New Global Temperature Data Reanalysis Confirms Warming, Blames CO2 - Reason Online (blog)

Richard Muller, the head of the Berkeley Earth Surface Temperature project, will publish an op/ed next week in the New York Times summarizing his group's findings with regard to global temperature trends. From a copy of the op/ed, Converted Skeptic, circulating on the web:

CALL me a converted skeptic. Three years ago I identified scientific issues that, in my mind, threw doubt on the very existence of global warming. Now, after organizing an intensive research effort involving a dozen scientists, I’ve concluded that global warming is real, that the prior estimates of the rate were correct, and that cause is human.

My turnaround is the result of the careful and objective analysis by the “Berkeley Earth Surface Temperature” team, founded by me and my daughter Elizabeth. Our results show that the average temperature of the Earth’s land has risen by two and a half degrees Fahrenheit over the past 250 years, and one and a half degrees Fahrenheit over the most recent 50 years. Moreover, it appears likely that essentially all of this increase is due to the human emission of greenhouse gases.

These findings are stronger than those of the Intergovernmental Panel on Climate Change, the United Nations group that defines the scientific and diplomatic consensus on global warming. In its 2007 report, the IPCC concluded only that most of the warming of the prior 50 years could be attributed to humans. It was possible, according to the IPCC consensus statement, that the warming before to 1956 could be due to changes in solar activity, and that even a substantial part of the more recent warming could be natural.

Our Berkeley Earth approach used sophistical statistical methods developed largely by our lead scientist Robert Rohde, and which allowed us to determine earth land temperature much further back in time. We carefully studied issues raised by skeptics: biases from urban heating (we duplicated our results using rural data alone), data selection (prior groups selected less than 20% of the available temperature stations; we used virtually 100%), poor station quality (we separately analyzed good stations and poor ones), and from human intervention and data adjustment (our work is completely automated and hands-off).  In our papers we demonstrate that none of these potentially troublesome effects unduly biased our conclusions. ...

How definite is the attribution to humans? The carbon dioxide curve gives a better match than anything else we’ve tried. Its magnitude is consistent with the calculated greenhouse effect â€" extra warming from trapped heat radiation. These facts don’t prove causality and they shouldn’t end skepticism, but they raise the bar: to be considered seriously, an alternative explanation must match the data at least as well as does carbon dioxide. ...

What about the future?  As carbon dioxide emissions increase, the temperature should continue to rise.  With a simple model (no tipping points, no sudden increase in cloud cover, a response to gases that is “logarithmic”) I expect the rate of warming to proceed at a steady pace, about 1.5 degree F over land in the next 50 years, less if the oceans are included.  But if China continues its rapid growth (it has averaged 10% per year over the last 20 years) and its vast use of coal (typically adding one new gigawatt per month), then that same warming could take place in less than 20 years.

Muller writes that all of their findings and statistical techniques will be available online for everyone to see and critique. More on this next week.