA 4.0
2019-01-29T18:59:58.817Z
@Bobson I tracked that plot down to its original source: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2008GL033611 very interestin, I'll add it to the answer.
Camilo Rada
CC BY-SA 4.0
2019-01-29T19:04:29.507Z
@CamiloRada The question explicitly says the the asker's debate opponent is arguing that it's "not clear that something unusual is going on, so the sea level rise is just something that was there, all natural not caused by human activity." It's not clear just from the graph that the rate is unusual, either, given historical (pre-written history, since you mention that) events. Hence more evidence is needed. Maybe that evidence exists, but this answer doesn't contain it.
jpmc26
CC BY-SA 4.0
2019-01-29T19:10:19.863Z
@jpmc26 So please write your own Answer dealing with the "all natural not caused by human activity" part of the Question.
Keith McClary
CC BY-SA 4.0
2019-01-29T19:18:22.650Z
@jpmc26 Mass-extinction-bearing-meteor-impacts are also natural, but that doesn't mean it is not "unusual", and worth worrying about. Natural or not, sea level changing at the current rate and faster are very challenging. And our best models suggest that lowering $\text{CO}_2$ emissions can make an impact in slowing it down in the upcoming centuries, so we should ACT NOW, and stop arguing if it was our fault in the first place or not. I'll add some of this to the answer, you are right that I didn't tackle that part of the question.
Camilo Rada
CC BY-SA 4.0
2019-01-29T20:44:26.723Z
Weird, I find this answer to be actually anti-convincing. Here's the way my mind is reading this: 3.8/1.7 is around 2x. Say over another 50 years it turns into 4x or even 10x. So this whole brouhaha about humanity destroying the planet is a mind-boggling exaggeration of what's really at worst just a 10x speedup of our inevitable fate? I feel like it's gotta be a bigger deal than that... (not saying I think it *isn't* a big deal, just that your answer isn't getting close to conveying it)
user541686
CC BY-SA 4.0
2019-01-29T20:47:21.230Z
@CamiloRada, thanks for your answer!  "best science and models suggest that lowering CO2 emissions can make a significant impact in slowing down sea level rise in the upcoming centuries" - Not sure if I got it right doest it implies that this phenomenon is either related to human activity or we predict that it will be related in the upcoming centuries?. I understand that we should act now, but unless people fully understand whats the relation between our activity and the sea level they will not act. Its like trash in the forest, "if its not mine I don't feel responsible for it"
Samuraka
CC BY-SA 4.0
2019-01-29T20:50:29.113Z
@CamiloRada: Could you please give us some details/links on "best science and models" ?
Samuraka
CC BY-SA 4.0
2019-01-29T20:58:56.390Z
@Samuraka The answer by Pedro links to the IPCC that summarize our best science and models. The citation he shows states that there are 10-20 cm difference in the projected sea level rise in the scenario where temperature by 2100 increase by 1.5°C compered with 2°C. And those scenarios differ mostly in human emissions. And in the scenario "business as usual", 8.5°C of increase is expected, and that will also produce more sea level rise. However the greater differences will show up beyond year 2100, because this is cumulative and it take a long time to warm up the sea and melt large ice sheets.
Camilo Rada
CC BY-SA 4.0
2019-01-29T21:01:45.200Z
@Mehrdad If you think that a sea level rising at 38 mm/yr would not be a big deal, I hope you live far from the shore and that you would be happy to welcome a few billion of displaced immigrants. At that rate the sea will rise one meter every 26 years.
Camilo Rada
CC BY-SA 4.0
2019-01-29T21:35:08.590Z
@CamiloRada: I think you missed my point. I'm trying to say that the fear of global warming extends far, *far*, ***far*** beyond coastal flooding, and yet the answer doesn't convey that at all. But it's extremely important that it does so, because if coastal flooding were the biggest issue, the rational/economic/potentially-easiest solution would be to e.g. just evacuate coastal cities over the next decades and keep burning through fossil fuels, instead of telling the entire world (including those in non-coastal areas) that they need to change their lifestyles as they know it.
user541686
CC BY-SA 4.0
2019-01-29T21:50:13.487Z
@Mehrdad I'm sorry I missed your point. I agree with you, but I wanted to focus on the question. My answer doesn't aim to convey all the impacts of climate change, I just wanted to explain what is there in that graph that makes it unusual and worrisome.
Camilo Rada
CC BY-SA 4.0
2019-02-18T18:30:54.333Z
How much forcing can we expect for each cm of sea level rise?  Does it force warmer or cooler?
elliot svensson
CC BY-SA 4.0
2019-02-18T18:48:48.863Z
...because higher sea level means less land and more ocean.
elliot svensson
CC BY-SA 4.0
2019-02-19T01:12:18.967Z
@elliotsvensson Ocean albedo is much lower than land, so it would be a positive forcing (warmer), but I don't know how much. You can post that as a question.
Camilo Rada
CC BY-SA 4.0
2019-01-27T22:33:54.720Z
2019-01-29T21:44:54.857Z
2019-01-29T21:44:54.857Z
Camilo Rada
<p>I'm discussing climate change with a friend who is a climate change denier, basically the argument is that looking at this graph, is not clear that something unusual is going on, so the sea level rise is just something that was there, all natural not caused by human activity. Could you please explain this ?
<a href="https://i.sstatic.net/1rldH.gif" rel="noreferrer"><img src="https://i.sstatic.net/1rldH.gif" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-01-27T22:54:40.833Z
Not well researched enough for a proper answer, but: The data fits what the models predict (where the reasons are heat expansion and melting due to the warming climate). Caveat: The models' parameters are edjusted precisely so that they fit past data, but should then provide reasonable estimates for the future. The  basic data and mechanisms are not in doubt.
Peter - Reinstate Monica
CC BY-SA 4.0
2019-01-28T08:31:15.173Z
I wonder where this graph comes from.
NoDataDumpNoContribution
CC BY-SA 4.0
2019-01-28T08:53:00.337Z
@Trilarion [NASA](https://climate.nasa.gov/climate_resources/133/sea-level-historic-data/) credits [CSIRO](https://research.csiro.au/slrwavescoast/sea-level/)
JollyJoker
CC BY-SA 4.0
2019-01-28T11:27:56.900Z
Unusual compared to what? How long have we been keeping accurate weather reports and how long has earth been around? Yes, something is changing... is it unusual, is it solely because of humans... none of that can be proven or disproved with current data sets.
BossRoss
CC BY-SA 4.0
2019-01-28T11:52:13.463Z
@BossRoss It's not like one does prove anything in natural sciences. You have a theoretical model like for example man made climate change and all observations should be congruent with that model at the very least. There might be different models also explaining all the data. Unusual in this context probably means human-made.
NoDataDumpNoContribution
CC BY-SA 4.0
2019-01-28T16:53:43.840Z
There's a broad swath of people that are labeled 'climate change deniers'. Without giving your definition, your showing a graph to prove what you believe is something is actually nothing.
Dunk
CC BY-SA 4.0
2019-01-28T18:20:30.207Z
Hard to believe nobody has posted [either](https://xkcd.com/1379/) of the relevant [XKCD](https://xkcd.com/1732/) links
Bill K
CC BY-SA 4.0
2019-01-29T00:16:05.537Z
I was hunting around for a graph that showed before 1880 and found this fun interactive graph: https://www.sealevels.org/
Wossname
CC BY-SA 4.0
2023-04-15T05:39:56.227Z
80 million years ago, sea level was 170 meters (550 feet) higher than current levels. 125,000 years ago, at the latest warm peak, sea level was 10 meters (33 feet) higher than current levels. This pretending that sea level 18,000 years ago, which was the absolute minimum for at least the last tens of millions of years, is somehow a normal baseline is why people are a little skeptical of chicken little arguments that make things look more extreme than they actually are. The truth should be alarming enough. Embellishing it just makes it seem like you're picking and choosing data.
Michael C
<climate-change><sea-level>
Is the sea level rise unusual?
Samuraka
# Is the sea level rise unusual?

