Learning from the past: polar ice caps and climate chaos

Months ago, I wrote a second article for The Natural Planet school magazine, but it has not been published and I suspect the editor rejected it without informing me. Then, I decided to include it in this blog, seeing as I have not written anything for ages. 

Since I was working against an upper word limit, I had to skipp the explanations to many of the processes involved, but if anything is unclear, please ask and I'll be happy to try to explain more comprehensively. 

We are all aware that the ice sheets at the poles are melting as you are reading this. We hear about its consequences on a regular basis: that the sea levels will rise, flooding cities and crop fields, that the polar bears’ natural habitats will be destroyed, and so on. However, exactly what will change in the future is very hard to tell. Maybe, just maybe, we could find some clues in prehistory: if we study what happened when the ice caps first formed and in what ways the world changed in response, perhaps we could tell something about what we can expect when we cause the reverse. 

Before the Eocene epoch (56-34 million years ago), Earth was in a greenhouse phase: high concentrations of atmospheric carbon dioxide and the absence of glaciers created a warm, humid world with productive oceans and dense tropical forests teeming with tiny mammals – no larger than modern rodents – since being small makes it easier to move through the thick vegetation.

What caused the Earth to cool down in mid-Eocene is not crystal clear, but it is likely a combination of several factors. A typical explanation is relating it to the Milankovitch cycles, a mathematical model for how the Earth’s orbit, change in tilt of the axis, and the way the axis wobbles, control surface temperatures.

In addition, the previous greenhouse conditions caused huge blooms of plants and algae; many of these were not decomposed, for some reason, so huge amounts of carbon were removed from the carbon cycle and atmospheric carbon dioxide decreased noticeably. (Today, by burning fossil fuels, we are reinserting massive amounts of carbon into the cycle, while deforestation and ocean pollution kills off the organisms that can sequester it from the air, which is why we see such an increase in carbon dioxide.)

Also, the movement of the continents caused changes in the ocean currents in such a way that the global heat transport to Antarctica was hindered: as South America and Tasmania detached from Antarctica, the Antarctic Circumpolar Current – a current of cold water that encircles the continent – effectively isolated the Antarctic region from warm water currents. With no heat influx, the continent quickly froze. Other tectonic rearrangements (e.g. the closure of the Tethys sea) may be accountable for the glaciers in the North Pole.

The polar glaciations bound huge amounts of water into ice, so, naturally, the sea levels regressed and the air was stripped of moisture. The next epoch, the Oligocene, thus saw the tropical jungles everywhere replaced by vast plains of grass, which is more resilient in dry, cold conditions. On these open spaces, the mammals grew much larger, and with tough, nutrient-poor grass as the main food, certain mammals with more sophisticated stomachs (especially the ruminants, such as deer, cows and goats) did extremely well and replaced their predecessors as the dominant herbivores.

This might not sound very dramatic, but this transition was actually a minor extinction event, where as much as 20% of all life at that time may have become extinct. The ones that did well did so because others could not cope with the drastic changes!

As the Eocene life perished, the plants and animals we are more familiar with today – most notably, grasses and cattle – emerged. They are adapted to such conditions, and, if we reverse the processes that brought them success, we could see our main food stocks crumble. Warmer, more moist conditions may favour increased yield in our crops, but it will favour interfering organisms such as weeds and insects more, forcing us to expend more resources – probably oil and nasty chemicals – on crop management. Even though we take special care of the crops and cattle so that they have little competition, the more unsuitable the global climate becomes, the harder it will be to maintain the food production, which is already dwindling.