Temperatures have risen about 3°F in Maine since the beginning of the 20th century. Winter temperatures have been increasing about twice as fast as summer temperatures. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.
Precipitation has increased during the last century. Increases in the frequency and intensity of extreme precipitation events have already occurred and are projected to continue.
Sea level at Portland has risen by about 8 inches since 1912. It is projected to rise another 1 to 4 feet by 2100.
Maine is located on the eastern margin of the North American continent. Its northerly latitude and geographic location exposes the state to both the moderating and moistening influence of the Atlantic Ocean, as well as the effects of the hot and cold air masses from the interior of the continent. Also, Maine is located within the primary storm track of the mid-latitudes. Maines climate is characterized by cold, snowy winters and mild summers. Mean annual winter temperatures range from 25°F in the far south to less than 15°F in the northern and interior portions of the state. Mean annual summer temperatures range from near 60°F in the far north to near 70°F in the south. Maine is approximately 90% forested with over 3500 miles of coastline, making forestry, seafood, hunting and fishing, tourism and ecosystem services all sensitive to a changing climate.
Temperatures in Maine have increased nearly 3°F since the beginning of the 20th century (Figure 1). Since the mid-1990s, the amount of winter warming has been approximately twice that of summer warming, with record high temperatures occurring in the last five years (2010–2014) (Figure 2a). The winter warming is reflected in a below average number of very cold nights (nights with minimum temperatures below 0°F) (Figure 3) over the last two decades (1995–2014). However, there has not been an increase in the occurrence of hot days (days with maximum temperature above 90°F) (Figure 2b). Winter warming has resulted in earlier ice-out dates on lakes. On Damariscotta Lake, the average ice-out date has changed from mid to late April in the early and middle part of the 20th century to early April now. The growing season has lengthened.
Mean annual precipitation in Maine has exhibited historically high values over the last 10 years (2005 to 2014) (Figure 2c). In the harsh winter months, average accumulated snowfall ranges between 10 and 80 inches from the Southern Interior to the Northern climate division, with the northern tip of the state receiving up to 125 inches. The number of extreme precipitation events (number of days with more than 2 inches) has been variable over the period of record, but the last decade (2005–2014) has seen a record number of such events (double the long-term average, Figure 4), similar to the rest of the northeastern United States. The estimated magnitude of the 24-hr, 100-year rainstorm has increased since 1961 (Fig. 2d), in some areas by more than 20%.
Heat waves and cold waves, droughts and severe rainstorms, nor’easters, ice storms, and tornadoes are all part of Maine’s normal climate. In general, nor’easters cause more disruption than any other type of extreme weather in Maine. Nor’easters are cold-season coastal storms that can generate a tremendous amount of precipitation (in the form of snow, sleet, or freezing rain), strong winds, coastal flooding, and damage to infrastructure. Wind speeds from nor’easters are commonly equal to or greater than wind speeds observed in hurricanes that have reached Maine. Nor’easters are prevalent in most years in winter, spring, and fall, while a landfalling hurricane is very rare. Since 1861, only three hurricanes have reached Maine with hurricane force winds, the last being Gloria in 1985. Since 2007, weather-related disasters have been declared in every county in Maine.
Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a lower pathway of greenhouse gas concentrations, temperatures are generally projected to exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records (Figure 1). The intensity of cold waves is projected to decrease while greater intensity of heat waves may increase the importance of such events in this normally moderate summer climate.
Annual mean precipitation is projected to increase most likely in the winter and spring (Figure 5). Maine is part of a large area in the higher mid-latitudes projected to see increases in precipitation, as well as increases in extreme precipitation events. An increase in the frequency of extreme precipitation events may also result in increased flooding risks and the degradation of surface water quality as greater runoff from more intense storms carries pollutants into freshwater resources.
Sea surface temperatures in the coastal waters of Maine have increased almost 2°F since 1970, and the rate of sea level rise has accelerated. The Gulf of Maine has warmed more than other coastal waters of the United States. Tide gauge records in Portland, show a sea level rise of approximately 8 inches since 1912. Changes in ocean and atmospheric circulation have caused temporary destructive increases in sea level, such as the 6-inch rise along the Maine coast in 2010. Global sea level is projected to rise another 1 to 4 feet by 2100 as a result of both past and future greenhouse gas emissions from human activities (Figure 6), with greater rises along the Maine coast possible. Future projections of sea level rise show that some coastal cities and towns in Maine stand to lose up to 30% of their land area. Sea level rise has caused an increase in tidal floods, a rise in water level above the minor flooding threshold (determined locally by NOAA’s National Weather Service) to cause nuisance flooding. Nuisance flooding has increased in all U.S. coastal areas, with more rapid increases along the East and Gulf Coasts. These floods can damage infrastructure, cause road closures, and overwhelm storm drains. Nuisance flooding events in Maine are likely to occur more frequently as global and local sea levels continue to rise.