(Asked by: username_0 on 2019-01-27)

I'm discussing climate change with a friend who is a climate change denier, basically the argument is that looking at this graph, is not clear that something unusual is going on, so the sea level rise is just something that was there, all natural not caused by human activity. Could you please explain this ?
[![enter image description here](https://i.sstatic.net/1rldH.gif)](https://i.sstatic.net/1rldH.gif)

**Tags:** climate-change, sea-level

> **Comments:**
> **username_1**: Not well researched enough for a proper answer, but: The data fits what the models predict (where the reasons are heat expansion and melting due to the warming climate). Caveat: The models' parameters are edjusted precisely so that they fit past data, but should then provide reasonable estimates for the future. The  basic data and mechanisms are not in doubt.  
> **username_2**: I wonder where this graph comes from.  
> **username_3**: @Trilarion [NASA](https://climate.nasa.gov/climate_resources/133/sea-level-historic-data/) credits [CSIRO](https://research.csiro.au/slrwavescoast/sea-level/)  
> **username_4**: Unusual compared to what? How long have we been keeping accurate weather reports and how long has earth been around? Yes, something is changing... is it unusual, is it solely because of humans... none of that can be proven or disproved with current data sets.  
> **username_2**: @username_4 It's not like one does prove anything in natural sciences. You have a theoretical model like for example man made climate change and all observations should be congruent with that model at the very least. There might be different models also explaining all the data. Unusual in this context probably means human-made.  
> **username_5**: There's a broad swath of people that are labeled 'climate change deniers'. Without giving your definition, your showing a graph to prove what you believe is something is actually nothing.  
> **username_6**: Hard to believe nobody has posted [either](https://xkcd.com/1379/) of the relevant [XKCD](https://xkcd.com/1732/) links  
> **username_7**: I was hunting around for a graph that showed before 1880 and found this fun interactive graph: https://www.sealevels.org/  
> **username_8**: 80 million years ago, sea level was 170 meters (550 feet) higher than current levels. 125,000 years ago, at the latest warm peak, sea level was 10 meters (33 feet) higher than current levels. This pretending that sea level 18,000 years ago, which was the absolute minimum for at least the last tens of millions of years, is somehow a normal baseline is why people are a little skeptical of chicken little arguments that make things look more extreme than they actually are. The truth should be alarming enough. Embellishing it just makes it seem like you're picking and choosing data.  

