| | | Global Dimming

From WikiVerde

A Darker World

Scientists and ecologists are using a new phrase these days – ‘global dimming’. What is this phenomenon? It has been observed that, over the last fifty years, the quantity of direct global irradiance has been slowly going down. We have been gradually getting less radiance from the sun, and this can have far-reaching consequences that even scientists may not yet have fully understood.

Global dimming is believed to be caused by the use of products like sulphur aerosols which are increasing the amount of particulates in the atmosphere. Such particulates take in the heat and light of the sun, and reflect it away. In addition, water gathers around these particles in small quantities, and the large number of small clouds thus formed reflects away larger quantities of sunlight. This reduction in the amount of solar energy reaching the surface of the earth is called global dimming.

Burning fuel of all kinds and auto emissions in the form of smog also contribute to global dimming. Some scientists believe that global dimming is also caused by global warming, as more water is evaporating from the earth’s oceans.

1 A Recent Phenomenon
2 What Causes Global Dimming?
3 The Effects of Global Dimming
4 A Brighter World Again?
5 Global Dimming & Global Warming
6 Global Dimming & the Hydrological Cycle
7 How Do We Deal With Global Dimming?
8 References

A Recent Phenomenon

Global dimming was first noticed in Israel, by Dr. Gerald Stanhill. Dr. Stanhill had measured the strength of sunlight forty years ago to help determine irrigation requirements. When he repeated his measurements twenty years ago, he found that that there was an amazing 22% reduction in the amount of sunlight. Although Dr. Stanhill published his discoveries, they were not taken seriously, even though they were substantiated by Dr. Beate Liepert in Germany, who found a similar situation in the Bavarian Alps. It was Dr. Stanhill who first called this phenomenon global dimming.

Only when scientists studying the pan evaporation rate of water in the nineties reported that the evaporation rate was decreasing, despite global warming, did the scientific world begin to sit up and take notice, and the work of Dr. Stanhill and Dr. Liepert was connected with the evaporate rate findings. The occurrence of the phenomenon of global dimming was finally acknowledged. Global dimming does not occur evenly all over the world, but on an average, there has been a 4% decrease in global irradiance, in the thirty year period between 1960 and 1990.

What Causes Global Dimming?

Global dimming is primarily caused by the air pollution that is a result of many human activities. When we burn fuel, small soot particles are discharged into the atmosphere, creating a smoky haze over urban areas. Studies in the Maldives in two areas, one with high levels of pollution and one with much cleaner air, showed that a three kilometer thick layer of pollution was reducing sunlight by 10%. In addition to filtering some sunlight, the pollutants also caused the formation of small clouds of water vapour, which, because of their diminished size, were not enough to cause precipitation. Also, each of these clouds reflects more light back to the sun. Jet trails also increase heat and light reflection.

The Effects of Global Dimming

Global dimming can have fatal effects, causing drought and famine, such as the eighties tragedy in Ethiopia, when the Sahel monsoon failed. Such climatic effects result in millions of deaths all over the world, and affect the lives of billions. Clearly, global dimming is disturbing earth’s precipitation patterns, not only in Africa, but all over the world.

As far as human health is concerned, the particulate matter in the atmosphere causes respiratory diseases and cancers. The long-term effects of global dimming on plants, and thus the rest of the food chain, will also be highly negative.

With regard to the environment, global dimming, far from counterbalancing the effects of global warming, will cause problems like acid rain. Forests with less water would be more prone to catch fire, vegetation will hard put to survive, and soil erosion will increase. Global dimming is believed to be cooling by 1.8˚ F. It has taken us a long time to understand and accept global dimming, but our actions to prevent the effects of this phenomenon should be quickly undertaken, for fear of irreversible changes to the ecology. If we don’t do something to prevent global dimming, our children could be living in a darker world, in more senses than one.

A Brighter World Again?

Since around 1990, there has been evidence that global dimming may be on the wane, particularly over the earth’s oceans. This is clearly connection in the decrease of aerosol levels, as a result of efforts to cut down on pollution. Legislations like America’s Clean Air Act and anti-pollution policies in Europe have mad a lot of difference.

Global Dimming & Global Warming

The fairly recent phenomenon of average temperature of surface air and oceans rising is called global warming. Global dimming tends to hide the global warming consequences of greenhouse gases, but these phenomena are linked, and policies to combat one problem should also consider the implications of the other. Both these problems have to be dealt with as an integrated whole.

Global Dimming & the Hydrological Cycle

The water cycle, or the hydrological cycle, refers to the constant, unending circle of water movement and transformation into other physical states. The Earth’s water remains roughly the same as it changes its form – between vapour, ice and liquid states. Global dimming affects the hydrological cycle by decreasing water evaporation. It can also cause droughts, by reducing rainfall.

How Do We Deal With Global Dimming?

It is of vital importance that we regulate our activities so that pollution during energy generation is reduced as much as possible. We can’t afford to hope that the effects of global dimming will cancel out the effects of global warming – we have to change the way we live. And we don’t have much time to make the changes that we must enforce if life on earth is to remain comfortable. Let’s make up our minds to give our children a clean, bright world … we owe it to them. Do your bit today!