Climate Change: Think Globally, Assess Regionally, Act Locally

Scientists must develop regional assessments of climate change that are essential to the local policymakers who will have to make the critical decisions about how to respond.

Climate change is here to stay. No matter how effectively governments and the private sector limit greenhouse gas emissions, average global temperatures will rise during the next several decades. Scientists know less well how climate change effects will be manifested regionally. And this information is critical because each region will have to decide how to adapt to change.

The evidence that global warming is already here and that its effect varies by region is strikingly apparent at the poles. Average temperature in the Arctic increased at nearly twice the global rate during the past 100 years, summer sea-ice area has decreased by 7.4% since satellite observations begin in 1978, and buildings and highways are threatened as the permafrost beneath them melts. The Greenland and Antarctic land ice sheets are changing rapidly, which is contributing to sea-level rise.

Change, somewhat less dramatic, is taking place across the globe. Mountain glaciers are retreating, glacial lakes are warming and growing, and spring runoff is occurring earlier. Spring events such as bird arrival and leaf unfolding are occurring earlier, and the summer growing season is lengthening. Plant and animal species are moving poleward or to higher elevations. Forests have increased in many areas but decreased in parts of North America and the Mediterranean basin. Oceanic primary production, the base of the marine food chain, has declined by about 6% in the past three decades, and the acidification of the oceans due to increased capture of carbon dioxide is making the fates of corals and other shelled creatures more precarious.

A sea change in public opinion is also in progress. People no longer focus exclusively on whether humans are responsible for climate change. The more pressing and practical question is how the world can adapt to the inevitable consequences of climate change and mitigate the most undesirable ones. The answers to those questions depend on where one is living.

Not only will climate change affect each community differently, but each community has a unique combination of environmental, economic, and social factors and its own ways of reaching decisions. Each community will have to decide how it can respond, so each needs information about how, when, and where climate change will affect the specific things it cares about. How will citizens know when they need to make decisions, or if they do?

Many of the responses to climate change will be local, and the variety of items that need attention is daunting. Infrastructure resilient to single stresses has been known to fail in a “perfect storm,” where vulnerability and multiple stresses combine. By analogy, localities are subject to social and environmental stresses that change simultaneously at different rates. These effects are often not simply additive; they can interact and reinforce one another in unexpected ways that can lead to potentially disastrous threshold responses or tipping points.

Not only do different multiple stresses interact differently in different places, but the ways in which people make decisions differ as well. Key decisions are made locally about land use, transportation, the built environment, fire management, water quality and availability, and pollution. For perfectly good reasons, local officials focus on the most concrete local trends and most visible social forces, and many of them perceive global warming as distant and relatively abstract.

All too often, local social, economic, political, legal, and cultural forces overshadow the warnings of the international scientific community. Besides, local officials understandably see global warming as an international issue that should be addressed by national and world leaders. And if local leaders were motivated to act, the effects of climate change do not respect jurisdictional boundaries, and they would find it difficult to marshal the necessary information and expertise to craft and harmonize their responses.

For these and other reasons, decision processes become dangerously long and complex. But time has run out for ponderous decisionmaking when every generation will have to adapt to a different climate. The scientific community needs to help by providing local leaders with the specific regional climate information they need to motivate and inform coordinated action.

Challenge of regional assessment

Regional climate differs in complexity and character from global climate. The factors that combine to drive global climate may have a different balance regionally. Today’s global models clearly delineate differences between the responses of oceans and continents and of high-latitude and tropical zones to climate change. A true regional assessment, however, differs from a regionalized global assessment in its spatial specificity; topography and coastal proximity create local climatic and ecological zones that cannot be resolved by contemporary global models, yet must be evaluated to make a regional impact assessment meaningful. Increasing global models’ spatial resolution is helpful but not sufficient; new analytic tools are needed to provide useful regional climate forecasts. Scientists must develop truly regional climate impact models that will help local leaders see what the future holds and understand how actions they can take will make a difference in their region.

Understanding how climate changes at the regional level is only the beginning of the evaluation of the ensuing ecological, economic, and social impacts. The next question to be answered is how climate change affects key natural systems such as watersheds, ecosystems, and coastal zones. Assessing the effect on natural systems is the starting point for assessing impacts on regionally important socioeconomic sectors such as health, agriculture, and infrastructure. For example, agriculture, a managed ecosystem, is subject to multiple environmental stresses: human practices, changes in water availability and quality, and the lengthening of the growing season.

And these human activities then influence local climate. Deforestation, irrigation, and agriculture affect local moisture concentrations and rainfall. The burning of fossil fuels plays a particularly complex role, only one dimension of which is its contribution to overall global warming. Inefficient combustion in poor diesel engines, open cooking fires, and the burning of coal and biomass produce aerosols with organic soots, or “black carbon,” as well as atmospheric brown clouds.