---

## 7 answers

### Answer by username_12 on 2019-01-27. Score: 72 | Accepted answer

The problem is the **increase** in the **rate** of sea level rise. I pulled out some approximate numbers from the figure you presented:

[![enter image description here](https://i.sstatic.net/AXhoH.png)](https://i.sstatic.net/AXhoH.png)

Can you see now how the sea level is rising much faster today than a century ago?

Sea level rise, as well as climate change are normal things on Earth history. However, most times they happen at a very slow rate, allowing ecosystems and other processes to adapt to the change.

For example, if the climate changes over several hundreds of years, animals and even tree populations can "move" towards the side of their distribution where climate is still good for them. But if the climate changes in 50 years, all the trees can die before they had time to grow in the areas where they could thrive in the new climate.

In the case of sea level rise. The delta of a river for example, stays in equilibrium with the sea level because of the accumulation of sediments carried by the river. If the sea level rises slowly, the sediments can fill the delta and keep it roughly at sea level. But if the see level rises too quick for the sedimentation to keep up, it will be flooded by the sea, killing all the animals and people that live on such fertile environments.

Analogously, coastal infrastructure have a given lifetime. Let's say 50 years. If the sea level doesn't change much over that period (8.5 cm at the 1880-1940 rate), there is no problem. Once the infrastructure gets replaced, the new building will be set a bit higher.
However, in the next 50 years the sea level could rise 50 cm, or even more (it would be 19 cm if we assume the last rate from the figure won't increase any further), and that is a big deal. That could mean that much coastal infrastructure will be flooded, and maybe destroyed during storms.

In places like Bangladesh there are hundred of millions of people that could be displaced due to sea level rise if the rate keeps increasing. People that will also need to find a new home.

Coastal infrastructure loss, coastal erosion and immigration could be some of the worst expressions of **fast** sea level rise.

**ADDITION**

Given the interest risen by this question I'm adding here some data beyond what is presented by the OP, and brought to my attention by @username_30 in the comments. It comes from the paper [Recent global sea level acceleration started over 200 years ago?](https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2008GL033611) and shows a sea level reconstruction going back to 1700, and it shows also the changes in rate over that period. This is summarized in their figure 3:

[![enter image description here](https://i.sstatic.net/NFD7a.png)](https://i.sstatic.net/NFD7a.png)

Here you can clearly see how, with some ups and downs, the rate of sea level rise have been increasing over the last few centuries. And notably the current rate, about 20 years after the end of this plot is already out of the scale, and around [3.2 mm/year](https://climate.nasa.gov/vital-signs/sea-level/) as pointed also by other answers.

I would highlight the following from their abstract:

> Sea level rose by 6 cm during the 19th century and 19 cm in the 20th
> century.Superimposed on the long-term acceleration are quasi-periodic
> fluctuations with a period of about 60 years. If the conditions that
> established the acceleration continue,then sea level will rise 34 cm
> over the 21st century. Longtime constants in oceanic heat content and
> increased ice sheet melting imply that the latest
> Intergovernmental Panel on Climate Change (IPCC) estimates of sea
> level are probably too low.

Regarding to whether this is caused by humans or not, I rather stay out of that argument and point that our best science and models suggest that lowering $\text{CO}\_2$ emissions can make a significant impact in slowing down sea level rise in the upcoming centuries, so **we should ACT NOW, and stop arguing whether it was or not our fault in the first place**.

