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Antarctica receives heat from the Sun every day, so how does it stay frozen?

I have some thoughts about the answer but I'm unsure of whether it is correct; I hope people here can clarify.

My idea: the heat that Antarctica receives from the Sun is always 'travelling' from one spot to another, but the heat does not stay in a spot long enough to melt the ice.

Please correct me if I'm wrong, thanks.

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  • $\begingroup$ The Earth is a complex system, so there are many factors at play. $\endgroup$
    – Jimmy360
    Mar 25, 2015 at 12:29
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    $\begingroup$ Not every day. There are months of darkness... $\endgroup$
    – mankoff
    Mar 29, 2015 at 11:25
  • $\begingroup$ The simple answer is that Antarctica does not receive enough heat, since surface is at a low angle to the incoming sunlight. Additionally, it is covered with snow & ice, which reflects a lot of the incoming energy. $\endgroup$
    – jamesqf
    Mar 30, 2015 at 21:32

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It doesn't stay frozen. Ice evaporates (or sublimates is the correct term) under direct sunlight, but that's at a molecular level, it doesn't melt, it goes from solid to gas under sunlight and in the cold, some of this newly formed water vapor goes back being to ice.

In an absolutely dry climate, well below freezing, ice would slowly sublimate and disappear. In a warm dry climate, ice would melt (much faster), then it would evaporate. The sun does sublimate ice off the antarctic ice sheet every day, but quite a bit less than is added by snow and condensation from moisture due to temperature change and brought over by wind. The antarctic ice sheet is also, always moving. Mostly Antarctica loses ice by pushing it into the ocean - over long periods of time and it gains ice by (see above) snow and condensation. The ice has been on Antarctica for over 30 million years, but as far as I know, the oldest ice core we've found there is about 1.5 million years old. Everything moves.

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First of all, the Earth does not receive heat from the Sun, it receives visible light that is absorbed by the surface of the Earth and then heat is re-radiated back into the atmosphere. If the surface is ice/snow, most of the light from the sun is reflected back to space. Sunlight will sublimate a little bit of the ice, but it is normally replenished at a faster rate than it is lost.

Ice endures through the summer in Antarctica, even as the air warms up. This is in contrast to the ice at the Arctic pole that completely melts every summer. This is for 2 reasons:

  1. Unlike the arctic, the ice in Antarctica is on a continental shelf, so there is no water beneath it to help melt the ice.
  2. Antarctica is the highest continent on Earth, with an average elevation of 8,200ft. At that elevation and within the polar region, ice can persist indefinitely because the average atmospheric temperature is very cold. At high elevations, there is little atmosphere to trap any heat radiated by the Earth, which is why the air is so cold at high elevations.

For these reasons, ice near the coast of Antarctica typically is lost much faster than ice in the mountains.

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  • $\begingroup$ the Earth does not receive heat from the Sun — what do you mean by this? The Earth receives 340 W/m² of heat from the Sun. Visible light carries the bulk of this heat. The Earth atmosphere only absorbs the solar heat mostly indirectly (when re-radiated from the Earth surface), but to state that the Earth does not receive heat from the Sun is probably not what you mean to state (since, of course, it does). $\endgroup$
    – gerrit ♦
    Oct 14, 2019 at 12:38
  • $\begingroup$ The earth receives solar radiation from the sun, not heat. In order to transfer heat, conduction is required. Space is void of enough material to sustain any significant temperature, so no measurable heat is conducted from the Sun to the Earth. Solar radiation is absorbed by the surface of the Earth and then the energy is radiated back to the atmosphere in the form of infrared, which is captured by the atmosphere and measured as "heat". $\endgroup$
    – f.thorpe ♦
    Oct 15, 2019 at 3:13
  • $\begingroup$ Heat can be transferred by conduction, convection, or radiation. The Sun transfers heat to the Earth (essentially) exclusively through radiation. Solar (visible) radiation carries energy exactly like terrestrial (infrared) radiation does, the difference being that the clear-sky atmosphere is mostly transparent to visible radiation and partially opaque to infrared radiation. Solar radiation turns into heat as soon as absorbed by the Earth surface (which then reradiates it to the atmosphere). Either way, the heat that the Earth receives is undoubtedly from nuclear fusion processes in the Sun. $\endgroup$
    – gerrit ♦
    Oct 15, 2019 at 7:32
  • $\begingroup$ Equating radiation to heat energy isn't appropriate. Heat energy of electromagnetic radiation can be calculated, but thermodynamic heat is not the same thing as electromagnetic radiation. $\endgroup$
    – f.thorpe ♦
    Oct 16, 2019 at 2:22
  • $\begingroup$ Indeed, electromagnetic radiation is not the same as heat, but the heat on Earth is clearly originating from energy carried by electromagnetic radiation energy transfer from the Sun. Radiation transfers heat. $\endgroup$
    – gerrit ♦
    Oct 16, 2019 at 7:28
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userLTK has explained that not all of the ice in the Antarctic stays frozen all the time. But perhaps there's a more basic view needed : sunlight in temperate areas melts all of the ice quite quickly, so why doesn't the same happen in Antarctica?

There are a number of reasons, but the simplest (and probably most important?) is one of geometry, and the way that sunlight reaches parts of the planet's surface.

Imagine that you are shining a torch onto a ball, where the beam from the torch is circular and much smaller than the ball.

  • If the beam hits the middle of the ball, it appears as a small circle on the ball's surface.
  • If the beam hits near the top or the bottom of the ball, it covers a larger area of the ball's surface - so that any given point receives less light.

The same is true for the earth. Near the poles, the light from the sun is "skimming" the planet rather than hitting at right angles, and so any given amount of energy leaving the sun is spread over a wider area near the poles, and is thus less intense. So, the amount of energy landing in Antarctica per square metre is much less than it is near the equator.

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