Ozone Damage to Vegetation Enhances Global Warming
13 Aug, 2007 11:20 am
The issues of air quality and climate change are even more connected than we thought. Changes in the concentration of ozone in the lower atmosphere are known to have contributed to climate change because ozone is a greenhouse gas.
There is a lot of evidence of damaging ozone effects on plants, in both polluted areas and experimental studies. We used a computer model of the land-surface which we adapted to include the effects of near-surface ozone on plant photosynthesis and leaf-stomatal opening (stomata are the pores of leaves which open to let carbon dioxide, and through which water flows out and ozone flows into the plant). The model was calibrated against the available manipulative experiments in which plants were exposed to elevated ozone concentrations, and tested against results from Free-Air CO2 Enrichment experiments.
Elevated atmospheric CO2 is known to fertilise plants, therefore vegetation can ‘mop up’ some of the excess carbon dioxide humankind is emitting into the atmosphere through fossil fuel emissions and deforestation. This process is already included in the current generation of global climate-carbon cycle models which predict the future development of the Earth’s climate.
Our current study suggests that the combined effect of CO2 increases and O3 increases will still be to increase net primary productivity (which is related to plant growth and crop yields). However, the CO2 fertilisation of photosynthesis, which seems to be largely responsible for the global land carbon sink, could be heavily suppressed by O3 increases.
Our research implies that lower atmosphere ozone increases could be twice as important for climate change as previously thought, quite apart from the known damaging impacts of ozone on human health and crop growth. It is therefore vital that measures to reduce the chemicals that lead to ozone increases (especially NOx emissions from vehicles without three-way catalytic converters) are enforced, alongside the ongoing efforts to control carbon dioxide emissions.
Reference: Sitch, Sephen. Nature 448, 396-397 (26 July 2007).