Each year our terrestrial biosphere absorbs about a quarter of all the carbon dioxide emissions that humans produce. This a very good thing; it helps to moderate the warming produced by human activities such as burning fossil fuels and cutting down forests.
But in a paper published in Nature today, we show that emissions from other human activities, particularly food production, are overwhelming this cooling effect. This is a worrying trend, at a time when CO2 emissions from fossil fuels are slowing down, and is clearly not consistent with efforts to stabilise global warming well below 2C as agreed at the Paris climate conference.
To explain why, we need to look at two other greenhouse gases: methane and nitrous oxide.