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Martin Cohen is one of a small number of philosophers (Simon Blackburn is another) who object to the Global Warming theory on both evidential and methodological grounds. In his popular and influential book, 101 Philosophy Problems (1999, 2002, 2007 and widely translated), Cohen accuses Global Warming theorists of fallacious reasoning. Firstly, he points out that climate is a complex and not a linear system, so that (for example) an increase in temperatures could cause a change in ocean currents which would then cause a change in precipitation and cloud cover, and a decrease in temperatures. Climate, he points out, is 'chaotic', it is simply not amenable to the imposition of the kinds of simple linear relationship the Global Warming theorists require.
He argues that there are many unknown factors in climate - the behavior of algae in the sea, the effects of sunspot activity - so that supposed models are completely arbitrary. Similarly, data is being cherry-picked to support the theory - so that a fall in temperatures in one region is also taken as evidence of global warming.
Cohen argues that much of the 'evidence' for the theory is opportunistic. As an environmental campaigner of long standing himself, he had experience of this, when in the 1990s. Cohen and other environmentalists were objecting to the threat to fish species in Yorkshire rivers after the privatised company, Yorkshire Water, imposed drought restrictions, in this traditionally very wet county in the north of England.
Example of an environmental group attempting to use 'Global Warming' for opportunistic political aims
Cohen and his group pointed out that in fact there was substantial rainfall in Yorkshire, but the company had avested inadequately in resvoirs and pipelines. The environmental group, Friends of the Earth, in London, however wanted to use the affair to illustrate the exceptional changes Global Warming supposedly hearalded, and so instructed all campaigners - even as the rain continued to pour in Yorkshire! - to use the water shortage as evidence of global warming. This was a decision taken contrary to the evidence and reflected a political rather than a scientific calculation. The Ilkley local group (which Martin Cohen co-ordianted) was one told to cease campaigning against Yorkshire Water for poor management practises - or to disaffiliate. Ilkley chose to publicise the scientific evidence and disaffiliated. Who was right? The rain has scarcely ceased to fall in Yorkshire. In due course, the head of Yorkshire Water resigned after these was shown to be responsible for the water shortages.
[end of example]
In general, Cohen, claims that scientists are following a kind of collective herd instinct, where it has now become career-death to oppose the theory. When climatologists speak out, they are accused by ill-informed media commentators and those wielding accusations of 'unprofessional behavior' - such as George Monbiot. In such circumstances, a consensus soon obtains - just as there was in the 1970s on the danger of a new 'ice age'. (the so-called 'White Earth Theory').