It is vital that scientists understand the complex and varied effects that such pollutant products will have on regional and global climates. Atmospheric brown clouds intercept sunlight in the atmosphere by both absorbing and reflecting it, thus cooling the surface and heating the atmosphere. The reduction in solar radiation at the surface, called dimming, strengthens in the presence of atmospheric moisture because aerosols nucleate more cloud drops, which also reflect radiation back to space. Because dimming cools ocean surface temperatures as well as land, Asian pollution has contributed to the decrease of monsoon rainfall in India and the Sahel. In addition, aerosols are carried from their local sources across entire ocean basins in a few days, and thus they have a global effect; the cooling due to dimming may have counteracted as much as 50% of the surface temperature increase expected from greenhouse warming.

Another powerful reason to undertake regional climate assessments is the impact of climate change on water availability. Global climate models predict that even if the total fresh water circulating in the hydrological system remains the same or even increases, there will be a redistribution of rainfall and snow, with more precipitation at high and equatorial latitudes and drying at mid-latitudes. If only because of redistribution, the study of changing water availability must be regional.

Topography, coastal and mountain proximity, land cover, prevailing storm tracks, and other factors all make regional water climate distinctive. These issues are best addressed on a watershed-by-watershed basis. At mountain altitudes, black carbon heats the air and turns white snow gray, which absorbs more sunlight. These effects are contributing to the melting of the Himalayan snowpack and glaciers, and this melting is, in turn, affecting the river water supply of more than 2 billion people in Asia.

The regional impacts of a change in water availability will depend on factors such as the number and types of ecological provinces, the balance of irrigated and nonirrigated agriculture, the urban/rural population balance, the state of water distribution infrastructure, and regulatory policy.

The decisions to be made will be locally conditioned. How should managed irrigation systems adjust to changes in the timing and volume of spring runoff? Which farmers and crops will be affected? Should farmers change their crop mix? How and when should investments be made in water delivery capacity, agricultural biotechnology, or monitoring systems? Rigorous and detailed regional climate change impact assessments are necessary to answer these questions.

Leading the way

The state of California has been a national and global leader in modeling, assessing, and monitoring potential climate change effects at its regional scale. California, home to extensive scientific expertise and resources, began to study the issues 20 years ago and two years ago committed to biennial formal assessments to identify and quantify effects on its massive water-supply systems, agriculture, health, forestry, electricity demand, and many other aspects of life. The accompanying illustration details findings of the first California assessment, Our Changing Climate, published in 2006. The complete results were published in March 2008 in California at a Crossroads: Climate Science Informing Policy, a special supplement to the journal Climatic Science.

The prediction in Our Changing Climate that the snow cover in the northern Sierra Nevada will decline by 50 to 90% by mid-century is particularly compelling, because California’s Central Valley, the nation’s most productive agricultural region, derives most of its water from rivers with headwaters in these mountains. In addition, northern Sierra water is a major source for the 20 million people living in arid southern California.

Our Changing Climate motivated California’s leaders to enact a series of climate-related measures and to forge cooperative programs with neighboring states and even some countries. This example shows how powerful regional assessments can be, because Californians learned how they will be affected, and this, in turn, motivated political action. Until people can answer the question, “What does it mean for me?,” they are unlikely to develop their own strategies for adaptation.

Since 2000, a multiagency team has monitored a suite of factors, including pollution and management practices as well as climate change, that affect the Sacramento River Delta and its interaction with San Francisco Bay. The Bay-Delta system transports water southward to the Central Valley and southern California. The team’s report, The State of Bay-Delta Science 2008, challenges many conventional assumptions about integrated ecosystem management, argues that the desire to maintain a steady state is misplaced, and suggests that present practices should be replaced by adaptive management based on comprehensive monitoring.

California and other well-equipped regions should translate their knowledge and techniques to other parts of the world. California’s experience in modeling, monitoring, and assessment could be useful to others. And California can continue to blaze the trail by expanding its efforts. For example, extending California’s assessment to include aerosols and black carbon would enable a more rigorous comparison with similar issues in Asia, Africa, and elsewhere. Such efforts should begin by monitoring the effects of black carbon and other aerosols on California’s climate and snowpacks. It also will be important to simulate regional climate change with and without aerosols and to connect the simulations to a variety of (already extant) models that link climate projections to snow and watershed responses to reservoirs and water-supply outcomes.

Although California has for many years actively managed all but one of its major rivers, it is not yet making adequate use of recent scientific research to inform its management decisions. The state’s water policies and practices are based in the experience of the 20th century and need to be adapted to the changing water climate of the 21st century. This process is beginning. The observational and modeling infrastructure that supported Our Changing Climate has already been applied to adaptive management of the state’s water supply and is now being extended to cope with the challenges ahead. California has learned that the capacity to assess and the capacity to manage are intimately related.

