Hjælp til 9. klasses afgangsprojekt

IPCC anfører i sin 2007-rapport, at over de sidste 1000 år har vulkansk aktivitet og måske også Solen med stor sandsynlighed påvirket middeltemperaturen på den nordlige halvkugle, og at sådanne påvirkninger kan forklare en betydelig del af temperaturvariationerne på 10-års skala. Naturlige faktorer kan også have påvirket klimaforholdene i længere perioder så som den kolde periode omkring år 1700. Men påvirkningen fra drivhusgasser kan detekteres i en række klimadata over de seneste ca. 50 år.

Britiske og schweiziske forskningsresultater, som er publiceret i juli 2007 (Lockwood, M. og Fröhlich, C., Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature, Proc.R. Soc. A), viser, at over de seneste 20 år har alle tendenser i Solen været i modsat retning i forhold til en global opvarmning, dvs. solpåvirkningen har virket afkølende.

Svensmark's failure to comment on the lack of a clear and significant long-term downward GCR (galactic cosmic ray) trend, and how changes in GCR can explain a global warming without containing such a trend, is one major weakness of his argument that GCR is responsible for recent global warming. This issue is discussed in detail in Benestad (2002). Moreover, the lack of trend in GCR is also consistent with little long-term change in other solar proxies, such as sunspot number and the solar cycle length, since the 1960s, when the most recent warming started.

The anticipated increase in temperature was predicted long before it was detectable in the atmosphere, indeed long before it was known that atmospheric CO2 really was increasing; it was first predicted by Arrhenius in 1896 using extremely simple radiation balance ideas, and was reproduced using modern radiation physics by Manabe and co-workers in the 1960's. Neither of these predictions rests on general circulation models, which came in during subsequent decades and made more detailed forecasts possible.

Still, the basic prediction of warming is founded on very fundamental physical principles relating to infrared absorption by greenhouse gases, theory of blackbody radiation, and atmospheric moist thermodynamics. All these individual elements have been verified to high accuracy in laboratory experiments and field observations. For a time, there was some remaining uncertainty about whether water vapor feedback would amplify warming in the way hypothesized in the early energy balance models, but a decade or two of additional observational and theoretical work has shown that there is no real reason to doubt the way in which general circulation models calculate the feedback. When modified by inclusion of the cooling effect of anthropogenic aerosols, the theory gives a satisfactory account of the pattern of 20th and 21st century temperature change.

No other theory based on quantified physical principles has been able to do the same. If somebody comes along and has the bright idea that, say, global warming is caused by phlogiston raining down from the Moon (læs Svensmarks teori), that does not make everything we know about thermodynamics, infrared absorption, energy balance, and temperature suddenly go away. Rather, it is the job of the phlogiston (cosmic ray) advocate to quantify the effects of phlogiston (cosmic rays) on energy balance, and incorporate them in a consistent way beside the existing climate forcings. Virtually all of the attempts to poke holes in the anthropogenic greenhouse theory lose sight of this simple and unassailable (uangribelig) principle.