1896 the Swedish chemist Svante August Arrhenius advanced the theory that carbon dioxide emissions from combustion of coal would increase the earth’s greenhouse effect and cause global warming.
   
   1924 the US physicist Alfred James Lotka speculates, based on the amount of coal used in 1920, that industrial activity would double the amount of carbon dioxide in the atmosphere in 500 years.
   
   1949 the British scientist Guy Stewart Callendar links the estimated 10 per cent increase in atmospheric carbon dioxide between 1850 and 1940 with the noticeable warming of northern Europe and North America which started in the 1880s.
   
   1954 the Yale biologist Hutchinson is the first one to suggest that deforestation may increase the carbon dioxide level in the atmosphere.
   
   1967 the first reliable computer simulation calculates that the global average temperature may increase by more than 4 degrees Fahrenheit when the atmospheric carbon dioxide level doubles from pre-industrial times.
   
   1976 scientists at different research institutes identify methane, nitrous oxide and chlorofluorocarbons (CFCs) as greenhouse gases.
   
   1979 a report of the National Academy of Sciences panel on climate change suggests that ‘A wait-and-see policy may mean waiting until it is too late.’
   
   1983 a NAS report confirms that if the atmospheric carbon dioxide levels double, global temperature will increase by three to eight degrees Fahrenheit. The same year, a US Environmental Protection Agency study says ‘agricultural conditions will be significantly altered, environmental and economic systems potentially disrupted and political institutions stressed.’
   
   1988 the Intergovernmental Panel on Climate Change establishes an internationally recognised set of assessments of the science on climate change, including the causes, impacts and possible responses. This is the first critical step in establishing the scientific foundation upon which global dialogue to push for action can be built. At the Toronto Conference on Changing Atmosphere, delegates from 46 countries call for a reduction of worldwide carbon dioxide emissions by 20 per cent from 1988 levels by 2005.
   
   1992 the conference in Rio de Janeiro produces the UN Framework Convention on Climate Change, but the US blocks calls for serious actions.
   
   1995 the second IPCC report points to a ‘signature’ of human-caused greenhouse effect warming, declares that serious warming is likely in the coming century
   
   1997 the Kyoto Protocol is drawn, setting targets to reduce greenhouse gas emissions if enough nations sign onto a treaty agreeing to follow the environmentally friendly guidelines. Toyota introduces Prius in Japan, first mass-market electric hybrid car.
   
   2005 the Kyoto treaty comes into effect. It is signed by major industrial nations except the US.
   
   2007 the fourth IPCC report warns that serious effects of warming have become evident; cost of reducing emissions would be far less than the damage they will cause.