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38 Impacts of Future Climate Changes Uncertainties in predictions The record of climate-induced change over the last million years indicates that human-caused climate change, if not slowed significantly, will have a major landscape-transforming impact across most of North America and its coastal ocean in the next 100 years and beyond. The lessons from the recent and distant past allow us to picture the likely impacts of future climate changes, but the picture is incomplete for several reasons. First, future climate changes will be unprecedented in many respects. Depending on human actions climate change over the next century may produce a temperature change as large as the difference between full glacial and full interglacial conditions, and with temperatures warmer than Earth has experienced in many millions of years. Second, if “business as usual” practices continue, climate change in coming decades will be exceptionally rapid, much more rapid on a sustained global basis than the transitions into and out of past ice ages. The only global-scale climate changes in Earth’s history that have happened more rapidly are probably those associated with major cataclysms, such as meteor impacts. Third, climate change will occur in a setting where human actions have fundamentally altered terrestrial, aquatic, and marine ecosystems. Land use for farming and forestry has disrupted migration routes for some plants and animals, while improving them for others. Coastal ecosystems are increasingly squeezed between rising oceans and extensive human development along the coasts. Many rivers are dammed, diverted, or polluted. Wild stocks of fish are in many cases seriously depleted by overfishing or by changes in coastal and river habitats. Finally, human actions are very effectively facilitating species movements, both intentionally and unintentionally, making it possible for species that are good at moving to spread around the world, often eliminating native species in their path. Making decisions in spite of uncertainty Although evidence from the recent and distant past is incomplete, we can draw some important lessons. Perhaps the most important is that ecosystem responses to climate change, especially with interacting stresses, are extremely complex. Interactions that were unimportant in one setting may become critical in another. Healthy populations may be ravaged by pathogens that are newly at home in a formerly hostile or resistant environment. And some rare species may surprise us with their tenacity. Strategies for managing ecosystems in the future will need to pay special attention to uncertainty—making the best decisions based on available information and implementing decisions in a way that makes them adjustable as additional information becomes available. Future climate change will affect many aspects of ecosystem composition, structure, and functioning. Some of these will have profound influences on ecosystem services. Others will have effects on the integrity of ecosystems and on their resilience (their ability to cope with future changes). Among all the possible impacts of climate change on ecosystems, the most permanent is extinction. Once a species is lost, it cannot be replaced. Everything that was unique about that species, perhaps its interactions with other species, perhaps its ability to deal with particular kinds of stresses, or perhaps its unique appearance or behavior, is lost forever. When we step back and probe the likely future consequences of human actions in causing climate change, increased extinctions are one of the key impacts. So far the number of known extinctions as a result of climate change is small, but quite a high number of species are currently considered functionally extinct, in other words, they are at risk of going extinct as the climate warms unless

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Impacts of Future Climate Changes 39 we directly intervene (Thomas et al. 2004). For example, species currently living at the top of mountains have no place else to go and will likely become extinct unless we capture them, move them to a more hospitable habitat and monitor them to make sure they survive in the new habitat (Hoegh-Guldberg et al. 2008). Such a response would require money, people power and political will. If a warming of 2-3ºC (3.6-5.4° F) occurs, the Intergovernmental Panel on Climate Change has estimated that about 20 to 30 percent of studied species could risk extinction in the next 100 years. (Fischlin et al. 2007). Given that there are approximately 1.7 million identified species on the globe, an estimated 300,000 to 600,000 species could be committed to extinction primarily due to human activities. An important reason why climate change is expected to have such a major impact on biodiversity is that in most ecosystems climate change is occurring in the context of ongoing pressures from a range of other important factors, including loss of habitat from human land use, overfishing, fertilizer and pesticide runoff, and the encroachment of invasive species (Sala et al. 2000). Indeed, we seem to be standing at the brink of a mass- extinction event, precipitated by the behavior of one species—Homo sapiens. What should we do about these trends? Climate change is undoubtedly one of the defining environmental and development issues of the 21st century. Never before have humans had the numbers and the technology to dramatically alter the climate of Earth at the global scale. Decisions about climate change over the coming decades will likely reverberate through centuries. This document is not intended to make policy recommendations. Rather, it is focused on characterizing some of the changes to ecosystems that have already occurred and that are likely to occur in the future, with different levels of climate change. There is no question that the impacts of climate change on ecosystems become increasingly profound as the magnitude and rate of climate change increases and that disruptions to ecosystem services, including potentially irreplaceable services from biological diversity, become more severe. The challenge is finding a set of policies, practices, and standards of behavior that provide long-term economic opportunities and improved quality of life around the world while maintaining a sustainable climate and viable ecosystems. Some authoritative recent analyses (Stern 2007; IPCC 2007c) conclude that on economic grounds alone, the world should invest in curtailing the amount of climate change that occurs and in adapting to the changes that cannot be avoided. The appropriate level of these investments and the way they are financed and structured are relevant questions for a wide-ranging discussion among all members of society—in communities, businesses, places of worship, schools, and families. Some of the issues are quite technical and can only be effectively addressed at the level of governments. This includes decisions like whether and how best to impose a price on carbon emissions to the atmosphere or the kinds of technological alternatives to fossil fuel energy to receive government subsidies. Other decisions can be best addressed at the individual or family level. Each time a car, home appliance, or light bulb is purchased, a decision is made that has a small influence on the change in climate being driven by human-caused greenhouse gas emissions. But many small decisions, made by billions of people, can combine to have very large effects. As has been illustrated throughout this report, climate change is not the only stress on our ecosystems. So another way that society can help reduce the negative ecological impacts of climate change is by creating conditions that make it easier for species in ecosystems to adapt. For example, the impacts of climate change on natural systems will be less harsh if other stresses on ecosystems that are in fact under human control are reduced. Ocean ecosystems could be

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40 Impacts of Future Climate Changes strengthened by eliminating overfishing, guarding against invasive species, and reducing nutrient runoff. Ocean ecosystems could also be helped by protecting as much habitat and biodiversity as possible in a fashion that is designed to allow movement of species, for example, with networks of marine reserves where no fishing is allowed). Comparable protection on land would include preserves and parks connected by corridors. Carefully considered approaches to and investment in conservation, sustainable agricultural practices, pollution reduction, and water management can all work together to help ecosystems withstand the impact of a changing climate and maintain critical ecosystem services. The climate challenge is big and complex. It is unlikely that it can be solved with any single strategy or by the people of any single country. But very likely it can be abated with the dedicated efforts of millions of people, working hard on diverse strategies, from many different angles.