Measuring climate

The tropical rainforest displays of the Glasshouse Range provide an ideal site, in terms of temperature, humidity and tropical plant species, to test a gas chromatograph instrument being developed by the Centre for Atmospheric Science for field use in Borneo. This group, led by Professor John Pyle and Dr Neil Harris in the Department of Chemistry, study the processes controlling the present state of the earth’s atmosphere and its evolution.
A major collaborative project is investigating the rainforests of Borneo.A major collaborative project is investigating the rainforests of Borneo.
There has been increasing interest in the activities of ozone in the lower levels of the atmosphere in recent years. Ozone helps control the atmosphere’s ‘oxidizing capacity’ - its ability to cleanse itself of pollution - but it is toxic to plants and causes respiratory problems in humans. In addition ozone is an important climate gas: it affects radiative heating of the atmosphere, but is in turn affected by climate change in a highly coupled system. Concentrations of ozone have risen over the last 100 years, and these concentrations are driven by oxides of nitrogen and volatile organic species (VOCs).

The majority of VOC emissions are biological, with plants naturally emitting large quantities, particularly in the tropics. These particles affect visibility and given rise to such things as the ‘Blue Ridge Mountain’ phenomenon. These VOC emissions will impact on ozone concentrations, so could climate-induced changes in their emissions be a factor during the coming century?

Isoprene, a VOC, is a very reactive molecule emitted from forest and woodland species, including oaks, oil palms and poplars. Emissions are very strongly temperature dependent, doubling in quantity between 20˚C and 40˚C. Changes in the temperature of the biosphere, especially in the tropics, could have important repercussions for air quality and climate.

To understand these processes, a major collaborative project is investigating the rain forest of Borneo. The Danum Valley Field Centre is located in pristine forest, but is close to secondary forest and to extensive oil palm plantations. Measurements of atmospheric composition and emissions, using the gas chromatograph, are being made in these different environments. We now have nearly two years of continuous measurements at two sites in Borneo, Danum Valley and at a nearby coastal site. There is evidence of very large emissions from the ocean, almost certainly from the coastal seaweed beds.

In Cambridge, the Centre for Atmospheric Studies is developing a sophisticated chemistry/climate model to monitor the impact of VOC emissions on local, regional and hemispheric scales. This will aid our understanding of measured concentrations and emissions of VOCs and address topics such as the impact on isoprene concentrations of replacing rain forest with oil palm plantations.

The more we look at the earth system, the more we see a highly coupled, interactive system. It is clear that a more complete description of how the biosphere, and its emissions affect these processes is needed. The Botanic Garden offers a major opportunity for involvement in the interdisciplinary research needed.

Professor John Pyle, University of Cambridge