‘Global warming is real’ says a new study released by researchers from the Berkeley Earth Surface Temperature group, which finds ‘reliable evidence’ of a global increase in the average land temperature of approximately 1°C since the mid-1950s.
The Berkeley Earth study looked at data from 15 sources (available here for those interested) which went back as far as 1800 in some cases, and addressed scientific concerns raised by those who continue to doubt the idea of global warming, ‘including the urban heat island effect, poor station quality, and the risk of data selection bias.’
“Our biggest surprise was that the new results agreed so closely with the warming values published previously by other teams in the U.S. and the U.K.,” said Berkeley Earth’s founder and scientific director, Professor Richard A. Muller. “This confirms that these studies were done carefully and that potential biases identified by climate change skeptics did not seriously affect their conclusions.”
Muller noted that the group had concluded previous studies had accurately estimated the extent of land surface warming despite their more limited datasets.
Robert Rohde, lead scientist for Berkeley Earth, noted that “the Berkeley Earth analysis is the first study to address the issue of data selection bias, by using nearly all of the available data, which includes about 5 times as many station locations as were reviewed by prior groups.” This was in response to concerns raised by scientists looking at studies carried out by NOAA, NASA, and the Hadley Center, who had also found that the land was warming by approximately 1°C since the mid-1950s. The concerns raised by sceptics suggested that these studies relied on ‘ad-hoc techniques that meant that the findings could not be duplicated.’
Elizabeth Muller, co-founder and Executive Director of Berkeley Earth, said she hopes the Berkeley Earth findings will help “cool the debate over global warming by addressing many of the valid concerns of the skeptics in a clear and rigorous way.”
Specifically, the Berkeley Earth study concludes that:
- The urban heat island effect is locally large and real, but does not contribute significantly to the average land temperature rise. That’s because the urban regions of Earth amount to less than 1% of the land area.
- About 1/3 of temperature sites around the world reported global cooling over the past 70 years (including much of the United States and northern Europe). But 2/3 of the sites show warming. Individual temperature histories reported from a single location are frequently noisy and/or unreliable, and it is always necessary to compare and combine many records to understand the true pattern of global warming.
- The large number of sites reporting cooling might help explain some of the skepticism of global warming,” Rohde commented. “Global warming is too slow for humans to feel directly, and if your local weather man tells you that temperatures are the same or cooler than they were a hundred years ago it is easy to believe him.” In fact, it is very hard to measure weather consistently over decades and centuries, and the presence of sites reporting cooling is a symptom of the noise and local variations that can creep in. A good determination of the rise in global land temperatures can’t be done with just a few stations: it takes hundreds — or better, thousands — of stations to detect and measure the average warming. Only when many nearby thermometers reproduce the same patterns can we know that the measurements were reliably made.
- Stations ranked as “poor” in a survey by Anthony Watts and his team of the most important temperature recording stations in the U.S., (known as the USHCN — the US Historical Climatology Network), showed the same pattern of global warming as stations ranked “OK.” Absolute temperatures of poor stations may be higher and less accurate, but the overall global warming trend is the same, and the Berkeley Earth analysis concludes that there is not any undue bias from including poor stations in the survey.
For anyone and everyone interested, Berkeley Earth have provided the four papers that they have submitted for peer review in the hopes to ‘invite additional scrutiny’ as well as their data sets, analysis programs and other aspects of their research.