When I first heard that anyone was attempting to reconstruct the past temperature of the Earth from the meteorological record I was, frankly, sceptical. It is such a hard thing to do properly, I thought it was impossible. I admired their chutzpah, but I didn’t pay much attention. I was wrong to be so dismissive.
There have been three peer-reviewed estimates of the air temperature above the land surface of Earth, known as NASA-GISS, NOAA-NCDC and HadCRU. They broadly agree and indicate that the Earth is warming by around 2 °C per century. Two more estimates are on the way.
I am on the steering committee for one effort, called the International Surface Temperatures Initiative (ISTI). My part is minor, but my colleagues are working to create a completely open database of the meteorological records, and an estimate of the Earth’s surface temperature through time that is derived through a completely transparent process.
The other recent effort is led by Richard Muller and is known as the Berkeley Earth Surface Temperature estimate – BEST for short :-). The BEST estimate of the air temperature above the land surface of the Earth is shown at the head of the page alongside the previous three estimates. The BEST estimate used a completely different technique for averaging, detecting discontinuities in temperature records and accounting for urban heat islands. But for all practical purposes, their results are in perfect agreement with the previous three results.
What is remarkable about this result is that before Richard Muller did this work he was openly scathing of the other three teams. In the You Tube video at the foot of this article he implies that the authors of the previous studies are – at best – dishonourable. Now that his team has done their own analysis he has completely changed his mind. Speaking before the US congress this March 2012 he said:
Prior groups at NOAA, NASA, and in the UK (HadCRU) estimate about a 1.2 °C land temperature rise from the early 1900s to the present. This 1.2 °C rise is what we call global warming. Their work is excellent, and the Berkeley Earth project strives to build on it.
None of the Berkeley papers have yet survived the thorny process of peer review, but I expect they will emerge eventually. Having read through the pre-prints I am impressed. They specifically examine the effect of poor-siting of meteorological stations (it makes no difference), and the effect of urban heat islands (they make no difference either). However I would like to highlight a different aspect of this work.
Richard Muller is a clever man – cleverer than me for sure. But in my opinion, I would say that he might not have made sufficient effort to understand how people could have done what they did from a good motivation. But which of us has not made that same error? In the end, Muller has been compelled by the data to acknowledge the strength of these other works. And so he has changed his mind. Great: that is the process by which we learn. In fact ‘changing ones mind’ is almost a definition of ‘learning’.
Below is a You Tube video of Richard Muller talking in 2010 on Global Warming and Carbon Policy. He uses all the rhetorical embellishments that he condemns in others so be careful, but it is a good talk (52 minutes long!)
Below is a short video of how the Berkeley team estimate the temperature of the Earth has changed.