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Saturday, October 11, 2008

Monitoring climate change | A is for earth | The Economist




A is for earth

Oct 6th 2008

The world will soon know more about carbon dioxide

SINCE the start of the industrial age, the concentration of carbon dioxide in earth’s atmosphere has increased by about 25%—from about 280 parts per million to over 370 parts per million. As concerns over climate change increase, scientists are being asked difficult questions about the extent to which carbon is being put into, and taken out of, the atmosphere. Precise answers to questions like these are necessary to reliably forecast changes in earth’s climate. But massive gaps remain in our understanding of what happens to carbon dioxide after it has been produced.

Unfortunately, essential data on the geographic distribution of CO2 does not yet exist. Currently, the Carbon Dioxide Information Analysis Center, based in the United States, monitors emissions from a global network of ground-based sites. But there are not enough stations to give the kind of resolution that climate modellers need. Consequently, the processes that regulate the exchange of CO2 between the oceans, atmosphere and biosphere are poorly known. This is a problem. For example, current measurements from ground stations suggest that only half of the CO2 released into the atmosphere has remained there. There rest has been absorbed by the oceans and land-based ecosystems, but understanding where, how and why this happens is difficult without more data.

NASA Artist's impression of the Orbiting Carbon Observatory

What is needed, then, is a high-resolution global map of CO2. And one may now be forthcoming, thanks to a planned new NASA satellite, the Orbiting Carbon Observatory (OCO), scheduled for launch on January 15, 2009 and discussed this week at the International Astronautical Congress in Glasgow.

The OCO’s mission, for the next two years, is to map in detail where carbon is being produced and where it is being lost. It will help to document the natural processes and human activities that regulate the abundance and distribution of this important greenhouse gas. Surprisingly, these will be the first space-based measurements of CO2.

During the OCO’s mission, it will fly in an orbit that allows it to observe most of the earth’s surface at least once every sixteen days. It will also fly in a loose formation with a series of other earth-orbiting satellites known as the Earth Observing System Afternoon Constellation, or the A-train. This formation flying will allow data from the OCO to be compared with those obtained by other earth-observing satellites.

And like that data, the OCO’s will have to be “ground truthed”—meaning it will have to be checked to ensure that they accurately measure what is happening on the ground. Scientists have to make sure that satellites that detect things such as forest, grassland, water vapour and CO2, are really seeing these things. To do this, scientists at the National Oceanic and Atmospheric Administration (NOAA) need to overcome some steep challenges.

Because the satellite measurements are essentially an average in a column of gas, it is important to know as much as possible how that measurement relates to the actual gas from the ground to the upper atmosphere. But this is where it gets tricky: while measurements can be regularly taken on the ground, and using airline flights, how do you regularly, and reliably, get into the high atmosphere?

Enter a project that seeks to take tourists into space using a high-altitude aircraft to carry a rocket of thrill seekers to 110km. The high-altitude aircraft, known as White Knight Two, will start its test flights this year. It will regularly fly above 50,000 feet, and as of next year will be carrying a series of experiments designed to support the OCO, which will allow scientists to profile the atmosphere of more than 90% of the atmospheric column.

The OCO heralds an important new era of climate change research. And this is relevant to all of us because climate change will likely affect everyone. Some places will warm but others could well cool. Jet streams, ocean currents and rainfall patterns may change. Understanding what might happen is essential. Even if we don’t like the answers.

Monitoring climate change | A is for earth | The Economist

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