<p>Polar regions are colder than equatorial ones for a simple reason - geometry.</p>

<p>More specifically, it is caused by the greater angle of the Sun's rays to the surface of the Earth. As you go farther north, the Earth's (mostly) spherical surface bends back from the direction of the Sun's rays, and the same amount of photons are spread over a larger area.</p>

<p>What's more, the closer you get to the poles, this already-attenuated sunlight has to go through more of the Earth's atmosphere, and so more sunlight is <a href="http://en.wikipedia.org/wiki/Rayleigh_scattering" rel="noreferrer">scattered</a>, and consequently less will reach the ground.</p>

<p>Here's an image (Thanks, Pont) to show the difference:
<a href="https://i.sstatic.net/WfajV.png" rel="noreferrer"><img src="https://i.sstatic.net/WfajV.png" alt="Insolation at different latitudes"></a><br>
<sup>Source: <a href="https://commons.wikimedia.org/wiki/File:Oblique_rays_04_Pengo.svg" rel="noreferrer">Wikimedia Commons</a>. License: CC BY-SA 3.0</sup></p>

<p>The sun's angle is more important to climate differences than the modest variation in Earth's distance to the sun, because the atmosphere is kept warm by the <a href="http://en.wikipedia.org/wiki/Greenhouse_effect" rel="noreferrer">greenhouse effect</a>. It's not the direct light that matters: Air is more or less transparent to the visible light that makes up most of the Sun's spectrum. Instead, the ground absorbs that light and reradiates it as infrared and microwave radiation. That longer-wavelength radiation is absorbed by the atmosphere, but if the ground is not radiating as much infrared because it absorbed less sunlight, the atmosphere above it doesn't get warmed quite so much.</p>

<p>Granted, if the Earth's orbit were much more eccentric then the variation in distance to the Sun would matter more to climate variation. But it doesn't.</p>

<p>This would happen even if Earth's axis weren't tilted. Polar regions would still be cold and equatorial regions would still be hotter. In fact, the difference would be greater because there'd be less mixing.</p>

<p>The image below shows the what happens to the energy the Earth receives from the Sun:</p>

<p><a href="https://i.sstatic.net/m5ZXz.png" rel="noreferrer"><img src="https://i.sstatic.net/m5ZXz.png" alt="Earth&#39;s energy budget"></a><sup>Source: <a href="https://earthobservatory.nasa.gov/Features/EnergyBalance/page6.php" rel="noreferrer">NASA</a></sup></p>

<p>That shows an average over the entire Earth. As you approach the poles, the percentage "reflected by clouds and atmosphere" goes up while total energy "absorbed by surface" per unit area goes down. And since ice has a high albedo, this is reinforced by the percentage "reflected by surface".</p>

CC BY-SA 3.0
2017-04-11T20:10:15.027Z
So does this mean that if I were to place a ball outside in the sun, that the equator line would be significantly warmer than the polar regions? Surely this would never happen.
bmende
CC BY-SA 3.0
2017-04-14T08:20:52.137Z
@bmende Depends on the size of the ball and its internal energy budget. The heat we are talking about in this context is transferred by radiation and everything is well explained in the answer and follows the most basic geometric rules.
user2821
CC BY-SA 3.0
2017-04-14T18:24:54.013Z
@bmende: If you placed the ball in a vacuum, so that it wasn't warmed by convection, and made it of an insulating material, it would be obvious.  Why not try it?  Or just compare common things - say a lawn chair with the back laid flat, vs with the back tilted perpendicular to the sun.
jamesqf
CC BY-SA 3.0
2017-04-15T14:42:01.010Z
@jamesqf Are you saying I will see the appropriate results with a vaccuum chamber? Unfortunately many answers to questions like these involve the invisible space vacuum, that's how they dodge questions like these. But they still won't be able to deal with the reality that the [earth doesn't curve](https://www.youtube.com/watch?v=8RXbEhkLt3U&t).
bmende
CC BY-SA 3.0
2017-04-15T19:10:25.007Z
@bmende: No, I'm saying that if you do the experiment in a vacuum, and make the ball out of a good thermal insulator, you will eliminate the effects of convection & conduction, and so see just the radiation effects.  As for your claim that Earth doesn't curve, sorry, but I've been high enough to see it for myself.
jamesqf
CC BY-SA 3.0
2017-04-17T13:41:40.843Z
Spencer - the image you posted is a partial extract from a Trenberth radiative flux diagram. Not sure where you got it like that or whether you have modified it yourself but it has had removed the very important figures for radiative flux (measured in W/m^2) apart from the one of 340 for incoming solar. This bastardisation of a diagram is abhorrent because it is likely to mislead and confuse. Can you get the correct full version posted instead please and make clear that radiative flux figures and directions are NOT heat transfer or energy transfer quantities/directions figures/directions .
user7733
CC BY-SA 3.0
2017-04-17T14:12:23.207Z
@user7733 There is an obvious link to NASA's website under the image. If you don't like it, take it up with them.
Spencer
CC BY-SA 3.0
2017-04-08T02:13:13.450Z
2017-04-15T21:21:23.870Z
2017-04-15T21:21:23.870Z
Spencer
<p>The major reason isn't Earth's distance to the sun. The major reason is that earth's axis is tilted. The Arctic circle, for example, sees 24 hours of darkness in the winter, and 24 hours of sunlight in the summer.</p>

