Loss of Species
QUOTE: "If we do not slow down the rate of global warming, many
species are likely to become extinct. In effect we are pushing them
off the planet." James Hansen, Goddard Institute for Space Studies
NASA Study Finds World Warmth Edging Ancient Levels
09.25.06
A new study by NASA climatologists finds that the world's temperature
is reaching a level that has not been seen in thousands of years.
http://www.nasa.gov/centers/goddard/news/topstory/2006/world_warmth.html
The study appears in the current issue of the Proceedings of the
National Academy of Sciences, authored by James Hansen of NASA's
Goddard Institute for Space Studies, N.Y. and colleagues from
Columbia University, Sigma Space Partners, Inc., and the University
of California at Santa Barbara (UCSB). The study concludes that,
because of a rapid warming trend over the past 30 years, the Earth is
now reaching and passing through the warmest levels in the current
interglacial period, which has lasted nearly 12,000 years. This
warming is forcing a migration of plant and animal species toward the
poles.
The study includes worldwide instrumental temperature measurements
during the past century. These data reveal that the Earth has been
warming at the remarkably rapid rate of approximately 0.2° Celsius
(.36° Fahrenheit) per decade for the past 30 years. This observed
warming is similar to the warming rate predicted in the 1980s in
initial global climate model simulations with changing levels of
greenhouse gases.
"This evidence implies that we are getting close to dangerous levels
of human-made (anthropogenic) pollution," said Hansen. In recent
decades, human-made greenhouse gases (GHGs) have become the dominant
climate change factor.
The study notes that the world's warming is greatest at high
latitudes of the Northern Hemisphere, and it is larger over land than
over ocean areas. The enhanced warming at high latitudes is
attributed to effects of ice and snow. As the Earth warms, snow and
ice melt, uncovering darker surfaces that absorb more sunlight and
increase warming, a process called a positive feedback. Warming is
less over ocean than over land because of the great heat capacity of
the deep-mixing ocean, which causes warming to occur more slowly
there.
Hansen and his colleagues in New York collaborated with David Lea and
Martin Medina-Elizade of UCSB to obtain comparisons of recent
temperatures with the history of the Earth over the past million
years. The California researchers obtained a record of tropical ocean
surface temperatures from the magnesium content in the shells of
microscopic sea surface animals, as recorded in ocean sediments.
One of the findings from this collaboration is that the Western
Equatorial Pacific and Indian Oceans are now as warm as, or warmer
than, at any prior time in the Holocene. The Holocene is the
relatively warm period that has existed for almost 12,000 years,
since the end of the last major ice age. The Western Pacific and
Indian Oceans are important because, as these researchers show,
temperature change there is indicative of global temperature change.
Therefore, by inference, the world as a whole is now as warm as, or
warmer than, at any time in the Holocene.
According to Lea, "The Western Pacific is important for another
reason, too: it is a major source of heat for the world's oceans and
for the global atmosphere."
In contrast to the Western Pacific, the researchers find that the
Eastern Pacific Ocean has not shown an equal magnitude of warming.
They explain the lesser warming in the East Pacific Ocean, near South
America, as being due to the fact this region is kept cool by
upwelling, rising of deeper colder water to shallower depths. The
deep ocean layers have not yet been affected much by human-made
warming.
Hansen and his colleagues suggest that the increased temperature
difference between the Western and Eastern Pacific may boost the
likelihood of strong El Ninos, such as those of 1983 and 1998. An El
Nino is an event that typically occurs every several years when the
warm surface waters in the West Pacific slosh eastward toward South
America, in the process altering weather patterns around the world.
The most important result found by these researchers is that the
warming in recent decades has brought global temperature to a level
within about one degree Celsius (1.8° F) of the maximum temperature
of the past million years. According to Hansen "That means that
further global warming of 1 degree Celsius defines a critical level.
If warming is kept less than that, effects of global warming may be
relatively manageable. During the warmest interglacial periods the
Earth was reasonably similar to today. But if further global warming
reaches 2 or 3 degrees Celsius, we will likely see changes that make
Earth a different planet than the one we know. The last time it was
that warm was in the middle Pliocene, about three million years ago,
when sea level was estimated to have been about 25 meters (80 feet)
higher than today."
Global warming is already beginning to have noticeable effects in
nature. Plants and animals can survive only within certain climatic
zones, so with the warming of recent decades many of them are
beginning to migrate poleward. A study that appeared in Nature
Magazine in 2003 found that 1700 plant, animal and insect species
moved poleward at an average rate of 6 kilometers (about 4 miles) per
decade in the last half of the 20th century.
That migration rate is not fast enough to keep up with the current
rate of movement of a given temperature zone, which has reached about
40 kilometers (about 25 miles) per decade in the period 1975 to 2005.
"Rapid movement of climatic zones is going to be another stress on
wildlife" according to Hansen. "It adds to the stress of habitat loss
due to human developments. If we do not slow down the rate of global
warming, many species are likely to become extinct. In effect we are
pushing them off the planet."
Find this article (with graphics) at:
http://www.nasa.gov/centers/goddard/news/topstory/2006/world_warmth.html
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