Key Studies on Air Pollution and Climate Change Impacts on Forests: An Introduction

Abstract

Global change can be viewed as the sum of all environmental pollution (Trevor, 2003). To sustain human activities, massive amounts of pollutants are discharged into the biosphere. The sum of all these activities results in warming the biosphere, weather extremes, loss of biodiversity and pollution of the water, air and soil components of the biosphere. Prior to 1940, when atmospheric concentrations of greenhouse gases (GHG) were low, solar radiation explains most of the northern hemisphere (NH) temperature changes. Since 1975, emission of GHGs and aerosols explains most of the observed temperature increases (National Assessment Synthesis Team, 2000). The largest change in climate may not be temperature but increased precipitation (a few tenths to 1% per decade in NH) and cloudiness (∼2% per decade in NH). Precipitation seems to be coming in the form of heavier events rather than being spread out over time. The additional water runs off into streams are predicted to cause erosion and flooding but not substantial increase of long-term soil moisture (Keller, 2003). Carbon dioxide (CO2), resulting mainly from burning of fossil fuels, is a main driver of climate change and in that regard is followed by methane (CH4), halocarbons and nitrous oxide (N2O) (IPCC, 2001). Aerosols and particulate matter can have either a positive or negative effect on climate depending on their composition. Tropospheric ozone (O3), the secondary pollutant generated from non-methane volatile organic compounds (VOCs), carbon monoxide (CO) and nitrogen oxides (NOx) in photochemical reactions, is particularly relevant for the linkages between climate change and air pollution. Climate change, especially high radiation and temperature, promotes increases in O3 concentrations when precursors are present. The steadily growing background O3 concentrations affect climate due to O3 being a potent GHG itself and indirectly influencing concentrations of other GHGs such as CH4 (Bytnerowicz et al., 2007). Ozone concentrations in NH have been increasing for more than 100 years. Highest peak concentrations were observed in 1950–1980 in the areas with high emissions of O3 precursors and high solar radiation. Classical example of extremely high levels of O3 is the Los Angeles Basin in southern California where in the 1960s and 1970s peak values occasionally were approaching 1 ppm. Even in the 1980s, the peak hourly O3 values as measured in the mountains surrounding Los Angeles occasionally Environ Monit Assess (2007) 128:1–3 DOI 10.1007/s10661-006-9408-1