Biodiversity Futures for the 21st Century
Continuing species extinctions far above the historic rate, loss of habitats and changes in the distribution and abundance of species are projected throughout this century according to all scenarios analyzed for this Outlook. There is a high risk of dramatic biodiversity loss and accompanying degradation of a broad range of ecosystem services if the Earth system is pushed beyond certain thresholds or tipping points. The loss of such services is likely to impact the poor first and most severely, as they tend to be most directly dependent on their immediate environments; but all societies will be impacted. There is greater potential than was recognized in earlier assessments to address both climate change and rising food demand without further widespread loss of habitats.
For the purposes of this Outlook, scientists from a wide range of disciplines came together to identify possible future outcomes for biodiversity change during the rest of the 21st century. The results summarized here are based on a combination of observed trends, models and experiments. They draw upon and compile all previous relevant scenario exercises conducted for the Millennium Ecosystem Assessment, the Global Environment Outlook and earlier editions of the Global Biodiversity Outlook, as well as scenarios being developed for the next assessment report of the Intergovernmental Panel on Climate Change (IPCC). They pay particular attention to the relationship between biodiversity change and its impacts on human societies. In addition to the analysis of existing models and scenarios, a new assessment was carried out of potential "tipping points" that could lead to large, rapid and potentially irreversible changes. The analysis reached four principal conclusions:
✤ Projections of the impact of global change on biodiversity show continuing and often accelerating species extinctions, loss of natural habitat, and changes in the distribution and abundance of species, species groups and biomes over the 21st century.
✤ There are widespread thresholds, amplifying feedbacks and time-lagged effects leading to "tipping points", or abrupt shifts in the state of biodiversity and ecosystems. This makes the impacts of global change on biodiversity hard to predict, difficult to control once they begin, and slow, expensive or impossible to reverse once they have occurred [See Box 21 and Figure 18].
✤ Degradation of the services provided to human societies by functioning ecosystems are often more closely related to changes in the abundance and distribution of dominant or keystone species, rather than to global extinctions; even moderate biodiversity change globally can result in disproportionate changes for some groups of species (for example top predators) that have a strong influence on ecosystem services.
✤ Biodiversity and ecosystem changes could be prevented, significantly reduced or even reversed (while species extinctions cannot be reversed, diversity of ecosystems can be restored) if strong action is applied urgently, comprehensively and appropriately, at international, national and local levels. This action must focus on addressing the direct and indirect factors driving biodiversity loss, and must adapt to changing knowledge and conditions.