Communist
16th October 2009, 03:36
Interesting report, thought you all might like to read it.
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Just How Sensitive Is Earth's Climate to Atmospheric
Carbon Dioxide? (http://www.scientificamerican.com/article.cfm?id=how-sensitive-is-climate-to-carbon-dioxide)
Two new studies look far back in geologic time to
determine how sensitive the global climate is to
atmospheric CO2 levels
By David Biello
Scientific American
October 8, 2009
Carbon dioxide levels climbing toward a doubling of the
280 parts per million (ppm) concentration found in the
preindustrial atmosphere pose the question: What impact
will this increased greenhouse gas load have on the
climate? If relatively small changes in CO2 levels have
big effects-meaning that we live in a more sensitive
climate system-the planet could warm by as much as 6
degrees Celsius on average with attendant results such
as changed weather patterns and sea-level rise. A less
sensitive climate system would mean average warming of
less than 2 degrees C and, therefore, fewer
ramifications from global warming.
Human civilization is now running an experiment (and
without a control) that will definitively determine the
answer. Scientists, however, have also realized that
history can be a guide: Two new papers published in
Science this week examine the historical record
preserved in a stalagmite and microscopic seashells,
respectively, to offer some clues.
Earth scientist Aradhna Tripati of the University of
California, Los Angeles's Department of Earth and Space
Sciences and her colleagues extracted a record of past
atmospheric concentrations of CO2 stretching back 20
million years from the shells of tiny creatures known as
foraminifera buried in a column of ocean mud and rock.
The microscopic animals build shells of calcium
carbonate out of minerals in seawater-a process that is
affected by the water's relative pH (acidity), which is,
in turn controlled by the level of CO2 in the
atmosphere. More CO2 in the atmosphere means a more
acidic ocean.
"The two species we picked to analyze [Globigerinoides
ruber and G. sacculifer] are both ones that are around
today, and the living animals actually have
photosynthetic algae as symbionts, which means that they
live in the surface ocean, since the algae require
sunlight to survive," Tripati explains. And that means
the fossil record of their shells will reveal the
relative acidity of the surface waters in the ratio of
boron to calcium as well as the specific chemical
signature of the boron itself. "When seawater is more
acidic, less boron gets incorporated into the calcium
carbonate shells," she adds.
The researchers first matched this fossil record secured
by the Integrated Ocean Drilling Program Expedition in
the western tropical Pacific to existing records from
bubbles trapped in Antarctic ice cores that stretch back
800,000 years, which preserve a precise record of past
atmospheric composition. Thus reassured of the
technique's accuracy, they plunged back into deep
geologic time.
"Modern-day levels of carbon dioxide were last reached
about 15 million years ago," Tripati says, when sea
levels were at least 25 meters higher and temperatures
were at least 3 degrees C warmer on average. "During the
middle Miocene, an [epoch] in Earth's history when
carbon dioxide levels were sustained at values similar
to what they are today [330 to 500 ppm], the planet was
much warmer, sea level was higher, there was
substantially less ice at the poles, and the
distribution of rainfall was very different."
Further, "at no time in the last 20 million years have
levels of carbon dioxide increased as rapidly as at
present," Tripati adds; CO2 concentrations have climbed
from 280 ppm to 387 ppm in the past 200 years. And "our
work indicates that moderate changes in carbon dioxide
levels of 100 to 200 parts per million were associated
with major climate transitions and large changes in
temperature"-indicative of a very sensitive climate.
A nearly 400,000-year record of Ice Age transitions
preserved in a stalagmite in the Sanbao and Linzhu caves
of Hubei Province in China would seem to offer evidence
in support of the sensitive climate scenario. The
stalagmites, composed of calcium carbonate leached from
dripping water, preserve a record of monsoon rainfall in
the region by their composition. Paleoclimatologist Hai
Cheng of the University of Minnesota and his colleagues
then compared this record with climatic transitions,
such as the shift into and out of an Ice Age.
The rock record reveals that such rainfall changes occur
at the same time as general alterations in the relative
strength of sunlight hitting the planet thanks to
periodic shifts in Earth's orbit, known as Milankovitch
cycles. At the same time as the solar heat increases,
according to the monsoon record published in Science,
CO2 levels also begin to rise.
"Climate systems are well linked worldwide, such as sea-
level, CO2, ice sheet[s], the Asian monsoon, regional
temperature and precipitation," Cheng says. "So a change
in one of them could trigger changes in others." And
that might mean the climate is too sensitive to tolerate
current levels of CO2 without changing the conditions
that have allowed human civilization to flourish in the
past 10,000 years.
