[Vision2020] NASA GISS: Dec. 8 2011: "Paleoclimate Record Points Toward Potential Rapid Climate Changes"

[Ted Moffett]

Monday Dec. 12, 2011 the "Lewiston Tribune" front page headline read
"Climate Deal Extends Status Quo."
http://lmtribune.com/editors_pick/article_e889c1b8-bb55-5783-9fb1-4635ca902dee.html
The article was sourced from "The Associated Press," authored by Maxx and
Ritter, so my comments do not directly apply to "Lewiston Tribune"
journalists

The headline might have read, to address the magnitude of the problem
humanity is potentially facing, "No Substantive Climate Deal Portends
Meters of Sea Level Rise by 2100" if the article was referencing credible
peer reviewed science on this issue ("Global sea level linked to global
temperature"
http://www.pnas.org/content/early/2009/12/04/0907765106.full.pdf  ).
Instead, the article meekly declared "Scientists say that if levels of
greenhouse gases continue to rise, eventually the world's climate will
reach a tipping point, with irreversible melting of some ice sheets and a
several foot rise in sea levels."

Several foot rise?  How about potentially meters of sea level rise by
2100?  With more to follow as climate change continues into the next
century:
National Academies Press: "Beyond the Next Few Centuries: Long-Term
Feedbacks and Earth System Sensitivity"
http://www.nap.edu/openbook.php?record_id=12877&page=217

Read this recent release from NASA's Goddard Institute for Space Studies,
regarding a paper now "in press" (abstract at bottom):

http://www.giss.nasa.gov/research/news/20111208/
Research News Paleoclimate Record Points Toward Potential Rapid Climate
Changes

Dec. 8, 2011
*Related NASA AGU news briefing materials may be found
here<http://www.nasa.gov/topics/earth/features/rapid-change.html>
.*
**

New research into the Earth's paleoclimate history by NASA's Goddard
Institute for Space Studies director James E. Hansen suggests the potential
for rapid climate changes this century, including multiple meters of sea
level rise, if global warming is not abated.

By looking at how the Earth's climate responded to past natural changes,
Hansen sought insight into a fundamental question raised by ongoing
human-caused climate change: "What is the dangerous level of global
warming?" Some international leaders have suggested a goal of limiting
warming to 2 degrees Celsius from pre-industrial times in order to avert
catastrophic change. But Hansen said at a press briefing at a meeting of
the American Geophysical Union in San Francisco on Tues, Dec. 6, that
warming of 2 degrees Celsius would lead to drastic changes, such as
significant ice sheet loss in Greenland and Antarctica.

Based on Hansen's temperature analysis work at the Goddard Institute for
Space Studies, the Earth's average global surface temperature has already
risen .8 degrees Celsius since 1880, and is now warming at a rate of more
than .1 degree Celsius every decade. This warming is largely driven by
increased greenhouse gases in the atmosphere, particularly carbon dioxide,
emitted by the burning of fossil fuels at power plants, in cars and in
industry. At the current rate of fossil fuel burning, the concentration of
carbon dioxide in the atmosphere will have doubled from pre-industrial
times by the middle of this century. A doubling of carbon dioxide would
cause an eventual warming of several degrees, Hansen said.

In recent research, Hansen and co-author Makiko Sato, also of Goddard
Institute for Space Studies, compared the climate of today, the Holocene,
with previous similar "interglacial" epochs — periods when polar ice caps
existed but the world was not dominated by glaciers. In studying cores
drilled from both ice sheets and deep ocean sediments, Hansen found that
global mean temperatures during the Eemian period, which began about
130,000 years ago and lasted about 15,000 years, were less than 1 degree
Celsius warmer than today. If temperatures were to rise 2 degrees Celsius
over pre-industrial times, global mean temperature would far exceed that of
the Eemian, when sea level was four to six meters higher than today, Hansen
said.

"The paleoclimate record reveals a more sensitive climate than thought,
even as of a few years ago. Limiting human-caused warming to 2 degrees is
not sufficient," Hansen said. "It would be a prescription for disaster."

Hansen focused much of his new work on how the polar regions and in
particular the ice sheets of Antarctica and Greenland will react to a
warming world.

Two degrees Celsius of warming would make Earth much warmer than during the
Eemian, and would move Earth closer to Pliocene-like conditions, when sea
level was in the range of 25 meters higher than today, Hansen said. In
using Earth's climate history to learn more about the level of sensitivity
that governs our planet's response to warming today, Hansen said the
paleoclimate record suggests that every degree Celsius of global
temperature rise will ultimately equate to 20 meters of sea level rise.
However, that sea level increase due to ice sheet loss would be expected to
occur over centuries, and large uncertainties remain in predicting how that
ice loss would unfold.

