Biosphere Capital

Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-twentieth century and its projected continuation.

The global average air temperature near the Earth's surface rose 0.74±0.18°C (1.33±0.32 °F) during the hundred years ending in 2005. The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the observed increase in globally averaged temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations" via the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward. These basic conclusions have been endorsed by at least thirty scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. While individual scientists have voiced disagreement with some findings of the IPCC, the overwhelming majority of scientists working on climate change agree with the IPCC's main conclusions.

What is happening: global warming

Why it happens: increasing atmospheric carbon dioxide concentration

It has been known since the 19th Century that molecules in the earth's atmosphere trap heat from the sun, causing the atmosphere to be some 23°C warmer than it would otherwise be. This phenomenon, known as the greenhouse effect, is illustrated in the figure below. Many different molecules contribute to the greenhouse effect. Water vapour (H2O), carbon dioxide (CO2), oxide (N2O), methane (CH4) and many others all contribute to the warming to a differing extent, depending on their abundance, lifetime in the atmosphere and ability to absorb infrared radiation. Of these molecules, CO2 is the most important, as it the molecule whose abundance is most directly influenced by human activities. In particular, much of world's energy needs are supplied by burning fossil fuels, e.g.:

Climate model projections summarized by the IPCC indicate that average global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century. The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity.

Increasing global temperature will cause sea level to rise, and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation. Other effects of global warming include changes in agricultural yields, trade routes, glacier retreat, species extinctions and increases in the ranges of disease vectors.

How it happens: the Greenhouse Effect

Many estimates of aggregate net economic costs of projected damages from climate change across the globe are now available. The Stern Review, a 2006 report by the former Chief Economist and Senior Vice-President of the World Bank Nicholas Stern, predicts that climate change will have a serious impact on economic growth without mitigation. The report suggests that an investment of one percent of global GDP is required to mitigate the effects of climate change, with failure to do so risking a recession worth up to twenty percent of global GDP.