What consensus?

It is often claimed that the science of man-made global warming or climate change is settled and there is a consensus to which 97% of (or 4,000) climate scientists subscribe. Yet there is no evidence for this claimed consensus 

John McLean analysed IPCC AR4 (the fourth IPCC report published in 2007) papers to determine how many scientists and authors explicitly supported the AGW theory. He found only 60 authors and reviewers could be regarded as explicitly supporting the claims about a significant human effect on climate.

Furthermore, 166 climate scientists issued a challenge to Ban Ki Moon on the eve of the Copenhagen Climate Summit in 2009 to provide proof of human induced global warming, saying

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Temperature records and Climategate

There are two types of temperature record, those directly recorded in real time and those which are recreated using a variety of techniques (referred to as proxy records) to try to understand changes in temperature long before recorded temperatures were available.

It is important to understand that there is no such thing as a global temperature.  What is referred to when talking about climate change is an approximation of global temperatures derived from a limited number of data sets. There is no definitive long term record of global temperatures. Surface temperature records go back to about 1850 but early records are restricted to a small number of locations mainly in the northern hemisphere. Later records are affected by the Urban Heat Island (UHI) effect: temperature recording instruments, once sited in remote locations, are now surrounded by urban environments. UHI exaggerates the perceived warming. Where records are missing, they’ve been estimated. Anthony Watts, a retired meteorologist, has undertaken extensive research into surface temperature data. http://wattsupwiththat.com/reference-pages/global-temperature/

Satellite data are probably the most reliable guide we have

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Are rising man-made CO2 emissions causing global warming?

Both sides of the global warming debate agree that there is a close correlation, over the last 800,000 years, of CO2 concentrations in the atmosphere with global temperatures.  Furthermore it is generally agreed that hitherto, the rise in temperatures preceded the rise in CO2 levels by an average of around 800 years.  

Inevitably the relationships are complex and this referenced article gives a much more detailed account of the evidence: CO2: Ice Cores vs. Plant Stomata by David Middleton

However, the IPCC and the pro-global warming lobby insist that it is now CO2 which is driving the rise in temperature with no hard evidence to support this illogical premise.  On the contrary, temperatures rose fairly rapidly from about 1900 to 1940 but then declined until the late 1970s during a period when CO2 emissions were rising in the post-war industrial boom.  According to satellite data,

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Anthropogenic Global Warming theory

The UK Met Office describes the Anthropogenic Global Warming (AGW) hypothesis as follows: “It is now clear that man-made greenhouse gases are causing climate change.  The rate of change began as significant, has become alarming and is simply unsustainable in the long term” and the greenhouse effect is depicted on their website thus:

greenhouse_effect

Solar rays hit the earth and heat up the surface (as shown on the left).  The earth’s surface emits infrared radiation back in to space thereby cooling the planet (depicted by two of the red arrows in the right hand picture).  Greenhouse gases in the troposphere trap some of the infrared rays reflecting heat back down to the surface.  The AGW theory suggests that increased CO2 concentration in the atmosphere, caused by humans, is raising global temperatures.

For the theory to hold true,

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