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Astronomy's carbon footprint is the strangest problem you've never thought about (Image: G. Hdepohl/ESO)

Astronomy produces a lot of carbon emissions, but it could be one of the greenest sciences if observatories harness their solar and wind resources

IF YOU were to draw up a list of the most pressing issues in science, it's unlikely that astronomy's carbon footprint would be on it. If it were, it would probably end up somewhere between effective male birth control and how to fold headphones to stop their wires getting tangled in your pocket.

Ueli Weilenmann, deputy director of La Silla Paranal Observatory in Chile, would disagree with that assessment. Recently, while grappling with the costs of running the place, he was shocked to discover the scale of the observatory's carbon emissions (see diagram). A bit of further digging revealed that the problem is not limited to Paranal: many other observatories exude more greenhouse gas than their size betrays.

This shouldn't be the case. By dint of their location, most observatories enjoy access to clean energy sources, but for various reasons they have been unable to exploit them. Now observatories all over the world are looking beyond obvious solutions, enlisting ingenious workarounds in their quest to go green. The possibilities for doing so run from the inspired to the mundane to the highly speculative. The potential carbon cutbacks won't save the world, but the people running these experiments are determined to prove that big science can be clean too.

The bigger telescopes get, the further they can peer into our universe, and the better the resulting images. But the barbed spiral galaxies and weather on distant exoplanets that have been captured by Paranal's Very Large Telescope (VLT) come at a high cost. Astronomy is an energy-intensive endeavour. "We are in a very isolated place and everything we do here has an associated energy cost," Weilenmann says. Paranal is so remote that even the water needs to be trucked in, not to mention food, staff and fuel.

The lion's share of the energy use, however, comes from running an instrument like the VLT and cooling its sensitive electronic equipment. Every day it sucks up 27 megawatt-hours of energy, or nearly 10 gigawatt-hours per year the annual consumption of 1000 US households.

But unlike those homes, Paranal is too far from the national grid to connect, so it must produce its own power. It does this using generators that burn butane. Fuel prices are volatile, and with observatories hardly swimming in cash, Weilenmann was investigating Paranal's energy use to try to keep expenses under control. It was then that he discovered its carbon footprint, 22,000 tonnes a year, equivalent to 46 tonnes of carbon dioxide for every peer-reviewed scientific paper produced there. It's equivalent to the emissions of a small town.

In a world where the energy budget of a data centre can rival that of a medium-sized city, those numbers won't raise many eyebrows, but for Weilenmann it was a matter of principle: the problem should not have existed in the first place. After all, the ideal locations for observatories happen to be green-energy sweet spots. "We never faced a situation where there was no sun and no wind for more than a day," says Rolf Chini of Ruhr University Bochum in Germany. Chini runs the observatory at Cerro Murphy which, like Paranal, sits on a peak in the Atacama desert, with 320 cloudless days a year on average and buffeted by strong winds.

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Green sky thinking: Astronomy's dirty little secret