Simply by breathing, humans have played a small part in the
planet-wide balancing act called the carbon cycle throughout our
existence. However, in the last few hundred years, we have taken a
larger role. Our activities, such as fossil fuel burning and
deforestation, are pushing the cycle out of its natural balance, adding
more and more carbon dioxide to the atmosphere.
Natural processes are working hard to keep the carbon cycle in
balance by absorbing about half of our carbon emissions, limiting the
extent of climate change. There's a lot we don't know about these
processes, including where they are occurring and how they might change
as the climate warms. To understand and prepare for the carbon cycle of
the future, we have an urgent need to find out.
In July 2014, NASA will launch the Orbiting Carbon Observatory-2
(OCO-2) to study the fate of carbon dioxide worldwide. "Right now, the
land and the ocean are taking up almost half of the carbon dioxide we
add to the atmosphere by burning fossil fuels, but the future is
fundamentally unknown," said Paul Wennberg, a professor of atmospheric
chemistry at the California Institute of Technology in Pasadena. "OCO-2
is a key to getting answers." The mission has been developed and is
managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Carbon dioxide is both one of the best measured greenhouse gases and
one of the least measured. The emissions that remain in the atmosphere
become evenly distributed around the globe in a matter of months. As a
result, the average atmospheric concentration can be monitored well by
existing ground stations (about 160 worldwide). The other half of our
emissions -- the half that is being absorbed through natural processes
into the land or the ocean -- is not evenly distributed. To understand
where that carbon dioxide is going, we need precise, comprehensive,
ongoing data about carbon dioxide absorption and emission by forests,
the ocean and many other regions. For some of these regions, we have far
too few observations.
"A research ship moves about the speed of a 10-speed bicycle," said
Scott Doney, director of the Ocean and Climate Change Institute at the
Woods Hole Oceanographic Institution, Woods Hole, Mass. "Think about the
size of the ocean. There's only so much research you can do at the
speed of a bicycle." Oceanographers have made up some of the
observational deficit by contracting with shipping lines to gather data
along commercial routes. But there's little shipping in the Southern
Ocean, and Doney said that's a region of high concern. "With warming, we
expect big changes. The winds are changing there, and carbon dioxide
uptake may change too."
On land, Earth's great forests might be the least understood areas.
In northern Siberia, a region with no permanent settlements and few
roads, there are only six year-round monitoring sites across seven time
zones. Forests remove carbon from the air during photosynthesis and
store it in wood and roots, making these forests what scientists call
carbon sinks. But droughts and wildfires can turn forests into carbon
sources, releasing the stored carbon back into the atmosphere. We don't
know when and how often forests cross the line from sink to source.
OCO-2 will not be the first satellite to measure carbon dioxide, but
it's the first with the observational strategy, precision, resolution
and coverage needed to answer these questions about these
little-monitored regions, according to Ralph Basilio, OCO-2 project
manager at JPL.
OCO-2's scientific instrument uses spectrometers, which split
sunlight into a spectrum of component colors, or wavelengths. Like all
other molecules, carbon dioxide molecules absorb only certain colors of
light, producing a unique pattern of dark features in the spectrum. The
intensity of the dark features increases as the number of carbon dioxide
molecules increases in the air that the spectrometer is looking
through.
Carbon dioxide concentrations in the atmosphere are measured in parts
per million, the number of molecules of carbon dioxide there are in
every million molecules of air. That number is currently around 400.
OCO-2's spectrometers can detect changes of one or two carbon dioxide
molecules out of the 400 -- an unprecedented level of precision, and one
that scientists think will be adequate to detect changes in natural
sources and sinks, once enough measurements have been collected.
OCO-2 will collect 24 measurements a second over Earth’s sunlit
hemisphere, totaling more than a million measurements each day. Fewer
than 20 percent of these measurements will be sufficiently cloud-free to
allow an accurate estimate of carbon dioxide, but that number will
still yield 100 to 200 times as many measurements as the currently
observing Japanese Greenhouse gases Observing SATellite (GOSAT) mission.
The measurements will be used as input for global atmospheric models.
Combined with data on winds and other conditions, the OCO-2 data will
allow modelers to better locate carbon sources and sinks at regional
scales -- areas the size of France or Texas.
"With atmospheric carbon dioxide at unprecedented levels, our sense
of urgency has only increased,” said Basilio. “What will happen if we
keep emitting carbon dioxide at the same rate? The ultimate goal for
OCO-2 is to provide data so that organizations and individuals
throughout the world can make better-informed decisions about carbon."
No comments:
Post a Comment