Ecosystem Effects FAQs

Climate change is affecting precipitation patterns around the country. Much of the country is experiencing an increase in the frequency and intensity of heavy precipitation events. Increased temperatures lead to more precipitation falling as rain rather than snow, earlier snowmelt and snowmelt-driven streamflow, and reduced spring snowpack, especially in the Western United States.

For more details, see the following resources:
National Climate Assessment, Chapter 3: Water (NCA 2018)
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC)

Changes in precipitation patterns can impact the timing and amount of runoff and streamflow. More frequent and intense heavy precipitation events can result in flooding and erosion.

Changes in winter precipitation, decreased snow cover, and earlier spring melt times from increased temperatures can also alter the timing of runoff into streams, with larger flows happening earlier in the season, possibly even flooding, followed by lower flows during the hotter growing season. Low flows in summer and fall can lead to water stress for plants, and lower water volume and higher temperatures in streams, which may negatively affect fish populations.

For more details, see the following resources:
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC)
Water Resources (CCRC Topic Page)
Climate Change, Forests, and Water (CCRC Topic Page)
National Climate Assessment, Chapter 3: Water (NCA 2018)

With warmer temperatures and altered precipitation patterns, drought events are increasing in many places around the country, particularly in the Southwestern United States. These changes will likely lead to increased drought frequency and severity. Overall, the range and extent of drought-affected areas are projected to increase.

For more details, see the following resources:
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC education module)
Water Resources (CCRC Topic Page)

More frequent and severe drought events with longer periods of higher temperatures and lower soil moisture, may cause trees and other vegetation to become stressed. Droughts and prolonged dry periods can damage or kill trees during insect outbreaks, because insects thrive on trees already weakened from low water availability. Dead and dying trees increase wildfire risk by temporarily increasing downed and standing fuel, which are especially combustible during droughts.

For more details, see the following resources:
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC education module)
Water Resources (CCRC Topic Page)

Warmer and drier spring and summer conditions are currently associated with more numerous fires, greater fire extent or area burned, and a longer fire season especially in the Western United States. In general, more large and severe fires are expected.

Insect pest outbreaks have increased in the last few decades as temperatures have increased and drier conditions have become more common. Minimum temperatures in winter have been rising across the United States, allowing insect pests to survive in more northern areas and to higher elevations. Temperatures are warm enough for pests to survive over the winter, and pest lifecycles are happening faster.

For more details, see the following resource (CCRC):
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC)
Insect Disturbances (CCRC Topic Page)
Wildland Fire (CCRC Topic Page)
National Climate Assessment, Chapter 6: Forests (NCA 2018)

Longer warm periods have lengthened the growing season, meaning that plants have a longer time to grow, which may increase the productivity of forest and grasslands if the plants have adequate water and nutrients.

Human use of fossil fuels is increasing atmospheric carbon dioxide, and some of this extra carbon dioxide can be used by plants to increase biomass. This is known as “carbon dioxide fertilization.”

As temperature increases and precipitation patterns change, suitable habitats for many plant species will also change. For example, suitable habitat range of some plant species may shift northward or upslope to higher elevations or follow changing moisture conditions. Species growing outside suitable habitats may experience more stress, reductions in productivity, or difficulty regenerating.

These climate changes can also influence invasive plant species establishment and spread. Invasives are nonnative species that are able to establish within native habitats, where they may alter how the ecosystem functions. Invasives can decrease native biodiversity, change the species composition of ecosystems, compete for resources with native species, reduce habitat for some wildlife species, and can affect soil nutrient cycling, water use, and disturbance patterns like wildfire regimes.

For more details, see the following resources:
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC)
National Climate Assessment, Chapter 7: Ecosystems, Ecosystem Services, and Biodiversity (NCA 2018)
Climate Change and Invasive Plants in Forests and Rangelands (CCRC Topic Page)

Temperature increases and changes in precipitation may cause the current habitats of many wildlife species to become unsuitable. These climate changes could shift the ranges and distributions of wildlife species northward, up in elevation, or decrease the amount of suitable habitat.

Higher temperatures and longer growing seasons can affect natural events cued by temperature such as migrations, breeding events, and pollination patterns, causing them to happen earlier than historically observed.

For more details, see the following resources:
Climate Change Effects on Forests and Grasslands: What You Need to Know (CCRC)
Wildlife and Climate Change (CCRC Topic Page)
Biodiversity (CCRC Topic Page)
National Climate Assessment, Chapter 7: Ecosystems, Ecosystem Services, and Biodiversity (NCA 2018)

Plant and animal species responded to historical climate variability by migrating to favorable environments. Wildlife moved to new locations for breeding and home ranges, and vegetation migration took place through seed and pollen transport.

Evolution and genetics also helped plant and animal species become more adapted to new climates over many generations. Genetic mechanisms such as mutation and natural selection allowed species to survive where genetic changes resulted in increased adaptation to new climate conditions.

If species were unable to migrate or if genetic changes were not sufficient for adaptation, then species could have experienced loss of fitness, population extirpation (loss of a population but not entire species), and species extinction as a result of climate change.

The current change in climate is outside of natural historic variability and is happening at a much faster rate. The extent and rate of climate change, combined with habitat fragmentation and land use changes, could affect the ability of plants and animals to respond to current climate changes as they have in the past, through evolution and migration.

For more details, see the following resources:
Landscape Analysis (CCRC Topic Page)
Biodiversity (CCRC Topic Page)