CMA

65 devastating unintended consequences. The presence of such species can alter habitat, profoundly affect food chains with the introduction of new predators, affect the ability of native species to compete for food and habitat acquisition due to the lack of local controls (disease and predators) to keep populations of exotic species in check, promote hybridization the inter breeding of native and non- native species resulting in the decline and extinction of native species, and introduce pest species that can cause disease or parasitic infestations. These impacts all combine to impact biodiversity by decreasing the number of native species, thus causing regional homogenization of ecosystems. Climate change: Scientists have documented the important role that climate plays in the geographic distribution of the world’s ecosystems. Climate variability and change can affect plants and animals in a number of ways, including their distributions, population sizes, physical structure, metabolism, and behavior. The Earth’s climate is vastly different now from what it was 100 million years ago when dinosaurs roamed about the planet and tropical plants thrived closer to the poles. It is different from what it was 20,000 years ago when ice sheets covered much of the Northern Hemisphere. Although the Earth’s climate will surely continue to change, climatic changes in the distant past were driven by natural causes, such as variations in the Earth’s orbit, sunspots or volcanic eruptions. In 2007, the Intergovernmental Panel on Climate Change (IPCC) reported that the warming of our climate is un-equivocal and that this increased warming is very likely due to human-caused increases in Green House Gases (GHGs) IPCC, 2007. Current and future climatic changes thus have an additional source of change – human activities. Many activities associated with human economic development have changed our physical and chemical environment in ways that modify natural resources. These include activities that burn fossil fuels that release carbon dioxide (CO2) use land for agriculture, or urbanization that causes deforestation. We are already feeling the climatic effects of having polluted the atmosphere with GHGs such as CO2. The atmosphere has a natural capacity to trap radiant heat near the Earth’s surface the so called greenhouse effect. This natural phenomenon acts as an atmospheric blanket, allowing solar energy to warm the climate by trapping long wavelength radiant energy called terrestrial infrared radiation near the Earth’s surface. The natural greenhouse effect is responsible for surface warming. But, human-induced emissions of GHGs are inadvertently modifying the climate by enhancing the natural greenhouse effect, and are projected to result in a global warming of 1.1–6.4 0C or higher in the twenty-first century IPCC, 2007. Such an increase in global mean temperature, even at the lower end of the range, will likely result in ecologically significant changes, which is why climatic considerations are fundamental in the discussion of the status and trends of ecological conditions. Quantitative evaluations of the potential effect of human activities in creating global change are needed. Such evaluations are also central to potential policy responses to mitigate global changes. (Schneider, 1997; Root and Schneider, 2005; IPCC, 2001, 2007). Nutrient loading and pollution: Human activities are responsible for much of the accelerating loss of biodiversity. Human activities produce pollution, which adversely affects ecosystems. Human generated pollution impacts water resources in the form of toxic discharges of metals, organic chemicals, and suspended sediments usually found in industrial and municipal effluents, which can inversely impact the biota (living organisms) in an ecosystem; bacterial contamination from human waste that can cause disease; and nutrient buildup of, for example, phosphorus and nitrogen that often originate as runoff from fertilizers applied on agricultural fields. Nutrient loading can result in excesses that stimulate rapid growth of algae and aquatic plants, ultimately limiting the amount of oxygen and light available to other organisms in the ecosystem. Air pollution generated by human activities causes significant damage to ecological resources by directly damaging plants, acidifying lakes, streams, and soil, and leading to concentrations of poisons in the food chain. Acid precipitation, usually caused by sulfur dioxide and nitrogen dioxide combining with moisture in the air, is extremely harmful to terrestrial plants as well as organisms that live in rivers and lakes. Such pollution directly affects crops. Ground-level ozone over time reduces plant growth and fruit production and renders plants more vulnerable to disease and insect attack. Particulate matter can stunt plant growth by scattering the sun’s rays and reducing sunlight. Poor agricultural practices degrade soil quality and promote the loss of topsoil. Furthermore, agriculture has resulted in local reductions and elimination of