Richard A Muller PhD is a physicist who has long expressed skepticism about the global mean temperature records used by groups such as the Intergovernmental Panel on Climate Change (IPCC) to measure historical global warming. While not himself a climate scientist, Muller examined the research and pointed out what he believed to be sources of error. Climate scientists largely disagreed with Muller, contending that the problems he identified were at worst not serious enough to make a significant difference in the conclusions.
An important principle of science is replication, and in 2010 Muller and his daughter Elizabeth assembled a team of scientists to compile an independent climate record starting from scratch that would avoid the problems Muller and others had objected to. They called the effort the Berkeley Earth Surface Temperature (BEST) project.
(The project was funded in part by the Charles G Koch Foundation established by one of the Koch brothers, fossil fuel multi-billionaires who have contributed vast sums in support of Republican candidates and underwritten propaganda efforts denying the existence of global warming. In addition, Elizabeth Muller works in the fossil fuel industry. In response to criticism about this, Muller pointed out that all the data and analyses would be made available on line and anyone was free to examine it for bias.)
In the following short video, Muller summarizes what the team did and the results they obtained:
In brief, they assembled what was describes as several times as many historical measurements as had been used by other groups, and using this mass of raw data they were able to create their own global mean surface temperature series going back more than a hundred years earlier than the one used by the IPCC. This new temperature series was then compared with multiple data representing multiple possible explanations for global warming that have been proposed, and even with series no one expected to explain the phenomenon.
Their global mean temperature series was not significantly different from those computed by other researchers. The Earth is indeed warming and doing so at an anomalous rates.
However, they disagreed with the IPCC with respect to the cause. The IPCC attributes warming since the mid-1950s almost entirely to human use of fossil fuels, with an slight increase in brightness of the Sun helping raise temperatures as well during the first half of the 20th century. Muller and his colleagues, however, concluded that solar variability was not a significant influence, and human use of fossil fuels alone explains almost all the warming measured.
As noted in another recent post (link), the collaboration is continuing the research and has lately concurred with NOAA, NASA, and the Japan Meteorological Agency that last year was the warmest on record despite the absence of an El Niño.