Old methane and modern climate change

Carbon is stored over thousands of years in many natural reservoirs in land and ocean ecosystems. This is vital for regulating global climate. These old carbon stores are vulnerable to climate change, which can cause this carbon to be released in the form of greenhouse gases such as methane. If these gases reach the atmosphere, they can drive further warming, which has implications for all life on Earth (see the figure) (1). But such positive feedback loops are a major uncertainty when predicting future climate change (2). On page 907 of this issue, Dyonisius et al. (3) describe their search for signals of old methane released to the atmosphere during the last deglaciation about 18,000 to 8000 years ago. This was when Earth last showed warming similar to what is predicted for our immediate future. They found that methane emissions from old carbon sources during this time were small, suggesting that substantial emissions of old methane may not be triggered in response to current and near-future climate change.

By Joshua F. Dean

Feb 21st, 2020

Old carbon reservoirs were not important in the deglacial methane budget

Methane is a potent greenhouse gas with large natural sources, reservoirs, and sinks. Dyonisius et al. found that methane emissions from old, cold-region carbon reservoirs like permafrost and methane hydrates were minor during the last deglaciation (see the Perspective by Dean). They analyzed the carbon isotopic composition of atmospheric methane trapped in bubbles in Antarctic ice and found that methane emissions from those old carbon sources during the warming interval were small. They argue that this finding suggests that methane emissions in response to future warming likely will not be as large as some have suggested.

By M. N. Dyonisius, et al.

Feb 21st, 2020