What does a reduction to 350 PPM of CO2 get you?

With some hubub recently over the 350.org day (designed to highlight the opinion that we must return the Earth to a 350 parts per million atmospheric CO2 level) I thought it might be a good idea to have a look at what the reversal might gain us.

For this, I’m drawing on the excellent guest post made by Bill Illis here on 11/25/2008 titled:

Adjusting Temperatures for the ENSO and the AMO

One of the graphs (along with a model in a zip file) that Bill presented in that guest post was this graph, which I’ve annotated to show the 350 PPM desired by activists, versus the 388 PPM (MLO seasonally corrected value) where we are now:

Here is the same graph, annotated again with intersecting lines and values, and zoomed on the areas of interest.

Depending on whether you believe the models or the actual observations determines what value would be gained from a  reduction to 350 PPM.

For belief in the models we’d get approximately 0.5°C drop in temperature.

For belief in the observations (RSS HadCRUT3 data) we’d get approximately 0.3°C drop in temperature.

Split the difference if you don’t like either and call it 0.4°C.

The key point here is that to get to 350PPM, it would be extremely difficult if not impossible to accomplish. Alternate energy just hasn’t risen to the challenge yet, and the world populace that depends on electricity isn’t likely to tolerate shutting down their energy use to get there.

China and India have said they won’t go along with suggested reductions, and are coming up with their own ideas prior to Copenhagen. Thus is the quandary faced by 350.org supporters.

As a side note, the 350PPM target was Dr. Jim Hansen’s idea:

Target Atmospheric CO2: Where Should Humanity Aim?

Since Hansen can’t even predict the effect of climate change 20 years out in his own neighborhood, one wonders why some people take the 350 PPM target suggestion seriously.