<p>If you go to the other side of the equator, you'll note that the seasons seem switched- the southern hemisphere is warmer in the winter than in the summer.</p>

<p>Take a look at how much sunlight each day has- you'll note that in the summer, the northern hemisphere has more hours of sunlight than the winter. The opposite is true for the southern hemisphere.</p>

CC BY-SA 3.0
2017-04-07T21:55:53.850Z
There is 24-hour arctic sun footage, but no 24-hour footage from the antarctic.
bmende
CC BY-SA 3.0
2017-04-08T01:54:20.420Z
Actually, if Earth's axis weren't tilted, polar regions would still be cold and equatorial regions would still be hotter -in fact, the difference would be greater because there'd be less mixing.
Spencer
CC BY-SA 3.0
2017-04-08T02:39:11.760Z
@Bmende there is midnight sun in Antarctica as well, during the southern summer. Also the days in e.g. Australia and South Africa are longer in December than in June.
user2821
CC BY-SA 3.0
2017-04-08T13:56:16.523Z
@bmende -- https://www.youtube.com/watch?v=BgZa9oZDN5g
David Hammen
CC BY-SA 3.0
2017-04-08T17:04:06.170Z
@DavidHammen It's fake. Take a look at this [screenshot](http://imgur.com/a/1C5Tv) I took. The rays disappear when they shouldn't. So then the question is, why are they faking it?
bmende
CC BY-SA 3.0
2017-04-08T17:41:59.850Z
@bmende those are clouds that block the sun
BarocliniCplusplus
CC BY-SA 3.0
2017-04-08T18:04:16.890Z
@bmende - Those are crepuscular rays. Go outside sometime; you can see those anywhere. I am getting the distinct impression that you are indeed a flat earther. If so, that's kinda sad.
David Hammen
CC BY-SA 3.0
2017-04-08T18:26:04.543Z
@BarocliniCplusplus The clouds aren't in the way of the rays though. If you watch at 2:06 in the video the sun disappears behind the tiny camera legs. The video is obviously fake.
bmende
CC BY-SA 3.0
2017-04-08T19:03:36.580Z
@bmende It really depends on where you pause it. You can pause it between the legs, you can clearly see the sun. The solid angle of the sun is rather small, so the fact that the sun was eclipsed by the camera legs do not discredit the video.
BarocliniCplusplus
CC BY-SA 3.0
2017-04-17T13:51:33.233Z
@David Hammen . Actually it's quite helpful to see flat earthers or any other minority theories here. The very act of debating one's own sound scientific views with those of an opposite persuasion is good practice for later. Because later on you might be in a cutting edge field where this kind of debate is between two 50/50 camps. We need the practice ! Therefore not sad, but actually welcome and helpful. (Sometimes amusing too but I try not to laugh at others ignorance as it can cause offence).
user7733
CC BY-SA 3.0
2017-04-07T17:58:10.820Z
2017-04-07T17:58:10.820Z
BarocliniCplusplus
<p>If the earth is a globe and the sun is 93 million miles away, why is the equator the hottest place on earth?</p>

<p>In terms of distances to the sun, the distance to the equator is almost equal to that as the distance to the poles.</p>

<p>Around January 3, the sun is said to be about 91.4 million miles away, but on July 7, the sun is said to be about 94.5 million miles away. The earth is warmer on July 7 (summer time), and yet it is 3 million miles further than when it is in January, how is this possible?</p>

