[Vision2020] "Nature" Journal: Rise in humidity caused by humans

[Ted Moffett]

http://news.yahoo.com/s/ap/20071010/ap_on_sc/global_warming_humidity

http://news.yahoo.com/s/ap/20071010/ap_on_sc/global_warming_humidity&printer=1;_ylt=AofYlnGgjojGV0Uw7eDBl_RxieAA

Study: Rise in humidity caused by humans

By SETH BORENSTEIN, AP Science Writer 28 minutes ago

With global warming, the world isn't just getting hotter — it's getting
stickier, due to humidity. And people are to blame, according to a study
based on computer models published Thursday.

The amount of moisture in the air near Earth's surface rose 2.2 percent in
less than three decades, the researchers report in a study appearing in the
journal Nature.

"This humidity change is an important contribution to heat stress in humans
as a result of global warming," said Nathan Gillett of the University of
East Anglia in the United Kingdom, a co-author of the study.

Gillett studied changes in specific humidity, which is a measurement of
total moisture in the air, between 1973-2002. Higher humidity can be
dangerous to people because it makes the body less efficient at cooling
itself, said University of Miami health and climate researcher Laurence
Kalkstein. He was not connected with the research.

Humidity increased over most of the globe, including the eastern United
States, said study co-author Katharine Willett, a climate researcher at Yale
University. However, a few regions, including the U.S. West, South Africa
and parts of Australia were drier.

The finding isn't surprising to climate scientists. Physics dictates that
warmer air can hold more moisture. But Gillett's study shows that the
increase in humidity already is significant and can be attributed to gas
emissions from the burning of fossil fuels.

To show that this is man-made, Gillett ran computer models to simulate past
climate conditions and studied what would happen to humidity if there were
no man-made greenhouse gases. It didn't match reality.

He looked at what would happen from just man-made greenhouse gases. That
didn't match either. Then he looked at the combination of natural conditions
and greenhouse gases. The results were nearly identical to the year-by-year
increases in humidity.

Gillett's study followed another last month that used the same technique to
show that moisture above the world's oceans increased and that it bore the
"fingerprint" of being caused by man-made global warming.

Climate scientists have now seen the man-made fingerprint of global warming
on 10 different aspects of Earth's environment: surface temperatures,
humidity, water vapor over the oceans, barometric pressure, total
precipitation, wildfires, change in species of plants in animals, water
run-off, temperatures in the upper atmosphere, and heat content in the
world's oceans.

"This story does now fit together; there are now no loose ends," said Ben
Santer, a scientist at Lawrence Livermore National Lab and author of the
September study on moisture above the oceans. "The message is pretty
compelling that natural causes alone just can't cut it."

The studies make sense, said University of Victoria climate scientist Andrew
Weaver, who was not part of either team's research.

It will only feel worse in the future, Gillett said. Moisture in the air
increases by about 6 percent with every degree Celsius (1.8 degrees
Fahrenheit), he said. Using the Intergovernmental Panel on Climate Change's
projections for temperature increases, that would mean a 12 to 24 percent
increase in humidity by the year 2100.

"Although it might not be a lethal kind of thing, it's going to increase
human discomfort," Willett said.

___

On the Net:

Nature:

http://www.nature.com/nature

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Vision2020 Post: Ted Moffett
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