Global Warming : Real or Not?

This is not the place to discuss this massive issue in detail. There is plenty of information out there . For what its worth my take on the evidence is as follows:
-Despite some uncertainties about the accuracy if the temperature record, yes. There is far too much evidence now, such as the melting of Arctic icecaps . There was a cooling trend between the 1940s and 1970s, but that was just a blip over a longer term warming trend which now seems to be accelerating.
- Is it man-made? That is less certain. There is fair amount of evidence that the sun has moved into a cycle of activity which warms the earth more than at any time for at least five hundred years, and possibly 8,000 years. There is a strong correlation between man made greenhouse gas emissions and temperature, but that may be coincidence: correlation does not mean proof. On balance however it does seem that human activity is making the effects worse, possibly markedly so. It is like taking a man with a fever, and putting him in a hot bath.
- Have there been similar variations in climate before? Over the very long term, much larger: we are in a 10,000 year old interglacial between ice ages. A thousand years ago, when the Vikings sailed from Greenland to North America the temperature was similar to today or a bit warmer. Three hundred years ago was the depths of the Little Ice Age: In the 1690s it was several degrees cooler on average (this was when the pack ice reached the Shetlands, and a third of the population of Scotland and Scandinavia may have died of famine as the crops froze) . So far the climate changes have been within the 10,000 yr historic margins of variation, but there are early signs that we may be moving into uncharted terrritory (such as the rapid rate of ice cap melting). Does it matter, or is this just another apocalyptic scare story? Yes it almost certainly does matter, for several reasons:
- if climate models are correct ( a big if) then the rate of change of temperature will be faster than ecosystems can adjust to
- more importantly, climate systems seem to be non-linear: they can “flip” from one state to another very rapidly .The latter might mean for example that the Gulf Stream switches off, as ocean currents reverse, with dire consequences for North America and Europe (extreme cold instead of heat); or even scarier a runaway greenhouse effect as positive feedback loops make the climate hotter and hotter. This may have happened 250m years in the Great Permian extinction, which wiped out 90% of the world’s species and was even bigger than the one at the end of the Cretaceous which wiped out the dinosaurs. A possible cause is that global warming due to volcanic eruptions melted the methane hydrates below the sea bed, and methane is a powerful greenhouse gas. It is all a question of how one rates a small risk with potentially huge consequences. Thus your chances of dying in a giant meteorite strike, though very small, are still larger than you might imagine for such rare events. It is just that each event might kill millions or even billions. If there is even a very small risk that a runaway greenhouse effect could kill billions or even wipe out human beings, then we cannot continue to carry out such a massive uncontrolled experiment on the earth.