United Nations Environment Programme

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Tool 6: Climate change and the greenhouse effect

The continued use of fossil fuels will change the global climate: More than 95% of the fuel used for transport (e.g. diesel, petrol or kerosene for aircraft) is fossil-based. When using "fossil fuels", carbon materials - such as oil or coal - are removed from the earth's crust, where they have been stored for millions of years. Extraction and use of these fuels emits the carbon as carbon dioxide (CO2).


Burning of fossil fuels increases atmospheric concentrations of carbon dioxide (CO2): The concentrations of CO2 in the atmosphere have increased from 280 ppm (parts per million) in 1800 - when humankind started large-scale use of fossil fuels - to ~370 ppm today.


Higher atmospheric CO2 concentrations reflect heat from the earth that otherwise would have dissipated into space. This has the effect of slowly heating the earth, thus changing the global climate (commonly referred to as "the greenhouse effect"). The rise in temperatures lasts for several centuries before the carbon dioxide is adsorbed into the sea.


Climate Change



Natural and human-induced greenhouse effects:
There is a natural greenhouse effect that warms the earth; without this natural “CO2 blanket”, the earth would have an average temperature of approximately -32°C. Naturally, higher concentrations of CO2 in the atmosphere increase this natural greenhouse effect – in other words, the earth’s “blanket” gets thicker. With atmospheric concentrations of CO2 increasing at their current rate, scientists have now observed a “human-induced greenhouse effect”. This human-induced greenhouse effect is resulting in higher average global temperatures. Already, an approximate increase of 0.6°C in average global temperatures has been measured. This is the fastest increase in average temperatures in 10 000 years!


Rising temperatures:
Current estimates have calculated an increase in global mean temperature of between 1.4 °C–5.8°C by the year 2100, unless we drastically reduce current rates of fossil fuel use. Although these estimated increases sound insignificant, even the most miniscule increase in global mean temperature will have enormous effects on the natural environment, people’s health, and society at large. The figure below shows the rise of temperatures over the last 140 years, since the time humans started large-scale use of fossil fuels. Before this time, the global average mean temperature had been very stable.




Figure 4. Variation in global average temperature. Source: IPCC



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