Feedbacks that cause ecosystems to emit more carbon will make the climate crisis more severe than expected, amplifying global warming by 20 to 30 per cent this century. It isn’t just fossil fuel emissions that raise temperatures. Warming itself creates more warming.
For instance, a hotter atmosphere absorbs more water vapour, which traps more heat in the atmosphere, which then holds more water vapour. Climate models already incorporate most global feedback loops like this one, and they have started to include feedbacks that are disrupting carbon storage in particular ecosystems. But no single model includes all ecosystem feedbacks.
Now, a study has shown that these natural feedbacks will heat the planet by an extra 0.2°C to 0.4°C by 2100, on top of at least 1°C to 2°C of global warming already expected between now and then. Earth’s carbon sinks are being eroded by climate change feedback loops “That suggests we’re going to go further over 1.5°C global warming than we thought, with all the extra risks that brings,” says Tim Lenton at the University of Exeter in the UK, who wasn’t involved in the new research. Christina Schädel at Woodwell Climate Research Center in Massachusetts and her colleagues estimated the emissions from four major natural feedbacks.
The first is mainly in the Arctic, in permafrost that once remained frozen year-round. As this ground thaws, microbes begin to decompose plant and animal remains that have been frozen for millennia, emitting carbon dioxide and methane. A second feedback involves wetlands, which also release more methane as temperatures rise.
This is because warmer water can hold less gas, and because microbes in the water decompose organic matter at a higher rate. The same processes lead to additional methane emissions from ponds and lakes, a third feedback. The fourth feedback kicks in as the air gets hotter, winters get shorter and soils get drier.
All of this increases the frequency and intensity of wildfires, which results in greater CO2 and methane emissions. In a climate scenario in which human emissions decline after 2050, the natural feedbacks add an average of 0.4°C of warming by 2100. The world’s biggest carbon sink may start emitting CO2 after net zero But even in a scenario in which emissions start declining today, the feedbacks add 0.2°C of extra warming this century, prolonging global warming.
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