- 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.
Four scientific papers setting out these conclusions have been submitted for peer review and will form part of the literature for the next IPCC report on Climate Change. They can be accessed on Berkeley Earth website at www.BerkeleyEarth.org. A video animation graphically shows global warming around the world since 1800.
Berkeley Earth is making its preliminary results public, together with its programs and dataset, in order to invite additional scrutiny. Elizabeth Muller said, “One of our goals is to make the science behind global warming readily accessible to the public.” Most of the data were previously available on public websites, but in so many different locations and different formats that most people could access only a small subset of the data. The merged database, which combines 1.6 billion records, is now accessible from the Berkeley Earth website.
What Berkeley Earth has not done is make an independent assessment of how much of the observed warming is due to human actions, Richard Muller acknowledged. As a next step, Berkeley Earth plans to address the total warming of the oceans, with a view to obtaining a more accurate figure for the total amount of global warming observable.
Source: Berkeley Earth.
