Vegetation and ecosystem habitats respond to a number of climatic and environmental forcings and boundary conditions. Photosynthetic processes, fundamental to the growth of vegetative biomass, involve stomatal dynamics that control the sequestration of carbon from the atmosphere as well as plant respiration and the exchange of gases such as CO2, O2, and H2O among other biochemical constituents. The primary climatic forcing parameters that vegetative growth or stress are sensitive to include temperature, precipitation/water availability, downward solar radiation at the surface and/or at the canopy level, downward long-wave radiation, relative humidity, and surface winds. These parameters affect stomatal resistance, carbon intake, and evapotranspiration among others. Solar radiation at the surface as well as longwave radiation are modulated by cloud cover. Water availability is determined not only by local//» situ precipitation but also soil moisture (vadose zone) and the groundwater table which are linked to surface water flows, and subsurface recharge and water transport from distant locations in space. Snow/ice accumulation and melt introduce time lags into the dynamics and responses of such a hydroecological system. Other environmental boundaries are important for ecosystems and vegetative health and growth as well as stress and decay, for example, soil nutrient supply as well as environmental conditions that could make particular species more or less susceptible to attack by fungi and other microbial virulence. A challenge to both observing and modeling programs is to de-convolve the complexity of the vegetation/ecosystem-climate relationship so that it may later be applied to investigate the impacts of projected climate change and global warming on the biosphere.
Satellite observing systems have been deployed for over 30 years to monitor a large array of environmental parameters, including those that are critical for ecosystem function such as surface temperature, moisture, precipitation, the surface radiation balance, soil moisture, and water supply, among others. An excellent, concise summary of the various aspects and impacts already seen of global warming together with satellite video (movie loops) imagery may be found at http://www.nasa.gov/ worldbook/global_warming_worldbook.html.
In a fascinating study, Balanya et al. linked global genetic changes to global climate warming. That climate change is altering the geographic ranges, abundances, phenologies, and biotic interactions of organisms has been demonstrated or alluded to by many researchers. Climate change may also alter the genetic composition of species, but assessments of such shifts require genetic data sampled over time. And, for most species, time series of genetic data are nonexistent or rare, especially on continental or global scales. For a few Drosophila species, time series comparisons of chromosome inversions are feasible because these adaptive polymorphisms were among the first genetic markers quantified in natural populations. Thus, historical records of inversion frequencies in Drosophila provide opportunities for evaluating genetic sensitivity to change in climate and other environmental factors. In this study, Balanya et al. determined the magnitude and direction shifts over time (24 years between samples on average) in chromosome inversion frequencies and in ambient temperature for populations of Drosophila subobscura on three continents. In 22 of 26 populations, climates warmed over the intervals, and genotypes characteristic of low latitudes (warm climates) increased in frequency in 21 of those 22 populations. Thus, they conclude, genetic change in this fly is tracking climate warming and is doing so globally.
Yet another recent study has implicated regional climate warming and its local effects on moisture, clouds, and day/night temperatures to the demise of frog varieties in Central and South America. According to the study, higher temperatures result in more water vapor in the air, which in turn forms a cloud cover that leads to cooler days and warmer nights. These conditions favor the chy-trid fungus to thrive in Costa Rica and neighboring countries. The fungus which reproduces best at temperatures between 63 °F (17.2 °C) and 77 °F (25 °C) kills frogs by growing on their skin and attacking their epidermis and teeth, as well as releasing a toxin. At least 110 species of vibrantly colored amphibians once lived near streams in Central and South America but about two-thirds disappeared in the 1980s and 1990s, including the golden toad. The fate of amphibians, whose permeable skin makes them sensitive to environmental changes, is seen by scientists as a possible harbinger of global warming effects.
Numerous other studies point to the impact already seen on ecological systems due to the lengthening of the growing season and changes to temperature, precipitation, and moisture regimes. There have been shifts in plant species to higher elevations or latitude. There also have been some cases of an unusual spread of spores from distant regions carried by changing atmospheric wind circulations or the temperature of ocean currents. It is unfortunately beyond the scope of this short article on the remote sensing of global ecology to include such detail. The reader is referred to the various and excellent papers published in journals such as Science or Nature.
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