# Antarctic Climate on Greenhouse Earth

Scenario: Say we have a massive release of greenhouse gases into Earth's atmosphere, however much for the ocean around Antarctica to get just warm enough for hurricanes to form during the summer (28.5 degrees Celcius). Let's also say that the Southern Ocean has circumpolar currents that are strong enough that it is a reasonable approximation to consider the continent as an isolated system where the climate is not really influenced by the layout of the continents and oceans in other parts of Earth. What would the climate of different regions of the continent look like?

I am aware of this thread, however I am concerned with what climate different areas of the continent would have. I have had a shot at modelling it below, and would be very interested in getting opinions:

I think that a number of factors make modelling the climate different at the poles than on other places on Earth.

1) Long polar days and polar nights mean that there is a lot of time for solar heat to create deep low pressure systems over land in summer, and powerful high pressure systems in winter. Like sea breezes during the day and land breezes at night, but with a lot more time for the pressure differential to really ramp up.

2) The Coriolis effect is stronger at the poles, meaning stronger deflection of winds that would otherwise flow from high pressure systems to low pressure systems. This would mean that these areas are more pronounced and persistent, with the end result that climate/weather can undergo more pronounced changes over shorter distances than elsewhere on the globe.

Specific to Antarctica, there are a number of geographic factors that I think will influence the climate (going by the map below):

1) Slightly to the top right of the centre, there is a large plateau region that is around 2,000 metres plus altitude. If this can hold a remnant of the ice sheet, then it will have a huge influence on the climate, similar to what the Tibetan Plateau did when it was glaciated during the the last Ice Age. Specifically, the albedo effect will cause a large high pressure system on top of it that persists through summer.

2) This high pressure system would draw dry air from the land areas in the top right of the map, down over the South Polar area, making this a desert. Around the South Pole, there are some areas that are below sea level but cut off from the ocean by ridges. My guess is that these would dry out and become basins rather than inland seas (and hence not moderate the climate).

3) The rest of the continental landmass would develop a low pressure system in summer. Since air flows around this clockwise, the top right part of the map would have a summer monsoon along the coast and for some distance inland. However during the polar night they will cool faster than the ocean, meaning that the high pressure system will be able to spread from the ice covered plateau all the way to the coast. Winters in the top right part of the map will be cold and dry.

4) In the bottom right quadrant of the map, there are two huge bays, however they are very shallow, and would hence not hold heat as well as a deep ocean. In summer they will be a source of moisture for the monsoon winds to pick up and dump on the landmass to the top of it. This effect will be less pronounced further away from the landmass, and people living on islands here face the risk of the summer monsoon coming late or failing in some years. However in winter they will be exposed to the winds blowing anti-clockwise around the expanding high pressure system. As these cold winds blow over the two bays, they will cause heavy snowfall similar to that seen in the Great Lakes snowbelts or NW Japan, though since the bays are so shallow, parts of them will eventually freeze over and shut the snowfall down in some areas.

5) Moving futher around the map, directly at the bottom there is a huge North-South mountain range with a deep gulf on one side and the previously discussed shallow bay region on the other. In winter, the high pressure system will cause air to flow anti-clockwise, causing the deep gulf side (on the left) to be windward and the shallow bay side (on the right) to be leeward. These mountains will be high enough to cause a rain shadow effect, meaning that the deep gulf side will get heavy rain and snow, and the shallow bay side will be dry. In summer, both sides of the range will be dry as they are surrounded by ocean with no large landmasses nearby, and will hence be smack bang in the middle of high pressure systems.

Is this climate system feasible? Or have I overlooked something?

• If you get water at that latitude to 28 C, what is happening elsewhere? – Sherwood Botsford Nov 6 '17 at 15:44

I would do this as a comment, as it's not an answer, but comments don't have enough room or allow paragraphs.

If you get water at that latitude to 28 C, what is happening elsewhere?

Remember that the arctic circles with an average solar elevation of something like 12 degrees so that over the year you are getting 20% of the solar flux that you get at the equator. Most of the heat in the arctic regions is imported.

OTOH, in warm periods the arctic regions had a much smaller temperature differential from the equator than they do now. Since I've heard of no 'vast deserts' at the equator of the time, equatorial temps were close to the same. But higher temps mean higher evaporation. Even 5 degrees at the equator would increase the moisture holding capacity of the air by 35 percent or so.

