"Let's say we found that the boreal forests in Canada and Siberia were the primary sinks of CO2 because of their incredibly rapid growth during
summer months when the Sun is up," speculated Dr Crisp.
"Well those environments are changing dramatically right now.
"Will they still be the primary absorbers of CO2 as time goes on? We don't really know how big an impact they're having right now.
"This is why OCO is so essential."
Reflected glory
The observatory carries a single instrument - a spectrometer that breaks the sunlight reflected off the Earth's surface into its constituent colours,
and then analyses the spectrum to determine how much carbon dioxide and molecular oxygen is present.
The data can be used to work out atmospheric concentrations.
OCO will map carbon dioxide over 1,600-sq-km (620 sq miles) regions of the Earth's surface to an accuracy of just fractions of 1%.
However, to locate the sources and sinks, scientists will need to combine the information with models that estimate how CO2 is being moved and mixed
through the air.
NASA'S A-TRAIN SATELLITE CONSTELLATION
1. OCO will head the 'train' of satellites when it gets into orbit. It will measure the concentration of carbon dioxide in the lower atmosphere
2. Aqua will lag OCO by 15 minutes. It is collecting information about the Earth's water cycle - water in the oceans, the air and on the land
3. Cloudsat will allow for the most detailed study of clouds to date. It should better characterise their role in regulating the climate
4. Calipso views clouds just moments after Cloudsat has looked at them. Its primary interest is the way aerosols interact with clouds
5. Parasol is a French satellite that can distinguish natural from human-produced aerosols. It makes polarised light measurements
6. Glory will join the train in June. One task will be to measure the 'energy budget' of Earth, to determine accurately global temperature
7. Aura also has a big European investment. It looks at atmospheric chemistry, and is producing remarkable global pollution maps
Once in orbit, OCO will join a fleet of other satellites - known as the A-Train - which carry a range of instrumentation to give a rounded picture of
Earth's atmospheric and water systems.
The spacecraft cross the equator in the early afternoon on a path that takes them over broadly the same observation point in quick succession.
OCO will be followed into orbit next year by a Japanese carbon mission known as the Greenhouse gases Observing SATellite (GOSAT).
Europe is considering two carbon observatories - A-SCOPE (Advanced Space Carbon and Climate Observation of Planet Earth) and a mission called BIOMASS
- which could fly in 2016.
Professor Quegan, from the UK's University of Sheffield, is working on the BIOMASS proposal.
"The spacecraft would measure global forest biomass at scales of about one hectare," he said.
"It's a crucial natural resource and ecosystem service - for materials, for energy, for biodiversity - there's a good correlation between how much
biomass you've got and how much biodiversity you've got - and for climate and water protection."
"So from a carbon cycle science aspect, forests have some critical parameters that need to be pinned down."
In the carbon cycle, natural fluxes are the biggest, accounting for about 330 gigatonnes per year, and are in near equilibrium
The roughly 7.5 gigatonnes coming from all human sources may be sufficient to tip this system out of balance, warming the Earth
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It seems is another thing to make us feel bad about ourselves