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manmade climate change
The role of human activity in accelerating climate change is beyond doubt. The fourth assessment report (4AR) of the UN scientific body, the Intergovernmental Panel on Climate Change (IPCC), confirmed that an overwhelming majority of scientists now accept the impact of human (anthropogenic) activity on our climate and fear that, if left unchecked, this could lead to runaway warming.
While previous changes in the climate have been a result of natural causes alone, this is not true of the present warming. Current human behaviour is leading to global warming by accentuating the greenhouse effect.
Human impact and the greenhouse effect
The greenhouse effect ensures that some of the warmth of solar radiation is trapped in our atmosphere, making life on earth possible. However, human activity is causing an unprecedented rise in the level of greenhouse gases in our atmosphere, and scientific modelling indicates this will lead to global temperature increases on a greater and more rapid scale than ever before.
The rapid growth in the extraction and burning of fossil fuels (like coal, oil and natural gas) has led to a massive increase in the amount of carbon dioxide (CO2) - one of the main greenhouse gases - being released into the atmosphere. This growth in the burning of fossil fuels, which has happened since the Industrial Revolution, has been used to create energy to power factories, heat homes, run vehicles and so on. Deforestation and land degradation (such as through poor farming practises) are other human activities that have led to the release of CO2 stored in the trees and the soil.
Humans have released an extra 2.3 trillion tonnes of CO2 to the atmosphere over the past 200 years, according to a report by the World Research Institute, with half of this being released over the past 30 years. This has resulted in the concentration of CO2 in the atmosphere increasing by over 30% since 1750 - this unprecedented 'atmospheric concentration' is now at almost 385 parts per million (ppm). CO2 emissions are now around 12 times higher than in 1900, as a result of ever greater use of fossil fuels.
A warming climate
The global temperature increased by 0.74° C over the last century but the climate is warming at a much faster level than ever recorded: the 17 warmest years have all occurred in the last 20 years, according to the Hadley Institute. The 2007 global temperature was 0.37° C above the 1961-90 average and 0.11° C warmer than 1999. Among the dramatic impacts this is already having, global ice mass is shrinking and sea levels are rising.
The two lowest levels of Arctic ice mass ever recorded occurred in the summers of 2007 and 2008. This is being compounded by glacier shrinkage around the world. According to the IPCC 4AR, global sea level rose about 17 centimetres (6.7 inches) in the last century. In the last decade, however, the rate of rise nearly doubled. Sea level rose an average of 3mm per year between 1994 and 2005.
The vicious circle of 'positive feedback'
Climate scientists fear that the current warming cycle will lead (or is already leading) to the release of greenhouse gases stored in natural 'sinks' across the earth. This includes: the release of methane (a greenhouse gas over 20 times more potent than CO2) as the permafrost in Siberia melts and ocean waters warm; increased rates of atmospheric water vapour (also a greenhouse gas); the diminished ability of oceans to sequester (or trap) CO2 as they warm; and the decline of rainforests and release of the CO2 they store.
This 'positive feedback', combined with manmade emissions, could lead to runaway warming (of over 6 degrees by 2100) with devastating consequences for our planet.