> **Comments:**
> **username_24**: Excellent answer which addresses the most frightening aspect of climate change: the rate.  
> **username_25**: This goes a long way to pointing out the real risk of CC - not so much that the planet becomes uninhabitable, but that changes in its habitability profile wrecks our complex, globalised economic system. This will lead to refugees, famines, the breakdown of international co-operation and a return to a geo-politcal landscape that was last seen in the 1930s. And we all know what happened then.  
> **username_26**: To be clear the sea levels has risen before, 8000 years ago you could walk from France to England. The end of the last glacial advance caused the  Early Holocene Sea Level Rise (60meters) and a lot of settlements were destroyed by that rise. But since then sea level has been very stable, until now. We know what caused that change and its not what is causing the current one.  
> **username_27**: this graph of the last 140 years cannot be used to prove anything, considering the earth is 4.5 billion years old, and the fact that the sea level has risen in the past much, much faster than even 4mm per year  
> **username_27**: @username_24 the sea level has risen much, much faster in the past http://www.climatewarmingcentral.com/images/sea_level_rise.jpg  
> **username_12**: @username_27 No doubt about that. The sea level have risen much faster in the past. But you still need to explain why it was stable for thousands of years and now is suddenly rising at a fast pace again.  
> **username_27**: @username_12 it's been through periods of stable and non-stable for billions of years  
> **username_12**: @username_27 Natural or not, we must worry because it is rising fast. And what you say is true, but every rise and drop have a reason, and the reason behind the current acceleration is not going to disappear overnight. I haven't discuss the reason here, I'm just pointing that the current rate, and acceleration are worrisome.  
> **username_28**: Your graphic is quite narrow in time range: https://en.wikipedia.org/wiki/Past_sea_level#/media/File:Post-Glacial_Sea_Level.png. I see rates on that graph somewhere around 2 to 5 times the highest on your graphic. This strikes me as being selective with your data, unless you can explain why the vastly more dramatic changes several millennia ago should just be ignored. Would be interesting to look at even older levels, but this came up pretty readily. So if the OP is trying to prove it's not natural, your answer seems like an easily disproven argument.  
> **username_29**: This is in all senses a terrible fit of the graph. If you're going to draw a line to delineate what you think would have been the tendency was no human action to take place, the minimum you could have done was to pick data going back to at least 100 years prior 1880 (preferably even more) so we could (more confidently) see a trend. This was nothing more than a shameless cherry-picking of the data. This tells us more about the poster than about a global warming trend.  
> **username_21**: @username_28 The "vastly more dramatic changes" were due to the continental ice sheets melting. It is flat for the last five millennia until recently.  
> **username_28**: @username_21 Yes, but the point is that those clearly didn't melt due to industrial carbon. The point is that merely showing a graph of recent flatness is insufficient to prove any claims about the human cause. Just plopping out a graph is basically the correlation-does-not-imply-causation flaw. More evidence is needed.  
> **username_30**: @username_29 - It's perfectly reasonable to add more data to the same graph that the original poster used, but you're right that more data can emphasize a trend.  So here's 1700-2002: http://www.justfacts.com/images/globalwarming/sea_level_since_1700.png  
> **username_21**: @username_28 I don't see that username_12 is explicitly making any claim about causation, he is just talking about observed SLR rates. He doesn't really answer the question IMO, so you should write your own answer based on your scientific logic and theory.  
> **username_12**: @username_28 Neither the question, nor the answer deal with the causation of sea level rise. However, you seem obsessed in reducing the discussion to whether humans caused it or not. The question was asking was in unusual of the current sea level rise in the context of the last couple centuries, and the answer is THE RATE, that is now much faster than any time in the written history, what caused it is secondary, we should ask instead if there anything we can do to slow down the rise and if we are prepared to face the challengers of the sea level rise that WILL happen.  
> **username_12**: @username_29 I never said any of those trends have anything to do with humans. I was explaining that the plot shows how sea level is rising at an increasing rate. The rate at the begin is slower than at the end, that's it. I don't know why you, username_28 and so many people focus only on causation. If you are in a sinking ship: would you spend your time figuring out if it was sabotage or "natural"? Or you will try to figure out if there anything you can do to keep the ship afloat longer? Our best science say that we CAN do something to slowdown sea level rise in the upcoming centuries.  
> **username_12**: @username_30 I tracked that plot down to its original source: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2008GL033611 very interestin, I'll add it to the answer.  
> **username_28**: @username_12 The question explicitly says the the asker's debate opponent is arguing that it's "not clear that something unusual is going on, so the sea level rise is just something that was there, all natural not caused by human activity." It's not clear just from the graph that the rate is unusual, either, given historical (pre-written history, since you mention that) events. Hence more evidence is needed. Maybe that evidence exists, but this answer doesn't contain it.  
> **username_21**: @username_28 So please write your own Answer dealing with the "all natural not caused by human activity" part of the Question.  
> **username_12**: @username_28 Mass-extinction-bearing-meteor-impacts are also natural, but that doesn't mean it is not "unusual", and worth worrying about. Natural or not, sea level changing at the current rate and faster are very challenging. And our best models suggest that lowering $\text{CO}_2$ emissions can make an impact in slowing it down in the upcoming centuries, so we should ACT NOW, and stop arguing if it was our fault in the first place or not. I'll add some of this to the answer, you are right that I didn't tackle that part of the question.  
> **username_31**: Weird, I find this answer to be actually anti-convincing. Here's the way my mind is reading this: 3.8/1.7 is around 2x. Say over another 50 years it turns into 4x or even 10x. So this whole brouhaha about humanity destroying the planet is a mind-boggling exaggeration of what's really at worst just a 10x speedup of our inevitable fate? I feel like it's gotta be a bigger deal than that... (not saying I think it *isn't* a big deal, just that your answer isn't getting close to conveying it)  
> **username_0**: @username_12, thanks for your answer!  "best science and models suggest that lowering CO2 emissions can make a significant impact in slowing down sea level rise in the upcoming centuries" - Not sure if I got it right doest it implies that this phenomenon is either related to human activity or we predict that it will be related in the upcoming centuries?. I understand that we should act now, but unless people fully understand whats the relation between our activity and the sea level they will not act. Its like trash in the forest, "if its not mine I don't feel responsible for it"  
> **username_0**: @username_12: Could you please give us some details/links on "best science and models" ?  
> **username_12**: @username_0 The answer by username_9 links to the IPCC that summarize our best science and models. The citation he shows states that there are 10-20 cm difference in the projected sea level rise in the scenario where temperature by 2100 increase by 1.5°C compered with 2°C. And those scenarios differ mostly in human emissions. And in the scenario "business as usual", 8.5°C of increase is expected, and that will also produce more sea level rise. However the greater differences will show up beyond year 2100, because this is cumulative and it take a long time to warm up the sea and melt large ice sheets.  
> **username_12**: @Mehrdad If you think that a sea level rising at 38 mm/yr would not be a big deal, I hope you live far from the shore and that you would be happy to welcome a few billion of displaced immigrants. At that rate the sea will rise one meter every 26 years.  
> **username_31**: @username_12: I think you missed my point. I'm trying to say that the fear of global warming extends far, *far*, ***far*** beyond coastal flooding, and yet the answer doesn't convey that at all. But it's extremely important that it does so, because if coastal flooding were the biggest issue, the rational/economic/potentially-easiest solution would be to e.g. just evacuate coastal cities over the next decades and keep burning through fossil fuels, instead of telling the entire world (including those in non-coastal areas) that they need to change their lifestyles as they know it.  
> **username_12**: @Mehrdad I'm sorry I missed your point. I agree with you, but I wanted to focus on the question. My answer doesn't aim to convey all the impacts of climate change, I just wanted to explain what is there in that graph that makes it unusual and worrisome.  
> **username_32**: How much forcing can we expect for each cm of sea level rise?  Does it force warmer or cooler?  
> **username_32**: ...because higher sea level means less land and more ocean.  
> **username_12**: @username_32 Ocean albedo is much lower than land, so it would be a positive forcing (warmer), but I don't know how much. You can post that as a question.  

