Advancing the Science of Climate Change (2010) / Chapter Skim
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2 What We Know About Climate Change and Its Interactions with People and Ecosystems
2 What We Know About Climate Change and Its Interactions with People and Ecosystems
Pages 27-82
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From page 27... ...
have synthesized the information specific to the nation, culminating in the report Global Climate Change Impacts in the United States (USGCRP, 2009a)
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The following sections elaborate on these statements and provide a concise, highlevel overview of the current state of scientific knowledge about climate change in 12 critical areas of interest to a broad range of stakeholders: • Changes in the climate system; • Sea level rise and risk in the coastal environment; • Freshwater resources; • Ecosystems, ecosystem services, and biodiversity;
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. The atmospheric concentrations of GHGs have increased over the past two centuries as a result of human activities, especially the burning of the fossil 2 http://www.globalchange.gov/publications/reports/scientific-assessments/us-impacts 3 http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm 4 http://national-academies.org/climatechange/ 5 For additional discussion and references, see Chapter 6 in Part II of the report.
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Earth Is Warming There are many indications -- both direct and indirect -- that the climate system is warming. The most fundamental of these are thermometer measurements, enough of which have been collected over both land and sea to estimate changes in global average surface temperature since the mid- to late 19th century.
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. pendent research teams collect, analyze, and correct for errors and biases in these data (for example, accounting for the "urban heat island" effect and changes in the instruments and methods used to measure ocean surface temperatures)
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The long-term trends in many other types of observations also provide evidence that Earth is warming. For example: • Hot days and nights have become warmer and more frequent; • Cold snaps have become milder and less frequent; • Northern Hemisphere snow cover is decreasing; • Northern Hemisphere sea ice is declining in both extent and average thickness; • Rivers and lakes are freezing later and thawing earlier; • Glaciers and ice caps are melting in many parts of the world (as described in more detail below)
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Improving understanding of natural variability patterns, and determining how they might change with increasing GHG emissions and global temperatures, is an important area of active research (see the end of this section and Chapter 6)
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Detailed worldwide records of fossil fuel consumption indicate that fossil fuel burning currently releases over 30 billion tons of CO2 into the atmosphere every year (Figure 2.3, blue curve)
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Collectively, the total warming associated with GHGs is estimated to be 3.0 Watts per square meter, or almost double the forcing associated with CO2 alone. While CO2 and N2O levels continue to rise (due mainly to fossil fuel burning and agricultural processes, respectively)
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Other human activities can influence local and regional climate but have only a minor influence on global climate. Feedback Processes Determine How the Climate System Responds to Forcing The response of the climate system to GHG increases and other climate forcing agents is strongly influenced by the effects of positive and negative feedback processes in the climate system.
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A variety of methods have been used to estimate climate sensitivity,, which . is typically expressed as the temperature change expected if atmospheric CO2 levels reach twice their preindustrial values and then remain there until the climate system reaches equilibrium, with all other climate forcings neglected.
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-- conclude that much of the observed warming since the start of the 20th century, and most of the warming over the last several decades, can be attributed to human activities. Models and Scenarios Are Used to Estimate Future Climate Change In order to project future changes in the climate system, scientists must first estimate how GHG emissions and other climate forcings (such as aerosols and land use)
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Future climate change, like past climate change, is also subject to natural climate variations that modulate the expected warming trend. After future forcing scenarios are developed, climate models are used to simulate how these changes in GHG emissions and other climate forcing agents will translate into changes in the climate system.
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, relative to the 1980-1999 average, by the end of the 21st century. The wide spread in these numbers comes from uncertainty not only in exactly how much the climate system will warm in response to continued GHG emissions, but also uncertainty in how future GHG emissions will evolve.7 Hence, the choices that human societies make over the next several decades will have an enormous influence on the magnitude of future climate change.
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Many of these changes are discussed below and described in detail in Part II of the report. Abrupt Changes May Occur Confounding all projections of future climate is the possibility of abrupt changes in the climate system, other environmental systems, or human systems.
