Thursday, April 03, 2014

The Exact Value of Climate Sensitivity Doesn't Much Matter

This is a really important point in Michael Mann's Scientific American article:
To my wonder, I found that for an ECS [equilibrium climate sensitivity] of three degrees C, our planet would cross the dangerous warming threshold of two degrees C in 2036, only 22 years from now. When I considered the lower ECS value of 2.5 degrees C, the world would cross the threshold in 2046, just 10 years later....

So even if we accept a lower ECS value, it hardly signals the end of global warming or even a pause. Instead it simply buys us a little bit of time—potentially valuable time—to prevent our planet from crossing the threshold.
It's easy to get fooled by not taking the exponential view (of emissions); our guesses usually take the linear view of things, and we end up failing to properly foresee the future.

With exponential emissions, the exact value of ECS doens't matter much. Of course, it matters whether it's 2 C or 4 C, but what's after the decimal point isn't crucial.


hengist mcstone said...

Hi David,
Am I right in thinkig the equilibrium wont be known 'til long in the future anyhow?

David Appell said...

If then. It probably won't ever be known from observations, because we aren't keeping track of aerosol emissions, which are a cooling force against GHG warming.