As Sea Ice Melts and Forests Burn, Will the World Heat More than We Feared?

When we get too hot, our bodies produce sweat, which cools us back down in what’s called a ‘negative feedback loop’. But what if it was the other way round, and getting warmer unleashed processes that made us even warmer? That’s what may be happening to the planet as a result of climate change.

We tend to think that future temperatures will be directly determined by our greenhouse gas emissions, but the reality is complicated by numerous feedback loops in the climate system. Some are negative feedbacks that serve to limit heating, but there are also numerous positive feedbacks that accelerate the warming process. 

They make the levels of future warming very complex to predict and, as a result, these feedbacks aren’t fully incorporated into climate models such as those used by the Intergovernmental Panel on Climate Change. And, as extreme temperatures and associated wild weather have rocked much of the world in recent months, we have seen signs of some of these feedbacks in action.  

It will have been hard to avoid coverage of burning forests, for example, particularly from the Mediterranean and Canada, where this year’s ongoing, record-breaking, wildfires have bathed a continent in deadly smoke.

Forests and other ecosystems store vast amounts of carbon, but they also act like sponges that absorb more carbon from the atmosphere. These ‘terrestrial carbon sinks’ currently absorb about a quarter of our emissions. But as the planet heats and forests increasingly burn, much of that stored carbon is emitted back into the atmosphere. If the forests don’t fully regrow then the sink will also be smaller, so there’ll be less of it to mop up our future emissions. 

The oceans are a carbon sink too, absorbing about 17% of our emissions, but a similar story is unfolding beneath the waves.

Ecosystems like seagrass beds and coral reefs store carbon just like forests do, but a record-breaking marine heatwave has been stressing many of them in ways they have never experienced. The waters around Florida in recent weeks have been as hot as bathwater, causing the corals to bleach. If these reefs now die, as seems probable, they too will release carbon and accelerate global heating.    

Some feedback loops don’t add carbon to the atmosphere, but instead affect what happens to the solar energy the planet receives.

Sea ice, for instance, is highly reflective and sends much of the sun’s energy back into space. But the dark ocean surface that replaces it when it melts absorbs much of that energy. This is a worry because recent reports suggest Arctic summers may be ice-free within decades, while there is currently a “truly remarkable” lack of ice around Antarctica for the time of year. 

Our knowledge of these feedback loops is very limited, and much of the research is in its infancy. So while we can understand them conceptually, we have little clear evidence of how much they are contributing to the climate crisis or how much worse their contribution may get.

For example, while recent forest fires have been emitting vast amounts of carbon, there are also negative feedback loops in the carbon cycle because increased levels of carbon dioxide can stimulate plant growth, and overall there’s no clear evidence that climate change is reducing the size of nature’s carbon sink. 

Nevertheless, it’s clear that these feedbacks are much more of a risk than is generally recognised, so it’s a concern that the levels of uncertainty involved make them too complex to fully integrate into climate models. In 2020, analysis carried out for Carbon Brief suggested feedbacks could result in warming up to 25% higher than the IPCC projections relied upon by governments and decision-makers. 

And that’s a problem because, even without fully incorporating feedbacks, these projections are highly alarming. Even without feedbacks, the IPCC’s sixth assessment report, published in March, projects global heating of 3.2°C by 2100 “without a strengthening of policies”.   

Though the figure didn’t generate many headlines, it’s a startling projection. While the world’s governments have committed to limiting heating to 1.5°C and made pledges aplenty, it is deeds not words that matter and current policies are dangerously inadequate.

It is particularly startling given that, even well below a 3°C rise, much of global agricultural land will become unsuitable for growing crops, vast swathes of the tropics will be uninhabitable to human beings, and sea level rise will have drowned drowned many of the world’s great cities.

It’s even more worrying when we consider that 2100 is no longer just some abstract future date – it is now just 77 years away, and my young nieces and nephews should still be trying to live through these unimaginable disruptions.

And yet, thanks to burning forests, dying corals and melting sea ice, this projection of a 3°C world is likely conservative. Global heating may be worse than we think. 

Needless to say, this has clear implications for climate policy. If there’s any risk that future climate change may be worse than we’re anticipating, then we must double-down on the task of decarbonisation even more urgently.

That will mean, most obviously, eliminating our emissions as fast as we can, and then going beyond net zero to net negative. And since fossil fuels are responsible for the bulk of our emissions, it means bringing an end to the fossil fuel era with the utmost urgency. 

That means the Government’s push to expand oil and gas production in the North Sea is wrong – and Just Stop Oil are right.

Charlie Gardner is Associate Senior Lecturer at the Durrell Institute of Conservation and Ecology, University of Kent