Typically scientists test models and theories by doing experiments, but we obviously cannot experiment in this case. Thus, we look for ana¬logues that can verify our models.
Burned cities. Unfortunately, firestorms cre¬ated by intense releases of energy have pumped vast quantities of smoke into the upper atmo¬sphere. San Francisco burned as a result of the 1906 earthquake, and whole cities were incinerated during World War II, including Dresden, Hamburg, Tokyo, Hiroshima and Nagasaki. These events confirm that smoke from intense urban fires rises into the upper atmosphere.
The seasonal cycle. In actual winter the cli¬mate is cooler because the days are shorter and sunlight is less intense; the simple change of sea¬sons helps us quantify the effects of less solar ra¬diation. Our climate models re-create the sea¬sonal cycle well, confirming that they properly reflect changes in sunlight.
Eruptions. Explosive volcanic eruptions, such as those of Tambora in 1815, Krakatau in 1883 and Pinatubo in 1991 provide several lessons. The resulting sulfate aerosol clouds that formed in the stratosphere were transported around the world by winds. The surface temperature plum¬meted after each eruption in proportion to the thickness of the particulate cloud. After the Pi¬natubo eruption, the global average surface tem¬perature dropped by about 0.25 degree C. Glob¬al precipitation, river flow and soil moisture all decreased. Our models reproduce these effects.
Forest fires. Smoke from large forest fires sometimes is injected into the troposphere and lower stratosphere and is transported great dis¬tances, producing cooling. Our models perform well against these effects, too.
Extinction of the dinosaurs. An asteroid smashed into Mexico’s Yucatán Peninsula 65 million years ago. The resulting dust cloud, mixed with smoke from fires, blocked the Sun, killing the dinosaurs. Massive volcanism in India at the same time may have exacerbated the ef¬fects. The events teach us that large amounts of aerosols in the earth’s atmosphere can change cli¬mate drastically enough to kill robust species.
We have used such analogues to test and im¬prove our models in the past. But we hope more people will do further work. Independent mod¬els that either verify or contradict ours would be very instructive. Agricultural impact studies, which we have not conducted, would be partic¬ularly welcomed.
Source of Information : Scientific American January 2010