A driller extracts a core of ice that holds clues to past climate, Near McMurdo Station, Antarctica (Image: David Boyer/National Geographic/Getty Images)
Read more: “Climate change: What we do – and don’t – know“
We can’t say how much Earth will warm over the coming years unless we know how much more greenhouse gas will end up in the atmosphere.
The biggest uncertainty is human. Were we to cut our emissions drastically tomorrow, CO2 levels might not rise much beyond 400 parts per million. But that is improbable: only a few countries – and not the biggest emitters such as China and the US – are promising cuts on anything like the scale needed, and the credibility of such promises is undermined by those same countries building more coal-fired power stations. Our current emissions trajectory is close to the worst-case scenario of the Intergovernmental Panel on Climate Change (IPCC). If we continue on this path, CO2 levels could hit 1000 ppm by 2100 – or perhaps even higher.
“Were we to cut emissions drastically tomorrow, C02 levels might not rise much more. That is improbable”
The second uncertainty is Earth’s response. So far about a third of our CO2 emissions have been sucked out of the atmosphere, mainly by the oceans. We can expect this buffering effect to decline. Currently, rising CO2 levels are driving global warming, but in the past CO2 levels have naturally risen in response to rising temperatures. We do not know why exactly, but the reduced solubility of CO2 in warm water and changes in biological activity have been suggested as…
