Maine: An Encyclopedia


Local Climate Changes

Earth’s atmosphere is experiencing unprecedented changes that are modifying global climate. Discussions continue around the world, the nation, and in Maine on how to reduce and eventually eliminate emissions of carbon dioxide (CO2), other greenhouse gases, and other pollutants to the atmosphere, land, and oceans. These efforts are vitally important and urgent. However, even if a coordinated response succeeds in eliminating excess greenhouse gas emissions by the end of the century, something that appears highly unlikely today, climate change will continue, because the elevated levels of CO2 can persist in the atmosphere for thousands of years to come.  (Maine’s Climate Future: An Initial Assessment)

Over the last century, the average temperature in Lewiston, Maine, has increased 3.4°F, and precipitation has decreased by up to 20% in many parts of the state. These past trends may or may not continue into the future.

Maine Climate Divisions from Maine's Climate Future

Maine Climate Divisions from Maine’s Climate Future. Long-term average temperature and precipitation (inches), based on NOAA’s National Climatic Data Center for 1895 through 2007. The divisions span 54%, 31%, and 15% of the state’s total area.

Over the next century, Maine’s climate may change even more. For example, based on projections made by one model, by 2100 temperatures in Maine could increase by 4°F (with a range of 2-8°F), slightly less in spring and fall and slightly more in summer and winter. Precipitation is projected to show little change in spring, increase by 10% in summer and fall (with a range of 5-15%), and increase by 30% in winter (with a range of 10-50%). Other climate models may show different results, especially regarding estimated changes in precipitation.

Currently, the coldest, driest areas are in northwestern Aroostook County at Allagash and Clayton Lake, and in northern Aroostook at Fort Kent and Van Buren.  The wettest location, Acadia National Park on the Downeast coast, is also among the warmest.  (See Degree Days and Normal Precipitation.)

The impacts described in the sections that follow take into account estimates from different models. The amount of precipitation on extreme wet or snowy days in winter is likely to increase. The frequency of extreme hot days in summer would increase because of the general warming trend. Although it is not clear how the severity of storms such as hurricanes might be affected, an increase in the frequency and intensity of winter storms is possible.

Human Health

Higher temperatures and increased frequency of heat waves may increase the number of heat-related deaths and the incidence of heat-related illnesses. Maine, with its occasional heat waves, could be susceptible. The elderly, especially those living alone, are at greatest risk. This study also shows that winter-related deaths will probably be unaffected by climate change in northern New England.

Climate change could increase concentrations of ground-level ozone. For example, high temperatures, strong sunlight, and stable air masses tend to increase urban ozone levels. In New England, a 4°F warming, with no other change in weather or emissions, could increase concentrations of ozone, a major component of smog, by 4%. Currently, ground-level concentrations exceed the national ozone health standard to a moderate extent in Portland and in southern counties along the coast. Ground-level ozone is associated with respiratory illnesses such as asthma, reduced lung function, and respiratory inflammation. Air pollution also is made worse by increases in natural hydrocarbon emissions such as emissions of terpenes by trees and shrubs during hot weather. If a warmed climate causes increased use of air conditioners, air pollutant emissions from power plants also will increase. Respiratory and eye allergies increase in warm, humid conditions.

Warmer temperatures could increase the incidence of Lyme disease and other tick-borne diseases in Maine, because populations of ticks, and their rodent hosts, could increase under warmer temperatures and increased vegetation.

Warmer winters, warmer temperatures, and heavy precipitation also can increase harmful algal blooms, that is, red tides; reduce water quality; and increase outbreaks of cryptosporidiosis and giardia. In addition, warmer seas could contribute to the intensity, duration, and extent of harmful algal blooms in the coastal waters of Maine. These blooms damage habitat and shellfish nurseries and can be toxic to humans.

Coastal Areas

Sea level rise could lead to flooding of low-lying property, loss of coastal wetlands, erosion of beaches, saltwater contamination of drinking water, and decreased longevity of low-lying roads, causeways, and bridges. In addition, sea level rise could increase the vulnerability of coastal areas to storms and associated flooding.

Maine has almost 3,500 miles of tidally influenced shoreline, consisting of rocky peninsulas and harbors, pocket beaches, islands, and complex estuaries. Because of the steep profile that is characteristic of the Maine coastline and a lack of low-lying land to be colonized by new marshes, there is likely to be a net loss of marshes in Maine under accelerated sea level rise.

At Rockland, sea level already is rising by 3.9 inches per century, and it is likely to rise another 14 inches by 2100. The rocky substrate of Maine may slow erosion due to sea level rise, and could complement efforts to protect the coastline. Possible responses to sea level rise include building walls to hold back the sea, allowing the sea to advance and adapting to it, and raising the land (e.g., by replenishing beach sand, elevating houses and infrastructure). Each of these responses will be costly.


The mix of crop and livestock production in a state is influenced by climatic conditions and water availability. As climate warms, production patterns could shift northward. Increases in climate variability could make adaptation by farmers more difficult. Warmer climates and less soil moisture due to increased evaporation may increase the need for irrigation. However, these same conditions could decrease water supplies, which also may be needed by natural ecosystems, urban populations, industry, and other users.

Understandably, most studies have not fully accounted for changes in climate variability, water availability, crop pests, changes in air pollution such as ozone, and adaptation by farmers to changing climate. Including these factors could change modeling results substantially. Analyses that assume changes in average climate and effective adaptation by farmers suggest that aggregate U.S. food production would not be harmed, although there may be significant regional changes.