---

### Answer by username_9 on 2019-01-28. Score: 14

The problem is that sea level is increasing faster than ever in last couple thousand years. It is currently rising at [3.2 mm/year according to satellite data](https://climate.nasa.gov/vital-signs/sea-level/):

[![enter image description here](https://i.sstatic.net/XufIa.png)](https://i.sstatic.net/XufIa.png)

The curve you showed is not a straight line, it is rising at an increasing rate.

And the trend is expected to continue: The [last IPCC report (2018)](https://www.ipcc.ch/site/assets/uploads/sites/2/2018/11/SR15_Chapter3_Low_Res-1.pdf) on the subject say:

> Projections vary in the range 0.26–0.77 m and 0.35–0.93 m for 1.5°C
> and 2°C respectively for the 17–84% confidence interval (0.20–0.99 m
> and 0.24–1.17 m for the 5–95% confidence interval).

And projected sea level incrase for year 2100 are summarized in table 3.1:

[![enter image description here](https://i.sstatic.net/EhMbd.png)](https://i.sstatic.net/EhMbd.png)


---

### Answer by username_10 on 2019-01-28. Score: 12

Sea level rise from thermal expansion is a very slow process: oceans are 3.7 km deep on average, and water has a very large [specific heat capacity](https://en.wikipedia.org/wiki/Heat_capacity).

Here's a related diagram from the [IPCC Third Assessment Report](https://web.archive.org/web/20080510080424/https://www.ipcc.ch/pdf/climate-changes-2001/synthesis-syr/english/summary-policymakers.pdf) (page 17):
[![sea level rise after emissions are reduced](https://i.sstatic.net/TTwjJ.jpg)](https://i.sstatic.net/TTwjJ.jpg)

Climate change didn't have much impact on the sea level, *yet*.

