Extreme weather found to be fueling climate change

We've been hearing for years now that climate change will drive more extreme weather events, but scientists have now also found that the opposite is also true — that extreme weather events are fueling climate change by altering the environment's ability to absorb carbon dioxide.

The Earth's global carbon cycle is a fairly balanced system, with carbon dioxide being absorbed and released all the time by the oceans and by ecosystems on land. The cycle is being thrown out of balance, though, by the excess carbon dioxide we're releasing through fossil fuel burning.

As the climate warms due to this excess carbon dioxide in the atmosphere, it's expected that ecosystems will be able to take up even more carbon dioxide than they already do. However, although that may be the case, scientists are finding that extreme weather events are actually reducing the ability of these ecosystems to absorb carbon dioxide, and by so much that it may offset any increased uptake that may happen.

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Examining 30 years worth of satellite imagery showing vegetation amounts, and data from 500 monitoring stations around the world that record carbon dioxide levels and wind flow, an international team of scientists used a sophisticated computer model to determine how much carbon ecosystems absorb and how much they release in the form of carbon dioxide. Relating this to extreme weather, they found that events such as droughts and storms reduced the ability of Earth's ecosystems to absorb carbon dioxide by around 11 billion tonnes per year.

"That is roughly equivalent to the amount of carbon sequestered in terrestrial environments every year," says Markus Reichstein, Director at the Max Planck Institute for Biogeochemistry in Jena, according to a statement. "It is therefore by no means negligible."

Droughts are especially damaging to ecosystems, as plants die off due to lack of water and trees are damaged and weakened. This not only decreases the amount of carbon dioxide the ecosystem can absorb, but it also increases the amount of carbon dioxide released into the atmosphere from rotting vegetation.

Extremes in the other direction have a similar effect. Flooding from extreme rainfall events (such as in southern Alberta in June) kills plants and trees by drowning them. Even those that survive are weakened, directly reducing their ability to remove carbon dioxide from the air, but also making them more vulnerable to pests and disease, which can weaken them further or kill them.

Further studies are planned, to look into these effects in more detail. Also, with research already showing that the frequency of extreme events is on the rise, with events that we only see every 20 years, 50 years or 100 years happening more often, the researchers want to go even further.

"We should also take account of events which so far have only happened once in 1,000 or even 10,000 years, because they are likely to become much more frequent towards the end of this century," said Michael Bahn, an ecologist at the University of Innsbruck that participated in the study, according to a press release from the Max Planck Institute.

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Weather and climate are extremely complicated, but as more and more studies like this are conducted, we are getting a much better sense of exactly how it all works. Not all of the news is good, though (in fact, very little of it seems to be good these days), and we're finding more and more of these unexpected side effects.

"As extreme climate events reduce the amount of carbon that the terrestrial ecosystems absorb and the carbon dioxide in the atmosphere therefore continues to increase, more extreme weather could result," said Reichstein. "It would be a self-reinforcing effect."

(Photo courtesy: Jonathan Hayward/The Canadian Press)

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