Flaws in the IPCC 2007 report on climate change

The presentation (sorry, in french) is very educative. It is pretty convincing: the global warming issue is not as well understood as the media and politics want us to believe, and it deserves more scrutiny and debate in the scientific community.

Vincent Courtillot is a geologist, whose research connected to the field of climate a few years back. He and his colleagues discovered evidence which suggests that sun activity could be the primary cause for climate changes in the last century, rather than carbon dioxide. This fits the new observations (temperatures falling in the last 10 years) better than the IPCC models (which predict continued rise in temperatures).
The presentation outlines many issues with the findings by the Intergovernmental Panel on Climate Change (IPCC). Clearly, the report overestimates the accuracy and its confidence in the key results, and deserves much scrutiny.

Much of the data requires great care because it is indirect and imperfect (quality, accuracy or resolution), such as estimating historical temperature using tree rings, using different instruments of measure over different time periods, or using ice cores as proxies for atmosphere contents.
Also, major factors are not sufficiently accounted for in the models, such as water/steam, which we have reasons to think do play a significant role in climate (heat and cosmic radiations create clouds which cool down the earth by reflecting sun rays away).
Finally, there are huge methodological difficulties, such as the notion of an average temperature (a meaningless physical concept, as temperature is not additive) or accounting for climate locality.
He points to and summarizes alternative studies, including some of his own, which attempt to replicate the key IPCC findings with greater care to data quality and improve on or contradict the IPCC results. Those often do not get as much attention in the media.

In his conclusion, he highlights a few points:
The modern scientific method for natural sciences is built on three pillars: observation, theory and modelling/simulation.
Models should be falsifiable. Models that need tweaking to fit new observations should raise questions.
Studies should be careful with margins of error and avoid exaggerated statements.
In particular, we cannot state at this point that the issue is understood with 90% probability, as the IPCC report does.
There is an interesting issue of mechanisms for building expert consensus and dealing with mediatic and political bias towards fear and simplification. Such discussions also need to be clear to separate the role of the scientist (what do we know?) and the citizen (what do you do about it?).
There is no science without verification and without debate. He worries of a backlash against the scientific community if the so-called “consensus” is found to be wrong.
He is concerned that important problems for the coming century are getting too little attention: drinkable water, garbage management, hunger.
There is climate change. There was a warming over 150 years, but it is irregular and not out of bounds in larger time scale (2000 years to millions of years). Climate has always been changing.
The models and observations are complex, but uncertainty is often not well accounted for in the models. 
Finally, there is a growing body of evidence that the variations in sun activity, the physics of water/steam in the atmosphere and cosmic radiations play a primary role on climate change, as opposed to man-produced CO2.

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