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NASA's CO2 satellite tanks, unlike CO2 levels themselves

By / February 24, 2009



OCO, we hardly knew ye!

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NASA's Orbiting Carbon Observatory, a highly touted project in the agency's Earth-observing effort, is now sitting at the bottom of the Southern Ocean near Antarctica instead of whizzing around Earth, tracking the comings and goings of CO2 between the ocean, atmosphere, and land.

You can read a bit more about Tuesday's launch mishap here. Suffice it to say a large group of scientists are not happy campers. The $273 million mission was designed to scan the globe for sources and natural holding bins for CO2, and with an extraordinary level of detail.

How detailed? Each individual measurement would have covered roughly 1 square mile of the Earth's surface. That's not just individual-forest scale; that's tiny-patch-of-individual-forest scale -- with each patch of ocean, forest, or grassland inhaling or burping CO2 at its own pace and exhibiting its own trends in uptake and release.

With each full orbit, OCO would have gathered between 33,000 and 35,000 individual measurements. After 16 days (8,000,000 measurements) it would return to its original orbital path to cover the same ground. It would do this for two years, building a exquisite picture of sources and sinks for CO2 as they change with seasons.

Where might such information come in handy? Journey if you will to the pages of the journal Nature. On Feb. 19, a team led by Simon Lewis with the University of Leeds in Britain published a study of carbon storage in "old growth" African tropical forests.

Unlike the Amazon basin, where scientists had shown that old-growth forests have increased the amount of carbon they store during the past several decades, data for Africa have been sorely lacking. In a sense, the continent's tropical sinks have been "missing."

Carbon sinks in Africa

No more. Dr. Lewis and a large international team of colleagues report that across 79 study plots covering a combined 403 acres, carbon stored in live trees between 1968 and 2007 has grown. Based on their measurements, plus some additional assumptions, they estimate that as a whole, Africa's tropical forests have been soaking up CO2 from the atmosphere at an average rate of about 375 million tons a year during the study period.

Helene Muller-Landua, who's done a lot of work in tropical forests in the Western Hemisphere, cautions that while this increase may be due in part to CO2's effect as a fertilizer (up to a point), the increase in biomass also could result as the forests recover from past degradation.

Whatever the mix between the two, extrapolating from 403 acres to nearly 2 million square miles is a reach. It's the best researchers can do with the techniques and data at hand. But it's still a stretch.

Give me some constraints!

In an email exchange before OCO splashed down, Dr. Simon wrote that results from OCO -- as well as from the successful Japanese CO2 satellite GOSAT, now in orbit -- will help "constrain our results showing a large carbon sink in tropical forest trees, alongside also constraining results showing carbon sources from deforestation."

"This data should be able to be combined with ground-based data (on both changes in undisturbed forest, and deforestation) to give a more accurate picture of the sources and sinks in the tropics. Importantly, the ground-based studies at present measure only the trees and not the soils, yet the view from the atmosphere will include soil fluxes as well, again adding new information. The satellite data could also be used to validate (or not!)  models of vegetation that are inside climate models. They will be a very important new tool to study the global carbon cycle."

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