Even during the warm periods, however, temps at the poles were still in the teens. Similar to, say, London, UK To get tropical temps to the poles you would have to either slow down radiation from the poles, or speed up heat transfer by another big dollop (50% more?) than it was during the warm periods.

To get another 50% increase in equatorial evaporation would require something like another 7 degree increase. Now you do have deserts on land, you have ocean surface temperatures at the equator in the upper 30's, likely semi-continuous hurricanes.

This could be negative feedback. Lots of bright white cloud tops reduce insolation at the equator, reducing absorbed light, lowering the temp. This may be one reason the equator didn't cook in the past.

So the tropical regions expand. The hurricane belt spans all oceans up to high latitudes.

Clouds block surface radiation. So rather than a huge increase in thermal flux to the poles, most of it happens with decreased radiation outbound.

If your high plateau acts the way you suggest, you will have cold air flowing off the plateau. Combined with warm wet air over your ocean, I suspect that you are going to get a ring of tornados and violent thunderstorms where these two systems collide.

• Thanks for the answer! As for climate lower latitude climate, I was also thinking that there would be a big increase in sea surface temperatures. However, I hadn't bothered to calculate if the climate would be desert or not, because ocean surface temperatures in the high 30s means air wet-bulb temperatures over 35, which humans can't survive without air conditioning. So there would be a band extending out from the equator where humans can't live at sea level. I'm sure some natural species would find a niche and form ecosystems, but humans would be restricted to isolated mountain pockets. – Worldbuilder_Wannabe Nov 7 '17 at 2:41
• I had guessed that there would be a ring of violent thunderstorms, but hadn't thought about tornadoes at all. Where would this ring be most likely to include tornadoes? Over land or over water? And what seasons would be most prone to them? As the ring is contracting during spring? At the ring's minimum point during summer? As it is expanding outwards again during autumn? Or at it's winter maximum? – Worldbuilder_Wannabe Nov 7 '17 at 2:44
• @Worldbuilder_Wannabe You're pushing my met knowledge. In the U.S. the worst tornados occur when a dense cold airmass is imported from Canada, and collides with soggy air off the Gulf of Mexico. Hurricanes often have embedded tornadoes. My guess is that the worst zone would be on the slope down to the ocean, as this would maximize mixing. You may be able to get areas of sub 35C wetbulb at the coast with the right combination of ocean and air currents. I said desert because most plants shut down at those temps too. – Sherwood Botsford Nov 7 '17 at 15:38
• Just did some reading on tornado formation. In addition to the airmass collision you described, it is also strongly enhanced by the following factors: 1) Presence of large bodies of land next to mountain range(s) running North-South 2) Absence of mountain ranges running East-West. This explains why Asia has nothing like America's tornado alley, in spite of having the conditions you describe (cold air from Siberia bumping up against warm moist air from the Pacific). So, excluding tornadoes associated with hurricanes, Antartica would have 2 "tornado alleys" at 12 and 2 o'clock. – Worldbuilder_Wannabe Nov 9 '17 at 15:45

# Don't forget isostatic rebound

When an ice sheet melts, the land under it, formerly crushed by miles of heavy ice, will rise. Given the relative densities of ice and aesthenosphere (the liquid-ish part of the mantle right under the crust that gets displaced by the weight of the ice) the ratio of ice to rebound is about 3.3:1. That means if you have 3.3 km of ice in parts of Antarctica (which you do) then the land will rise about 1 km once the ice is melted.

The rebound can happen relatively fast at first, many centimeters per year. Since it would take centuries to melt the Antarctic ice sheet anyways, by the time your cap is melted and the southern circumpolar is up to a balmy 28 C, you would be looking at hundreds of meters of rebound. Even today, 12,000 years after the end of the last glacial maximum, Northern Europe and the area around Lake Superior are rising at over 1 cm per year.

# Don't forget changing sea levels

The antarctic ice sheet has 26.5 million km$^3$ of ice. The world's oceans have a surface are of 510 million km$^2$. Ignoring density changes, you are looking at at least 50m of sea level rise if the Antarctic Ice sheet melts.

Combined with isostatic rebound, these two effects can dramatically change the geography of future Antarctica.