Effects of ozone on agriculture, forests and grasslands.

The damage and injury that ground level ozone (O) causes vegetation has become increasingly evident over the past half century with a large body of observational and experimental evidence demonstrating a variety of effects at ambient concentrations on crop, forest and grassland species and ecosystems. This paper explores the use of experimental data to develop exposure-response relationships for use in risk assessment studies. These studies have typically identified the USA mid-West, much of Europe, the Indo Gangetic Plain in South Asia and the Eastern coastal region of China as global regions where O is likely to threaten food supply and other ecosystems. Global risk assessment modelling estimates yield losses of staple crops between 3 to 16% causing economic losses of between US$14 to 26 billion in the year 2000. Changes in anthropogenic emissions of O precursors in recent decades have modified O concentration profiles (peaks versus background O) and global distributions with the Northern Hemisphere seeing increases in O levels of between 1 and 5 ppb/decade since the 1950s and the emergence of Asia as the region with the highest O concentrations. In the future, O mitigation could focus on methane (CH) and nitrogen oxide (NOx) emissions; these will differentially influence global and local/regional O concentrations and influence daily and seasonal profiles. The consequent effects on vegetation will in part depend on how these changes in O profile alter the exceedance of detoxification thresholds for plant damage. Adaptation options may play an important role in enhancing food supply while mitigation strategies are being implemented. An improved understanding of the mechanisms by which O affects plants, and how this might influence detoxification thresholds and interactions with other environmental variables such as water stress and nutrients, would help develop O deposition and impact models to support the development of crop, land-surface exchange and ultimately earth system models for holistic assessments of global change. This article is part of a discussion meeting issue 'Air quality, past present and future'.