Monday, September 04, 2017

The Strange Future Hurricane Harvey Portends

Climate change is pushing more water into the atmosphere—with bizarre consequences.

A Syrian refugee walks toward his tent at Zaatari refugee camp through puddles and in front of storm clouds. The new water cycle could push monsoons around the world and cause the Sahara to bloom. (Credit: Mohammad Hannon / AP) Click to Enlarge.
Humans have begun an international project to move water around the world, far more ambitious than any network of aqueducts or hydroelectric dams ever constructed or conceived.  The drivers of this global system are billowing vapors, which trap heat and propel the world’s water faster and farther around the globe. The first results of this project may already be seen in the outrageous rainfall totals of storms like Hurricane Harvey, or in landslides on remote mountain hillsides, and even in the changing saltiness of the oceans.

The Earth system is getting warmer.  Water is evaporating faster.  There’s more of it in the air. It’s moving through the system faster.  As a result, the coming centuries will play out under a new atmospheric regime, one with more extreme rain, falling in patterns unfamiliar to those around which civilization has grown.

“Basically the idea is that as the climate warms there’s more energy in the atmosphere,” says Gabriel Bowen, a geochemist at the University of Utah.  “That drives a more vigorous water cycle:  Evaporation rates go up, precipitation rates go up—there’s just more water moving through that cycle faster and more intensely.”

For each degree Celsius of warming the atmosphere is able to hold 6 percent more water.  For a planet that’s expected to warm by 4 degrees by the end of the century, that means a transition to a profoundly different climate.

“Rainfall extremes have increased in intensity I think at every latitude in the northern hemisphere,” says Massachusetts Institute of Technology climate scientist Paul O’Gorman.

In 2012 a study led by Lawrence Livermore National Laboratory oceanographer Paul Durack found that the global water cycle was actually speeding up at twice the rate predicted by climate models, likely intensifying by 16 to 24 percent by the end of the century.
Hurricane Harvey was a truly one-off storm, one whose unusual path—strangely stalling out over East Texas for days—can explain much of its destructiveness.  But imagine if, in its sojourn over Houston, Harvey had dumped out 25 percent more rain, as O’Gorman and colleagues have forecast is possible by the end of the century.  In the tropics rainstorms may well become even wilder.

But perhaps even more important than how fast water is moving through the system, is where it may move thanks to human intervention.  The Intertropical Convergence Zone is a band of precipitation that flirts with the equator—where the trade winds meet in the tropics and hot air rises, dumping out prodigious amounts of rain.  The ITCZ feeds monsoons and, throughout history, entire civilizations.  Its position on the planet has meant life or, in the case of Classic Mayan civilization, perhaps death.  Their collapse is linked to a subtly shifting ITCZ and the droughts that followed.  And the movement of the ITCZ under a warming climate, and the waters it carries, is one of the most urgent and unresolved questions in climate modeling today, with some forecasts calling for dramatic shifts and expansions.

Read more at The Strange Future Hurricane Harvey Portends

No comments:

Post a Comment