> **Comments:**
> **username_10**: Downvoter: Constructive criticism is welcome!  
> **username_11**: Quick question: in the chart, when $CO_2$ emissions drop to very low levels, why does $CO_2$ stabilization (presumably $CO_2$ levels) not decrease?  
> **username_12**: @username_11 For the same reason that if you stop putting water into the bath tub the water level in it doesn't go down. For the $\text{CO}_2$ level to go down you need a $\text{CO}_2$ sink.  
> **username_13**: I'll not downvote, but cannot upvote because this answer is tangential to the question in this current form. Maybe you cam imporove it if you compare it with the most important factors in sea rising, like ice caps melting and explaining why natural processes takes ages, literally  
> **username_10**: @username_13: There's a curve for "sea-level rise due to ice melting" on the diagram, and it appears to be really flat in the beginning. So it seems to fit well with the "not clear that something unusual is going on" argument in the original question. Also, the simple fact that oceans have a very large volume and can absorb a lot of heat is a good explanation why the process takes many centuries. If you want a more detailed explanation, the IPCC summary for policymakers is linked.  
> **username_13**: @username_10 The link is a good start but as a good practice you can copy the main parts and elaborate about it. Also note while the papaer is still correct it dates back to 2001  
> **username_10**: @username_13 To each his own. I think the diagram is the most important part of the answer, along with the small explanation of ocean's heat capacity. Finally, laws of thermodynamics didn't change much since 2001. ;)  
> **username_13**: @username_10 I'm just trying to help. While the dynamics don't chance much over two decades our understand of it increases. Anyway refer to it https://earthscience.stackexchange.com/help/how-to-answer  
> **username_10**: @username_13: The most relevant part from the link is the diagram, which answers the question pretty well IMHO. The diagram is uploaded to imgur. The linked pdf is an archive on the [wayback machine](https://archive.org/web/) so it's probably not going anywhere soon. Which part of "How To Answer" do you think could help my answer, exactly?  
> **username_12**: @immibis Yes, that happen and is known as $\text{CO}_2$ fertilization. But the effect is rather small compared with the main $\text{CO}_2$ sinks and sources.  

---

### Answer by username_14 on 2019-01-30. Score: 10

I think [this XKCD](https://xkcd.com/1732/) says it all:

[![enter image description here](https://i.sstatic.net/lWHMb.png)](https://i.sstatic.net/lWHMb.png)

> **Comments:**
> **username_15**: I really love this graph. I had seen it before and it really makes the point completely clear  
> **username_14**: @username_15 Yeah, it's so vivid.  
> **username_16**: That graph is very compelling!  But then I looked at it a second and third time and noticed something.  Is the solid part the part where we have recordings of temperatures, and the dashed part where we're making projections either forward or back in time?  
> **username_14**: @username_16 I believe so. Solid is where we have direct measurements. Dotted into the past is where we work out past temperatures based on other evidence (ice cores, tree rings, etc) and dotted into the future are estimates at the time this was made (2016)  
> **username_16**: That's a lot of extrapolation!  I imagine small changes to the past values could greatly change the overall story.  
> **username_14**: @username_16 The past is neither extrapolation nor projections. It's real figures derived from real data - just not by direct measurement of temperature as we don't have those records.  
> **username_16**: Fare enough, extrapolation is a bit of an overstatement with regard to the past data as I know we have a lot of different data points from the past.  But with regard to temperature it does still represent an extrapolation, just one that agrees with a number of other data sets.  Basically much of what we know from the far past has to be extrapolated, and we aim for agreement between the different extrapolated measurements (e.g. temperature, atmosphere, etc.).  Is that accurate?  Not a scientist, so I may be off base here.  
> **username_14**: @username_16 Extrapolated means taking a trend and extending it beyond the known points. i.e. if you have 1, 2, 3 then you can interpolate 1.5 as half way between 1 and 2 and extrapolate 4, 5 as coming after 3. Extrapolation can go wrong fast (interpolation can also go wrong, but generally not as badly). For historical data we neither interpolate nor extrapolate. We use indirect methods using temperature proxies and combine the results from those proxies. - https://www.theguardian.com/environment/2012/mar/07/past-climate-temperature-proxies  
> **username_8**: There have been documented 'Meltwater pulses' of rapid sea level rise in very short periods of time in the past. This chart conveniently ignores all three that have occurred since the chart begins, again rather conveniently, at the lowest sea levels in at least the last 4 million years.  
> **username_8**: @username_14 Even the chart itself admits (in a note between 15,500 BCE and 16,000 BCE) that localized spikes are very likely and not reflected by the interpolated average presented. If you want folks to take you seriously, at least acknowledge what has been documented rather convincingly regarding at least three Meltwater pulse events since the last glacial maximum.  
> **username_14**: @username_8 Yes, sea levels have risen before.  And when they did we didn't have millions of humans living in or depending on the soon-to-be-flooded land.  So maybe we should try not to raise them again, hmm?  
> **username_8**: @username_14 "We" didn't raise them the last three Meltwater pulses. Natural processes that we still don't fully understand did. As I say in my answer, this isn't an "Earth" problem, it is a "human" problem. As I also say in my answer, the current trend needs to be considered and acted upon if it can be shown that we have the capability to slow the rate at which sea level is rising. Otherwise in a couple of centuries most coastal *cities* will be under water. There will still be plenty of arable land to live on, it will just require mass migrations (like the last ice age did).  

---

### Answer by username_17 on 2019-01-28. Score: 8

In addition to other answers...

