Monday, September 17, 2012

This Q & A is part of the Guardian's ultimate climate change FAQ

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measures from 1960 to early 1990, supported by a wide range of data and a number of independent studies have shown that there was a significant decrease in the amount of solar energy reaching the surface earth. This reduction is called "global change".

The observed "darkening" has strong regional differences in the world. While the southern hemisphere has seen modest attenuation in the period 1961-1990 (which has continued to this day), the northern hemisphere has declined much more important (% reduction 4-8). Since then, some parts of the world such as Europe and North America have experienced a partial recovery (known as "brightness"), while other regions (especially China and India) saw more mixed although regional decreases.

global dimming is not thought to be due to changes in the brightness of the sun, because they were too small to explain the magnitude of the observed attenuation. However, air pollution by human activity is considered as the main contributor. Aerosols are formed by direct contamination can reflect and absorb radiation before it reaches the surface of the planet and make clouds brighter and more, meaning that reflect more sunlight.

Although we can not rule out the possibility that natural variations in the Earth's climate (through natural variation clouds) contributed to global dimming, the effects are so closely correlated with trends air pollution there is strong evidence that human activity is a major player. For example, in Europe and North America air quality laws in the 1990s reflected the light in these regions. In contrast, China and India have seen beyond the regulation, which is increasing rapidly industrializing pollution.

global dimming is believed to have been a number of significant impacts. For example, there is evidence to suggest that history has obscured some of the warming caused by greenhouse gas emissions. In fact, the areas that have undergone rapid heating shine.

future global regulatory changes can be expected to be closely related to disseminate emissions. Another factor that has not always played a big role, but perhaps more important in the future is the impact of greenhouse gases on global warming regulations. The higher levels of heating of the atmosphere increases the atmospheric water vapor, which absorbs some of the energy of the solar radiation before it reaches the surface. If the future of global warming turns out to be significant, mitigation generalized water vapor may be a consequence - but the cooling effect of which would be likely to reduce the global warming trend

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This article was written by Ben Booth, a climate scientist at the Met Office, in collaboration with The Guardian

. The response last updated: 08/05/2012
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