In recent decades warmer temperatures have led to shorter winters, and in the UK the plant growing season is now a full month longer than it was in 1990. The same is true across much of the northern hemisphere, and this extra plant growth has helped to mop up atmospheric carbon dioxide and keep a lid on global warming. But no longer.



New measurements of atmospheric carbon dioxide reveal that plants have reached saturation point, and that since 2006 the amount of carbon dioxide absorbed by plants has been declining. “It’s the first evidence that we are tipping over the edge, potentially towards runaway or irreversible climate change,” says James Curran, former chief executive of the Scottish Environment Protection Agency.

Together with his son, Sam, he analysed the ups and downs in atmospheric carbon dioxide concentration, recorded at the Mauna Loa Observatory in Hawaii since 1958. During the northern hemisphere summer, carbon dioxide levels dip as fresh plant growth draws down carbon dioxide. But the Currans’ analysis shows that since 2006 the size of the dip has diminished and vegetation has become poorer at soaking up carbon dioxide, contributing another China’s-worth of carbon dioxide to the atmosphere every year. Previous estimates had suggested that Earth would not reach “peak-carbon” until at least 2030. “It suggests to me that we urgently need to get to grips with declining biodiversity across the globe, and consider radical new policies such as re-wilding large areas of landscape,” says Curran, whose findings are published in the journal Weather . Quite how our weather will respond to the extra carbon dioxide remains to be seen...