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1.1.1 Virtually all of Earth’s ecosystems have been significantly transformed through human actions. In the second half of the 20th century ecosystems changed more rapidly than at any other time in recorded human history. Some of the most significant changes have been the conversion of forests and grasslands into cropland, the diversion and storage of freshwater behind dams, and the loss of mangrove and coral reef areas.
The most rapid changes are now taking place in developing countries, but industrial countries experienced comparable changes in the past. However, current transformations seem to occur at a faster pace than changes prior to the industrial era. More...
1.1.2 Ten categories of ecosystems have been assessed: More...
(the links below provide further information and maps)
See also: Comparative table of the assessed ecosystems
1.1.3 Within marine ecoystems, populations of fished species have been affected by the world’s growing demand for food and animal feed. Since industrial fishing began, the total mass of commercially exploited marine species has been reduced by 90% in much of the world.
Freshwater ecosystems have been modified by the creation of dams and the withdrawal of water for human use, which have changed the flow of many large river systems. This in turn has had other effects such as reducing sediment flows, the main source of nutrients for estuary ecosystems.
Within terrestrial ecosystems, more than half of the original area of many types of grasslands and forests has been converted into farmland. The only types of land ecosystems which have been changed relatively little are tundra and boreal forests, but climate change has begun to affect them.
1.1.4 Globally, the transformation of ecosystems into farmland has begun to slow down. Opportunities for further expansion of farmland are diminishing in many regions of the world because most of the suitable land has already been converted. Increased agricultural productivity is also reducing the need for more farmland. Moreover, in temperate regions some cropland areas are now reconverted into forest or taken out of production. More...
The capacity of ecosystems to provide benefits to humans, that is to provide ecosystem services, derives from environmental cycles of water, nitrogen, carbon, and phosphorus. These processes have in some cases been significantly modified by human activity. Changes have been more rapid in the second half of the 20th century than at any other time in recorded human history. More...
1.2.1 Water cycle: Water withdrawals from rivers and lakes for irrigation, urban uses, and industrial applications doubled between 1960 and 2000. Globally, humans use slightly more than 10% of the available renewable freshwater supply. However, in some regions such as North Africa, groundwater is withdrawn at a faster pace than it is renewed. More...
1.2.2 Carbon cycle: In the last two and a half centuries, the concentration of carbon dioxide in the atmosphere has increased by one third. Land ecosystems were a net source of carbon dioxide during the 19th and early 20th century and became a net carbon sink sometime around the middle of the last century. This reversal is due to increases in plant growth brought about by, for example, new forest management and agricultural practices. More...
1.2.3 Nitrogen cycle: The total amount of nitrogen made available to organisms by human activities increased nine-fold between 1890 and 1990, especially since 1950 because of the use of synthetic fertilizers. Human activities are now responsible for as much nitrogen made available as all natural sources combined.
1.2.4 Phosphorus cycle: The use of phosphorus fertilizers and the rate of phosphorus accumulation in agricultural soils nearly tripled between 1960 and 1990, but has declined somewhat since. The flow of phosphorus into the oceans is now three times the natural flow. More...
A change in an ecosystem necessarily affects the species which are part of it, and changes in species in turn affect ecosystem processes. More...
1.3.1 The distribution of species on Earth is becoming more homogeneous. This is caused by the extinction of species or loss of populations that had been unique to particular regions and by the invasion or introduction of species into new areas. For example, of the non-native species in the Baltic Sea, a high proportion are native to the North American Great Lakes. Likewise, some of the non-native species in the Great Lakes can be found naturally in the Baltic Sea. More...
1.3.2 Within many species groups, the majority of species have faced a decline in the size of their population, in their geographical spread, or both. Certain species may not decline, for instance if they are protected in natural reserves, if particular threats to them are eliminated, or if they thrive in human-modified landscapes. Within well-studied groups (conifers, cycads, amphibians, birds, and mammals), 10 to 50% of species are currently threatened with extinction. More...
1.3.3 Species extinction is a natural part of Earth’s history. However, over the past centuries humans have increased the extinction rate by 50 to 1,000 times compared to the natural rate. More...
1.3.4 Overall, the range of genetic differences within species has declined, particularly for crops and livestock. This has also been noted for wild species that have been heavily exploited for commercial uses. For other wild species information is limited. In cultivated ecosystems, intensification of agriculture and the lesser use of traditional local species in favor of fewer modern varieties have reduced the genetic diversity of domesticated plants and animals. The permanent loss of genetic diversity has been partially prevented by maintaining seed banks. More...
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