Global Fingerprints of Greenhouse Warming

Summarizes findings from several scientific articles that link human activities to global warming, and outlines the major impacts that can be observed from climate change over the past 100 years

Soil consumption of atmospheric methane: Importance of microbial physiology and diversity

Thesis (Ph.D.) University of Alaska Fairbanks, 1996Recently, atmospheric CH\sb4 concentration has risen dramatically, apparently due to human activities. Since is CH\sb4 is involved in several atmospheric processes that regulate Earth's climate, it is important that we understand the factors that control its atmospheric concentration. One such factor is biological CH\sb4 consumption in well-drained soils. Although this sink may comprise nearly one-tenth of the annual destruction of atmospheric CH\sb4, We know relatively little about it. I conducted a research project to investigate the influences of CH\sb4 supply, soil moisture, dissolved salts, and NH\sb4\sp+-fertilizer on the activity of soil CH\sb4 oxidizers. When starved of CH\sb4, two upland taiga soils gradually lost their capacities to oxidize CH\sb4, indicating that the process was not merely fortuitous, and that the organisms involved were truly methanotrophic. The relationship between soil moisture and CH\sb4 consumption was parabolic, with maximum oxidation occurring at a moisture level that achieved the maximum possible CH\sb4 diffusion rate, while minimizing water stress on the methanotrophs. Optimal soil moisture occurred in a relatively narrow range among an array of physically dissimilar soils, providing that moisture content was expressed as a percentage of the water holding capacity fo a particular soil, rather than as absolute water content. In recent years, one of the most intensely investigated controls on soil CH\sb4 consumption has been its inhibition by NH\sb4\sp+-fertilizer. In addition to NH\sb4\sp+, however, I found that other ions inhibited CH\sb4 oxidation. In some soils non-NH\sb4\sp+ ions were so toxic that they completely masked the NH\sb4\sp+ effect. It is crucial, therefore, to control for salt effects when investigating NH\sb4\sp+-inhibition. In both field and laboratory experiments, CH\sb4 consumption in a birch soil was sensitive to NH\sb4\sp+, whereas a spruce soil was unaffected. In the birch soil, NH\sb4\sp+ apparently inhibited methanotroph growth, rather than enzymatic CH\sb4 oxidation, whereas methanotrophs in the spruce soil were apparently insensitive to NH\sb4\sp+. These results suggest that the primary landscape-level control over the response of soil CH\sb4 consumption to NH\sb4\sp+-fertilization is the cross-site distribution of physiologically distinct CH\sb4 oxidizers

Extreme Weather and Climate Change: Understanding the Link, Managing the Risk

Examines recent extreme weather events, their consequences, and links to larger statistical trends toward higher frequency and severity. Calls for a probability-based risk management framework for adapting to and mitigating the effects of climate change

Climate Change & International Security: The Arctic as a Bellwether

Examines how the trend toward seasonally open Arctic waters as a result of global climate change affects geopolitics. Analyzes 2008-12 policy statements and actions by Arctic states, other states with Arctic interests, and multilateral organizations