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HomepageIan Gallon
We have all heard of the Greenhouse Effect and Global Warming, and yet we have just experienced one of the coldest winters in recent times. To understand this we must understand what is meant by the Greenhouse Effect and Global Warming and also the distinction between climate and weather.
The sun has a surface temperature of around 6000 oC which is why it radiates so much light. It also emits a great deal of energy as infrared radiation, which is just the same as light except that the wavelength is too long for us to see, although we feel it as heat. The Earths atmosphere is transparent to this radiation. On reaching the ground most of the infrared radiation and a lot of the light is absorbed, this energy being converted into heat. All hot objects radiate infrared radiation, though because the temperature on Earth is so much less than the sun, the wavelength is very long. In the pre-industrial age the atmosphere was very transparent to this long-wave radiation, which meant that most of the heat absorbed during the day was radiated into space during the night. This meant that there was a balance between heat gained and heat lost, and the yearly average temperature was fairly constant.
Climate is defined by temperature, humidity, rainfall and a number of other parameters averaged over a long period in a particular region, and there are a number of classification schemes. With this definition it can be seen that global warming is changing the various climates around the world. In contrast to this weather is the sum of the activity in an area at a specific time, such as whether it is raining, how strong the wind, and how hot it is.
The weather depends in a complex way on the weather in other parts of the world. One of the main drivers is the high altitude winds caused by the temperature difference between the equator and the poles. These winds, called the jet stream, stir the lower atmosphere causing cyclones and anticyclones, as shown on the weather maps on television. The direction of the jet stream is highly changeable and as it moves it causes the regions of low and high pressure, which move in general west to east, to move northwards or southwards. The electrical storms we experience are due to the clash of a two such regions with different humidity, temperature and densities. Large polar cyclones have a cold core. A group of these cyclones moved south of their normal path and passed over northern Europe, causing the cold winter.
Industry now produces vast amounts carbon dioxide and other gases, and farming produces methane, these two gases being very efficient at absorbing the long-wave infrared and re-radiating half of it back to Earth. The build-up of gases in the atmosphere has led to an imbalance, the Earth making a net gain of heat each day. The initial change was quite slow, but a number of effects come into play that accelerate the change, even causing the rate of acceleration to increase. And yet we pump more and more carbon dioxide into the air.
The polar ice caps reflect a lot of heat, but the borders of the ice fields are retreating, and as the area of ice decreases, so the Earth warms a bit more. This heating has already uncovered thousands of square miles, but of even greater significance, the ground contains vast amounts of methane which is now beginning to be released, and methane is ten times more effective as a greenhouse gas than carbon dioxide.
Seventy percent of the Earths surface is ocean, and the oceans hold a lot of dissolved carbon dioxide. As the oceans warm this carbon dioxide will be released. On the ocean floors there is something called a clathrate, which is methane held in water by weak chemical bonds. There will come a time when these bonds will be broken, releasing catastrophic volumes of methane.
The effects of this warming are on the verge of catastrophic. The temperature around the equator is only a few degrees below the temperature at which cold-blooded animals can survive. They will die or migrate. Humans are not immune, and we will see mass migrations as the temperature becomes unbearable. But before that happens the ice on Greenland, across northern Canada, and the Antarctic is beginning to melt. The ice cover of Greenland alone is sufficient to raise the sea level by 7 metres. The immense weight of this ice compresses the rocks below. As it melts and flows away the rock expands, and this causes a compensating lowering of the Earth’s crust to the south. In addition the extra melt water is raising the sea level. Roughly 20% of the increase in sea level is due to the expansion of the oceans as they warm up (New Scientist 10, March 09). A few centimetres rise in sea level will flood many South Sea Islands, and some have already been affected. Half a metre will flood a large area of Bangladesh. One metre will flood London, New York and most of the large coastal cities around the world.
Despite the prospect of a Mediterranean climate in Britain, it is possible that our climate could become much colder. Our climate at present is much milder than the climates of other regions at a similar latitude due to the Gulf Stream, a current of warm water that flows from the Caribbean. On meeting the icy waters of the Polar Regions the stream cools, becoming more dense. The water then falls to the ocean floor and returns to the equator. As the Polar Regions warm, less of the Gulf Stream falls to the ocean floor and some returns on the surface. This reflection of the stream is taking place at lower and lower latitudes, and current estimates are that a third of the Gulf Stream has turned back before reaching Britain.
These few examples show how complex the relationship between weather, climate, ocean currents and greenhouse gasses is. It is this complexity that gives the uncertainty of the predictions. The way the predictions are arrived at is to form a mathematical model that calculates the factors required to define the climate and a set of numbers is found so that the model reproduces the historical record of the worlds climate which has been obtained from studies of air trapped in deep layers of ice in Greenland, Canada and Antarctica and the distribution certain isotopes. This record clearly shows the increase in global warming beginning at the start of the industrial revolution. Having fitted the model to history it is then run forwards, adding the increasing supply of carbon dioxide. Each model, and there are about thirty such models, has to make certain assumptions, and when they are all plotted on the same graph there is a spread of about a factor of 2 between the most optimistic and the most pessimistic. The present prediction gives us between 50 and 100 years to the tipping point.
Global warming has increased at twice the rate predicted two years ago, reducing the estimated amount of time we have before the changes become irreversible. The problems we, or if not us, certainly our grandchildren, will face is not the lack of technology. A combination of solar, wind and wave power deployed across the world, coupled with a reduction in the consumption of power using low energy lighting would be more than enough to allow the limited use of oil and still reverse or at the least reduce global warming. This would give the extra time required for the development of hydrogen power and possibly fusion power, or even to build nuclear power stations (note that such stations take around 15 years to build if you have the trained engineers, and there are not many of them around now!). The problems will be largely political, or rather political inertia. The poorest nations will suffer the most as world heats up, destroying their crops. They will be forced to migrate mainly northwards, and the population of more affluent nations will also begin to drift northwards. This will cause internal stresses and territorial disputes and these will intensify as we approach the tipping point, the change into irreversible global warming. The sea level will continue to rise at an even greater rate, reducing the area of habitable land. The world population today is around 7 billion, and is expected to rise to around 9 billion by the end of the century. For these people to survive, society would have to be restructured.
The predicted time scale to the tipping point is so close to the time required to develop and install the necessary technology and to educate the world on the necessity of changing their lifestyle that it is essential that we all contribute in whatever way we can by changing our lifestyle, by talking to those who don’t believe, or don’t care or even prefer to believe the isolated scientists and the occasional tele-celebrity ( who are usually proud to admit that they do not understand physics) who deny global warming is occurring! We must convince the politicians here and around the world, to act now- a dead planet does not require a banking system!
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