Notwithstanding the array of weasel word qualifications used throughout the summary, the IPCC wants us to believe that "most" of the rise of global average temperature since the mid-20th century was "very likely" caused by human-generated greenhouse gas emissions.
In the last report (AR-4, 2007) the IPCC experts were "90 percent confident" - whatever that meant - of this statement. Now they are reported as being "95 percent confident." One critical review (SEPP) notes that "The IPCC presents no physical evidence substantiating that it is 'extremely likely' that more than half of the [global temperature] increase during the past 60 years stems from rising greenhouse gas emissions or a rigorous method of calculating the 95 to 100 percent probability that the term 'extremely likely' embodies." The most crucial linchpin in the IPCC's argument is its assumed sensitivity of climate to increases in atmospheric carbon dioxide. The new Summary report defends its previously assumed sensitivity.
As climatologist Dr. Roy Spencer points out, "this is the entire political issue.
Spencer continues "A best estimate for climate sensitivity - unarguably THE most important climate change variable - is no longer provided, due to mounting contradictory evidence on whether the climate system really cares very much about whether there are 2, or 3, or 4, parts of CO2 per 10,000 parts atmosphere.
Yet the IPCC claims their confidence has DOUBLED (uncertainty reduced from 10 percent to 5 percent) regarding their claim that humans are most of the cause behind the warming trend in the last 50 years or so."
The Summary also runs away from the fact that that there has been no statistically significant rise in surface temperatures for over 15 years. The Wall Street Journal offered this translation: "Temperatures have been flat for 15 years, nobody can properly explain it - and the IPCC doesn't want to spend much time doing so because it is politically inconvenient and shows that the computer models on which all climate-change predictions depend remain unreliable." Dr. Richard Lindzen, the dean of American climatologists recently retired from MIT, observes "The latest IPCC report has truly sunk to level of hilarious incoherence. It is quite amazing to see the contortions the IPCC has to go through in order to keep the international climate agenda going."
It should also be explained that contrary to the practice in almost every scholarly profession, the IPCC releases its always-alarming Summary months before the release of the scientific working group reports on which the Summary is supposedly based. During the intervening months the IPCC's political commissars are tasked with making very sure that the working group findings corroborate the Summary.
Critics have recently graphed the 73 different computer projections of global temperature since 1990, and added in the actual observed temperatures over the same period. The result is an eye-opener.
Beginning in 1998 the actual temperatures on the graph lie below every one of the 73 projections on which the IPCC has based its scary predictions. Furthermore, the computer projections utterly fail to reproduce global temperatures beginning in 1950 (or 1900), the actual trends in which are already known. At least the IPCC deserves some credit for abandoning Michael Mann's notorious "hockey stick" graph contrived 15 years ago to terrify policy makers and the media about Planet Earth progressively boiling in its own juices.
The earth has been warming since the end of the Little Ice Age around 1850.
There is no evidence that human release of greenhouse gases has any detectable effect on global temperatures.
Those who want to put governments in charge of all fossil fuel combustion (and shower subsidies on "renewable energy") need to find a scientifically respectable case for their claims.
So far they have embarrassingly failed, and the forthcoming IPCC report won't do them much good.
John McClaughry is vice president of the Ethan Allen institute (www.ethanallen.org).