Ron Bailey makes a dreadful hash of things in this article on the IPCC 4AR. He tries to describe how projections of warming by 2100 have changed as each of the IPCC’s four assessment reports has come out. Unfortunately, Bailey confuses warming projections with climate sensitivity (how much warming will eventually occur if CO2 doubles). For the First Assessment Report he gives us the climate sensitivity:
In 1990, the FAR found that computer climate models projected that global mean surface temperature as a result of doubling atmospheric carbon dioxide was unlikely to lie outside the range 1.5 to 4.5 degrees Celsius
For the Second Assessment Report he gives us the projected increase:
In 1996, the SAR lowered the projected increase in average global temperatures by 2100 of about 1.0 to 3.5 degrees Celsius
For the Third Assessment Report, the projected increase:
In 2001, the TAR widened the projected range of projected temperature increases by 2100 to 1.4 to 5.8 degrees Celsius
And for the Fourth Assessment Report, he reports climate sensitivity (wrongly calling it the projected increase).
The 4AR more or less drops the range of average global temperatures anticipated for 2100. The Summary says the temperature is “likely to be in the range 2 to 4.5 degrees Celsius … Basically, IPCC global temperature projections are back to where they were in 1990 in the FAR.
Actually what happened is that the estimate of climate sensitivity hardly changed in all the Assessment Reports.
Bailey also gets the sea level increase in the 4AR wrong:
By 2100 sea level is expected to rise between 28 to 43 centimeters
Actually the range is 18 to 59 cm if you ignore ice flow changes, and 28 to 79 cm if you include an estimate for ice flow changes.
Bailey has been writing about global warming for many years, so really ought to be able to do better than this.
Update: Bailey has now corrected the article.