<p>I was able to dig up this (although without being able to find full sources):</p>

<p><a href="https://i.sstatic.net/scD2h.gif" rel="noreferrer"><img src="https://i.sstatic.net/scD2h.gif" alt="ice age temp map"></a></p>

<p>It shows a pattern where the temperatures are dramatically lower where ice sheets have built up relative to today. Interestingly, a lower overall temperature means weaker mixing across latitudes, so some areas are actually warmer.  Boston gets chilled by -20 according to the map.</p>

<p>Also note the altitude effect. If the surface is raised by 1 kilometer, then due to the <a href="https://en.wikipedia.org/wiki/Lapse_rate" rel="noreferrer">lapse rate</a>, the temperature at the new surface will drop by 6.5 degrees. This is a <em>very</em> important factor in stabilizing large ice sheets.</p>

CC BY-SA 3.0
2017-07-22T04:09:26.480Z
Very cool. No pun intended. Also, first I'd heard of lapse rate. Thanks for the answer!
nwhaught
CC BY-SA 3.0
2017-07-21T07:04:03.950Z
2017-07-21T07:04:03.950Z
Andrew Jon Dodds
<p>Let me state upfront, I'm not arguing the existence of climate change, just trying to clarify my own understanding of something that doesn't make sense to me yet. With apologies for the layman's question...</p>

<p>I've seen similar numbers frequently, but let's use <a href="https://xkcd.com/1379/" rel="nofollow noreferrer">this xkcd</a> 
as a reference. It states that a 4.5 C change in the global climate is the difference between Boston under a half mile of ice, and the temperate zone it is today. Boston's current annual average temp is <a href="http://www.usclimatedata.com/climate/boston/massachusetts/united-states/usma0046/2017/1" rel="nofollow noreferrer">10.75</a> (~15 average high, ~7 average low). Looking for an analog for a city that's about 4.5 C cooler than Boston gives a location like <a href="https://www.currentresults.com/Weather/Canada/Cities/temperature-annual-average.php" rel="nofollow noreferrer">Moncton, New Brunswick.</a> Colder, yes, but not buried under half a mile of ice. </p>

<p>My brain says that a place covered by ice is far colder than current temps minus 4.5 C, and that since the ice sheets covered so much of the earth, I can safely skirt the "climate is global, you're looking at local temps" hangup. So what gives? <strong>How can a climate like Boston's cool by "only" 4.5 C and support such enormous glaciers?</strong> It would seem that the presence of such enormous ice sheets would imply that the average temperature must have been far colder than that...</p>

