It’s wrong to wish on space hardware

A number of satellite related issues have come up this weekend: The NSIDC reminded us that satellite sensors are (like all kinds of data) not perfectly reliable and do not last forever. Two satellites collided by accident last week, littering the orbit with dangerous amounts of debris. In San Diego this weekend, I was fortunate enough to attend a meeting with some of the Apollo astronauts and some of the scientists involved in Cassini and the Mars Phoenix missions. And yesterday morning we heard that the Orbiting Carbon Observatory mission launch failed to insert the satellite into orbit, and it is presumably measuring carbon dioxide somewhere at the bottom of the Southern Ocean. Coincidentally, when it came up on the news, I was in a meeting with one of the scientists who had been working on setting up a climate model to assimilate the OCO data in order to pin down the carbon sinks.

All of these events have served to remind me at least, that although the space age is 50 years old, we are a long way from the point where we can take our ability to launch and control off-planet machines for granted. Getting into space was, and remains, a tremendous challenge. This makes the successes we’ve had all the more incredible, and a testament to the hard work the engineers and scientists do over many years before a launch to give the missions the best chance of success.

For the climate-related satellites/instruments – SSM/I for the sea ice, OCO for high-precision CO2 concentrations – there is some redundancy with other existing missions. The JAXA AMSR-E sensor can still be used for sea ice extent (and indeed, SSM/I is still sending enough data back to construct 3 day mean pictures). For CO2, the substitutes are slightly orthogonal – the Japanese Ibuki satellite launched last month will measure CO2 but with a very different footprint than OCO would have used, and the AIRS instrument on Aqua has recently been used to produce a timeseries of mid-troposphere CO2 concentrations since 2004. Nonetheless, both of these other missions should provide some of the information that was anticipated from OCO – though not at the spatial resolution envisaged.

It’s worth discussing a little what OCO was going to be useful for. It wasn’t because we don’t know the average amount of CO2 in the atmosphere and how much it’s increasing – that is actually pretty well characterised by the current station network (around 386 ppm growing at ~2ppm/year). However, the variations about the mean (tens of ppm) have a lot of extra information about the carbon cycle that are only coarsely resolved. The measurements would have been from nearer the surface than the AIRS data, and so closer to the sources and sinks. You would have been able to see point sources quite clearly and this would have been a good check on the national inventories of fossil fuel use, and may have been useful at constraining the rather uncertain deforestation contribution to the anthropogenic carbon dioxide sources. More importantly, the OCO data combined with inverse modelling might have helped with constraining the terrestrial sinks. We know they exist from residual calculations (what’s left over from knowing how much we are adding, and seeing how much is in the air and what is in the ocean), and they’ve mainly been associated with boreal ecosystems from the inverse modelling done so far, but there are quite large uncertainties (see 7.3.2 and fig 7.7 in AR4 Chp. 7). The Ibuki and AIRS data will help with this same issue, but OCO data would have been somewhat orthogonal.

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