Global Dimming

Global dimming is an extremely alarming phenomenon that has captured the attention of climatologists across the globe.

According to the definition given on Wikipedia: “Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth’s surface that has been observed for several decades after the start of systematic measurements in 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, since 1990, the trend has reversed. “

Also, we know that clouds are formed when water droplets are seeded from air-borne particles such as pollen grains. However, due, to air pollution, polluted particulate matter attaches itself to water droplets resulting in the formation of polluted clouds which are more reflective than unpolluted clouds. This reduces the amount of sun’s rays reaching the earth.

Global dimming, in simple words, is a phenomenon which produces forces opposite to global warming. Global dimming causes the amount of sun’s rays reaching the earth’s atmosphere to reduce & causes a drop of temperatures around the globe. In addition, global dimming interferes with the hydrological cycles and reduces evaporation.

Presently, it is widely believed that due to the cooling effect created by global dimming, the true estimates of global warming are being masked. The present estimates which predict a 5 degree rise in temperatures over the next century may well be an under-estimation.

Air pollution is the main causative factor; however, many studies have proven that sulphate aerosols have been the primary cause of this phenomenon. Climatologists have argued that in order to reduce pollution, many developed countries reduced sulphate emissions as sulphates had the most damaging effects on human populations. This resulted in a reversal of the global dimming trend in 1990 and temperatures started increasing.

It has also been theorized that aircraft contrails (also called vapour trails) are a causative factor. The near-total shutdown of civil air traffic during the three days following the September 11, 2001 attacks afforded a rare opportunity in which to observe the climate of the United States absent from the effect of contrails. During this period, an increase in diurnal temperature variation of over 1 °C (1.8 °F) was observed in some parts of the U.S., i.e. aircraft contrails may have been raising night-time temperatures and/or lowering daytime temperatures by much more than previously thought. (Source:

Scientists are now worried that dimming, by shielding the oceans from the full power of the Sun, may be disrupting the pattern of the world’s rainfall. There are suggestions that dimming was behind the droughts in sub-Saharan Africa which claimed hundreds of thousands of lives in the 1970s and 1980s.

There are disturbing hints the same thing may be happening today in Asia, home to half the world’s population. “My main concern is global dimming is also having a detrimental impact on the Asian monsoon,” says Prof Veerhabhadran Ramanathan, one of the world’s leading climate scientists. “We are talking about billions of people.”

Now, in present circumstances, we need to consider the combined effects of global warming & global dimming. This leads us to a catch 22 situation.

At present, globally, efforts are being undertaken to combat global warming. But scientists believe that the reason that Global Warming is accelerating is because we are reducing the amount of Particulate pollution in the atmosphere, this is reducing the Global Dimming phenomena, the opposing force that has kept Global Warming in check.

If we go on reducing Particulate pollution and do nothing about CO2 emissions then the rate of increase of Global Warming will go on accelerating.

The current research on this issue, thus concludes, that we can combat the combined forces of global dimming and global warming only by reducing carbon emissions in all forms & taking steps which reduce the use of fossil fuels.

Many scientists, such as Professor Flannery from Australia, have stated that it is already too late to cut down on emissions. They suggest that burning of sulphur in the atmosphere to remove the greenhouse gases. However, other scientists are unwilling to accept this as sulphur is known to harm human health.

Many other radical solutions have been suggested. The production of technologies capturing CO2 has been suggested. Led by Klaus Lackner, a physicist at Columbia University in New York, they plan to build and demonstrate a prototype within two years that could economically capture a tonne of CO2 a day from the air, about the same per passenger as a flight from London to New York.

At the recent Bali summit, the delegates also came up with the REDD plan of action [ REDD : Reducing Emissions From Deforestation and Degradation] This plan is widely perceived to reward those developing countries who do not cut their tropical rainforests in order to further “development” & awards them with additional carbon credits.

I believe that there is a need for the delegates attending these summits & climate change meeting to put aside their own political ambitions & think about planet Earth. Developed countries should hasten the process of green technology transfer to developing countries. They should aid environmental research and training in the developing countries. On their part, developing countries should take initiatives towards protecting their forests & wildlife. The United States of America should set an example for the world by cutting its own emissions by 50% within the next 7 years instead of blaming India & China.

The world must come together and reduce the aggregate demand for oil. It is essential that we work towards developing alternative sources of energy such as solar energy, hydro-electricity, and wind-energy.

Also, a US-led research should be conducted in the area of bio-fuels. It should be understood that at present, they are causing more harm than good. The amount of oil being used to produce ethanol is presently higher than the amount being saved by the use of ethanol as an alternative fuel. Also, many developing countries are blaming the USA of diverting a scarce commodity (food) towards the production of ethanol. There needs to be a thorough research on the viability of bio-fuels as a permanent source of alternative energy.

Also, nuclear waste disposal mechanisms need to be enhanced before we can fully switch to nuclear energy as an alternative fuel. France being the only country in the world to have a nuclear waste disposal mechanism should take the lead & collaborate with countries around the world for the proper development of this technology.

The phenomenon of global dimming reiterates that we are living on borrowed time. Each individual must play his part by reducing fuel consumption, creating awareness, curbing consumption of non-essential commodities, walking, planting trees or just by being an aware citizen of this so-called globalized world.

Mitali Nikore

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