Wednesday, March 21, 2007

Ray Evans' 'Nine facts about climate change' debunked. Pt. 4.

Short post tonight.

The point that Ray makes comes up over and over again in denialist circles. It is so dim-witted and obviously false, that I’m sure no one with any interest in climate science, contrarian or not, believes it.

The reason it is constantly raised is to trick the unwary; those with only a casual interest in climate change who are looking for an impossibly simple explanation as to why the scientific consensus is wrong.

This is truly the ultimate AGW straw man.
4. The evidence linking anthropogenic (man-made) carbon dioxide emissions and current warming is limited to a correlation which holds only for the period 1976 to 2000. Attempts to construct an holistic theory in which atmospheric carbon dioxide controls the radiation balance of the earth, and thus determines average global temperatures, have failed.
There is not, has not, and never will be, any attempt to construct a theory, holistic or otherwise, in which atmospheric CO2 controls the radiation balance of the earth, and thus determines average global temperatures.

Many factors impact on average global temperature apart from atmospheric CO2. There’s internal variation, of which the ENSO cycle is an example. There’s solar radiation, which isn’t constant. There are many other anthropogenic radiative forcing components. Unsurprisingly, the recent IPCC summary covers this with a nice simple, colourful pic:

As other factors have impacted on global average temperature, it is not expected that there will be a close correlation with atmospheric CO2 levels over the past 100 years. When these other factors are accounted for, along with CO2, temperatures for the past 100 years can be reasonably accurately modeled.

This graph demonstrates why only a recent ‘sort-of’ correlation with CO2 exists.

None of this means or implies that increased atmospheric CO2 due to human activity is not the largest radiative forcing component currently.

As for the solar guff, the problem for Ray is that there is no conceivable way that either solar cycle amplitude, period or abstract theories involving cosmic rays, can explain recent warming when subjected to rigorous scientific enquiry.

Solar forcing is real, but its magnitude is insufficient to explain recent warming.

Sad for denialists, but very true.