Land-use change continues as the main short-term threat, with climate change, and the interactions between these two drivers, becoming progressively important. Tropical forests continue to be cleared, making way for crops and biofuels. Species extinctions many times more frequent than the historic "background rate" - the average rate at which species are estimated to have gone extinct before humans became a significant threat to species survival - and loss of habitats continue throughout the 21st century. Populations of wild species fall rapidly, with especially large impacts for equatorial Africa and parts of South and South-East Asia. Climate change causes boreal forests to extend northwards into tundra, and to die back at their southern margins giving way to temperate species. In turn, temperate forests are projected to die back at the southern and low-latitude edge of their range. Many species suffer range reductions and/or move close to extinction as their ranges shift several hundred kilometres towards the poles. Urban and agricultural expansion further limits opportunities for species to migrate to new areas in response to climate change.
Impacts for people:
The large-scale conversion of natural habitats to cropland or managed forests will come at the cost of degradation of biodiversity and the ecosystem services it underpins, such as nutrient retention, clean water supply, soil erosion control and ecosystem carbon storage, unless sustainable practices are used to prevent or reduce these losses. Climate-induced changes in the distribution of species and vegetation-types will have important impacts on the services available to people, such as reduced wood harvests and recreation opportunities.
Alleviating pressure from land use changes in the tropics is essential, if the negative impacts of loss of terrestrial biodiversity and associated ecosystem services are to be minimized. This involves a combination of measures, including an increase in productivity from existing crop and pasture lands, reducing post-harvest losses, sustainable forest management and moderating excessive and wasteful meat consumption.
Full account should be taken of the greenhouse gas emissions associated with large-scale conversion of forests and other ecosystems into cropland. This will prevent perverse incentives for the destruction of biodiversity through large-scale deployment of biofuel crops, in the name of climate change mitigation [See Figures 19 and 20]. When emissions from land-use change rather than just energy emissions are factored in, plausible development pathways emerge that tackle climate change without widespread biofuel use. Use of payments for ecosystem services, such as Reducing Emissions from Deforestation and Degradation (REDD) mechanisms may help align the objectives of addressing biodiversity loss and climate change. However, these systems must be carefully designed, as conserving areas of high carbon value will not necessarily conserve areas of high conservation importance - this is being recognized in the development of so-called "REDD-Plus" mechanisms.
Tipping points are most likely to be avoided if climate change mitigation to keep average temperature increases below 2 degrees Celsius is accompanied by action to reduce other factors pushing the ecosystem towards a changed state. For example, in the Amazon it is estimated that keeping deforestation below 20% of the original forest extent will greatly reduce the risk of widespread dieback. As current trends will likely take cumulative deforestation to 20% of the Brazilian Amazon at or near 2020, a programme of significant forest restoration would be a prudent measure to build in a margin of safety. Better forest management options in the Mediterranean, including the greater use of native broad-leaf species in combination with improved spatial planning, could make the region less fire-prone. In the Sahel, better governance, poverty alleviation and assistance with farming techniques will provide alternatives to current cycles of poverty and land degradation.
Avoiding biodiversity loss in terrestrial areas will also involve new approaches to conservation, both inside designated protected areas and beyond their boundaries. In particular, greater attention must be given to the management of biodiversity in human-dominated landscapes, because of the increasingly important role these areas will play as biodiversity corridors as species and communities migrate due to climate change.
There are opportunities for rewilding landscapes from farmland abandonment in some regions - in Europe, for example, about 200 000 square kilometers of land are expected to be freed up by 2050. Ecological restoration and reintroduction of large herbivores and carnivores will be important in creating self-sustaining ecosystems with minimal need for further human intervention.