NIGEL FOX reckons he can silence the climate change deniers. Those who insist on arguing that the change is simply not our fault had better watch out. The problem, as Fox sees it, is in the measurements beamed back from the dozens of Earth observation satellites.

"Earth observation data is disputable," says Fox, head of science at the Optical Radiation Measurement group at the National Physical Laboratory (NPL) in Teddington, south-west London.

Slightly different results

"We just don't know if the instruments used to gather it are accurate enough once they've been in space for a couple of years. What we do know is that they all seem to produce slightly different results, which provides wriggle room for those that dispute the evidence for human origins of climate change."

That wriggle room allows climate change sceptics to argue that the human impact is either unproven or is negligible. It also produces a wide variation of results in models that seek to predict the outcomes of climate change.

So Fox has done what his team at NPL does best — come up with a device that can calibrate satellites. His GBP60m washing machine-sized satellite, called Truths, would orbit the earth and use its 99.999 per cent perfect radiometer, which is more accurate than anything available in space at the moment, to set benchmarks for the light reflected off certain parts of the planet.

When another satellite flies over the same point, it can adjust its instruments to match. With the same standard for all satellites, the data they send back will be directly comparable, the uncertainty will be reduced drastically and the wriggle room will disappear. And as a bonus, Truths could also play a role in the implementation of the Kyoto protocol by policing carbon trading and monitoring localised pollution.

Coordinating the measurements of the earth's temperature, weather systems, pollution levels and countless other bits of information into a robust model that can predict change occupies thousands of scientists around the world.

As a result, the accuracy of the data is vital in assessing what the manmade bits of climate change are. The importance of the sun cannot be overstated. A 0.3 per cent drop in its output in the 16th century caused a mini ice age in the northern Atlantic region. The need to accurately monitor tiny changes is, therefore, crucial. But scientists have to grapple regularly with the spread of data coming back from the scores of earth observation satellites launched in the last three decades. The variation between these is of the order of 0.5 per cent — a tiny amount but enough to provide that infamous wriggle room.

Joanna Haigh, professor of atmospheric physics at Imperial College London, says: "Two current instruments give measurements that are adrift by about a third of a per cent — and that allows for a substantial amount of doubt. Without some sort of reference point we can't really tell if a data shift is due to faulty instruments or trends in the sun. "

There are plenty of reasons why the wriggle room happens. Each satellite is calibrated slightly differently, the stresses of launch might knock some of them slightly out of kilter, or they simply degrade over time. Fox says that Truths will reduce the uncertainty.

"We can get a baseline set in the sand that says the uncertainty on this data is small enough that we can measure and monitor subtle changes that are occurring," says Fox. "In that way, we will have the evidence to see if we are truly seeing changes and what those changes are and to be able to detect them earlier."

Cyrogenic radiometer

It will be done with a small box sitting at the core of Truths. This is Fox's cryogenic radiometer, essentially an astonishingly accurate thermometer. "Any radiation going onto a surface will warm that surface and you can measure a temperature rise," he says.

"If you make that surface very, very black, so it's very absorbing, in this case 99.999 per cent absorbing, then you know that everything on it is totally absorbed." In effect, it becomes a light meter. The Truths satellite would work by looking at certain reference points on earth, such as deserts, and recording numbers for the light reflected off the surface. Other satellites could upload those figures. "Any time that any other satellite passed over these targets, it would be able to update its own calibration coefficients to those defined by the Truths satellite."

Truths would also do plenty of its own science to justify the high cost. A camera will monitor the output of the sun and also record the electromagnetic radiation bouncing off the Earth's surface. The spatial resolution of this device would make it ideal for pinpointing phenomena such as localised atmospheric pollution.

"With more accurate measurement we can be quicker off the mark with our detection of pollution " says Fox. "Everything on the planet has its own unique spectral signature," says Fox, "not just every single species but also through its life cycle."

This means that Truths could be used to look at a field of crops, assess how old it is, how close it is to being harvested or even when it is under stress.

Fox says that Truths could also help ensure that the carbon sinks being negotiated in climate change treaties such as Kyoto are doing their jobs. After all, the effectiveness of a sink is only as good as the health of the trees in it.

Several satellites already do similar things but their focus has always been global. As such, their resolution is hundreds of metres or even kilometres.

He argues that Truths could be used for directed action at highly specific sites around the world.

- Guardian Newspapers Limited 2005

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