About 30 gases produced by human activity have been identified as contributing to the greenhouse effect. These are sometimes called greenhouse gases. The main ones are carbon dioxide, methane, CFCs and nitrous oxide. Sunlight reaches the Earth's surface, is reflected off it, and is prevented from escaping from the atmosphere by this layer of gases, which acts like glass in a greenhouse.
Up to a point, the greenhouse effect is a natural process, and naturally occuring carbon dioxide is not dangerous. Without greenhouse gases, the average temperature of the Earth would be -19C , in other words, too cold for us to live. However, the concentration of the greenhouse gases in the atmosphere has changed dramatically: since the 18th century, carbon dioxide has increased by 30%.
There is disagreement among scientists about the seriousness of global warming. Most scientists agree that the global temperature is rising. They do not agree on more specific elements of the issue: How much will it warm up? What will happen if it does warm up? How far are humans responsible? What should we do to stop it?
Scientists believe that if we go on producing gases at the rate we do now, it is likely that the Earth's average temperature will rise by about 0.3 degrees C every ten years. This does not sound much, and it might be pleasant to have hotter summers in Britain, but it could have a huge effect on all living things on Earth. Changes in global temperature of the kind predicted could have considerable effects on rainfall and wind, as well as warmer weather. They can also affect ocean currents, which can greatly affect the weather, and the unusual weather experienced during El Nino is an example of the effect the ocean has on the weather.
Sea level rise is another effect of climate change. This will happen as temperatures rise, and warm water will occupy more space than cold water, flooding low lying areas (sea level rise is not primarily due to melting polar ice caps). Again, there is disagreement as to how much the sea level will rise. Many of the world's cities and much agricultural land are in the threatened zones.
As the global temperature rises, the distribution of plants and animals will be changed. Again, the consequences are unpredictable, but countries that now have rich agricultrual land could find these less productive: others may find poor areas improved.
Wildlife already faces a number of threats and many species and habitats are vulnerable to human activities. Although we. re not sure how climate change will affect wildlife, it is clear that its impact will make things worse.
Many types of wildlife depend on natural signals, such as temperature or day length, to time their life cycles, and if some of these signals alter due to climate change, the timing of life cycles will change. A study of birds across the UK from 1971 to 1995 shows that 63% of the species are showing a tendency to nest earlier. Twenty species of UK breeding bird are laying their first egg an average of nine days earlier than they did 20 years ago.
Most scientists accept that global warming will cause wildlife to shift northwards, or to move higher in altititude: this is what happened, very slowly, after previous Ice Ages, as the Earth has warmed up again. However, some species may not be able to move if climate change is so rapid they they, or the other species on which they depend for food, cannot move into new areas where the climate is suitable for them. Plants, for example, may not be able to disperse themselves fast enough to keep pace with the shift in the location of their optimal climate conditions.
Animals that migrate may be affected by global warming. The success of migration depends upon the right places being available at the right times of year, with the right food needed to complete the migration. If the links in the chain of areas vital to migration are damaged, migrants' survival is threatened. In the US, Delaware Bay is a vital feeding ground for knots, which feed on the eggs of the horseshoe crab. Eggs are a vital fuel source to sustain the knots in the Arctic. Any changes in the timing and availability of eggs or the arrival of the knots will have an adverse impact on the success of the birds in reaching their destination. Food supplies at staging areas during the spring migration may affect not only a bird. s ability to reach its destination, but also its breeding success, as is the case for some arctic nesting geese.
World economy would be affected by Global warming because the richer countries would lose wealth and status and the poor countries would get richer.
The most likely cause of this rapid global warming over such a short period is the release of methane into the atmosphere. Methane is 60 times more powerful than CO2 as a greenhouse gas but only remains in the atmosphere for about ten years and so looses it's greenhouse effect quickly compared to CO2 which remains in the atmosphere for 100 years. CO2 would not be available in sufficient quantities to achieve the rapid warming and if CO2 was the cause then the raised temperatures would last a lot longer.
Methane hydrates occur extensively today all over the world. They consist of methane stored within unstable water bound deposits that if disturbed release the methane. They occur in major river deltas such as the Amazon delta and in old delta areas such as the Gulf of Mexico. Major rivers carry millions of tons of silt containing vegetable matter that continues to decay after the silt is deposited in the river delta. This anaerobic decay produces methane which gets trapped in the silt as methane hydrates until the conditions of water temperature and pressure change which can release the methane in vast quantities very quickly. Another form is a frozen slush/ice methane hydrate where the methane is trapped in an ice/water mixture which releases the methane when it warms up or the pressure on the ice is reduced. Frozen methane hydrates can contain 170 times their own volume of methane. These frozen hydrates occur in the seabed deposits of the Arctic Ocean.
Methane can also be trapped by permafrost layers which over-lay lower unfrozen layers of vegetable material that is decaying and producing methane which remains trapped by the frozen permafrost on top. If the permafrost layer were to melt then the methane in the layers below would escape into the atmosphere. Given the vast areas of permafrost in northern latitudes there is a significant potential for methane to be trapped that would be released if the permafrost melted as a result of global warming.
The theory for these rapid rises and falls of temperature, based on the geological records from 55 million years ago, is that gradual global warming due to some natural cause had resulted in temperatures 5 to 7 degrees centigrade higher than average ( i.e. higher than today's temperatures). At this point methane trapped in methane hydrate deposits started to be released into the atmosphere and accelerated the rate of warming. This would result in further warming releasing more methane. As the atmosphere warmed different types of methane deposits would start to be released and so a cycle of methane release leading to increased warming leading to more methane release from other areas of methane deposits elsewhere in the world would become established as global warming effected different areas of the world.