CC BY-SA 3.0
2017-04-07T18:07:44.417Z
Ignoring such things as axial tilt, seasons, and atmospheric transport, it's because the Earth is a globe.  At any given latitude (which I think you've confused with longitude: https://en.wikipedia.org/wiki/Longitude ) the insolation per unit area is proportional to the cosine of the latitude.  So if you had a solar panel and wanted to get the maximum energy from it, at the equator you'd lay it flat on the ground, while at the poles you'd stand it upright.
jamesqf
CC BY-SA 3.0
2017-04-07T22:13:56.280Z
@jamesqf This doesn't explain how a 3 million mile difference  in location of sun results in no expected temperature difference for earth. If the sun is 10k degrees ferenheight, 3 percent of that temperature is 300 degrees. The earth is supposed to be 3 percent closer to the sun during winter.
bmende
CC BY-SA 3.0
2017-04-08T00:12:10.777Z
@bmende actually it explains it perfectly, but I think it's a tiny bit complex if you don't understand.    A picture being worth 1000 words and all that:   http://www.windows2universe.org/earth/climate/images/sun_angle_insolation_big.jpg   It's all about the angle the sun is in the sky - hence, cosine of the latitude.
userLTK
CC BY-SA 3.0
2017-04-08T02:01:49.003Z
@userLTK so does this mean that if the earth were actually 88.4 million miles away during January (instead of 91.4) that there would be no change in earth's climate?
bmende
CC BY-SA 3.0
2017-04-08T02:08:04.843Z
@bmende No, both distance and angle matter.   Winter is, in one sense, colder because the sun is lower in the sky.   It's also in the sky less time.  The angle to the sun is generally more important, unless you vary the distance enormously.   The 3% distance variation between December and June is pretty small.  The change in angle of the sun in the sky and the length of a day varies much more than 3% unless you live very near the equator.  Both matter, the tilt or angle matters a lot more for most of the Earth.
userLTK
CC BY-SA 3.0
2017-04-08T04:51:19.607Z
@bmende: The reason the varying distance from the sun has no obvious effect is that it's much smaller than the variation caused by axial tilt.  If the Earth had no tilt, we'd possibly notice mild seasonal variation due to orbital eccentricity (like Pluto does).
jamesqf
CC BY-SA 3.0
2017-04-08T14:15:54.827Z
@bmende People often don't realize summer and winter are not global phenomenon, when it is winter in [most of] south america it is summer in north america. The earth is actually closer to the sun in northern winters [january].
John
CC BY-SA 3.0
2017-04-11T08:29:12.117Z
@bmende: put it this way bmende: the highest the sun gets at a Pole is 23.5° on solstice [source](http://keisan.casio.com/exec/system/1224682331). Compare that to another location using [this great tool](http://www.suncalc.org/#/37.7528,-100.0171,13/2017.06.21/18:53/1/2) (use the slider, it took me some getting used to). Dodge City, KS drops to the same elevation June 21st about 6:55 PM CDT. Despite the built-up heat from the peak of the day, by 7 PM CDT, it's indeed well cooling down. Or 94 minutes before sunset (or after sunrise) at the equator. Just don't get a lot of energy at that angle.
JeopardyTempest
CC BY-SA 3.0
2017-04-11T08:32:06.773Z
@bmende: And if you aren't convinced of increasing energy received when solar angle is higher, or how high the sun gets, compare your own observations. You can also get continual observation of solar energy in OK by looking at the bottom of mesonet.org/index.php/weather/meteogram (orange is actual measured solar energy received, grey is theoretical maximum). And http://www.mesonet.org/index.php/weather/mesonet_averages_graphs#series%5B%5D=nrmn%3Asrad_sm%3Aaverage%3AN%3A0%3A%230d233a%3AN%3A1%3AN&cptr=2 gives you tools to make an annual plot of daily maximums to see the annual variation.
JeopardyTempest
<climate><temperature>
If the earth is a globe, what causes temperature differences across lines of latitude?
bmende
# If the earth is a globe, what causes temperature differences across lines of latitude?

(Asked by: username_0 on 2017-04-07)

If the earth is a globe and the sun is 93 million miles away, why is the equator the hottest place on earth?

In terms of distances to the sun, the distance to the equator is almost equal to that as the distance to the poles.

Around January 3, the sun is said to be about 91.4 million miles away, but on July 7, the sun is said to be about 94.5 million miles away. The earth is warmer on July 7 (summer time), and yet it is 3 million miles further than when it is in January, how is this possible?