This curve isn't a good comparison to the "natural" state of the Earth, because it starts in 1880. The [Industrial Revolution](https://en.wikipedia.org/wiki/Industrial_Revolution) had been in full swing for some time by then, and by that point it had been fuelled by coal for around a century. Every factory was powered by coal, every house was heated by coal or coal gas, and every light used coal gas.

Even then, the Earth's temperature and sea level graphs didn't change too dramatically. By the mid-20th century though, climate models fitted to past data [were extrapolating to a mini Ice Age](https://en.wikipedia.org/wiki/Global_cooling). No big deal - the climate cycles like that, [as the historical climate record shows](https://en.wikipedia.org/wiki/Milankovitch_cycles).

Except the climate didn't behave that way. Instead of following the natural cycles that have been observed over hundreds of years, the temperature escalated as the graph shows. So climate scientists had to improve their models to cover dramatic differences to "normal" climate behaviour, modelling climate events which normally would only be seen in a disaster [such as massive volcanic eruptions](https://www.skepticalscience.com/volcanoes-and-global-warming.htm).

The result is that [with all this work, they can predict](https://en.wikipedia.org/wiki/History_of_climate_change_science) a lot of the causes and effects of rising global temperatures due to fossil fuel usage (amongst other things). Your friend needs to not just look at the graph of what the Earth is currently doing, but also consider what climate scientists even as far as the 1970s who looked at the historical record were expecting the Earth to do, which assumed not burning stuff.

Even then, the Earth will survive. The idea of "saving the Earth" is nonsense - the Earth will survive. Many species will go extinct, but that's happened a lot in the past too. Many major cities (and some entire countries) will be lost too, which is more of an issue for humans. The question is whether your friend is prepared to accept humans having control over whether this happens or not.

> **Comments:**
> **username_18**: Not a bad answer but it could do with some actual data...  
> **username_19**: "natural cycles that have been observed over hundreds of years"?  
> **username_17**: @username_18 Added a few links.  I doubt they'd convince a hardcore climate-change denier, but then we already know that they hold that position through faith and not evidence.  
> **username_17**: @username_19 Added links.  
> **username_19**: No, I was wondering, you said "over hundreds of years". I don't think that people for example measured temperatures for hundreds of years, and then wrote it somewhere. Or, am I wrong?  
> **username_17**: @username_19 I meant "cycles over hundred of years have been observed".  Although we've got directly-measured records starting in the 1850s, so that's 160 years of solid observations.  We've got a number of older records as well, from ships' captains and from various gentleman scientists, which are not global records but give us documentation for specific locations (or journeys). The oldest records apparently go back to the 1650s.  https://www.earthmagazine.org/article/earliest-instrumental-temperature-record-recovered  
> **username_20**: The earth might *not* survive: https://en.wikipedia.org/wiki/Runaway_greenhouse_effect  
> **username_17**: @username_20 The Earth will still be there.  Creatures on it, less so... :)  Hansen's hypothesis isn't really fact-based anyway.  Yes, if we burned an order of magnitude more fuel than exists on Earth, then things would go wrong - but that's got a "magic happens" step of where this fuel comes from.  Assuming a Coal Fairy doesn't exist, the Earth isn't really going to turn into Venus.  TBH though, I think it'd stop being a good place to live well before that anyway, and "civilisation" would already have either collapsed or left the planet; either way the human problem goes away.  
> **username_21**: [Figure 7: World Coal Consumption 1860-2007](https://www.resilience.org/stories/2009-04-20/peak-people-interrelationship-between-population-growth-and-energy-resources/)  
> **username_8**: @username_17 The problem remains, though, that the margin of error for the accuracy of those measurements is often less than the total amount of the changes we're supposedly documenting between then and now. Sediment and fossil records, on the other hand, when combined with study of tectonic plate movements can give us a much better measure of maximum and minimum sea levels at various times over the past millions of years, even if they're less definitive as to exactly how long ago those minimums and maximums were.  
> **username_22**: No clear warming signal would have occurred from the Industrial Revolution - coal use was just a few nations back then, with coal still dug and shoveled by hand. We made more emissions in the past 5 years than the whole of the 1800's. Too much opinion, not enough answer.  
> **username_17**: @username_22 Which is why, as I said, "*Even then, the Earth's temperature and sea level graphs didn't change too dramatically.*"  Some effect, but not enough to notice.  It took a lot more coal consumption to clearly tip the scales.  
> **username_8**: The predictions of another ice age 50-60 years ago were inaccurate due to flawed models, not due to emissions that exceeded estimates at that time. It was never a prediction of natural cycles, it was based on human activity. They overestimated the effect of particulates in the air preventing sunlight's energy to reach and heat the ground without taking into account the particulates themselves would absorb heat and have an effect on atmospheric temperatures.  
> **username_8**: We're still emerging from the last ice age that peaked 18,000 years ago and have not reached the typical maximum before the next ice age begins. Whatever anthropogenic effect there is will only accelerate the increase in temperature. Interglacial periods during Icehouse Earth climates (such as we've been for the past 2.5M years) have been  on a 41,000 year cycle based on the eccentricities of the Earth's tilt and orbit around the sun. Ice ages do not occur naturally more than once ever 41,000 years.  

