CLIMATE SCIENCE: by Peter WestmoreNews Weekly
How IPCC climate models exaggerate global warming
, November 9, 2013
The recently-released report of the Intergovernmental Panel on Climate Change (IPCC) — called its Summary for Policymakers — has claimed that there is increasing certainty that CO2 will cause dangerous climate change over the course of the 21st century.
This assertion is based on an aggregate of computer models of the world’s climate, developed by climate modelling groups around the world, including the Bureau of Meteorology in Australia.
While the climate modellers work separately from one another, the World Meteorological Organisation brings together the different climate models, in a project called the World Climate Research Program. Within this program a body known as the Working Group on Coupled Modelling produces standardised model simulations.
Recently, one of America’s top meteorologists, Dr Roy Spencer, charted the predictions from 90 of the world’s climate models for the period 1983 to 2028, and compared it with the average temperature measured at the earth’s surface.
Dr Spencer is a well-respected scientist who runs his own climate web site at www.drroyspencer.com. He has been critical of both the IPCC and those who deny that CO2 is causing increased surface temperatures.
There are two main sets of surface temperature data. One comes from satellite measurement of the lower atmosphere, published monthly by the University of Alabama, Huntsville Campus (UAH).
Satellite measurements of atmospheric temperature are made with microwave sensors, and are completely independent of surface thermometer measurements.
The other, published by the UK Meteorological Office, are monthly temperature records formed by combining the sea-surface temperature records compiled by the Hadley Centre of the UK Met Office and the land surface air temperature records compiled by the Climatic Research Unit (CRU) of the University of East Anglia. These are called HadCRUT data, and the latest version is called HadCRUT4.
There has been some criticism of the British figures, based on the fact that land air temperatures are often measured in cities, where they are subject to the heat-island effect, and on the availability of land temperature measurements across the world. (For example, many of the former temperature stations in the former Soviet Union were closed down after 1990.)
However, the HadCRUT figures are readily available, and can be compared with the satellite data, and the climate models.
Dr Spencer charted the predictions of 90 climate models, and compared them with the two surface temperature data sets (UAH satellite data, and HadCRUT’s surface temperature measurements).
His chart, shown on this page, is highly revealing.
It shows that, in the period since 1983, the computer models generally predicted steadily increasing rates of global warming up to 1988, a decline until 1995, and then rising temperatures from then into the future.
In contrast, the measured temperature sets show an interrupted increase until about 2005, then approximately flat temperatures since then.
What is perhaps most significant is that the gap between the computer models (going steadily upwards) and the measured temperatures continues to widen.
Dr Spencer said, “As seen in the following graphic, over the period of the satellite record (1979-2012), both the surface and satellite observations produce linear temperature trends which are below 87 of the 90 climate models used in the comparison.”
The IPCC’s reliance on computer models, and its failure to address the growing gap between the models and actual measured temperatures, highlight the main flaw in the IPCC project.
Dr Spencer had previously described the IPCC report as “a dogged attempt to salvage the IPCC’s credibility amidst mounting evidence that it has gone overboard in its attempts to scare the global public over the last quarter century. The recent approximately 15-year lull in warming is hardly mentioned at all.”