CC BY-SA 3.0
2017-07-21T04:05:50.207Z
you are mixing apples and oranges.  It says the GLOBAL climate changes by 4.5 C.  That doesn't mean Boston's climate changes by 4.5 C.  Keep in mind that the average global temperature change will not be evenly distributed.  You should expect high latitudes and high altitudes to undergo the most temperature change, while the ocean surface and tropical zones will undergo the least temperature change.
f.thorpe
CC BY-SA 3.0
2017-07-21T04:09:38.570Z
ok...makes sense. could you direct me to any layman-friendly resources to get a better handle on how the climate change might realistically be distributed? From your comment, I'm imagining something along the lines of "70-90 latitudes drop by 15 C, 50-70 latitudes drop by 10 C, 30-50 drop by ..." etc. Is that idea (if not the numbers, which I just made up...) roughly accurate?
nwhaught
CC BY-SA 3.0
2017-07-21T05:08:00.733Z
Ugh, I don't know of any images that show global cooling scenarios.  Will warming work for you?  You can see this image:  https://www.ipcc.ch/report/graphics/images/Assessment%20Reports/AR5%20-%20Synthesis%20Report/SPM/SPM.07_rev1-01.png  RCP 2.6 is "a little warming" and RCP 8.5 is more of a worst case scenario.
f.thorpe
CC BY-SA 3.0
2017-07-21T05:09:33.610Z
oh, absolutely. I'm using cooling to get my head around the problem, since we actually have the historical data, warming is just turning the problem around, and is what I'm really trying to understand anyway. Thanks very much!
nwhaught
CC BY-SA 3.0
2017-07-21T06:03:02.583Z
Perhaps one factor that's missing is that glaciers flow.  For a northeast glaciation, the snow probably starts accumulating in northern Canada, with ice flowing south as it reaches sufficient depth.  (Scooping out the Great Lakes, Finger Lakes, and other features on the way.)  And of course, since ice & snow are reflective, the temperature on the glacier tends to be much lower than average, leading to further snow accumulation...
jamesqf
CC BY-SA 3.0
2017-07-21T06:09:22.433Z
I haven't either heard of any global cooling scenarios.. It would be an interesting research topic though: make sun suddenly emit less and see how and where the glaciers will grow. By the way xkcd had the palm trees wrong, palm trees would die at the poles due to half a year without sunlight.
Communisty
CC BY-SA 3.0
2017-07-21T07:07:20.457Z
@Communisty - Even in today's cold climate (historically), we have many trees living north of the Arctic circle, limited more by temperature than sunlight. It's easy ti imagine a species of palm tree that is adapted to months without sunlight, given warm enough conditions.
Andrew Jon Dodds
CC BY-SA 3.0
2017-07-21T07:24:17.003Z
@AndrewJonDodds easy to imagine, but many factors play against it. The very shape of palm trees is optimal for near zenith angle sunlight, while e.g. spruce is better for low angle. Even with ten degrees global warming the continental Antarctic would still experience freezing temperatures that kill most trees without needles. Currently no trees live right at the poles. Antarctic continent would probably look more like current arctic tundra (no trees at all).
Communisty
CC BY-SA 3.0
2017-07-21T10:08:38.460Z
@Communisty - https://en.wikipedia.org/wiki/Polar_forests_of_the_Cretaceous  Remember that the Cretaceous was fantastically warm compared to the present day.
Andrew Jon Dodds
CC BY-SA 3.0
2017-07-21T10:28:14.583Z
@AndrewJonDodds from that wiki page: 'In this Cretaceous greenhouse world, Arctic conifer forests were considered predominantly deciduous, while those that grew on Antarctica contained a significantly greater proportion of evergreens'. And during that time, similar to now, the north pole wasn't continental and the south pole was.
Communisty
<climate-change>
Making sense of the math of climate change
nwhaught
# Making sense of the math of climate change

(Asked by: username_0 on 2017-07-21)

Let me state upfront, I'm not arguing the existence of climate change, just trying to clarify my own understanding of something that doesn't make sense to me yet. With apologies for the layman's question...

I've seen similar numbers frequently, but let's use [this xkcd](https://xkcd.com/1379/)
as a reference. It states that a 4.5 C change in the global climate is the difference between Boston under a half mile of ice, and the temperate zone it is today. Boston's current annual average temp is [10.75](http://www.usclimatedata.com/climate/boston/massachusetts/united-states/usma0046/2017/1) (~15 average high, ~7 average low). Looking for an analog for a city that's about 4.5 C cooler than Boston gives a location like [Moncton, New Brunswick.](https://www.currentresults.com/Weather/Canada/Cities/temperature-annual-average.php) Colder, yes, but not buried under half a mile of ice.

My brain says that a place covered by ice is far colder than current temps minus 4.5 C, and that since the ice sheets covered so much of the earth, I can safely skirt the "climate is global, you're looking at local temps" hangup. So what gives? **How can a climate like Boston's cool by "only" 4.5 C and support such enormous glaciers?** It would seem that the presence of such enormous ice sheets would imply that the average temperature must have been far colder than that...

