Freezing tundra a source of greenhouse gas methane

Tundra areas in the far north emit extra quantities of the greenhouse gas methane, as soon as winter falls. Sander Houweling from SRON Netherlands Institute for Space Research concludes this with his Swedish, Danish and American colleagues in the 1 December issue of the leading scientific journal Nature. Measurements on Greenland gave rise to the new insights. Houweling: ‘Future measurements from space will have to confirm our suspicion.’

Groenland gezien vanuit de ruimte door milieusatelliet ENVISAT (beeld: ESA)

The Earth’s atmosphere remains a reaction vessel full of poorly understood processes. Scientists agree that the emission of carbon dioxide by humans strengthens the greenhouse effect, with global warming as a consequence. Yet the process of climate change can also result in new gases being released into the atmosphere, such as the greenhouse gas methane that is produced during the breakdown of dead plants.

‘Methane is far less prevalent in the atmosphere than carbon dioxide, yet its effect as a greenhouse gas is 20 times stronger’, says Sander Houweling. ‘The permanently frozen tundra areas in the far north are full of methane. Global warming is causing an increasing number of these areas to defrost in the summer and freeze again in the winter with a resultant emission of methane. That process can further enhance the greenhouse effect so that even more methane is released: a self-enhancing process.’

Houweling’s Swedish colleagues allowed their equipment on Greenland to continue measuring after they had left the observation station due to the onset of winter. It was already known that methane is released from the tundra soil as soon as this starts to defrost. However, to everybody’s surprise the Swedish researchers measured a new peak in the methane emission at the moment the soil froze. This peak could be accounted for in the computer simulations of the atmosphere which Houweling had developed. ‘This extra methane emission therefore appears to be a significant factor’, says Houweling. ‘Satellite measurements must eventually reveal how this methane emission contributes to the global situation.’

Testopstelling voor het prototype van de methaansensor voor TROPOMI (beeld: SRON)

SRON’s laboratories are working hard on this problem. The prototype for a new space sensor for methane is currently being trialled in a freezer. A small quantity of methane released via a hose into the sensor’s line of view produces an unmistakable signal on the computer connected to the sensor. The sensor, developed in cooperation with TNO and Dutch Space, is part of the new Dutch space instrument for Earth observation, TROPOMI. Thanks to a revolutionary technological invention, the space researchers have succeeded in producing a methane detector 40 times smaller than was previously possible: an important benefit for space projects.

The equipment works superbly in the laboratory. Researchers will have to wait until at least 2014 before TROPOMI can scan the Earth’s atmosphere from a satellite of the European Space Agency (ESA). The data collected then will further clarify the contribution of methane to the greenhouse effect.

TROPOMI is a joint programme between SRON, KNMI , TNO and Dutch Space. NIVR is responsible for the project management, while KNMI and SRON share responsibility for the scientific aspects of the programme.