Permafrost puts heat on climate targets

As the planet warms, this frozen northern soil is going to continue to thaw - and as it thaws, it's going to release carbon dioxide and methane into the air. Photo / AFP

With only days left, tensions in Paris are rising as countries race to resolve outstanding differences and forge an agreement that - hopefully - will set the planet on a path to avoiding the worst consequences of climate change.

The goal is an agreement that would set the world on a path to limit warming to below 2C, or perhaps even 1.5C, above pre-industrial levels. But at a news conference at the Le Bourget conference centre, scientists pointed out a factor that could make hitting these targets quite a lot harder.

It's called permafrost.

As the planet warms, this frozen northern soil is going to continue to thaw - and as it thaws, it's going to release carbon dioxide and methane into the air. A lot of it, it turns out. Potentially enough to really throw off the carbon budgets that have been calculated in order to determine the maximum emissions that we can release and still have a good chance of keeping warming to 2 C or below.

Susan Natali of the Woods Hole Research Centre explained that with a very high level of warming, permafrost emissions this century could be quite large. "We're talking about another emitting region that's currently not included in our emissions scenarios," she said.

Natali and her Woods Hole colleague and fellow permafrost expert Max Holmes also noted that permafrost emissions don't end at 2100 - they are expected to continue after that and even get worse.

"Most of the release will happen after 2100," said Natali.

That's a big problem because the global carbon budget is fixed, and after it is exceeded there can be zero further emissions.

Because carbon dioxide lasts so long in the atmosphere, you don't get to start with a fresh budget in the next century. So permafrost emissions beyond 2100 would also have to be taken into account, and would restrict the budget even further.

Permafrost is a potential carbon bomb because over thousands of years, dead plant life has been slowly swallowed up by the soil but has not decomposed. Plants pull carbon out of the atmosphere as they grow, but release it again when they die and decompose. As permafrost warms and thaws, microbes will have more ability to break down the plant life it contains, which is what will trigger a steady stream of emissions.

"It's just like you put celery in your freezer and then you turn your freezer into a refrigerator, and it starts to rot," said Holmes.

How bad can it get?

Heatwaves: 1.5 billion people will be exposed to heatwaves every year by 2100 under 2C, according to Avoid 2, a British government-funded consortium of climate change research institutes. A severe heatwave could happen once every four years in a 2C-warmer world, and biennially under 3C, according to French climatologist Jean Jouzel.

Flooding: An estimated 30 million people would be affected by flooding every year by 2100 under 2C, says Avoid 2. This would rise to about 60 million under 3C.

Rising seas: According to Jouzel, sea levels would be about 40cm higher by 2100 in a 2C-warmer world by 2100, 60cm at 3C. Ice sheets in Greenland and Antarctica would shed mass faster than ever, melting glaciers, and oceans that expand as they warm.

Water dilemma: Global warming can lead to long-running droughts and devastating floods, meaning some parts of the world will not have enough water and others too much.

Humanitarian crises: Millions more people will be pushed into poverty, conflict ove0r water, while other dwindling resources could fuel mass migration or war.

Loss of treasures: From the coral of the Great Barrier Reef to Mount Fuji and the canal-crossed city of Venice, global warming may spell the ruin of some of the most precious jewels of nature and civilisation.

- Washington Post, Bloomberg, AFP