In Maine, production agriculture is a $500 million annual industry, half of which comes from crops and the other half from livestock, mainly poultry and dairy. Very few of the farmed acres are irrigated.

The major crops in the state are potatoes and hay. Climate change could reduce potato yields by 2-23%. Hay and pasture yields could fall by as much as 39% as temperatures rise beyond the tolerance level of the crop. Estimated changes in yield vary, depending on whether land is irrigated. It is possible that Maine farmers could alter their cropping practices to take advantage of longer growing seasons and thus limit income losses due to reductions in hay and potato yields.

Water Resources

A warmer climate would lead to an earlier spring snowmelt, and earlier “ice out” dates on lakes, resulting in higher streamflows in winter and spring and lower streamflows in summer and fall. Warmer summer temperatures and longer summers could exacerbate water quality problems in rivers such as the Androscoggin, where industry is significant and pollution has traditionally been a problem. Warmer water temperatures also reduce dissolved oxygen levels, adversely affecting fish habitat, and lower summer streamflows could reduce the ability of rivers to assimilate waste.

With more intense rainfall, increased flooding is possible, particularly in steep headwater areas and along well-developed floodplains. Greater and more intense rainfall could also increase erosion in agricultural and timber-harvesting areas, resulting in deposition of sediment in lakes and streams. Less rainfall, particularly during the summer, could reduce streamflow, lake levels, and groundwater levels. Streamflow reduction and warmer temperatures would reduce habitat for cold water fish. This could reduce water supplies in areas such as southwestern coastal Maine, which is experiencing growing water demands due to population growth and increased tourism.


Trees and forests are adapted to specific climate conditions, and as climate warms, forests will change. These changes could include changes in species composition, geographic range, and health and productivity. If conditions also become substantially drier, the current range of forests could be reduced and replaced by grasslands and pasture. Even a warmer and wetter climate could lead to changes; trees that are better adapted to warmer conditions, such as oak, hickory, and pines, would prevail. Under these conditions, forests could become more dense. These changes could occur during the lifetimes of today’s children, particularly if the change is accelerated by other stresses such as fire, pests, and diseases. Some of these stresses would themselves be worsened by a warmer and drier climate.

Although the extent of forested areas in Maine could change little because of climate change, a warmer climate could change the character of those forests. Maple-dominated hardwood forests could give way to forests dominated by oaks and conifers, species more tolerant of higher temperatures, especially along the coast. This change would diminish the brilliant autumn foliage as the number of maple trees declines. The spruce-fir forests in Maine (and other New England states) are near the southern limit of their extent. These forests are sensitive to climatic stresses and have experienced significant declines in recent decades. Across the state, as much as 35-60% of the hardwood forests could be replaced by warmer-climate forests with a mix of pines and hardwoods and, in some areas in the southeast, by grassland and pasture. The extent and density of the spruce and fir forests at higher altitudes, which support a large variety of songbirds, also could be reduced by as much as 40-50%.


The state of Maine is blanketed by northern hardwood/pine forests in the south and a mosaic of hardwood/spruce and higher elevation spruce-fir forests in the north and east. Maine’s aquatic resources include the St. John River, a section of which is the longest free-flowing river segment in the northeastern United States and home to over 30 species of rare plants, including the endangered Furbish’s lousewort. The state’s long coastline harbors estuarine barrier islands and marshes that provide habitat for endangered species such as bald eagles, peregrine falcons, piping plovers, and roseate terns.

The conifer forests found in higher elevations in the White Mountains could be especially vulnerable to climate change. Climate change could hasten the expansion of broad-leaved forests into these pine forests, a transition that is already taking place as a result of selective and intensive logging. The ranges of spruce grouse, gray jays, boreal chickadees, snowshoe hares, marten, and moose could be affected by reduced pine forests and shifts in forest types. The already high threat of insect pest outbreaks in the northern forest could be exacerbated by warming-induced changes in the timing of spring frosts. If precipitation and runoff increase, the increased flooding of sensitive riparian areas could destroy valuable and unique aquatic and riverine habitats. Similarly, sensitive coastal ecosystems could be damaged by increased tidal flooding associated with increases in severe storms.

From Climate Change and Maine (80K; publication EPA 236-F-98-007k), which is available in Adobe Acrobat (pdf) format.

Additional resources

Fobes, Charles Bartlett. Climatic Divisions of Maine. Orono [University of Maine]. 1946. (Orono, Me. University Press)

Lincoln, Benjamin, 1733-1810. Observations on the Climate, Soil and Value of the Eastern Counties, in the District of Maine: written in the year 1789 . . . .[Maine] 196-?. [Orono. University of Maine. Raymond H. Fogler Library. Special Collections.]

Maine’s Climate Future: An Initial Assessment. Orono, Me. The University of Maine. 2009.

McMahon, Janet. The Biophysical Regions of Maine: Patterns in the Landscape and Vegetation. Orono, Me. 1990 (Thesis (M.S.) in Botany and Plant Pathology–University of Maine, 1990.) [Orono. University of Maine. Raymond H. Fogler Library. Special Collections.]

Perley, Sidney. Historic Storms of New England. Beverly, Massachusetts: Memoirs Unlimited. 2001. (Originally published in 1891)

Stoddard, Michael D. Climate Change Roadmap for New England and Eastern Canada. Rockport, ME. Environment Northeast. c2006.

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