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However, coastal managers and property owners are concerned about how these risks are being and will be intensified by sea level rise and other climate changes. 9 For additional discussion and references, see Chapter 7 in Part II of the report.
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. Observations of Sea Level Rise Sea level has been systematically measured by tide gauges for more than 100 years.
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Ice in the world's glaciers and ice sheets contributes directly to sea level rise through melt or the flow of ice into the sea. The major ice sheets of Greenland and Antarctica contain the equivalent of 23 and 197 feet (7 and 60 meters)
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Sea level rise can potentially affect all of these activities and their accompanying infrastructure, and it could also magnify other climate changes, such as an increase in the frequency or intensity of storms (see below)
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Coastal ecosystems such as dunes, wetlands, estuaries, seagrass beds, and mangroves provide numerous ecosystem goods and services, ranging from nursery habitat for certain fish and shellfish to habitat for bird, mammal, and reptilian species, including some endangered ones; protective or buffering services for coastal infrastructure against the onslaught of storms; water filtering and flood retention; carbon storage; and the aesthetic, cultural, and economic value of beaches and coastal environments for recreation, tourism, and simple enjoyment. The impact of sea level rise on these and other nonmarket values is often omitted from economic impact assessments of coastal areas because of difficulties in assigning values.
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Research Needs for Advancing Science on Sea Level Rise and Associated Risks in the Coastal Environment While global sea level rise is certain to continue, the physical science of sea level rise and related climate changes remains incomplete, making future projections uncertain. Moreover, social and ecological understanding of place-based vulnerability and adaptation options in coastal regions of the United States is lacking.
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Moreover, snowpack is melting as much as 20 days earlier in many areas of the West. Snow is expected to melt even earlier under projections of future climate change, resulting in streams that have reduced flow and higher temperatures in late summer.
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Storm Patterns and Intensities May Change How storm patterns may change in the future is of obvious importance to water managers, but considerably less is known in this area than in the hydrologic changes discussed above. Changes in the intensity of hurricanes have been documented and attributed to changes in sea surface temperatures, but the link between these changes and climate change remains uncertain and the subject of considerable research and scientific debate.
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However, the complex processes involved in the hydrologic cycle prevent simplistic conclusions about how to manage water supplies based on climate model projections. In many regions, the uncertainties associated with projections of rainfall and runoff coupled with uncertainties in other changes, such as changes in land use and land cover, leads to cascading uncertainties about changes in freshwater resources.
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Significant gaps remain in the knowledge base that informs both projections of climate impacts on water resources and governance strategies that can build adaptive capacity of water systems to climate effects. Key research needs, which are explored in more detail in Chapter 8, include the following: • Improve projections of changes in precipitation and other water resources at regional and seasonal time scales.
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Future Climate Change Will Affect Land-Based Ecosystems in a Variety of Ways Both the amount and rate of warming will influence the ability of plants and animals to adapt. In addition, temperature changes will interact with changes in CO2, precipitation, pests, soil characteristics, and other factors.
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1960-1990 Hadley scenario 2070-2100 Canadian scenario 2070-2100 FIGURE 2.7 Potential changes in the geographic ranges of the dominant forest types in the eastern United States under projections of future climate change. Many forest types shift their ranges northward or shrink in areas, while some expand their areas.
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Changes have also been observed in ocean productivity, which measures the photosynthetic activity of organisms at the base of the marine food web. Model projections suggest that some habitats, such as polar seas and areas with coastal upwelling, may see increases in productivity as climate change progresses.
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If CO2 emissions continue to increase at present rates, ocean acidification could intensify by three to four times this amount by the end of this century. In addition, ocean acidification may reduce the ability of the ocean to take up CO2; this represents a positive feedback on global warming because it would lead to faster CO2 accumulation in the atmosphere.
