Figure A.3. The relative magnitude of radiative forcing associated with greenhouse gases, ozone in the atmosphere, and sulfates.
dioxide. The Figure A.3 is based on the recent report of the IPCC (The Intergovernmental Panel on Climate Change) where the magnitude of the radiative forcing associated with greenhouse gases, ozone in lower and upper layers of the atmosphere and sulfate aerosols (cooling) are compared. Only those factors where the level of scientific understanding is high is indicated in the figure (the original IPCC figure included other contributors such as burning of biomass or fossil fuels mineral dust and aerosols .
Global average temperatures have already edged up at a rate of about 0.6oC (+ or —0.2oC) over the 20th century. There is consensus among leading researchers that at least in the past 50 year period most of the observed warming of the earth is mainly the result of increased greenhouse gases in the atmosphere . While a direct correlation between the rise in global average temperature and the concentration of these gases is difficult to demonstrate, the available evidence increasingly points to anthropogenic factors causing global climate change . Careful measurements show a clear warming trend in the sea environment as well , both in the Southern and Northern Hemispheres. Unless carbon emissions into the atmosphere are drastically controlled, global warming is likely to continue unabated in to the future years. According to the best estimates, the average global temperatures are expected to rise by 1.4-5.8°C by 2100. Therefore nearly all land areas are likely to warm above the present global average, with more extreme hot days and heat waves and fewer cold days becoming increasingly common. Assumptions made in the models used to estimate these introduce a certain degree of uncertainty as to the exact number of degrees of warming expected and how such warming might be geographically distributed. However, at the present time there is worldwide consensus that global warming is indeed well underway, that anthropogenic greenhouse emissions50 are primarily responsible for it, and on the likely consequences of this phenomenon. Even if the estimates are only partly correct, the future generations will face the unpleasant prospect of living on earth that will be the warmest ever since human beings evolved51. It is important to appreciate that despite the few degrees increase anticipated in global average temperature, the effect on the environment and biosphere could be devastating. After all, during the last Ice Age the global average temperature was less than 6°C lower than it is at present!
As the global warming process is already under way the associated environmental consequences are beginning to be apparent. Careful extrapolation of these effects to higher levels of warming and other studies of likely impacts, yield possible global consequences to be expected at a possibly warmer future time. The more serious of these effects are likely to be regional where extreme weather events such as drought heat waves and heavy rainfall are expected to increase over the next 100 years in affected parts of the world. Other regions will actually be cooler than at the present time. Some particularly serious consequences of global warming are as follows.
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