Global atmospheric carbon dioxide levels have reached 400ppm. Normal seasonal fluctuation in CO2 are unlikely to ever average below this level again. The Guardian has an excellent article that explains the measurements and what, although an arbitrary number, crossing the 400ppm threshold means to continued global warming.
“We’re going into very new territory,” James Butler, director of the global monitoring division at the US National Oceanographic and Atmospheric Administration, told the Guardian.
When enough CO2 is pumped into the atmosphere from burning fossil fuels, the seasonal cycles that drive the concentrations up and down throughout the year will eventually stop dipping the concentration below the 400ppm mark. The 400ppm figure is just symbolic, but it’s psychologically powerful, says Butler.
We can't turn back the clock on this one. The CO2 in the atmosphere is going to drive warming even if we were to arrest any future growth.
Butler also emphasised that this CO2 is locking in future warming. “It’s like lying in bed with your electric blanket set to three. You jack it up to seven – you don’t get hot right away but you do get hot. And that’s what we’re doing.”The CO2 concentrations are driving what appears to be runaway climate change around the world.
The consequences of what is already locked in place are't in the future. They are showing up on a global basis today.
Take a look at this illustration of the increase of average global temperature since 1850.
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