**Tags:** climate, temperature

> **Comments:**
> **username_1**: Ignoring such things as axial tilt, seasons, and atmospheric transport, it's because the Earth is a globe.  At any given latitude (which I think you've confused with longitude: https://en.wikipedia.org/wiki/Longitude ) the insolation per unit area is proportional to the cosine of the latitude.  So if you had a solar panel and wanted to get the maximum energy from it, at the equator you'd lay it flat on the ground, while at the poles you'd stand it upright.  
> **username_0**: @username_1 This doesn't explain how a 3 million mile difference  in location of sun results in no expected temperature difference for earth. If the sun is 10k degrees ferenheight, 3 percent of that temperature is 300 degrees. The earth is supposed to be 3 percent closer to the sun during winter.  
> **username_2**: @username_0 actually it explains it perfectly, but I think it's a tiny bit complex if you don't understand.    A picture being worth 1000 words and all that:   http://www.windows2universe.org/earth/climate/images/sun_angle_insolation_big.jpg   It's all about the angle the sun is in the sky - hence, cosine of the latitude.  
> **username_0**: @username_2 so does this mean that if the earth were actually 88.4 million miles away during January (instead of 91.4) that there would be no change in earth's climate?  
> **username_2**: @username_0 No, both distance and angle matter.   Winter is, in one sense, colder because the sun is lower in the sky.   It's also in the sky less time.  The angle to the sun is generally more important, unless you vary the distance enormously.   The 3% distance variation between December and June is pretty small.  The change in angle of the sun in the sky and the length of a day varies much more than 3% unless you live very near the equator.  Both matter, the tilt or angle matters a lot more for most of the Earth.  
> **username_1**: @username_0: The reason the varying distance from the sun has no obvious effect is that it's much smaller than the variation caused by axial tilt.  If the Earth had no tilt, we'd possibly notice mild seasonal variation due to orbital eccentricity (like Pluto does).  
> **username_3**: @username_0 People often don't realize summer and winter are not global phenomenon, when it is winter in [most of] south america it is summer in north america. The earth is actually closer to the sun in northern winters [january].  
> **username_4**: @username_0: put it this way username_0: the highest the sun gets at a Pole is 23.5° on solstice [source](http://keisan.casio.com/exec/system/1224682331). Compare that to another location using [this great tool](http://www.suncalc.org/#/37.7528,-100.0171,13/2017.06.21/18:53/1/2) (use the slider, it took me some getting used to). Dodge City, KS drops to the same elevation June 21st about 6:55 PM CDT. Despite the built-up heat from the peak of the day, by 7 PM CDT, it's indeed well cooling down. Or 94 minutes before sunset (or after sunrise) at the equator. Just don't get a lot of energy at that angle.  
> **username_4**: @username_0: And if you aren't convinced of increasing energy received when solar angle is higher, or how high the sun gets, compare your own observations. You can also get continual observation of solar energy in OK by looking at the bottom of mesonet.org/index.php/weather/meteogram (orange is actual measured solar energy received, grey is theoretical maximum). And http://www.mesonet.org/index.php/weather/mesonet_averages_graphs#series%5B%5D=nrmn%3Asrad_sm%3Aaverage%3AN%3A0%3A%230d233a%3AN%3A1%3AN&cptr=2 gives you tools to make an annual plot of daily maximums to see the annual variation.  

---

## 2 answers

### Answer by username_5 on 2017-04-08. Score: 18

Polar regions are colder than equatorial ones for a simple reason - geometry.

More specifically, it is caused by the greater angle of the Sun's rays to the surface of the Earth. As you go farther north, the Earth's (mostly) spherical surface bends back from the direction of the Sun's rays, and the same amount of photons are spread over a larger area.

What's more, the closer you get to the poles, this already-attenuated sunlight has to go through more of the Earth's atmosphere, and so more sunlight is [scattered](http://en.wikipedia.org/wiki/Rayleigh_scattering), and consequently less will reach the ground.

Here's an image (Thanks, Pont) to show the difference:
[![Insolation at different latitudes](https://i.sstatic.net/WfajV.png)](https://i.sstatic.net/WfajV.png)  
Source: [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Oblique_rays_04_Pengo.svg). License: CC BY-SA 3.0

The sun's angle is more important to climate differences than the modest variation in Earth's distance to the sun, because the atmosphere is kept warm by the [greenhouse effect](http://en.wikipedia.org/wiki/Greenhouse_effect). It's not the direct light that matters: Air is more or less transparent to the visible light that makes up most of the Sun's spectrum. Instead, the ground absorbs that light and reradiates it as infrared and microwave radiation. That longer-wavelength radiation is absorbed by the atmosphere, but if the ground is not radiating as much infrared because it absorbed less sunlight, the atmosphere above it doesn't get warmed quite so much.

Granted, if the Earth's orbit were much more eccentric then the variation in distance to the Sun would matter more to climate variation. But it doesn't.

This would happen even if Earth's axis weren't tilted. Polar regions would still be cold and equatorial regions would still be hotter. In fact, the difference would be greater because there'd be less mixing.

