But even then, he adds, the Asian haze has far different effects from greenhouse gases, mainly carbon dioxide, which cause global warming. Aerosols are particles about a millionth of a centimetre in diameter, consisting of sulphates, soot, organic carbon and mineral dust and are produced naturally and by human activities. Mitra says that although aerosols have definite effects on climate, these are readily reversed by ways such as the beneficiation of coal, a major fossil fuel that is used in India and China, by encouraging better cooking practices, and by controlling automobile and industrial emissions. He adds that while there is a need to control aerosols emissions, it should not be used shift focus away from long-lasting greenhouse gases like carbon dioxide. According to Mitra, the good news is that steps to control greenhouse gases under the Kyoto protocol, which binds industrialised countries to cut emission of these gases, will automatically reduce aerosol emissions — which have yet to be covered by any international regime. In cities like New Delhi, the brown haze is nothing new.
Tourists wear face masks as they climb Jingshan Hill beside the Forbidden City as heavy air pollution shrouded Beijing on February World Health Organization guidelines say that a PM2. In the meantime, official explanations for the severe smog— large amounts of emissions, poor air dispersion —seem comically inadequate , leaving a frustrated public hungry for more innovative explanations. A couple of arguments support the idea that the U. An excellent study published in Proceedings of the National Academy of Sciences PNAS in January found that a small but significant amount of air pollutant emissions in China can be attributed to the production of goods later exported to the U. A second, more tenuous argument for U. However, arguments suggesting U.
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 s. However, after discounting an anomaly caused by the eruption of Mount Pinatubo in , a very slight reversal in the overall trend has been observed. Global dimming is thought to have been caused by an increase in particulates such as sulfate aerosols in the atmosphere due to human action. It has interfered with the hydrological cycle by reducing evaporation and may have reduced rainfall in some areas.
The results show that the brown haze - a mixture of pollutants, mainly soots, sulfates, nitrates, organic particles, fly ash and mineral dust, formed by fossil fuel combustion and rural biomass burning - is reducing the amount of sunlight reaching the tropical Indian Ocean surface, thousands of kilometers from its source, by as much as 10 percent; with larger percentage reduction over the Indian Subcontinent. The researchers tracked the haze over an area of about 10 million square kilometers, and believe it forms over much of the Asian continent, home to more than half the world's people. The scientists plan to establish a network of ground-based monitoring stations throughout Asia to study the composition and seasonal pattern of the haze. UNEP has pledged to facilitate the continued research program and, in the longer-term, look to coordinate policy responses to address the problem.