Why do scientists disagree about climate change?

I promised a further essay on climate change, and this is it. It focuses on disagreement, the disagreement between scientists on various aspects of the issue. There is a belief, shared by climate activists, that all serious scientists are of one mind: that climate change is real, serious and potentially catastrophic unless we abandon the use of fossil fuels. If that were true, then the game would be over. There would be global agreement by governments, global action to phase out fossil fuels, and we would get used to much higher prices for electricity. What we would do for industries like smelting, for air travel and for back-up for hospitals and other critical users of electricity I don't know. There is a large too-hard basket in all of this. Perhaps those questions would be put off until 2050, the new 'time by which' great decisions must be made.

In fact, it's not like that at all. The notion that 97 per cent of scientists agree about CAGW is and always has been rubbish, and I've written about it trenchantly before. I came across a useful discussion paper in the NIPCC (Non-governmental International Panel on Climate Change) series a while ago, and feel it is time to summarise it for readers here. Let's start with this statement:

...the claim of "scientific consensus" on the causes and consequences of climate change is without merit. There is no survey or study showing "consensus" on any of the most important scientific issues in the climate change debate. On the contrary, there is extensive evidence of scientific disagreement about many of the most important issues that must be resolved before the hypothesis of dangerous man-made global warming can be validated.

At this point some readers will say, 'Ah that's the Heartland Institute, funded by coal interests. Why read anything more?' This is one of the real handicaps in anything to do with a highly contentious issue: the critic shoots the messenger, and does not engage with the message. I try hard not to do this, and in any case much of the document was written by the late Bob Carter, who was a friend from the early 1980s to his death nearly five years ago, a man who knew what he talked about and wrote well into the bargain. In a way, this essay is a kind of tribute to Bob Carter. And the Heartland Institute is not funded from corporate money of any kind. They say so, and I believe them. Those who disagree should provide the contrary evidence.

Why do scientists disagree? My summary goes like this.

First, climate science is a huge field. All those who work in it write from a particular perspective, based on their own disciplinary backgrounds. There is, then, no well-rounded, authoritative climate scientist. Very few scholars have mastery of more than one or two of these disciplines.Practitioners will disagree on a given issue because they rely on their own disciplines and are sceptical of the worth and contribution of others.

Second, There is no survey or study showing "consensus" on the most important scientific issues in the climate change debate…The articles and surveys most commonly cited as showing support for a "scientific consensus" in favor of the catastrophic man-made global warming hypothesis are without exception methodologically flawed and often deliberately misleading.

Third, The hypothesis implicit in all IPCC writings, though rarely explicitly stated, is that dangerous global warming is resulting, or will result, from human-related greenhouse gas emissions… In contradiction of the scientific method, IPCC assumes its implicit hypothesis is correct and that its only duty is to collect evidence and make plausible arguments in the hypothesis's favour.

Fourth, IPCC and virtually all the governments of the world depend on global climate models (GCMs) to forecast the effects of human-related greenhouse gas emissions on the climate… GCMs systematically over-estimate the sensitivity of climate to carbon dioxide (CO2), many known forcings and feedbacks are poorly modelled, and modelers exclude forcings and feedbacks that run counter to their mission to find a human influence on climate.

Fifth, Neither the rate nor the magnitude of the reported late twentieth century surface warming (1979–2000) lay outside normal natural variability. The late twentieth century warm peak was of no greater magnitude than previous peaks caused entirely by natural forcings and feedbacks.

Sixth, Melting of Arctic sea ice and polar icecaps is not occurring at "unnatural" rates and does not constitute evidence of a human impact on the climate. No convincing relationship has been established between warming over the past 100 years and increases in extreme weather events.

Seventh, Rather than rely exclusively on IPCC for scientific advice, policymakers should seek out advice from independent, nongovernment organizations and scientists who are free of financial and political conflicts of interest… Individual nations should take charge of setting their own climate policies based upon the hazards that apply to their particular geography, geology, weather, and culture.