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(called "insolation"). It is worth seeing how the SPM handles the between solar activity and the warming record. A correct assess- variable insolation that is now generally accepted to occur. ment would be that solar variation is a plausible, but as yet unver- At the time of the SAR, the theory that solar variation ified, explanation for all the warming shown in the surface record. contributed to the 20th-century surface temperature run-up was = The TAR SPM assessment of this science is quite different, and well known but considered speculative. So the SAR dismissed therefore quite biased. this influence and argued that the entire increase was due to Moreover, the acceptance of the significant role of solar varia- human interference. Since then, the influence of solar variation tion in the first warming period raises a broader issue. on climate change has been generally accepted, and the TAR —_ Greenhouse gas levels have been rising for over 140 years, but SPM acknowledges it. However, it does so in a way that both their warming effect, if any, is increasingly confined to just the obscures and minimises the effect. last 20 years or so. This is a significant change since the 1995 The discussion of solar variation is on page 9, beginning with SAR in the basis for the human interference theory, yet it is not the following headline: "Natural factors have made small con- _ acknowledged. One would expect a corresponding decrease in tributions to radiative forcing over the past century." This head- the projected future impact of increasing GHGs, but this, too, is line dismisses the effect of all natural variations as "small". But missing. the two variations actually considered are solar radiation and vol- Finally, given that we have only recently verified the significant canic aerosols. For solar, on the very preceding page in figure 3, role of solar variation in the first period of recorded warming, it our understanding of the degree of forcing is said to be "very seems logical to suspend judgment on the cause of the second- low". This statement therefore expresses a period warming—especially since there are false degree of confidence. known reasons to believe that it, too, may be By the IPCC's own assessment, the solar solar in origin, in whole or in part. forcing could be quite large. This is actually This caution is doubly called for, given acknowledged, but then dismissed, in the first that there are several other climate variations paragraph: "The radiative forcing due to that can equally well claim to cause the two changes in solar irradiance for the period . . . observed warming periods. Contrary to what since 1750 is estimated to be about +0.3 This caution IS the TAR SPM asserts, the scientific situation W/m’, most of which occurred during the ubl lled for is completely open at this point. first half of the 20th century. Since the late do b y ea ed hp 1970s, satellite instruments have observed given that there are Natural Climate Variation small oscillations due to the 11-year solar 9 Evidence of naturally variable climate cycle. Mechanisms for the amplification of several other climate processes, including natural warming, has solar effects on climate have been proposed, variations that can mushroomed since the 1995 IPCC Second but currently lack a rigorous theoreti- Il Tl | . Assessment. But the Third cal or observational basis." equa y well Claim Assessment SPM does not even The first sentence is quite telling, for mention most of these processes, nor it admits that solar variation is to cause the two do the climate models include these observed warming periods. generally accepted to have contributed powerful variables. These are major significantly to the first of the two systematic omissions. In fact, the recorded 20th-century warming SPM concludes on page 10 that: periods. As SPM figure la shows, all "There is new and stronger evidence of the lasting warming in the 140-year that most of the warming observed surface record occurred in just two over the last 50 years is attributable to relatively brief periods—from 1910 to human activities." 1940, and from 1980 to the present. What the SPM ignores is that there Some well-known scientists argue that is also "new and stronger evidence" solar variation is sufficient to explain that all of the warming is attributable all of the warming in the first period, to natural variation. This is an artful which is what the first sentence alludes to but studiously fails to subterfuge. It is a paradox in the logic of evidence that there can discuss. Instead, it "estimates" the forcing to be small, ignoring be at once "new and stronger evidence" for each of two contend- our "very low" understanding. That the variation is small is well ing theories in science. known. The size of the effect, however, is unknown and In fact, there are now multiple natural variations, any one of extremely controversial. which can explain the observed warming in the surface tempera- The second sentence is an attempt to refute well-known argu- ture record. Some of these are listed below: ments that solar variation can also explain the warming in the sec- ¢ To begin with, there is the discovery of two enormous natural ond period. The SPM acknowledges that there has been variation climate oscillators on the decade-to-century scale. These are during this period, an observation verified by satellite, but again called the Pacific Decadal Oscillation and the North Atlantic dismisses the effect as "small". Oscillation. The temperature variations associated with these The third sentence is the most egregious as far as biased assess- oscillators are sufficient to explain the entire rise shown in the ment is concerned. It first acknowledges, then dismisses out of 140-year surface temperature record. But the SPM does not even hand the large amount of scientific literature on how a small solar —_— mention them. variation might amplify to affect climate significantly. This sen- * Secondly, there is a dramatic finding regarding the Moon's tence is actually false, because there are both theoretical and _ possible influence on climate. The ocean drives the climate and observational bases for these proposals. In fact, the starting point — two-thirds of the ocean's mixing energy comes from the Moon, for this literature is the strong, and well-known, correlation which stirs the oceans twice a day. It has been demonstrated that doubly called for, given | that there are -P cab LIfe a equally well claim to cause the two periods. NEXUS ¢ 29 This caution is several other climate variations that can observed warming | OCTOBER — NOVEMBER 2002 www.nexusmagazine.com