Hansen notes that ice sheet disintegration will not be a linear process.
This non-linear deterioration has already been seen in vulnerable places
such as Pine Island Glacier in West Antarctica, where the rate of ice mass
loss has continued accelerating over the past decade. Data from NASA's
Gravity Recovery and Climate Experiment (GRACE) satellite is already
consistent with a rate of ice sheet mass loss in Greenland and West
Antarctica that doubles every ten years. The GRACE record is too short to
confirm this with great certainty; however, the trend in the past few years
does not rule it out, Hansen said. This continued rate of ice loss could
cause multiple meters of sea level rise by 2100, Hansen said.

Ice and ocean sediment cores from the polar regions indicate that
temperatures at the poles during previous epochs — when sea level was tens
of meters higher — is not too far removed from the temperatures Earth could
reach this century on a "business as usual" trajectory.

"We don't have a substantial cushion between today's climate and dangerous
warming," Hansen said. "Earth is poised to experience strong amplifying
feedbacks in response to moderate additional global warming."

Detailed considerations of a new warming target and how to get there are
beyond the scope of this research, Hansen said. But this research is
consistent with Hansen's earlier findings that carbon dioxide in the
atmosphere would need to be rolled back from about 390 parts per million in
the atmosphere today to 350 parts per million in order to stabilize the
climate in the long term. While leaders continue to discuss a framework for
reducing emissions, global carbon dioxide emissions have remained stable or
increased in recent years.

Hansen and others noted that while the paleoclimate evidence paints a clear
picture of what Earth's earlier climate looked like, but that using it to
predict precisely how the climate might change on much smaller timescales
in response to human-induced rather than natural climate change remains
difficult. But, Hansen noted, the Earth system is already showing signs of
responding, even in the cases of "slow feedbacks" such as ice sheet changes.

The human-caused release of increased carbon dioxide into the atmosphere
also presents climate scientists with something they've never seen in the
65 million year record of carbon dioxide levels — a drastic rate of
increase that makes it difficult to predict how rapidly the Earth will
respond. In periods when carbon dioxide has increased due to natural
causes, the rate of increase averaged about .0001 parts per million per
year — in other words, one hundred parts per million every million years.
Fossil fuel burning is now causing carbon dioxide concentrations to
increase at two parts per million per year.

"Humans have overwhelmed the natural, slow changes that occur on geologic
timescales," Hansen said.
Web Link

NASA/GISS Science Brief: Earth's Climate History: Implications for
Tomorrow<http://www.giss.nasa.gov/research/briefs/hansen_15/>
Reference

Hansen, J.E., and Mki. Sato, 2011: Paleoclimate implications for human-made
climate change <http://pubs.giss.nasa.gov/abs/ha05510d.html>. In Climate
Change: Inferences from Paleoclimate and Regional Aspects. A. Berger, F.
Mesinger, and D. Šijači, Eds. Springer, in press.

----------------------------------------

http://pubs.giss.nasa.gov/abs/ha05510d.html
Publication Abstracts Hansen and Sato 2011, in press

Hansen, J.E., and Mki. Sato, 2011: Paleoclimate implications for human-made
climate change. In Climate Change: Inferences from Paleoclimate and
Regional Aspects. A. Berger, F. Mesinger, and D. Šijači, Eds. Springer, in
press.

Paleoclimate data help us assess climate sensitivity and potential
human-made climate effects. We conclude that Earth in the warmest
interglacial periods of the past million years was less than 1°C warmer
than in the Holocene. Polar warmth in these interglacials and in the
Pliocene does not imply that a substantial cushion remains between today's
climate and dangerous warming, but rather that Earth is poised to
experience strong amplifying polar feedbacks in response to moderate global
warming. Thus goals to limit human-made warming to 2°C are not sufficient —
they are prescriptions for disaster. Ice sheet disintegration is nonlinear,
spurred by amplifying feedbacks. We suggest that ice sheet mass loss, if
warming continues unabated, will be characterized better by a doubling time
for mass loss rate than by a linear trend. Satellite gravity data, though
too brief to be conclusive, are consistent with a doubling time of 10 years
or less, implying the possibility of multi-meter sea level rise this
century. Observed accelerating ice sheet mass loss supports our conclusion
that Earth's temperature now exceeds the mean Holocene value. Rapid
reduction of fossil fuel emissions is required for humanity to succeed in
preserving a planet resembling the one on which civilization developed.

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Vision2020 Post: Ted Moffett
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