Something to think about: Global dimming / global warming

Global dimming is a term describing the gradual reduction in the amount of sunlight observed reaching the Earth's surface since the 1950s.
The effect varies by location but globally is of the order of a 5% reduction over the three decades 1960-1990; the trend has reversed during the past decade. Global dimming creates a cooling effect that may have led scientists to underestimate the effect of greenhouse gases on global warming dimming may have caused large scale changes in weather patterns.
Climate models speculatively suggest that this reduction in sunshine at the surface may have led to the failure of the monsoon in sub-Sharon Africa during the 1970s and 1980s, together with the associated famines, caused by Northern hemisphere pollution cooling the Atlantic.
This is not universally accepted and is very difficult to prove.Some scientists now consider that the effects of global dimming have masked the effect of global warming, and that resolving global dimming may therefore have a major and previously unpredicted impact on temperatures and sea levels.
Initial work to incorporate the effects of global dimming suggest that world temperatures may rise by 2 °C by 2030, and as much as 10 °C by 2100; this is a doubling of the widely accepted figure of a 5 °C rise in global temperature this Century.
If this were to be so, such large increases would lead to the melting of the Greenland icecap, major reductions in the extent of tropicreinforcingsts, and significant rises in sea levels.
A further speculation is that such a rise in temperature would trigger a rapid and irreversible release of the huge deposits of methane hydrates currently locked beneath the ocean floor, releasing methane gas, one of the most powerful of the greenhouse gases.
A similar mechanism is one of the theories proposed to explain the Permian-Triassic extinction event approximately 252 million years ago, and the extinctions associated with the Paleocene-Eocene Thermal Maximum around 55 million years ago.
It is estimated that it took the planet as long as 100,000 years to recover to a "normal state" following the Thermal Maximum.