Recently, Houston’s Cedar Bayou suburb had 52 inches of rain in less that a week, courtesy of Tropical Storm Harvey; a new record for the US mainland. Meanwhile, a hemisphere away, and much less reported, more than 1,000 people died in this year’s monsoon with almost 700,000 homes destroyed in Bangladesh.
As the Times reminded us (and chemists everywhere already knew) two scientists who would not be surprised by this would be the 19th century scientists Clausius and Clapeyron. They worked out the exponential relationship between the temperature of a body of gas (e.g. the Earth’s atmosphere) and its capacity to hold water vapour.
The Clausius-Clapeyron equation indicates that, that for every 1 degree Celcius the average sea surface temperature rises, the atmosphere’s water content should increase by some 7%. Since the 1970s, the US military has measured a 0.6 degree increase in average sea surface temperature and a 4% increase in atmospheric water vapour. This is just what the Clausius-Clapeyron equation predicts. This 4% means to an extra 500 cubic kilometres of water in the atmosphere, all of which enters the the water cycle with much inevitably falling as rain somewhere or other.
To add to the knowledge bank on recent changes in sea level “Inevitable Surprises in the Atlantic Ocean”, in the NERC “Planet Earth” Winter 2015 edition (also available on line).. It reports on a decade of research from 2004 into AMOC, the Atlantic Meridional Overturning Circulation. I think this is the technical name for what we might know as the Gulf Stream. The AMOC transports heat Northward across the Equator. The warm northward flow is balanced by a cold deep return flow, as the waters cool and sink having given up their heat to the atmosphere above. AMOC is what gives the UK and NW Europe their temperate climate. Ironically we could end up cooler as AMOC models predict it to slow down under global warming due to a weakening circulation. Already the AMOC flow seems to vary far more than expected. In 2009-10 it decreased by almost 30% perhaps contributing that unusually severe winter. The decline has also been linked to an unprecedented sea-level rise on the eastern seaboard of the USA over the same period.Another big surprise was that over this first decade of the on-going study the AMOC had declined TEN TIMES FASTER than climate models had predicted!