With climate change expected to bring more heatwaves, violent
storms and heavy rainfall, the impact on human society is likely to
be significant. As if we didn't have enough to adapt to, a new
paper suggests extreme weather could further contribute to rising
carbon dioxide levels by reducing how much carbon plants draw out
of the air.
Growing plants take carbon dioxide out of the atmosphere and
store it as living plant matter. The world's ecosystems have
absorbed about a third of the
carbon dioxide humans have put into the atmosphere
fossil fuel burning. In effect, by reducing the amount of
carbon dioxide in the atmosphere, plants keep global temperature
below what it might otherwise be.
The new Nature review
paper suggests extreme weather events - especially
heatwaves, droughts and fires - weaken ecosystems' ability to act
as a buffer against climate change. And the situation is likely to
worsen as temperatures rise further and extreme events become
more frequent or more severe, the authors say.
heatwave in central Europe in 2003 gave scientists a
chance to look closely at how water scarcity affects the amount of
carbon dioxide forests take up. And the results suggested the
consequences are much more serious than first thought.
Soon afterwards, scientists from eight different countries
launched an international project to investigate the connection
between extreme events and the carbon cycle.
The impacts of extreme weather can be pretty immediate if vast
swathes of vegetation are killed off by drought or wildfire and
stop taking up carbon dioxide, say the authors. But there are less
obvious effects that take a while to appear. Changes in temperature
or rainfall extremes can make trees and plants less resistant to
pests and diseases, for example.
While most of these impacts are relatively well known, the
new paper is the first to put a figure on how much less
carbon dioxide ecosystems absorb as a result of extreme events.