Climate Change Indicators: Ecosystems
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A Closer Look:
Ecosystems provide humans with food, clean water, and a variety of other services that can be affected by climate change. This chapter looks at some of the ways that climate change affects ecosystems, including changes in wildfires, streams and lakes, bird migration patterns, fish and shellfish populations, and plant growth.
Why does it matter?
Changes in the Earth’s climate can affect ecosystems by altering the water cycle, habitats, animal behavior—such as nesting and migration patterns—and the timing of natural processes such as flower blooms. Changes that disrupt the functioning of ecosystems may increase the risk of harm or even extinction for some species. While wildfires occur naturally, more frequent and more intense fires can significantly disrupt ecosystems, damage property, put people and communities at risk, and create air pollution problems even far away from the source.
While plants and animals have adapted to environmental change for millions of years, the climate changes being experienced now could require adaptation on larger and faster scales than current species have successfully achieved in the past, thus increasing the risk of extinction or severe disruption for many species.
Summary of Key Points
- Wildfires. Since 1983, the United States has had on average 70,000 recorded wildfires per year. The top 10 years with the largest acreage burned since 1983 have all occurred since 2004 with many of the largest increases occurring in western states. The proportion of burned land suffering severe damage each year has ranged from 5 to 22 percent. On average, the peak of the wildfire season in the western United States is occurring earlier.
- Streamflow. Changes in temperature, precipitation, snowpack, and glaciers can affect the rate of streamflow and the timing of peak flow. Over the past 83 years, minimum, maximum, and average flows have changed in many parts of the country—some higher, some lower. Among rivers and streams strongly influenced by snowmelt, peak flow from winter-spring runoff is happening at least five days earlier than it did in the mid-20th century.
- Stream Temperature. Stream temperatures have risen throughout the Chesapeake Bay region—the area of focus for this indicator. From 1960 through 2014, water temperature increased at 79 percent of the stream sites measured in the region. Temperature has risen by an average of 1.2°F across all sites and 2.2°F at the sites where trends were statistically significant.
- Tribal Connection: Trends in Stream Temperature in the Snake River. Between 1960 and 2022, water temperatures increased by 2.2°F in the Snake River at a site on tribal lands in eastern Washington. Several species of salmon use the Snake River to migrate and spawn, and these salmon play an important role in the diet, culture, religion, and economy of the region’s Native Americans.
- Lake Temperature. Since 1985, summer surface water temperatures have increased in 32 of the 34 lakes with long-term records that this indicator tracks across North America. A total of 24 lakes warmed by more than 1°F, and 15 by more than 2°F.
- Great Lakes Water Levels and Temperatures. Water levels in most of the Great Lakes appear to have declined slightly over the last few decades. The past few years, however, have shown notable increases toward the top of the historical range. Water levels in lakes are influenced by water temperature, which affects evaporation rates and ice formation. Since 1995, average surface water temperatures have increased slightly for each of the Great Lakes.
- Bird Wintering Ranges. Some birds shift their range or alter their migration habits to adapt to changes in temperature or other environmental conditions. Long-term studies have found that bird species in North America have shifted their wintering grounds northward by an average of more than 40 miles since 1966, with several species shifting by hundreds of miles. On average, bird species have also moved their wintering grounds farther from the coast, consistent with inland winter temperatures becoming less severe.
- A Closer Look: The Black Guillemots of Cooper Island. Scientists have studied a colony of black guillemots on Cooper Island in northern Alaska for almost 50 years. These birds depend on Arctic sea ice for survival. The number of breeding pairs at Cooper Island reached a peak of more than 200 in the late 1980s, but the number has decreased by more than 80 percent since then.
- Marine Species Distribution. The average center of biomass for 157 marine fish and invertebrate species along U.S. coasts shifted northward by nearly 17 miles between 1989 and 2019. These species also moved an average of 0.6 feet deeper. Shifts have occurred among several economically important fish and shellfish species. For example, American lobster, black sea bass, and red hake in the Northeast have moved northward by an average of 145 miles since the 1970s.
- Leaf and Bloom Dates. Leaf growth and flower blooms are examples of natural events whose timing can be influenced by climate change. Observations of lilacs and honeysuckles in the contiguous 48 states and Alaska suggest that first leaf dates and bloom dates show a great deal of year-to-year variability. In general, leaf and bloom events are happening earlier throughout most of the contiguous 48 states and Alaska but later in much of the South and part of the Upper Midwest.
- Community Connection: Cherry Blossom Bloom Dates in Washington, D.C. Peak bloom dates of the iconic cherry trees in Washington, D.C., recorded since the 1920s, indicate that cherry trees are blooming slightly earlier than in the past. Bloom dates are key to planning the Cherry Blossom Festival, one of the region’s most popular spring attractions.