Building a mosaic

Global climate models have met the highest standards of scientific rigor, but there is a new need to extend that effort to create a worldwide mosaic of regional impact assessments that link the global assessment process to local decisionmaking.

The effects of climate change will be felt most severely in the developing world. Although developing nations may not always have the capacity to assess regional climate change by themselves, they understand their social, economic, and political environment better than do outsiders. Thus, developing nations should take the lead by inviting developed-world scientists to collaborate with them in conducting regional assessments that can influence local actions.

The world needs a new international framework that encourages and coordinates participatory regional forecasts and links them to the global assessments. Such a framework for collaboration will not only help build assessment capacity in the nations and regions that need it, but will also generate the local knowledge that is a prerequisite for making the response to climate change genuinely global.

Of course, the globe cannot be subdivided neatly into nonoverlapping regions with sharp boundaries, nor will regions be able to restrict themselves to the same geographical area for the different kinds of sectoral assessments they need. Each physical, biological, and human system has a natural spatial configuration that must be respected. The focus therefore should be on developing a complex hierarchical network of loosely connected, self-assembled regional assessments rather than a unitary project.

In moving toward a suitable international framework for regional assessments, it will be useful to examine a number of questions. What lessons can be learned from the regional assessments done to date? How should global and regional assessments relate to one another? Should regional assessment panels be connected to the Intergovernmental Panel on Climate Change, and if so, how? What are good ways for the international community to incubate regionally led assessments? Are there best practices that promote interaction between scientists and decisionmakers? Do these differ regionally? What are good ways to encourage coordination among regional assessments? What standards should regional assessments adhere to? Who should define them? Who should certify compliance? How should assessment technologies be transferred? How should assessment results be disseminated and archived? How can assessments be designed so that assessment infrastructure can be used later in decision support?

Before formal framework discussions can take place, these and other issues will have to be debated in a variety of international and regional forums. These will certainly include the World Meteorological Organization, the Group on Earth Observations, and the United Nations Environment Programme. It is equally critical that discussions be organized in every region of the world and that partnerships among groups from industrialized and developing regions be struck.

It is clear, however, that the world must not wait for the creation of the perfect framework. It is by far preferable to learn by doing. Ideally, the framework will be an emergent property of a network of already active regional assessments that connect global assessments to local decisionmaking.

A good place to start is the critical issue of water. The effects of climate on water must be understood before turning to agriculture and ecosystems. The capacity to model and monitor exists, and it can be translated relatively easily. The path from assessment to decision support to adaptive management has been reasonably well charted. All parties now need to do all they can to launch assessments of the climate/water interface in every region of the world.

Recommended Reading

  • T. P. Barnett, R. Malone, W. Pennell, D. Stammer, B. Semtner, and W. Washington, “The Effects of Climate Change on Water Resources in the West: Introduction and Overview,” Climatic Change 62, no. 6 (2004): 1–11.
  • California at a Crossroads; Climate Change Science Informing Policy” in Climatic Change 87, supplement 1 (2008): 1–322.
  • Intergovernmental Panel on Climate Change (IPCC), The Physical Science Basis (Contribution of Working Group I to the Intergovernmental Panel on Climate Change Fourth Assessment Report, 2007) (available at
  • IPCC, Impacts, Adaptation, and Vulnerability (Contribution of Working Group II to the Intergovernmental Panel on Climate Change Fourth Assessment Report, 2007) (available at
  • G.A. Meehl, W. E. M. Washington, W.D. Collins, J. M. Arblaster, A. Hu, L. E. Buja, W. G. Strand, H. Teng, “How Much More Global Warming and Sea Level Rise?” Science 307 (2005): 1769–1772.
  • Our Changing Climate, Assessing the Risks to California, a summary report from the California Climate Change Center (
  • The State of Bay-Delta Science 2008: Summary for Policymakers and the Public (
  • V. Ramanathan, C. Chung, D. Kim, T. Bettge, L. Buja, J. T. Kiehl , W. M. Washington, Q. Fu , D. R. Sikka , and M. Wild, “Atmospheric Brown Clouds: Impacts on South Asian Climate and Hydrological Cycle,” Proccedings of the National Academy of Sciences of the United States of America 102, no. 15 (2005): 5326–5333 (published online March 4, 2005, 10.1073/pnas.0500656102).
  • V. Ramanathan1 and G. Carmichael, “Global and Regional Climate Changes Due to Black Carbon,” Nature Geoscience 1 (2008): 221–227 (published online March 23, 2008, 10.1038/ngeo156).
  • T. M. L. Wigley, “The Climate Change Commitment,” Science 307 (2005): 1766–1769.

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Cite this Article

Kennel, Charles F. “Climate Change: Think Globally, Assess Regionally, Act Locally.” Issues in Science and Technology 25, no. 2 (Winter 2009).

Vol. XXV, No. 2, Winter 2009