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发帖数: 29576 | 1 98年以后竟然没变暖，咋办？研究发现是太平洋变冷造成的，作者指出马上就要恢复变
暖了， 这几年就是turning point，以后变暖会变本加厉。
Cool Pacific Ocean Slowed Global Warming
The Pacific Ocean has been a planetary air conditioner for the past two
decades, but the relief may soon end, a new study finds.
The Pacific and Atlantic oceans undergo decades-long natural oscillations
that alter their sea surface temperatures. These natural cycles flip-flop
between cooler and warmer phases. Over the past 130 years, the tempo of
global warming has revved up or slowed down in tune with changing ocean
temperatures, researchers reported today (Feb. 26) in the journal Science.
For instance, cool temperatures in the northern Atlantic Ocean slowed global
warming in the early 20th century, the study found. But since the 1950s,
aerosol pollution and greenhouse gases have overwhelmed the natural signal,
the researchers said.
The Pacific Ocean wielded its mighty influence starting in 1998, when it
interrupted the rapid climb of global temperatures, the study reported.
"The Pacific Ocean appears to be driving the slowdown in warming over the
past 15 years," said lead study author Byron Steinman, a climate scientist
at the University of Minnesota-Duluth.
The period since 1998 is often called a global warming pause or global
warming hiatus, because the planet's thermometer slowed its steady climb.
However, it's more accurate to call the intervening years a global warming
slowdown. Temperatures never stopped rising, and the 10 hottest years ever
recorded have all happened since 1998. And though global surface
temperatures have plateaued, the oceans are still warming — studies have
found the "missing" heat is going into deeper layers of the sea. [6
Unexpected Effects of Climate Change]
The slowdown coincides with a remarkable trend toward cooler temperatures
across much of the Pacific Ocean, the researchers said. "This is the largest
natural excursion we see in the record," said study co-author Michael Mann,
a climate scientist at Pennsylvania State University.
The natural oscillations underlying the 17-year slowdown include the Pacific
Multidecadal Oscillation (PMO) and the shorter El Niño cycle, the
researchers said. The newly coined PMO is a longer version of the more
familiar Pacific Decadal Oscillation, the researchers said. The PMO flips
every 50 to 70 years, while the Pacific Decadal Oscillation is on a 16- to
20-year cycle, according to the study.
The El Niño cycle tends to produce more El Niños (warm) or La Ni&#
241;as (cool) on a 20-year rhythm. During an El Niño year, the ocean
releases heat, triggering a spike in global surface temperatures. Since 1998
, when the slowdown started, there have been more La Niña years than El
Niño years.
Moving on up
Historical patterns suggest the cycles will flip back toward warm in the
next few decades, the study predicts. Instead of dragging down global
temperatures, the Pacific will turbo-boost global warming.
"We are in a turning point right now, and the slowdown will presumably
reverse in the decades ahead," Mann said. "When we do, we may see warming
even faster than what the models are predicting."
However, the temperature changes triggered by the oceans only account for
about 0.03 degrees Fahrenheit (0.15 degrees Celsius) of the ups and downs in
global temperatures, the researchers reported. The warming due to human
activities, such as greenhouse gas emissions, swamps this natural signal,
said Michael England, a professor at the University of New South Wales in
Australia who was not involved in the study. The planet's thermometer has
steadily climbed by 1.4 F (0.8 C) since 1880. Global temperatures may rise
another 4 to 7 F (2 to 4 C) by 2100.
"This study does support work that points to the Pacific as a primary driver
of decadal variability," England said.
Steinman, Mann and co-author Sonya Miller, also of Penn State, tested the
influence of decadal oscillations on global temperatures with state-of-the-
art climate models. The team drew on 150 computer models from research
centers around the world, and compared their results to historical
observations since 1854. The simulations were averaged together to remove
the influence of external factors such as pollution, volcanic eruptions and
the sun's 11-year cycle.
The new findings highlight potential shortcomings in current climate models,
which have not captured the natural variations that contributed to the
global warming slowdown, said Ryan Sriver, an atmospheric scientist at the
University of Illinois at Urbana-Champaign who was not involved in the study.
http://news.yahoo.com/cool-pacific-ocean-slowed-global-warming- |
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