A major new study involving 37 scientists from 18 countries has concluded that global temperature estimates since 1850 have been heavily contaminated by the growth of urban heat where the thermometers are sited. The UN-backed Intergovernmental Panel on Climate Change (IPCC) claims that urban heat accounts for less than 10% of recorded global warming, but the scientists found that figure is nearer 40%. They observe that a rural-and-urban blend of temperatures indicates a long-term warming trend of 0.89°C per century, while a rural-only collection shows only a rise of 0.55°C in the same time period.
The IPCC bets the ranch on humans causing all or most global warming in the modern age. It promotes the idea that temperatures have risen since 1850 by 1.09°C, with natural influences contributing only –0.1°C to +0.1°C – statistical-speak for zero. As I argued in the Daily Sceptic on Sunday, this is a political construction designed to promote Net Zero. Given our current state of scientific knowledge, it is impossible to calculate how much of the recent warming is due to the small amount of carbon dioxide humans produce by burning fossil fuel compared to natural climatic variations.
It is perhaps not generally known that the IPCC’s position that humans cause all global warming is mainly based on a comparison of global temperature estimates, with ‘hindcasts’ produced by computer models. The authors of the new study explain that these are retrospective ‘forecasts’ of past climate produced by CMIP6 model simulations. They argue that these simulations are contaminated by urban heat distortions, and the use of a “low solar variability” estimate. Both problems could significantly affect the IPCC anthropogenic attributions made in the fifth assessment report (AR5), and repeated in the latest edition known as AR6. The charge is that the IPCC downplays the effect of solar irradiance (sunshine) which can explain a great deal of the warming since the late 19th century.
The graphs above demonstrate the two different estimates of Northern Hemisphere land air temperatures from 1850-2018. Both series were generated from the Global Historical Climatology Network (GHCN), a database of temperature records from 180 countries compiled by the U.S. weather service NOAA. They show clearly that in rural areas away from heat generated by humans, the warming is much less, particularly in recent times during a period of large urban expansion. It is obvious that temperatures avoiding any human corruption provide the best guide to any long-term climate trend.
This latest paper, published in the scientific journal Climate, is one of a series of academic warnings that global temperature datasets are severely contaminated by unadjusted urban heat effects. The IPCC continues to hide its head in the sand, stating that no recent findings have emerged to alter its view that any uncorrected effects from urbanisation, or from changes in land use or cover, have raised land surface air temperature trends by more than 10%. The IPCC was set up in 1988 only to look at human influences on the climate, so it is not hard to understand why it doesn’t seem to try very hard to investigate the problem. No such reticence holds back Dr. Roy Spencer and Professor John Christy of the University of Alabama in Huntsville. They looked at the GHCN and found that up to a fifth of all global warmingreported by 20,000 weather stations was invalid due to corruptions from non-climatic data. Worse, they found that NOAA, far from removing urban heat distortions, was on average “spuriously warming station temperature data trends when it should be cooling them”.