NASA's CO2 satellite tanks, unlike CO2 levels themselves

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OCO, we hardly knew ye!

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.

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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."

If African tropical forests have been a "missing sink," at least in the sense that no one has been able to quantify the pace at which they've been soaking up CO2, then imagine other places scientists might find sinks if they can reach, via satellite, areas that are inaccessible or are poorly studied.

Such information can be valuable for land-use planning, either to save existing sinks like old-growth tropical, temperate, and boreal forests, or to change the use of land in ways that enhance its uptake of carbon dioxide.

The same holds true for pinning down sources, or at least sinks which may be growing less efficient in taking up CO2 as the climate warms and concentrations rise.

Come on up for the risin' CO2  emissions

And rising they are. The growth rate in atmospheric carbon dioxide concentrations rose for the third year in a row in 2008, according to preliminary data gathered by the National Oceanic and Atmospheric Administration.

The measure? The number of carbon-dioxide atoms per million atoms in a given volume of air. Last year's growth rate of 2.28 parts per million per year led to an overall concentration of 384.89 ppm. That's well above the typical peaks over the past 600,000 years, and it's the highest level in at least 200,000 years.

By another measure, raw tonnage of CO2 pumped skyward, emissions have grown by an average of 3.5 percent a year since 2000, according to data gathered by Chris Field, director of the department of global ecology at the Carnegie Institution of Washington. That compares with a rate of increase of 0.9 percent a year between 1990 and 1999.

"This puts emissions outside the envelope of possibilities considered" in the major reports on climate released in 2007 by the Intergovernmental Panel on Climate Change, he said recently during a briefing in Chicago at the American Association for the Advancement of Science's annual meeting. "We are looking at a future climate that's beyond anything we've considered seriously in climate model simulations."

Dr. Field takes part in annual CO2 emissions studies compiled by the Global Carbon Project. Its next major scorecard is expected to come out in early July.

Raising the emissions-reduction bar

The upshot after taking into account sinks for CO2 and feedbacks in the climate system, as well as the rapid run-up in atmospheric CO2: "To hit any given stabilization target, we're going to have to avoid emitting substantially more carbon dioxide than we thought a couple of years ago," Field says.

(Wait? If scientists are just discovering new sinks, how can Field have taken them into account? Because even if you don't know if one particular spot on the planet is a source or sink, what's in the air is what remains after individual sources and sinks on land and in the ocean have done their collective thing.)

That leaves two choices, he concludes: Start emissions reductions early, or start later, but really stomp on the breaks.

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