Tipping points - Frans-Jan W. Parmentier

Not content with the summer weather? Try a holiday in Siberia! The remote arctic village of Verkhoyansk was – until now – famous for being the coldest inhabited place in the world since they hold the record with a temperature of 67.8 degrees below zero. But that was 128 years ago. Last month, temperatures rose to 38 °C, which is unprecedented for any location above the Arctic Circle.

You may have been unaware that summers in Siberia can get quite hot. I didn't know that either until I experienced it for myself. I almost got sunstroke during the traditional celebration of Yhyakh, the midsummer festival of the Sacha in Yakutsk. I have also experienced temperatures close to 30 °C on the northeast Siberian tundra, not far from the Arctic Ocean – while I was cooling my feet in a pool of icy water on top of the thawing permafrost. In other words, some heat isn't that uncommon – but this year is different.

Temperatures have been about 3 to 7 degrees above normal in most of Siberia since January. Such a large temperature deviation over such a long period is so unusual that a group of climate scientists calculated that this would have been virtually impossible if we had not polluted the atmosphere with greenhouse gases. This is worrisome. Global warming, driven by humans, may push the climate system beyond a tipping point.

I already mentioned permafrost, which is ground that is permanently frozen – sometimes for thousands of years. Most of it is located in Siberia. This frozen soil contains immense amounts of carbon, mainly from old plant and animal remains that have been well preserved. So well in fact, that mammoths are found in the permafrost with their fur still perfectly attached.

If the permafrost thaws, all that organic matter starts to rot, releasing CO₂ or the even stronger greenhouse gas methane. This creates a self-amplifying effect: the additional greenhouse gases cause a warming of the atmosphere, which leads to more permafrost thaw and yet another release of greenhouse gases. This then leads to even more warming and so forth.

But that's not all. On top of the thawing permafrost stands a vast forest: the Siberian taiga. The heat and persistent drought of this summer caused hundreds of wildfires to erupt, emitting some 56 megatonnes of CO₂ in June alone – according to satellite measurements from ESA. For comparison, that's only a few megatonnes above the annual greenhouse gas emissions of Sweden. Much of that CO₂ is taken up again when the forest grows back, but in the meanwhile the blackened soil will absorb much more sunlight than usual, causing the soil to heat up further and the permafrost below to thaw deeper. Again, a self-reinforcing effect.

The numerous forest fires also emit large amounts of soot. When the soot settles on snow and ice, it will become darker and melt faster. And sea ice was already at a low point due to the exceptional heat: on July 14th, 187,000 km² of sea ice melted within one day. That is over half the surface area of Norway. It is quite possible that sea ice will hit an all-time low in September.

When sea ice melts, it not only directly affects life in the Arctic Ocean, such as polar bears, seals, fish and algae, but it also affects the climate. Sea ice reflects most sunlight, while seawater absorbs most solar radiation. More open water causes the ocean to heat up, which means that it takes longer for the sea to freeze back up again in the autumn. As a result, air temperatures above the nearby land remain higher, which means that there is no snow, and soils take longer to freeze over. In this way, one tipping point – the disappearance of sea ice – can accelerate another tipping point, such as the release of greenhouse gases from permafrost soils.

These are examples from just one part of the world, but there are many other tipping points, such as a change in the Gulf Stream, the destruction of the Amazon, and the rise in sea level due to the melting of glaciers and ice caps on Greenland and Antarctica. These tipping points have in common that we are aware of their widespread consequences, but that there is a high uncertainty on when and how forceful they will strike, or how they influence each other.

The corona crisis has shown us that governments, despite being faced with major uncertainties, are able to enforce strict measures. Risks surrounding the new, unknown virus were minimized as much as possible following the precautionary principle. But in the climate crisis, governments act towards the opposite: It seems to be their aim to emit as much CO₂ as possible in the vain hope that no tipping point will be crossed – even if we don't know where that limit may be. In that regard, Siberia's symptoms should be seen as a serious warning: that it is high time to cure the patient, rather than to sicken her knowingly.