Believe it or not, the sun is dimming. The earth surface is experiencing less light now-a-days compared to even recent past. From the late 1950s to the early 1990s, at least a 10 percent drop in sunshine reaching the earth surface was recorded by the scientists. In some regions like Asia, the United States and Europe, the drop was even steeper. In Hong Kong sunlight decreased 37 percent.
This stunning event was first brought to public notice by Atsumu Ohmura, a researcher of Swiss Federal Institute of Technology in 1989 which was confirmed by Gerald Stanhill of Israel’s Agricultural Research Organization in 1992. The Global dimming was also coined by Dr. Stanhill.
In an environment, where global warming was taking place, it was normal to do research on global cooling. Atsumu Ohmura for example was checking, as a part of his studies, into climate and atmospheric radiation, levels of sunlight recorded around Europe. His discovery came in the process. Gerry Stanhill, on the other and, got a job in 1990s helping to design irrigation schemes in Israel. His task was to measure how strongly the sun share over Israel. Stanhill collected his first set of data sometimes in 1960s. In the 1980s, almost twenty years later, he decided to repeat his measurement to check whether they will still valid. And than he discovered the sun is dimming.
Like global warming, global dimming also the outcome of fossil fuel burning. When fossil fuel burn, on the one hand, it emits greenhouse gases in the air and on the other releases particulate matters, such as soot and ash in the atmosphere. These particulate matters, by changing the properties of clouds, create global dimming. Clouds are formed when water droplets are seeded by air-borne particles. Now as a result of fossil-fuel burning more and more particles gather in the atmosphere. Hence large number of water droplets are also formed. These small droplets than cluster together to form larger size droplets. When water droplets from in the atmosphere they reflect sunlight back into space. This act of reflection becomes easier when water droplets become large in size. Thus by creating larger size water droplets fossil-fuel burning calls forth global dimming.
However fossil-fuel burning is not always responsible for global dimming. Recently it was discovered that the vapor from high-flying planes, also reflect sunlight significantly.
The immediate effect of global dimming is changes of temperature of earth surface. The particulate matters in the air works in two ways. On the one hand, it reflects sunlight back to the space, and on the other, the heat radiation of the earth back to the planet itself.
Therefore, during the day global dimming gives us a cooling effect and at night it slows down the heat process of the earth surface.
Global dimming has its effect on photosynthesis as well declines. However, there is a debate on the issue. Some argue that in some cases photosynthesis increases with increasing global dimming due to appearance of diffuse, broken light. When light is scattered, even the lower surface of a leaf can get in touch with sunshine. he diffuse can also penetrate into deep forest. These are the reasons why photosynthesis may increase with increasing dimming.
Another effect of global dimming is low rainfall. When less light comes to the earth surface, evaporation rate from hydrosphere falls automatically. The outcome of this process is lower rainfall, drought. In fact during the 1970s and 1980s the sub-Saharan Africa experienced a severe drought which the scientist suspect, was the outcome of global dimming.
Both global dimming and global warming are the outcome of a single event, fossil-fuel burning. What is argued by scientist is that global dimming is hiding the true power of global warming. If sunshine are not reflected by air pollutants, as in the case of global dimming, the earth will get hotter. Recently studies on global warming predict a 5 degrees increase in temperature over the next century. But if global dimming effect could be eliminated the temperature rise would be 10 degrees instead of 5 degrees. The reason is very simple. When more light will come to the earth more heat will be absorbed by the green house gases and the earth will get hotter. And not only getting hotter, every possible effects of a hot surface will come as a result.
In fact our planet has already experienced this kind of effect. In Europe various measures have been taken in recent years to reduce pollutants that create smog and other problems. However no measures were taken to reduce greenhouse gases. The scientists expressed their doubt that the European heat wave in 2003 that killed thousands in France, saw forest fires in Portugal and caused many other problems throughout the continent was the outcome of the move to address global dimming without paying any attention to global warming.
The real threat of global dimming thus lies in the fact that it cannot be solved as a separate environmental problem. Thus the time has now come to deal with both global dimming and warming together as early as possible.