By how many degrees would the average temperature of the Earth rise if carbon dioxide levels doubled? Scientists have been pursuing an accurate estimate of this figure since the late 19th century—it’s the “holy grail of climate science,” writes Justin Gillis in The New York Times. Most experts believe that this “climate sensitivity” figure lies somewhere just above five degrees Fahrenheit.
That may not sound like a particularly scary number to many people — after all, we experience temperature variations of 20 or 30 degrees in a single day. But as an average for the entire planet, five degrees is a huge number.
The ocean, covering 70 percent of the surface, helps bring down the average, but the warming is expected to be higher over land, causing weather extremes like heat waves and torrential rains. And the poles will warm even more, so that the increase in the Arctic could exceed 10 or 15 degrees Fahrenheit. That could cause substantial melting of the polar ice sheets, ultimately flooding the world’s major coastal cities.
Some recent studies, though, have proposed estimates below four degrees, stirring climate change skeptics and making some wonder if the future might look better than expected. But the well-regarded climate scientist James Annan warns against dismissing the threat of global warming. Gillis concludes:
Even if climate sensitivity turns out to be on the low end of the range, total emissions may wind up being so excessive as to drive the earth toward dangerous temperature increases.
So if the recent science stands up to critical examination, it could indeed turn into a ray of hope — but only if it is then followed by a broad new push to get the combustion of fossil fuels under control.
Alternatively, we might be able to put excessive carbon dioxide into storage.