---

### Answer by username_23 on 2019-01-31. Score: 5

I just took the sea level elevation rate (mm/yr) graph from [username_12's answer](https://earthscience.stackexchange.com/a/16079/981) and added:

* A vertical axis at zero (when the curve is at the point, it means the sea level did not change that year).
* Red and green colors showing the trend.

Hopefully it will speak more to your friend.

[![enter image description here](https://i.sstatic.net/RssLq.png)](https://i.sstatic.net/RssLq.png)

> **Comments:**
> **username_23**: @gansub: All of the explanation and the sources are in username_12's answer at https://earthscience.stackexchange.com/a/16079/981 I did not want to duplicate his/her prose.  

---

### Answer by username_8 on 2023-04-15. Score: 2

Is rapid sea level rise unusual?

Yes.

Is It unprecedented?

No.

That then prompts the question: Is a less than 0.25 meter rise in sea level over the past 140 years or so considered "rapid" in terms of geological time?

There have been three documented *meltwater pulse* events during which sea level rose dramatically in relatively short periods of time following the most recent glacial period that reached maximum ice around 18,000 years ago.

From the Wikipedia article ['Past Sea level'](https://en.wikipedia.org/wiki/Past_sea_level):

> Meltwater pulse 1A was a 13.5 m rise over about 290 years centered at 14,200 years ago and Meltwater pulse 1B was a 7.5 m rise over about 160 years centered at 11,000 years ago.

and

> Meltwater pulse 1C was centered at 8,000 years ago and produced a rise of 6.5 m in less than 140 years, such that sea levels 5000 years ago were around 3m lower than present day, as evidenced in many locations by fossil beaches.

Pulse 1A was approximately 27X the rate of change since 1880.  
Pulse 1B was approximately 26X the rate of change since 1880.  
Pulse 1C was approximately 26X the rate of change since 1880.

Compared to rates of change approximately six meters (6,000mm) per 140 years, is a rise of less than 0.25m (250mm) over 135 years considered "rapid"?

Maybe. Maybe not. After all, for the next 5,000 years following Pulse 1C sea level has only risen about 3 meters (3,000mm). This equates to a rate about 1/3 that observed over the past 140 years. So is 3X the rate of the last 5,000 years "rapid"? Or is it only "slightly elevated" when compared to past events which showed roughly 75X the average rate of change of the past 5,000 years?

Should this be cause for concern?

With regard to human culture, absolutely. If current trends continue, in a few centuries many coastal cities will be underwater. That's a serious problem that needs to be considered and acted upon if it can be shown that we have the capability to slow the rate at which sea level is rising.

Does this mean we should base our argument of what is "normal" on selective data that makes things look worse and more anomalous than they actually are?

No, doing that just makes us look like we're a bunch of Chicken Littles crying that the sky is falling when we choose the absolute minimum sea level for the past tens of millions of years, at the height of the most recent ice age 18,000 years ago, as our baseline for what is "normal".

Just for some very long term context:

[80 million years ago](https://news.mongabay.com/2008/03/cretaceous-sea-levels-were-550-feet-higher-than-today/) sea level was 170 meters (550 feet) higher than current levels.

[Three million years ago](https://www.usgs.gov/media/images/coastline-eastern-us-changesslowly) sea level was 50 meters (165 feet) higher than current levels.

[125,000 years ago](https://www.e-education.psu.edu/earth107/node/1496), at the most recent warm peak, sea level was 8-10 meters (26-33 feet) higher than current levels.

At its lowest during the last ice age around 18,000 years ago, when roughly one-third of Earth's total land mass was covered in ice, sea level was 122 meters (400 feet) lower than current levels. As far as we can tell, that's the lowest sea level has been for at least 100 million years, and likely for much longer.

Anthropogenic climate change is accelerating the rate at which the Earth is warming. How much of the current rate of change is anthropogenic and how much is due to other factors, such as solar activity variation, irregularities in the Earth's orbit, and plate tectonics is arguable.

It is no less foolish to pretend that without anthropogenic factors the Earth would not be warming at all than it is to pretend none of our current warming is anthropogenic. In the long term the Earth will almost certainly continue a warming trend for the next several tens of thousands of years with or without humans living on its surface. After all, the Earth is still emerging from the last ice age 18,000 years ago.

Unfortunately for humans, our culture and societies also emerged during a time when the Earth has been considerably cooler than is historically typical and we're best adapted to live in a world that is cooler than has historically been the case over the past hundreds of thousands of years. That's not an Earth problem. That's a human problem.


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