Global Dimming

haze dimming britain

Global Dimming is the term given by various bodies from across the international scientific community to the process that over the last 50 years has seen the intensity of sunlight decrease 10% to 30% depending on the region being monitored. Israel, which first monitored its sunlight intensity back in 1952 for purposes of building national irrigation systems, has seen a drop in sunlight intensity of 22%. The UK has seen a 10% drop in sunlight intensity over the last couple of decades.

Pan Evaporation Experiment

pan evaopration

This, as the name suggests, is a simple experiment where the amount of water evaporating from a pan is measured on daily. It has been found that humidity, wind and sunlight are the main factors in pan evaporation, with sunlight intensity being the most important factor. The evidence from Pan Evaporation Experiments from across the globe, and going back decades, seems to back up the measurements of decreased sunlight that are being reported.


polluted clouds

It is believed that the decreased sunlight intensity that has been measured over recent years is due to pollution from man-made sources and directly related to the particulates produced from man’s industry. The particulates, mainly soot and carbon products, once in the atmosphere act as a trigger in the right environment and allow water molecules to coalesce on them and thus form water droplets that should eventually fall as rain. However, since these droplets are more numerous than would be available in nature, the clouds that they form are more reflective of sunlight and it is this that is leading to less sunlight reaching the Earth’s surface.

Climate Cooling

dead cattle drought

The effect of less sunlight reaching the Earth’s surface has the effect of cooling the Earth’s climate. The reason scientists believe that we are not observing a global climate cooling is that the effect of global warming, which is caused by carbon dioxide and other green house gas emissions, is more than countering this effect. It is believed, however, that Global Dimming is responsible for changing the Earth’s monsoon patterns amongst other things and evidence suggests it may have been a key factor in the Ethiopian droughts in the early 1980s.

Increased Global Warming

contrails european city

The Earth’s industrial nations are now doing something about their particulate emissions by the fitting of catalytic converters to cars and ‘scrubbing emissions’ for power stations and manufacturing plants. In Western Europe, at least, it seems the air quality is slowly improving. The question that is now worrying scientists is what happens when we stop or reduce the Global Dimming effect on the planet without addressing Global Warming. It is believed by various parts of the scientific community that this will cause an increase in Global Warming and its devastating climatic effects including melting of the Greenland ice sheet and Antarctic glaciers and give us even less time than previously thought to take action.

For further information see Global dimming: does it affect the UKCIP02 climate change scenarios? by Geoff Jenkins and Jim Haywood, Hadley Centre, Met Office, Exeter.