lunedì 17 novembre 2014

written by Lucrezia Zito

In the last two decades, since I was born, I have heard, infinitive times, people speaking about the Greenhouse Effect and the phenomenon of Global Warming. It looks like people have finally realized the consequences of their lifestyle from a climate perspective. The way they were living was contributing to increase the average temperature of the world. What makes me puzzled is that people have barely spoken about Global Dimming and Global Brightening during all this time. Indeed, if the world began to warm up only starting from the 90s it is not only due to Global Warming but also to the transition from Global Dimming to Global Brightening. 
By the expression Global Dimming, scientists mean the reduction of solar radiation reaching the ground. The trials that led to the discovery of this phenomenon began 60 years ago with the work of Gerry Stanhill. Mr. Stanhill was an English scientist working in Israel. Comparing Israeli sunlight records from the 1950s with current ones, Stanhill found a sharp decrease in solar radiation of 22%.
Afterwards, with other studies, carried out in different geographical areas, Mr Stanhill reached the conclusion that the decline of solar radiation amounted to 1-2% globally per decade between the 1950s and the 1990s.
However, only recently, when his conclusions were confirmed by Australian scientists, using a completely different method to estimate solar radiation, climate scientists at last woke up to the reality of Global Dimming.

Dimming appears to be caused by air pollution (burning coal, oil and wood, whether in cars, power stations or cooking fires) and its consequences have been numerous. An example could be that Dimming has disrupted the pattern of the world's rainfall, in fact there are suggestions that it was behind the droughts in sub-Saharan Africa which claimed hundreds of thousands of lives in the 1970s and 1980s.
But perhaps the most alarming aspect is that it may have led scientists to underestimate the real power of the greenhouse effect for a long period.
Indeed it was only in the 1990s, when Global Dimming gradually transformed into Global Brightening,  that people started to seriously worry about Global Warming. Due to a decrease of aerosol burden, cloud-free atmosphere returned to be more transparent (comparing with the period of the Global Dimming) causing an increase of the solar radiation thanks to the effective clean-air regulation adopeted in many countries. This fact, if on one hand has limited the negative effects of the Global Dimming, on the other hand has contributed to warm up the planet.  
So, if we are now in such a critical situation it is partially because for a long time we have undertaken the Global Warming due to the Global Dimming, that was “ balancing” the negative effects.



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