Global Dimming

BBC TWO's Horizon series broadcast of 13 January 2005

BBC TWO's Horizon broadcast of 13 January 2005 helped to introduce information to the wider public about the devastating affects that are increasingly being attributed by scientists to a hitherto unsuspected climatic phenomenon that they are calling global dimming

Over recent decades the climate has been changing markedly and much of this has been attributed to the pollutive side effects of human industrial and domestic activities YET the presence of what is now thought of as global dimming was effectively unrealised.

Some climatologists had noticed that the heat of the sun had been dropping dramatically for several decades - for example by up to 10% in the USA and 16% in parts of Britain - the scientific community in general however, and indeed the wider public, took little notice because the loss of heat from the sun had been in practice offset by global warming.

The dimming is a bizarre by-product of the fossil fuels that help to cause global warming. It is caused by tiny airborne particles of soot, ash and sulphur dioxide acting as hosts for the accumulation of tiny rain droplets (too tiny to actually fall as rain!!!) that form into clouds that reflect back the heat of the sun.

It is not this loss of "Sun bestowed heat" that worries the scientists given the presence of the current tendency towards global warming but it is rather the likelyhood of other forms of climatic unpredictability arising from global dimming.
The scientists have become persuaded that the heat of the sun is vital for seasonal rains like monsoons and it may be the case that the failure of the rains in Sub-Saharan Africa in the Eighties and the consequent appalling famine in Ethiopia for example may be attributable in large part to global dimming related effects on rainfall patterns.

In the eighties then a most significant African catastrophe may have been partly caused by air pollution from cars and power stations. The peoples of the world continues to generate heat and greenhouse gases on an increasing scale. The Asian rim where billions of people live figures as one of the most rapidly economically developing regions on the planet. The monsoon has been noticed as coming later and later to the Indian sub-continent. there are worries that as the years pass it will be curtailed or even fail in areas that have relied on its effects to counteract other months of dry weather in an annual cycle of seasons. Mass famine and other forms of severe dislocation would probably ensue.

It may well be the case that the deleterious effects of global dimming itself could be largely cured by a cleaning up of particle emissions from industry, transportation and households but this necessary cure for one set of problems may then help to intensify another - that of Global Warming itself.
The reflection of Solar heat that seems to have been taking place may well have been masking the full intensity of the rise in temperatures due to the burning of fossil fuels and the greenhouse effects of Carbon Dioxide and other gases the concentrations of which have been rased in the atmosphere due to human activity.

In the days immediately after the destruction of the Twin Towers of the World Trade Center on 9/11 the entire United States commercial airfleet was grounded for three days. This unlooked for interruption in what had become the norm in terms of air traffic over the United States gave Dr David Travis of the University of Wisconsin an opportunity to investigate his belief that the vapour trails of aircraft were themselves a significant contributor to solar dimming. Dr. Travis found that their three day absence alone resulted in a massive jump in the daily temperature range - (the difference between the highest daytime temperature and the lowest night time temperature) - further studies led him to conclude that no similar change in daytime temperature range was evident in the meterological records for over thirty years.

There are good reasons for trying to eliminate the particle emoissions that help to cause global dimming - the particles themselves may well be generally harmful to respiratory health whilst the failures of rains can lead to mass famine yet there are increasing concerns lest the reduction of particle emissions would lead to a lessening of the amount of Solar heat being reflected. Scientist have been working in a scenario where the global warming due to the burning of fossil fuels and the associated rapid rise in greenhouse gases could lead to an increase in global temperatures of five degreees Celsius by the end of the twenty-first century.
This presuption however is largely based on studies which took no account of a countervailing tendency of global dimming!!! As the causes of global dimming are tending to be removed the impact on global temperatures could be huge. Factoring global dimming into the models for global warming has a dramatic effect on predictions about possible future global temperature levels. The presumptions about the temperatures at the end of the twenty-first century now have to include a scenario where global temperatures might rise by an average ten degrees Celsius.

Were events to lead to this scenario to be realised then in just twenty years the temperatures would rise by two degrees - this is considered to be sufficient to initiate an irreversible melting of the presently immense ice sheet of Greenland. This ice sheet presently retains enough water to raise the oceans and seas of the world by seven to eight metres. Quite apart from any associated climatic complications the onset of such a rise in sea levels would dramatically threaten many low lying areas including many major cities leading to catastrophic dislocations of population.

The Brazilian rain forest - in many ways a lung for the planet - could be threatened with withering due to lack of rain. The nig