| Title | Human Sulfate Emissions Dry the Tropics and Juice Mid-Latitude Storms | |
| Date | Sunday February 15 2015, @05:51PM | |
| Author | janrinok | |
| Topic | ||
| from the its-our-fault-again dept. | ||
http://theconversation.com/air-pollution-from-europe-and-america-is-making-the-tropics-drier-37395
Air pollution pumped out by factories and power plants in Europe and North America has led to drier spells in the tropics, thousands of miles to the south. Scientists had long suspected this was the case and even had modelled the change in computer simulations, but now for the first time we have direct evidence – straight from a cave in Belize.
Precipitation in the tropics, including Belize, is governed by the Intertropical Convergence Zone (ITCZ) – a belt of monsoon rainfall encircling the Earth near the equator that migrates seasonally between the hemispheres. The relative temperature difference between the hemispheres plays a crucial role in controlling the position of the ITCZ and hence, rainfall distribution in the tropics.
What we found was a distinct drying trend in Belize since 1850 that coincides with a steady rise in industrial aerosol emissions in North America and Europe. This presents strong evidence that industrial sulfate emissions have shifted the position of the ITCZ through reflecting the Sun’s incoming radiation and therefore moderating warming in the northern hemisphere.
Our claims are backed up by the volcano record. Emissions from volcanoes are similar to those produced by burning fossils fuels – basically lots of sulphur – and we identified short-lived drier spells in the northern tropics following very large volcanic eruptions in the northern hemisphere, such as the Icelandic Laki eruption in 1783.
I'm not sure why they single out North America and Europe as sources of sulfates, but probably because of proximity to their tropical study site, Belize. Asia, dominated by India and China, is the largest source region of sulfates. It's been known for some time that they affect downstream weather in the Pacific, the North American West coast, and probably further downstream in the continent. They act in a number of ways, by reflecting sunlight directly, and also by seeding clouds, which gives more energy to storms allowing their convective currents to reach higher. Much as volcanoes lead to short term cooling by sulfates and long term warming by carbon dioxide, so do fossil fuels. When Asia cleans up their sulfate emissions, we're in for a big surprise downstream. For more on this, check out this January 26, 2015 release from NASA.
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