On the Persistenceof Climate Change

[danieldwilliam]

In converation with Andrew Ducker I wondered aloud how long the effects of climate change would continue for after we stopped emitting carbon dioxide.

 

The best guess seems to be 1,000 years. Some modelling done by the Canadian Center for Climate Modeling and Analysis suggests that even if we stopped emitting CO2 into the atmosphere we would still be experiencing the impact a millenium from now.

 

This appears to be due to the persistence of CO2 and other greenhouse gases in the atmosphere in the atmosphere. We can expect elevated levels of greenhouse gases for hundreds of years after we stop emitting them. Along side the continued warming effect of greenhouse gases it takes a long time for the additional heat trapped on the surface of the planet to make its way into the various climate systems. The key system for the long tail of climate change seems to be the deeper levels of the southern oceans. Additional heat moves slowly into these systems until it ends up next to the Antartic ice-sheets. These in turn eventually melt leading to an increase in sea-levels of 4 meters.

 

If we stopped emitting CO2 in 2100 the model predicts some 55% of excess carbon emitted during the industrial period would still be in the atmosphere in the year 3000. The changes in climate as a result of the two effects of accumulated climate change persisting into the future and the unwinding of climate change as the distribution of CO2 changes seem to drive significant regional variation with the southern hemisphere seeing increases in tempreture after 2100 and the nothern hemisphere seeing tempretures fall back after 2100.

 

Two big worries flagged up by the model are continuing warming of Antartic seas and the consequent loss of ice from Antartica and a drying effect on northern Africa.

 

The modelling goes out for thousand years and doesn’t appear to show the effects peaking and then reversing over the model’s period.  They are still accumulating a thousand years from now.

 

As a caveat, this is one study. The climate is probably the very definition of a non-linear chaotic system and I think climate change modelling is highly dependent on all sorts of best estimates about things we don’t really understand at all well.  But it’s the best we have.

 

I have to say I’m surprised and dismayed. I’d thought that we would start to see a reversal of climate change within a hundred years or so of us reducing carbon emissions below their aborbsion rates.

 

My source for this is here

 

http://sos.noaa.gov/Docs/ngeo1047-aop.pdf