Basically this evidence looks at three sources of temperature data: two from satellites, and two from surface stations. Three of the sources are in good agreement. The fourth source (from NASA) shows lower temperatures before 1998, and higher temperatures after 1998 – precisely what you'd need to make a case for AGW.
The conclusion from the article linked above:
If you've been paying attention to this issue at all, you won't be surprised to see Jim Hansen's name associated with this. He's a believer, like Al Gore, and it seems that no amount of factual evidence will dissuade him (a peculiar attitude for someone who is allegedly a scientist).NASA staff have done some recent bookkeeping and refined the data from 1930-1999. The issues has been discussed extensively at science blog Climate Audit. So what is the probability of this effort consistently increasing recent temperatures and decreasing older temperatures? From a statistical viewpoint, data recalculation should cause each year to have a 50/50 probability of going either up or down - thus the odds of all 70 adjusted years working in concert to increase the slope of the graph (as seen in the combined version) are an astronomical 2 raised to the power of 70. That is one-thousand-billion-billion to one. This isn't an exact representation of the odds because for some of the years (less than 15) the revisions went against the trend - but even a 55/15 split is about as likely as a room full of chimpanzees eventually typing Hamlet. That would be equivalent to flipping a penny 70 times and having it come up heads 55 times. It will never happen - one trillion to one odds (2 raised to the power 40.)
Particularly troubling are the years from 1986-1998. In the 2007 version of the graph, the 1986 data was adjusted upwards by 0.4 degrees relative to the 1999 graph. In fact, every year except one from 1986-1998 was adjusted upwards, by an average of 0.2 degrees. If someone wanted to present a case for a lot of recent warming, adjusting data upwards would be an excellent way to do it.
Looking at the NASA website, we can see that the person in charge of the temperature data is the eminent Dr. James Hansen - Al Gore's science advisor and the world's leading long-term advocate of global warming.
Who are you going to believe: Jim Hansen or your lyin’ eyes?
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