I could see how global warming does not make the impact it should on most people. When people hear of a global temperature rise of 2 to 3 degrees, most people in the UK would say, please give me a bit of that, it would be nice to be warmer, and reducing my heating bill would be a bonus. But what does it mean globally?
The 2007 IPCC report narrowed the range of warming from 2.4 to 4.6 degrees Celsius above pre-industrial levels by 2100. Climate scientists estimate that a temperature rise between 1 and 3 degrees Celsius will bring about the melting of the Greenland ice sheet and if that were to happen it would result in the world's oceans rising by around seven metres. Imagine the devastation that would bring to the lives of millions!
Under the heading "Arctic expert predicts final collapse of sea ice within four years" the Guardian reports Professor Peter Wadhams of Cambridge University thus:
"As the sea ice retreats in summer the ocean warms up (to 7C in 2011) and this warms the seabed too. The continental shelves of the Arctic are composed of offshore permafrost, frozen sediment left over from the last ice age. As the water warms the permafrost melts, and releases huge quantities of trapped methane, a very powerful greenhouse gas, so this will give a big boost to global warming."
Climate predictions are so complex, some would say, and the scientists are not in agreement about whether it is human-induced and the extent of it; so why worry about it! Actually the overwhelming majority of scientists believe that global warming is real, it is human-induced and could have catastrophic consequences for humanity and all life on our planet. There are, it is true, some scientists who disagree with some of the above conclusions.
In order for those of us who are not climate scientists to assess their findings, it is worthwhile going to fundamentals to untangle the argument.
Sunlight (short-wave) radiation will go through the greenhouse gases in the atmosphere, thus heating the earth; heat radiated back from the earth is in the form of thermal infrared (long-wave) radiation. A property of greenhouse gases is that they absorb some of the heat, depending on their concentration, and emit some of it back to earth, in effect trapping it and preventing it from escaping back to space. This mimics the heating in a greenhouse on a sunny day, although the mechanism is somewhat different.
For nearly three million years the natural carbon cycle has ensured the atmosphere contained around 300 parts per million (ppm) of CO2, just the right amount to sustain our planet at a temperature suited to the variety of life on it. Estimates show (Wikipedia) that since the industrial revolution (the last two to three centuries) the burning of fossil fuel (coal, gas, and oil) has increased the concentration of CO2 by 42%, from 280 ppm to 397 ppm. Increasing CO2 will mean more heat is absorbed and consequently more heat radiated back to earth, thus producing the increase in global temperature.
There are, of course, other factors, such as volcanic eruptions and ocean cycles such as El Nino, that may slow the rate of warming from year to year or over a number of years, but when these factors are removed from the equation the correlation between global temperature change and CO2 concentration is consistent and convincing over hundreds of thousands of years. The jump in the concentration of CO2 in the atmosphere since the industrial revolution, combined with the strong correlation between global temperature and CO2, represent overwhelming evidence that global warming is real and it is human-induced.
What is unprecedented in the history of the earth is the ability of humanity to extract huge quantities of fossil fuels and burn them at an enormous rate to power our civilization, thus releasing these large stores of carbon through CO2 into the atmosphere. That such action would produce a rise in global temperature should come as no surprise to anyone. Carbon stored in fossil fuel, that took millions of years to accumulate, released in such a short time is bound to produce an imbalance in the equilibrium of our planet; global warming is the result of this human intervention in the natural carbon cycle.
There are people who would argue that it is too expensive to do anything about it; the selfishness, shortsightedness, and immorality expressed in such a view is summed up by Dr. Steven Chu, the departing US Energy Secretary:
"Ultimately we have a moral responsibility to the most innocent victims of adverse climate change. Those who will suffer the most are the people who are the most innocent: the world's poorest citizens and those yet to be born. There is an ancient Native American saying: 'We do not inherit the land from our ancestors, we borrow it from our children.' A few short decades later, we don't want our children to ask, what were our parents thinking? Didn't they care about us?"
Doing nothing or very little is not an option.