1. Because they are misled into thinking (as apparently you are too) that it is a matter of belief. Do you "believe" that 2+2=4? Do you "believe" that science has shown that species evolve over millions of years and were not all created 6000 years ago? Do you "believe" that men landed on the moon in 1969? If these things are framed as a matter of "belief," then any nutcase "belief" is in some sense as legitimate as any other "belief." Look at http://www.skepticalscience.com/argument.php for the long list of laughably inconsistent anti-science "beliefs" about human-caused global climate alteration.
2. Because many such deniers of climate science are NOT conservative in any real sense of the word, except "fake conservative." They are hypocrites and liars with few principles. THAT (not some obsolete "right" vs "left" dichotomy of dubious relevance) is why they find it easy to lie or BS about science they don't understand.
3. Because Michael Crichton wrote a widely selling sci-fi novel (heavily featuring what answerer Rolando on this page calls "reds under the beds") which Denier-in-chief Senator James Inhofe pretends to think is based on science rather than deceptions about science and smears against it.
4. Because the fossil fuel industry poured money into slick anti-science disinformation campaigns in the 1990s, and -on a more discrete and limited basis- is still doing so today.
5. Because nearly the entire leadership of the majority party in the U.S. House of Representatives has found it expedient to pander to anti-science denial, and convenient for fund-raising purposes too.
6. Because most deniers are poorly educated and not very intelligent, and climate science is complicated, and it feels better if the whole thing is hoax rather than being too hard to understand.
Here is the science and history that they deny:
U.S. National Academy of Sciences, 2010:
http://books.nap.edu/openbook.php?record_id=12782&page=1
“Climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems.”
http://nationalacademies.org/morenews/20100716.html
“Choices made now about carbon dioxide emissions reductions will affect climate change impacts experienced not just over the next few decades but also in coming centuries and millennia…Because CO2 in the atmosphere is long lived, it can effectively lock the Earth and future generations into a range of impacts, some of which could become very severe.”
http://www.physics.fsu.edu/awards/NAS/
“The Academy membership is composed of approximately 2,100 members and 380 foreign associates, of whom nearly 200 have won Nobel Prizes. Members and foreign associates of the Academy are elected in recognition of their distinguished and continuing achievements in original research; election to the Academy is considered one of the highest honors that can be accorded a scientist or engineer.”
http://www.aip.org/history/climate/timeline.htm
http://www.aip.org/history/climate/index.htm
http://www.aps.org/publications/apsnews/200602/backpage.cfm
http://www.newscientist.com/topic/climate-change
http://www.skeptic.com/eskeptic/12-02-08/#feature
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