_____________________________________________
----------------------------------------------------------
__________________________________________________ ____
________________________________________________
_________________________________________
_________________________________
_________________________
Just How Sensitive Is Earth's Climate to Atmospheric
Carbon Dioxide? (http://www.scientificamerican.com/article.cfm?id=how-sensitive-is-climate-to-carbon-dioxide)
Two new studies look far back in geologic time to
determine how sensitive the global climate is to
atmospheric CO2 levels
By David Biello
Scientific American
October 8, 2009
Carbon dioxide levels climbing toward a doubling of the
280 parts per million (ppm) concentration found in the
preindustrial atmosphere pose the question: What impact
will this increased greenhouse gas load have on the
climate? If relatively small changes in CO2 levels have
big effects-meaning that we live in a more sensitive
climate system-the planet could warm by as much as 6
degrees Celsius on average with attendant results such
as changed weather patterns and sea-level rise. A less
sensitive climate system would mean average warming of
less than 2 degrees C and, therefore, fewer
ramifications from global warming.
Human civilization is now running an experiment (and
without a control) that will definitively determine the
answer. Scientists, however, have also realized that
history can be a guide: Two new papers published in
Science this week examine the historical record
preserved in a stalagmite and microscopic seashells,
respectively, to offer some clues.
Earth scientist Aradhna Tripati of the University of
California, Los Angeles's Department of Earth and Space
Sciences and her colleagues extracted a record of past
atmospheric concentrations of CO2 stretching back 20
million years from the shells of tiny creatures known as
foraminifera buried in a column of ocean mud and rock.
The microscopic animals build shells of calcium
carbonate out of minerals in seawater-a process that is
affected by the water's relative pH (acidity), which is,
in turn controlled by the level of CO2 in the
atmosphere. More CO2 in the atmosphere means a more
acidic ocean.
"The two species we picked to analyze [Globigerinoides
ruber and G. sacculifer] are both ones that are around
today, and the living animals actually have
photosynthetic algae as symbionts, which means that they
live in the surface ocean, since the algae require
sunlight to survive," Tripati explains. And that means
the fossil record of their shells will reveal the
relative acidity of the surface waters in the ratio of
boron to calcium as well as the specific chemical
signature of the boron itself. "When seawater is more
acidic, less boron gets incorporated into the calcium
carbonate shells," she adds.
The researchers first matched this fossil record secured
by the Integrated Ocean Drilling Program Expedition in
the western tropical Pacific to existing records from
bubbles trapped in Antarctic ice cores that stretch back
800,000 years, which preserve a precise record of past
atmospheric composition. Thus reassured of the
technique's accuracy, they plunged back into deep
geologic time.
"Modern-day levels of carbon dioxide were last reached
about 15 million years ago," Tripati says, when sea
levels were at least 25 meters higher and temperatures
were at least 3 degrees C warmer on average. "During the
middle Miocene, an [epoch] in Earth's history when
carbon dioxide levels were sustained at values similar
to what they are today [330 to 500 ppm], the planet was
much warmer, sea level was higher, there was
substantially less ice at the poles, and the
distribution of rainfall was very different."
Further, "at no time in the last 20 million years have
levels of carbon dioxide increased as rapidly as at
present," Tripati adds; CO2 concentrations have climbed
from 280 ppm to 387 ppm in the past 200 years. And "our
work indicates that moderate changes in carbon dioxide
levels of 100 to 200 parts per million were associated
with major climate transitions and large changes in
temperature"-indicative of a very sensitive climate.
A nearly 400,000-year record of Ice Age transitions
preserved in a stalagmite in the Sanbao and Linzhu caves
of Hubei Province in China would seem to offer evidence
in support of the sensitive climate scenario. The
stalagmites, composed of calcium carbonate leached from
dripping water, preserve a record of monsoon rainfall in
the region by their composition. Paleoclimatologist Hai
Cheng of the University of Minnesota and his colleagues
then compared this record with climatic transitions,
such as the shift into and out of an Ice Age.
The rock record reveals that such rainfall changes occur
at the same time as general alterations in the relative
strength of sunlight hitting the planet thanks to
periodic shifts in Earth's orbit, known as Milankovitch
cycles. At the same time as the solar heat increases,
according to the monsoon record published in Science,
CO2 levels also begin to rise.
"Climate systems are well linked worldwide, such as sea-
level, CO2, ice sheet[s], the Asian monsoon, regional
temperature and precipitation," Cheng says. "So a change
in one of them could trigger changes in others." And
that might mean the climate is too sensitive to tolerate
current levels of CO2 without changing the conditions
that have allowed human civilization to flourish in the
past 10,000 years.
_____________________________________________