I like David Frum's paragraph about the chicken littles. It is so easyto argue against the chicken littles because they exaggerate their position into being so fantastic that anyone can poke holes in it. Indeed even the ipcc has never supported the ridiculous claims of al gore and his accolytes. It is hard to have a conversation with the hysterical. No wonder they just lie and say the science is settled. Manzi Uses the IPCC to Take Down Al Gore
In his relatively new position as “in-house critic” at The New Republic, Manzi criticized a characteristically alarmist piece that Al Gore had published in the same venue. Manzi wanted to show that Gore was misleading the public on what the “scientific consensus” actually had to say about the risks of climate change.
First Manzi quoted Gore who had written:
Over the last 22 years, the Intergovernmental Panel on Climate Change has produced four massive studies warning the world of the looming catastrophe that is being caused by the massive dumping of global-warming pollution into the atmosphere.
To which Manzi responds:
According to the IPCC’s currently-governing Fourth Assessment Report, under a reasonable set of assumptions for global economic and population growth (Scenario A1B), the world should expect to warm by about 3°C over roughly the next century (Table SPM.3). Even in the most extreme IPCC marker scenario (A1F1), the best estimate is that we should expect warming of about 4°C over roughly the next century. How bad would that be? Also according to the IPCC (page 17), a global increase in temperature of 4°C should cause the world to have about 1 to 5 percent lower economic output than it would otherwise have. So if we do not take measures to ameliorate global warming, the world should expect sometime in the 22nd century to be about 3 percent poorer than it otherwise would be (though still much richer per capita than today).
Prior to consideration of the more detailed economic issues—e.g., costs versus benefits of attempts to forestall the problem; the danger of worse-than-expected outcomes, etc.—pause to recognize that according to the IPCC the expected economic costs of global warming under the plausible scenarios for future economic growth are likely to be about 3 percent of GDP more than 100 years from now. This is pretty far from the rhetoric of global destruction and Manhattan as an underwater theme park. [Emphasis in Manzi's original.]
Manzi is entirely correct: If you wade hip-deep into the actual chapters of the IPCC AR4 report, you will find that yes, most practicing scientists in the relevant fields believe that human activities are leading to climate change, and in particular global warming.