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. If the balance between CO2 absorption and emissions by ecosystems were to change in response to either future climate changes or changes in management, this could lead to a significant positive or negative feedback on atmospheric CO2 levels.
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Land management practices that reduce deforestation and degradation, or that enhance storage of carbon in land ecosystems, could provide potentially low-cost options to reduce GHG concentrations in the atmosphere and thus limit the magnitude of future climate change. Changes in land use can also influence temperatures by changing the reflective properties of the Earth's surface and by altering rates of transpiration of water.
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Climate change increases the complexity of this challenge because of its multiple impacts on agricultural crops, livestock, and fisheries. Agricultural management may also provide opportunities to reduce net human GHG emissions.
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. However, most analyses and projections of future climate change do not include critical factors such as changes in extreme events (especially intense rainfall and drought)
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Impacts of climate change on aquaculture are not well studied, but ocean acidification and the difficulty of moving aquaculture infrastructure to new locations as fish habitats shift may pose significant challenges to aquaculture production. Science for Adaptation in Agricultural Systems The ability of farmers and the food production, processing, and distribution system to adapt to climate change will to a large extent determine the impacts of climate change on food production.
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Modifying Food Production Systems Could Potentially Help Limit the Magnitude of Future Climate Change Food production systems are not only affected by climate change; they also contribute to it through GHG emissions of CO2, CH4 (primarily from livestock and flooded rice paddies) , and N2O (primarily from fertilizer use)
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• Develop and improve technologies, management strategies, and institutions to reduce GHG emissions from agriculture and fisheries and to enhance adap tation to climate change. PUBLIC HEALTH13 Weather and climate influence the distribution and incidence of a variety of public health outcomes.
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Warming temperatures may also reduce exposure and health impacts associated with cold temperatures, although the extent of any reduction is highly uncertain, and analyses and projections of the impacts of temperature changes on human health are complicated by other factors. In particular, death rates depend on a range of circumstances other than temperature, including housing characteristics and personal behaviors, and these have not been extensively studied in the context of future climate projections.
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Overall, older adults, infants, children, and those with chronic medical conditions tend to be more sensitive to the health impacts of climate change. Susceptibility varies geographically, with the status of public health infrastructure playing a large role in determining vulnerability differences between populations.
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Given their concentration of people, industry, and infrastructure, cities and built environments are expected to face significant direct and indirect impacts from climate change. These include impacts associated with sea level rise because a large number of cities in the United States and worldwide are located in coastal zones.
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Cities and settlements adjacent to fire-prone habitats are projected to confront increasing threats of fire, and desert cities, such as those in the American West, will likely confront water shortages. Potential for Changes in Cities to Limit Future Climate Change As the geographical focus of most production and consumption, cities offer opportunities to reduce GHG emissions in both absolute and per capita terms, while also improving air quality and urban heat island effects.
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GHG emissions can be attributed to the transportation sector, with the overwhelm 15 For additional discussion and references, see Chapter 13 in Part II of the report.
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Limiting Transportation-Related Emissions Reducing the total volume of transportation activity is one way to limit GHG emissions from this sector. The most obvious target for such reductions is the transport of passengers and goods on highways, which is responsible for 75 percent of the energy used in transportation.
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On the other hand, higher Arctic temperatures could provide longer ocean transportation seasons and possibly make a northwest sea route available. Rising sea levels could increase flooding and erosion of transportation infrastructure in coastal areas, and changes in storm patterns could lead to disruptions in transportation services and infrastructure designed for historical climate conditions.
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Research is needed to better understand the nature of these impacts as well as ways to reduce GHG emissions from the transportation sector. Some key research needs, which are explored in further detail in Chapter 13, include the following: • Improve understanding of what controls the volume of transportation activity and what strategies might be available to reduce volume.
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Energy Efficiency Many proposed strategies to limit the magnitude of future climate change focus on increasing energy efficiency, especially in the near term. A substantial body of research backs up the technical potential for large energy efficiency improvements.
