Global Dimming

SUBHEAD: Global dimming from pollution creates a cooling effect that partially masked the effect of greenhouse gases on global warming. Image above: View from Clark Air Base on 6/12/91 of Mount Pinatubo erupting in the Philippines. Besides cooling and dimming the planet this volcano closed US Navy's Subic Bay Base and Clark AFB. From ( By Tineke Bennema on 9 March 2010 in Tilburg University Press - ( Unique data from weather stations The recently observed reduction in air pollution implies that more solar radiation reaches the Earth’s surface. This could lead to a far more rapid increase in the Earth’s temperature in the coming decades than has previously been expected based on calculations of CO2 emissions alone. In order to successfully combat global warming, it is crucial that we incorporate both effects – reductions in air pollution and increases in CO2 emissions – in the calculations. These are the claims of econometricians Jan Magnus, Bertrand Melenberg, and Chris Muris from Tilburg University based on unique solar radiation data collected from weather stations between 1959 and 2002. Their calculations show that in order to prevent an increase in global temperatures of more than two degrees we will have to reduce CO2 emissions by an additional 56 million tons to compensate for the increased solar radiation reaching the Earth's surface. Everyone is familiar with the effect of CO2 emissions on the Earth’s temperature: the greenhouse effect. Less well known is the effect of solar radiation reaching the Earth's surface, and its development over time. Besides solar fluctuations, the amount of radiation is also affected by small particles called aerosols. The more aerosols are present in the atmosphere, the less solar radiation reaches the Earth. Large quantities of aerosols actually help to cool down the Earth and to temper (‘dim’) the greenhouse effect. Without this reduction in solar radiation, the Earth’s temperature would have increased by an additional one degree during the last fifty years. Man-made pollution Man-made pollution affects the quantity of aerosols in the atmosphere: soot particles emitted by cars, for example, exacerbate aerosol concentrations. Measures to reduce soot emissions and the subsequent pollution have been adopted by numerous countries in recent years. These measures have reduced the quantity of aerosols in the atmosphere, thus allowing more solar radiation to reach the Earth’s surface, and increasing global temperatures. Ground-breaking research The statistical analysis in this study uses solar radiation data over a forty-year period. Based on these data, the researchers at Tilburg University conclude that, given the increased levels of solar radiation, existing global warming forecasts for the next few years could be far too conservative. They claim that in order to compensate for the increased levels of solar radiation, greater efforts will be needed to reduce CO2 emissions. If action is not taken soon, global warming could accelerate and temperatures could soar by more than four degrees instead of the agreed maximum target of two degrees. The researchers developed a statistical model to separate the impact on temperature of the two effects. This produces different scenarios that demonstrate the effect on temperature of varying solar radiation levels and CO2 emissions. Relationship to global warming

Some scientists now consider that the effects of global dimming have masked the effect of global warming to some extent and that resolving global dimming may therefore lead to increases in predictions of future temperature rise.[43] According to Beate Liepert, "We lived in a global warming plus a global dimming world and now we are taking out global dimming. So we end up with the global warming world, which will be much worse than we thought it will be, much hotter."[44] The magnitude of this masking effect is one of the central problems in climate change with significant implications for future climate changes and policy responses to global warming.[43]

Interactions between the two theories for climate modification have also been studied, as global warming and global dimming are neither mutually exclusive nor contradictory. In a paper published on March 8, 2005 in the American Geophysical Union's Geophysical Research Letters, a research team led by Anastasia Romanou of Columbia University's Department of Applied Physics and Mathematics, New York, also showed that the apparently opposing forces of global warming and global dimming can occur at the same time.[45] Global dimming interacts with global warming by blocking sunlight that would otherwise cause evaporation and the particulates bind to water droplets. Water vapor is the major greenhouse gas. On the other hand, global dimming is affected by evaporation and rain. Rain has the effect of clearing out polluted skies.

Brown clouds have been found to amplify global warming according to Veerabhadran Ramanathan, an atmospheric chemist at the Scripps Institution of Oceanography in La Jolla, CA. "The conventional thinking is that brown clouds have masked as much as 50 percent of global warming by greenhouse gases through so-called global dimming... While this is true globally, this study reveals that over southern and eastern Asia, the soot particles in the brown clouds are in fact amplifying the atmospheric warming trend caused by greenhouse gases by as much as 50 percent."[46]

Global dimming ( From Wikipedia, the free encyclopedia

Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4% reduction over the three decades from 1960–1990. However, after discounting an anomaly caused by the eruption of Mount Pinatubo in 1991, a very slight reversal in the overall trend has been observed.[1]

It is thought to have been caused by an increase in particulates such as sulfate aerosols in the atmosphere due to human action. The switch from a "global dimming" trend to a "brightening" trend in 1990 happened just as global aerosol levels started to decline.

Global dimming has interfered with the hydrological cycle by reducing evaporation and may have reduced rainfall in some areas. Global dimming also creates a cooling effect that may have partially masked the effect of greenhouse gases on global warming.

Deliberate manipulation of this dimming effect is now being considered as a geoengineering technique to reduce the impact of global warming.

Video above: Documentary film "Global Dimming" From (

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