The image below shows the what happens to the energy the Earth receives from the Sun:

[![Earth's energy budget](https://i.sstatic.net/m5ZXz.png)](https://i.sstatic.net/m5ZXz.png)Source: [NASA](https://earthobservatory.nasa.gov/Features/EnergyBalance/page6.php)

That shows an average over the entire Earth. As you approach the poles, the percentage "reflected by clouds and atmosphere" goes up while total energy "absorbed by surface" per unit area goes down. And since ice has a high albedo, this is reinforced by the percentage "reflected by surface".

> **Comments:**
> **username_0**: So does this mean that if I were to place a ball outside in the sun, that the equator line would be significantly warmer than the polar regions? Surely this would never happen.  
> **username_6**: @username_0 Depends on the size of the ball and its internal energy budget. The heat we are talking about in this context is transferred by radiation and everything is well explained in the answer and follows the most basic geometric rules.  
> **username_1**: @username_0: If you placed the ball in a vacuum, so that it wasn't warmed by convection, and made it of an insulating material, it would be obvious.  Why not try it?  Or just compare common things - say a lawn chair with the back laid flat, vs with the back tilted perpendicular to the sun.  
> **username_0**: @username_1 Are you saying I will see the appropriate results with a vaccuum chamber? Unfortunately many answers to questions like these involve the invisible space vacuum, that's how they dodge questions like these. But they still won't be able to deal with the reality that the [earth doesn't curve](https://www.youtube.com/watch?v=8RXbEhkLt3U&t).  
> **username_1**: @username_0: No, I'm saying that if you do the experiment in a vacuum, and make the ball out of a good thermal insulator, you will eliminate the effects of convection & conduction, and so see just the radiation effects.  As for your claim that Earth doesn't curve, sorry, but I've been high enough to see it for myself.  
> **username_7**: username_5 - the image you posted is a partial extract from a Trenberth radiative flux diagram. Not sure where you got it like that or whether you have modified it yourself but it has had removed the very important figures for radiative flux (measured in W/m^2) apart from the one of 340 for incoming solar. This bastardisation of a diagram is abhorrent because it is likely to mislead and confuse. Can you get the correct full version posted instead please and make clear that radiative flux figures and directions are NOT heat transfer or energy transfer quantities/directions figures/directions .  
> **username_5**: @username_7 There is an obvious link to NASA's website under the image. If you don't like it, take it up with them.  

---

### Answer by username_8 on 2017-04-07. Score: 4

The major reason isn't Earth's distance to the sun. The major reason is that earth's axis is tilted. The Arctic circle, for example, sees 24 hours of darkness in the winter, and 24 hours of sunlight in the summer.

If you go to the other side of the equator, you'll note that the seasons seem switched- the southern hemisphere is warmer in the winter than in the summer.

Take a look at how much sunlight each day has- you'll note that in the summer, the northern hemisphere has more hours of sunlight than the winter. The opposite is true for the southern hemisphere.

> **Comments:**
> **username_0**: There is 24-hour arctic sun footage, but no 24-hour footage from the antarctic.  
> **username_5**: Actually, if Earth's axis weren't tilted, polar regions would still be cold and equatorial regions would still be hotter -in fact, the difference would be greater because there'd be less mixing.  
> **username_6**: @username_0 there is midnight sun in Antarctica as well, during the southern summer. Also the days in e.g. Australia and South Africa are longer in December than in June.  
> **username_9**: @username_0 -- https://www.youtube.com/watch?v=BgZa9oZDN5g  
> **username_0**: @username_9 It's fake. Take a look at this [screenshot](http://imgur.com/a/1C5Tv) I took. The rays disappear when they shouldn't. So then the question is, why are they faking it?  
> **username_8**: @username_0 those are clouds that block the sun  
> **username_9**: @username_0 - Those are crepuscular rays. Go outside sometime; you can see those anywhere. I am getting the distinct impression that you are indeed a flat earther. If so, that's kinda sad.  
> **username_0**: @username_8 The clouds aren't in the way of the rays though. If you watch at 2:06 in the video the sun disappears behind the tiny camera legs. The video is obviously fake.  
> **username_8**: @username_0 It really depends on where you pause it. You can pause it between the legs, you can clearly see the sun. The solid angle of the sun is rather small, so the fact that the sun was eclipsed by the camera legs do not discredit the video.  
> **username_7**: @username_9 . Actually it's quite helpful to see flat earthers or any other minority theories here. The very act of debating one's own sound scientific views with those of an opposite persuasion is good practice for later. Because later on you might be in a cutting edge field where this kind of debate is between two 50/50 camps. We need the practice ! Therefore not sad, but actually welcome and helpful. (Sometimes amusing too but I try not to laugh at others ignorance as it can cause offence).  

---

