The most comprehensive review of the earth’s temperature records attempted so far has just returned its official results: “global land temperatures have increased by 1.5 degrees C over the past 250 years.”
This doesn’t tell us anything we didn’t already know, but the Berkeley Earth Surface Temperature project (BEST) is worth mentioning for two reasons. First, it combines more land temperature records than any study before it – 1.6 billion different individual measurements. Second, it has sought to engage constructively with climate sceptic arguments and includes weather station quality in its considerations, and volcanic and solar activity.
The results of those objections?
- Weather station quality: “the difference in temperature change rate between Poor and OK stations is not statistically significant at the 95% confidence level. The absence of a statistically significant difference indicates that these networks of stations can reliably discern temperature trends even when individual stations have nominally poor quality rankings.”
- Volcanic activity: “The historic temperature pattern we observe has abrupt dips that match the emissions of known explosive volcanic eruptions; the particulates from such events reflect sunlight and cool the Earth’s surface for a few years. There are small rapid variations attributable to El Nino and other ocean currents such as the Gulf Stream. The gradual but systematic rise of 1.5 degrees C is best explained by the record of atmospheric carbon dioxide”
- Solar activity: “In its 2007 report the IPCC concluded only that “most” of the warming of the past 50 years could be attributed to humans. It was possible, according to the IPCC, that increased solar activity could have contributed to warming prior to 1956 … The Berkeley Earth team was able to conclude that over 250 years, the contribution of solar activity to global warming is negligible.”
- It’s also worth noting that the Berkeley study is based on compiling the best possible temperature record, and then comparing it to data on solar activity, carbon emissions and other factors. It does not rely on a climate model.
So what does appear to be the main factor?
“The good match between the new temperature record and historical carbon dioxide records suggests that the most straightforward explanation for this warming is human greenhouse gas emissions.“
The study does not claim that it has proved the link between carbon emissions and global warming. It simply says that no other explanation fits the data. Again, nothing new there, although the results did surprise to the project’s founder, Richard Muller. “I was not expecting this” he says, “but as a scientist, I feel it is my duty to let the evidence change my mind.”
Given that Anthony Watts, Fred Singer and others have endorsed the BEST study in the past, I wonder if they will have the integrity to let the evidence change their minds too.
- To help you make up your own mind, BEST have a wealth of data online to explore at your leisure.