What evidence is there that man isn

Hi Elena,



Its perhaps not so much that theres *evidence* that man isnt causing global warming, more that theres other possible explanations.



What I mean by this is that there are a number of alternative explanations that have been proposed over the years. However, when examined objectively and critically none of these other ideas can explain the present warming. This doesnt prove that man is or isnt causing global warming, what it does demonstrate is that no alternative explanation has come to light. Ill explain the proof part later.



For example, its often claimed that the present warming is being caused by natural cycles. The skeptics tend to leave it at that and hope that the argument sounds convincing enough. In reality, because theyre cycles they come and go at regular intervals, this means that theyre entirely predictable. There are numerous natural cycles and when we add together all the different effects we find that Earth should have been cooling very slightly for some time now.



Quite often people blame the Sun. It wont come as any surprise to learn that for decades weve been monitoring the Sun and can measure with incredible accuracy the amount of energy being received. Whilst theres an 11 year cycle associated with the solar cycles, the overall trend is one of very slightly decreasing solar output; thus we should be cooling and not warming.



Mike uses another popular argument and claims that every planet in the solar system is also warming. This is completely untrue. Seven of the 189 moons and planets in the solar system are warming (Earth, Enceladus, Mars, Triton, Pluto, Io and Jupiter) and in each case the cause is unique to that solar body.



Ottawa Mike then talks about a lack of a warming trend in the last 10 to 15 years, this is another argument which is popular amongst the skeptics. In climatology a trend is based on events over periods of at least 30 years, anything less is subject to too many short term variables. When we look at the 30 year temperature trend we find that Earth has warmed every year since 1966. Heres a graph I produced 3 weeks ago, its constructed from several billion readings taken over the last 160 years, the red line is the 30 year trend http://www.flickr.com/photos/trevorandcl



For the absolute proof that humans are a factor we need to delve into both chemistry and physics.



The explanation for why global warming occurs (natural and manmade) can be found at the atomic level. In essence, the vibrational frequency of thermal radiation is the same as that of the greenhouse gases thus allowing for absorption and retransmission of the heat energy. What this means is that the more greenhouse gases there are in the atmosphere the more heat will be retained.



Where the chemistry side comes into play is through isotopic analysis. Carbon has three different isotopes - the same atom but with a different number of neutrons. The carbon within the carbon dioxide that is released by human activities such as the burning of fossil fuels, has a different isotopic ratio to naturally occurring carbon dioxide and thus we can establish just how much of the CO2 in the atmosphere is from human sources.



For millions of years the amount of CO2 in the atmosphere varied between 180 and 290 parts per million by volume, in the last 100 years it has rocketed to 394ppmv.



All told, there are now 40% more greenhouse gases in the atmosphere than at any time since the earliest humans walked on the planet.



With such a dramatic increase in the concentrations of greenhouse gases the atmosphere has no alternative other than to retain more heat energy.
The entire problem with this issue is a lack of evidence.



There is little concrete evidence which supports or recants man