**Tags:** climate-change

> **Comments:**
> **username_1**: you are mixing apples and oranges.  It says the GLOBAL climate changes by 4.5 C.  That doesn't mean Boston's climate changes by 4.5 C.  Keep in mind that the average global temperature change will not be evenly distributed.  You should expect high latitudes and high altitudes to undergo the most temperature change, while the ocean surface and tropical zones will undergo the least temperature change.  
> **username_0**: ok...makes sense. could you direct me to any layman-friendly resources to get a better handle on how the climate change might realistically be distributed? From your comment, I'm imagining something along the lines of "70-90 latitudes drop by 15 C, 50-70 latitudes drop by 10 C, 30-50 drop by ..." etc. Is that idea (if not the numbers, which I just made up...) roughly accurate?  
> **username_1**: Ugh, I don't know of any images that show global cooling scenarios.  Will warming work for you?  You can see this image:  https://www.ipcc.ch/report/graphics/images/Assessment%20Reports/AR5%20-%20Synthesis%20Report/SPM/SPM.07_rev1-01.png  RCP 2.6 is "a little warming" and RCP 8.5 is more of a worst case scenario.  
> **username_0**: oh, absolutely. I'm using cooling to get my head around the problem, since we actually have the historical data, warming is just turning the problem around, and is what I'm really trying to understand anyway. Thanks very much!  
> **username_2**: Perhaps one factor that's missing is that glaciers flow.  For a northeast glaciation, the snow probably starts accumulating in northern Canada, with ice flowing south as it reaches sufficient depth.  (Scooping out the Great Lakes, Finger Lakes, and other features on the way.)  And of course, since ice & snow are reflective, the temperature on the glacier tends to be much lower than average, leading to further snow accumulation...  
> **username_3**: I haven't either heard of any global cooling scenarios.. It would be an interesting research topic though: make sun suddenly emit less and see how and where the glaciers will grow. By the way xkcd had the palm trees wrong, palm trees would die at the poles due to half a year without sunlight.  
> **username_4**: @username_3 - Even in today's cold climate (historically), we have many trees living north of the Arctic circle, limited more by temperature than sunlight. It's easy ti imagine a species of palm tree that is adapted to months without sunlight, given warm enough conditions.  
> **username_3**: @username_4 easy to imagine, but many factors play against it. The very shape of palm trees is optimal for near zenith angle sunlight, while e.g. spruce is better for low angle. Even with ten degrees global warming the continental Antarctic would still experience freezing temperatures that kill most trees without needles. Currently no trees live right at the poles. Antarctic continent would probably look more like current arctic tundra (no trees at all).  
> **username_4**: @username_3 - https://en.wikipedia.org/wiki/Polar_forests_of_the_Cretaceous  Remember that the Cretaceous was fantastically warm compared to the present day.  
> **username_3**: @username_4 from that wiki page: 'In this Cretaceous greenhouse world, Arctic conifer forests were considered predominantly deciduous, while those that grew on Antarctica contained a significantly greater proportion of evergreens'. And during that time, similar to now, the north pole wasn't continental and the south pole was.  

---

## 1 answers

### Answer by username_4 on 2017-07-21. Score: 6 | Accepted answer

I was able to dig up this (although without being able to find full sources):

[![ice age temp map](https://i.sstatic.net/scD2h.gif)](https://i.sstatic.net/scD2h.gif)

It shows a pattern where the temperatures are dramatically lower where ice sheets have built up relative to today. Interestingly, a lower overall temperature means weaker mixing across latitudes, so some areas are actually warmer. Boston gets chilled by -20 according to the map.

Also note the altitude effect. If the surface is raised by 1 kilometer, then due to the [lapse rate](https://en.wikipedia.org/wiki/Lapse_rate), the temperature at the new surface will drop by 6.5 degrees. This is a *very* important factor in stabilizing large ice sheets.

> **Comments:**
> **username_0**: Very cool. No pun intended. Also, first I'd heard of lapse rate. Thanks for the answer!  

---

