The Alan Sondheim Mail Archive

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Date: Thu, 05 Feb 2009 13:58:10 -0800
From: NASA Jet Propulsion Laboratory <info@jpl.nasa.gov>
To: "sondheim@panix.com" <sondheim@panix.com>
Subject: NASA Carbon Mission to Improve Future Climate Change Predictions




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Feature                                                               February
5, 2009

NASA Carbon Mission to Improve Future Climate Change Predictions

Recent years have seen an increase in record-setting events related to
climate change. For example, 2005 was the warmest year globally in more
than a century, and in 2007, Arctic sea ice retreated more than in any
other time in recorded history. A new NASA mission set to launch later
this month will help scientists better understand the most important
human-produced greenhouse gas contributing to climate change: carbon
dioxide. Called the Orbiting Carbon Observatory, the satellite may help
us better predict how our climate may change in the future.

Scientists rely on models to forecast future impacts of carbon dioxide on
Earth's climate. When the carbon dioxide concentrations used in, or
predicted by, these models are not accurate, the resulting climate
projections can have a large degree of uncertainty. To accurately predict
atmospheric carbon dioxide concentrations in the future, we need to
understand natural and human sources of carbon dioxide, as well as the
natural "sinks" that remove this gas from our atmosphere.

The rapid buildup of carbon dioxide from the burning of fossil fuels is a
relatively well understood and predictable source. Other impacts,
however, such as forestry and agricultural practices, which can act as
either sources or sinks, are far harder to predict with confidence. More
importantly, measurements from a global network of greenhouse gas
monitoring stations indicate that more than half of the carbon dioxide
emitted by human activities is currently being absorbed by the ocean and
by plants on land. But the current ground-based carbon dioxide monitoring
network does not have the coverage or resolution needed to identify
sufficiently the natural sinks responsible for absorbing this carbon
dioxide. In addition, the amount of carbon dioxide absorbed by natural
sinks varies dramatically from year to year, for reasons that are largely
unknown. Because the nature, location and processes controlling these
natural sinks are not well understood, it is impossible to accurately
predict how much carbon dioxide they might absorb in the future as the
climate changes. The Orbiting Carbon Observatory aims to help resolve
these and other open carbon-cycle questions.

"The Orbiting Carbon Observatory will provide the initial steps in the
journey of measuring carbon dioxide from space, and the discoveries will
be profound-we'll gather basic information about the distribution of
carbon that we wouldn't have been able to do any other way," says Graeme
Stephens of Colorado State University, Fort Collins, a co-investigator on
the Orbiting Carbon Observatory science team.

Researchers have shown that warming, particularly from greenhouse gases
including carbon dioxide, is driving Earth's climate toward "tipping
points." Those are the points at which temperatures could set in motion
processes that are very difficult to reverse. One potential example is
the runaway disintegration of Arctic sea ice and of the West Antarctic
ice sheet. In this scenario, warmer temperatures melt more ice and create
more open water, which absorbs more heat. This, in turn, melts more ice,
in a process that feeds upon itself.

Research by James Hansen of NASA's Goddard Institute for Space Studies in
New York, and colleagues suggests that to avoid dangerous tipping points,
Earth's atmosphere should be limited to a carbon dioxide concentration of
450 parts per million at the most, and potentially much lower. Today, the
level of carbon dioxide is about 385 parts per million, and over the last
few decades that number has been rising by about two parts per million
per year. But arriving at models that accurately predict how carbon
dioxide levels will change in the future depends, in part, on whether
researchers can collect enough data to untangle the mysteries of the
carbon cycle.

  "As human-caused emissions change, what will happen to the carbon budget
[the contribution of carbon dioxide's various sources]?" Stephens asked.
"There's a gross lack of understanding as to where the re-absorbed carbon
is going because it's currently impossible to make global observations to
see how carbon dioxide varies on both global and regional scales."

Currently, a sparse network of stations across the globe collects precise
measurements of carbon dioxide near Earth's surface, but the number of
stations is limited and most are located far away from power plants,
automobiles and other sources of carbon dioxide. The Orbiting Carbon
Observatory will complement the ground-based network by collecting
thousands of times as many measurements over the sunlit side of Earth.
The Atmospheric Infrared Sounder instrument on NASA's Aqua satellite now
routinely provides global maps of carbon dioxide at altitudes between 5
and 13 kilometers (3 and 8 miles) high, where it is most efficient as a
greenhouse gas. Orbiting Carbon Observatory measurements will complement
those from the Atmospheric Infrared Sounder because they are much more
sensitive to the concentration of carbon dioxide near Earth's surface,
where most of it is emitted by sources or absorbed by sinks.

Measurements from ground stations and the Atmospheric Infrared Sounder
have already shown that the level of carbon dioxide is more varied
throughout the atmosphere than was previously believed. The levels
fluctuate with weather and temperature and are influenced by land plants
and the ocean. It's the goal of carbon cycle models to explain and
ultimately predict the response of this complex system.

"It's like a domino effect," Stephens said. "The climate system is so
interconnected, and the carbon dioxide system is an integral part of that
system."

A new generation of climate modelers already considers the interactions
of carbon between land, ocean and atmosphere. These models predict that
the growth rate of atmospheric carbon dioxide and of global warming will
accelerate as Earth's land and ocean show a decreased capacity to absorb
carbon dioxide. But with the current scant observations of the carbon
system, the magnitude and timing of such model predictions are highly
uncertain. The next generation of carbon-climate models will better
represent these systems, thanks to more abundant global carbon dioxide
data from the Orbiting Carbon Observatory and other future satellite
missions. And while the data from these new satellites may not be as
precise as data from ground stations, the models will nonetheless improve
due to the tremendous volume of data from across the globe and throughout
the atmosphere.

Researchers expect the volume of carbon dioxide data to increase
dramatically. "This is tremendous," says Inez Fung of the University of
California, Berkeley, a co-investigator on the Orbiting Carbon
Observatory science team. "There is much horizontal and vertical
variation of carbon dioxide in the atmosphere due to sources and sinks
and turbulent mixing processes that vary between day and night, from
place to place, and from season to season. The Orbiting Carbon
Observatory will give scientists a much more complete global picture of
how the carbon cycle works."

The observatory will measure the percentage of carbon dioxide present
within columns of the atmosphere that span less than 4.1 square
kilometers (1.6 square miles) on the surface and extend all the way up to
the satellite 705 kilometers (438 miles) above. "This is a major advance
over the traditional surface observations, which are sparse and which
sample only at fixed heights and mostly near the ground," Fung said.

The Orbiting Carbon Observatory information will allow researchers to
"see" for the first time carbon dioxide sources and sinks. The
information will allow researchers to assess, or "rank," the performance
of carbon-climate models and will help to flag areas that need additional
study. Researchers also expect the observatory to turn up surprises where
little or no carbon dioxide data have been taken, such as over Africa,
Eurasia and the open ocean.

"I am extremely excited-I have been working on the carbon cycle for over
25 years and have been hampered by the data scarcity," Fung said.
"Christmas is coming."

For more information on the Orbiting Carbon Observatory,
see: http://www.nasa.gov/oco .

This image shows the past half-century of carbon dioxide trends,
beginning in 1950 when global industrialization took off. A more complete
understanding of Earth's carbon cycle gained from the Orbiting Carbon
Observatory will help researchers arrive at models that better predict
future trends. Credit: NASA

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