Climate Change in the Midwest: A Synthesis Report for the National Climate Assessment
The diverse landscapes of the U.S. Midwest, and the natural processes, livelihoods, and infrastructure associated with them, are vulnerable to climate change. This report, pre- pared as a contribution to the Third National Climate Assessment, addresses the poten- tial impacts of climate change on natural systems, human health, and several important economic sectors within the Midwest. Key findings of the report include the following:
- Annual mean temperature in the Midwest has warmed since approximately 1900, with annual precipitation generally increasing from the mid 1930s to present. Increases in both the number of wet days and the frequency of heavy precipitation events contribute to the larger precipitation totals. Climate projec- tions developed from global climate models (GCMs) consistently project warmer temperatures for the region by mid-to-late century. Although the majority of climate projections suggest increased precipitation during winter, there is little agreement on the sign of the projected change for other times of the year. Regardless of season, intensification of high magnitude precipitation events is anticipated.
- During the period 1948-1999, net basin supply within the Lake Superior basin declined in spring but increased in autumn, whereas regional streamflow has increased since approximately 1940. Projections of future Great Lakes water levels and streamflow that have been made over most of the last 25 years, where temperature is used as a proxy for potential evapotranspiration, suggest substantial reductions. However, recent projections that simulate evapotrans- piration using an energy-based approach are inconsistent in terms of the sign (positive or negative) of future streamflow and lake level changes.
- Changes in Great Lakes water levels, regardless of the sign of the projected change, will have a large impact on hydrogeomorphologic features such as beaches and dunes, and will create vulnerabilities for coastal ecosystems, infra- structure, and communities. Lake level fluctuations may disrupt Great Lakes commercial shipping and result in increased channel maintenance costs at Great Lakes ports.
- • Great Lakes surface water temperatures have increased over the past few decades. Continued warming will impact the timing and extent of thermal strati- fication, winter ice cover, and the availability of dissolved oxygen
- The region’s ecosystems are highly vulnerable to the direct impacts of climate change and to climate-related exacerbation of current stressors such as invasive species, pollution, and pests and pathogens. The capacity of many species to adapt is limited by historical and on-going land conversion and fragmentation of habitats. An acceleration in the rate of species declines and extirpations is anticipated, as adjustments to temperature change would necessitate rapid and perhaps unrealistic movement of plant and animal species if they are to main- tain pace with expected shifts in habitat ranges.
- Traditional and modern cultural connections to forest systems likely will be altered by climate change. Changes in the presence and availability of culturally- important species, such as white cedar and paper birch, are anticipated. Addi- tionally, changes in contemporary and iconic forms of forest-based recreation can be expected. Forest ecosystems also may be less likely to provide a consis- tent supply of some forest products, especially if the dominant species in those ecosystems are at the southern edges of their ranges.
- Changes in the variability, timing and amount of growing season precipitation will have a substantial impact on future crop yields and the number of work- able field days, and an increased likelihood of extreme heat events will impact Midwestern meat, milk, and egg production. Perennial crops may be at a greater risk of freeze damage, as flower buds lose hardiness and become sensitive to damaging cold temperatures earlier in spring.
- Flooding along the region’s major rivers, including the Mississippi River, has serious consequences for riverine communities and on transportation. The risk of levee failure during a major riverine flood is a significant regional hazard, as many of the nearly 4,000 linear miles of levees in the region are in poor condition.
- Winter sports, especially those activities that depend on natural snow and ice (e.g., cross country skiing, ice fishing, snowmobiling), will likely be negatively impacted by climate change. Warmer springs and falls will increase the attrac- tiveness of the Midwest for activities such as camping, boating, and golf.
- The region has a number of climate-sensitive diseases or health conditions, and, on balance, adverse health ramifications are anticipated to outweigh beneficial health outcomes. Greater frequency of heat waves, decreased air quality, and greater risk of waterborne disease, especially given the aging municipal water systems in the region, are of concern.
- National and state climate change policies, such as the Clear Air Act, have had a large influence on planning and investment decisions within the region’s energy sector, and continued impacts of these policies on the provision and cost of energy services are anticipated.
The challenge for the Midwest will be to design and implement creative and effective adaptation strategies to reduce the region’s vulnerability to climate change, while capi- talizing on potential co-benefits of mitigation policies.