If catastrophic climate change is to be avoided, it is critical that the massive stock of greenhouse gas held in the Arctic permafrost and in undersea deposits called methane clathrates not be allowed to enter the atmosphere. The permafrost and clathrates contain methane: a gas that is about 25 times more powerful than carbon dioxide, when it comes to preventing infrared radiation from escaping into space, keeping it within the Earth system and warming the planet. As the planet heats up from human greenhouse gas emissions, the threat of all this methane getting released increases.
Right now, there is even more methane on Earth than there was before the Paleocene-Eocene Thermal Maximum (PETM), a period about 56 million years ago when the methane bound up in the north got released over the course of several thousand years. Back then, those emissions made the planet’s temperature rise between 5°C and 9°C – far beyond the level which would be dangerous for human beings. And remember that this warming is on top of whatever warming arises directly from human emissions. According to the modeling conducted by the Met Office in the United Kingdom, if our emissions continue on a business-as-usual course, they will generate 5.5 – 6.1°C of warming by 2100. Just imagine what impact melting clathrates and permafrost could have in addition.
The PETM happened fairly slowly, but was nonetheless accompanied by the extinction of about half the planet’s marine life. Other species migrated hundreds or thousands of kilometres, as the climate in different regions changed. There were no ice sheets during the PETM, whereas Earth currently has enough ice in Greenland and Antarctica to raise sea levels by more than sixty metres. Human-induced climate change is happening far faster than what happened during the PETM. That makes it even harder for plants and animals to adapt. It also means there is less time for negative feedbacks (like increased weathering of rocks) to blunt the edge of the warming.
In addition to the vanishing multi-year sea ice, we are already seeing worrisome degradation of the Arctic permafrost. For instance, researchers in Quebec have found that the edge of where permafrost is found in one region has moved 130 km in just 50 years. The threat of kicking off a PETM-type event is one major reason why the warming caused by human beings must be limited. Because the amount of warming we produce is directly related to how many fossil fuels we burn, it is critical that humanity make the conscious choice to limit our fossil fuel usage. For the sake of protecting a planet that provides the foundation for human prosperity and survival, we need to leave fossil fuels underground and move to a clean and renewable global energy system that can keep operating forever.