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Carbon capture and storage (CCS) technology could be used to remove CO2 from the exhaust gases of power plants fueled by fossil fuels or biomass (as well as exhaust gases from industrial facilities)
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Research Needs for Advancing Science in the Energy Supply and Consumption Sector Because energy is a dominant component of human GHG emissions, major investments are needed in both the public and private sectors to accelerate research, development, and deployment of climate-friendly energy technologies. Research is also needed on behavioral and institutional barriers to adoption of new energy technologies.
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Although few, if any, voices are promoting SRM as a near-term alternative to GHG emissions-reduction strategies, the concept has recently been gaining more serious attention as a possible "backstop" measure, because strategies attempted to date have failed to yield significant emissions reductions, and climate trends may become significantly disruptive or dangerous. Further research is necessary to better understand the physical science of the impacts and feasibility of SRM as well as issues related to governance, ethics, social acceptability, and political feasibility of planetary-scale, intentional manipulation of the climate system.
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FIGURE 2. Various geoengineering options, including both solar radiation management and carbon dioxide removal. For further details see 2.9.pdf Figure 15.1.
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Finally, it should be noted that a major shortcoming of SRM approaches is that, while they have the potential to offset GHG-induced warming of the atmosphere, they would not offset ocean acidification or other impacts of elevated CO2. Governance Issues Due to the global nature of SRM, and especially considering the drawbacks and potential negative impacts, an international framework is needed to govern SRM research, development, and possible deployment.
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Changes in temperature, sea level, precipitation patterns, and other elements of the physical climate system can add substantial stresses to infrastructure and especially to the food, water, energy, and ecosystem resources that societies use. Key concerns regarding the interactions between climate change and security include direct impacts on military operations; potential impacts to regional strategic priorities; causal links between environmental scarcity and conflict; the role of environmental conservation and collaboration in promoting peace; and relationships between environmental quality, resource abundance, and 18 For additional discussion and references, see Chapter 16 in Part II of the report.
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Military Operations Climate change may affect military assets and operations directly: through physical stresses on military systems and personnel, severe weather constraints on operations due to increased frequency and intensity of storms and floods, increased uncertainty about the effects of Arctic ice and ice floes on navigation safety both on and below the ocean surface, or risks to coastal infrastructure due to sea level rise. Climate change is expected to increase heavy rainfalls and floods, droughts, and fires in many parts of the world and could lead to changing storm patterns.
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Research Needs for Advancing Science on National and Human Security Implications of Climate Change Scientific understanding of the national and human security implications of climate change are considerably less well understood than many of the other impacts of climate change. As a result, there are a wide variety of research needs for improving understanding of the relationship between climate change and security, including the following:
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Because climate change is becoming an increasingly important public policy concern in the United States and many other countries, additional research to support climate policy design and implementation is needed. International Policies for Limiting the Magnitude and Adapting to the Impacts of Climate Change At the international level, examples of climate policies include the United Nations Framework Convention on Climate Change, the Kyoto Protocol, and the Copenhagen Accord.
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Constraints to monitoring compliance with and the effectiveness of such policies include lack of adequate and reliable methods for measuring GHG emissions, lack of mechanisms for accurately accounting for GHG emissions and for offsets, and lack of technical capacity to monitor and enforce policies nationally and across international borders. Assessing Benefits and Costs of Climate Action Benefit-cost analyses seek to translate climate change impacts, including lost or gained ecosystem services, into a monetary metric so that they can be compared to estimates of the costs and benefits associated with policies to limit the magnitude or adapt to the impacts of climate change.
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Research Needs Related to Climate Policy Development and Implementation Research needs in this area, explored in further detail in Chapter 17, include the following: • Continue to improve understanding of what leads to the adoption and imple mentation of international agreements on climate and other environmental issues and what mechanisms are most effective at achieving their goals. • Develop and evaluate protocols, institutions, and technologies for monitoring and verifying compliance with international agreements.
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