Rather they are limited to alterations that are reported and quantified in the peer-reviewed scientific literature. Land use practices have far greater impact on ocean ecosystems than is generally appreciated. Two-thirds of the major marine fisheries are fully exploited, over exploited or depleted. The consensus within the scientific community is that the increase in CO 2 and other greenhouse gases have probably already affected climate. There is uncertainty about how fast the planet will continue to warm and how this and other climate-related changes will affect the land and oceans.
Humanity currently utilizes over half the available surface freshwater.
Above and beyond the ramifications of these numbers for an explosively growing human population, this figure has critical implications for water flow through estuaries and bays, and therefore habitat quality, e.g. for salmon. Examples include the conversion of wetlands and forests to urban and industrial areas or of grasslands to pastures and agricultural fields. The resulting alterations in biogeochemical cycles, precipitation patterns, and habitat availability affect ocean ecosystems directly and indirectly. The recent listing of nine salmon and steelhead populations in the Pacific Northwest highlight some of the consequences to marine species of land transformation due to logging, grazing, hydroelectric power generation, agriculture and urbanization. The amount of nitrogen that enters the nitrogen cycle each year has more than doubled over the past century as a result of human activities.