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Climate change is a pervasive and growing global threat to biodiversity and ecosystem services. However, developing appropriate adaptation plans can be challenging because species, populations, and even entire ecosystems may respond to climatic changes in different ways. This publication, by lead NCASC authors Sarah Weiskopf and Madeleine Rubenstein, NCASC co-author Laura Thompson, and Northeast CASC co-authors Toni Lyn Morelli and Michelle Staudinger, builds upon the 4^th National Climate Assessment to provide a timely review of climate change impacts and ecosystem responses across the country.

Understanding the direction and magnitude of these responses allows researchers to better anticipate environmental changes and adapt as necessary. Weiskopf and her team found that rising temperatures, for instance, have influenced some species to change their behavior, such as altering feeding schedules to make better use of shade. Other species respond to warming climates by changing physically, changing the timing of biological events (i.e. phenology), or shifting their geographic range in order to adapt to new conditions. However, even species that are demonstrating these responses may be adapting too slowly to keep pace with climate change.

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Key ecosystem-level characteristics and properties have also been affected by climate change and often vary regionally. For example, almost all life on Earth relies on primary producers, or organisms with the ability to turn sunlight into energy. These organisms produce oxygen and form the foundation of most food webs. Warming ocean temperatures in tepid seas restricts the circulation of important deep-ocean nutrients thought to stimulate primary production by phytoplankton, microscopic marine organisms responsible for half of all primary production. In contrast, warming climates near frigid oceans reduces sea ice, thereby increasing sunlight availability, fostering growth in phytoplankton populations, and catalyzing primary production in these regions. Variability in species' exposure and responses to climate change are also altering interactions between species, which has the potential to transform ecosystem structure and function. In addition, the duration, magnitude, and frequency of extreme events, including droughts, forest fires, and heatwaves have also been changing, with significant impacts to ecosystems.

Climatic changes can also impact the benefits and services that natural ecosystems provide to society. Although not all effects are negative, even positive changes may require costly societal adjustments. For instance, the impacts of changes in primary production on the aquatic food web will influence the maintenance of sustainable fisheries. The combination of higher nutrients and rising temperatures increases the severity of harmful algal blooms. Furthermore, as climate change alters the ability of ecosystems to provide jobs, recreational opportunities, and restorative experiences, communities will experience declines in mental and physical health. The adaptive capacity of human communities to deal with changes in ecosystem services will partly determine the magnitude of impacts on well-being. Natural resource managers need proactive, flexible adaptation strategies that consider historical and future data to minimize long-term regional impacts, but use of such strategies is still inconsistent across the country.

Findings from this research suggest that managers would benefit from understanding which species are most at risk and why. This can be accomplished through climate change vulnerability assessments that examine species exposure, sensitivity, and adaptive capacity to climate change. Limiting invasive species spread can also help managers maintain biodiversity, ecosystem function, and resilience of regional resources. Restoring habitats to enable wildlife connectivity across the landscape is another adaptation strategy which can lead to the restoration of species populations in some instances. In coastal communities, utilizing natural and nature-based infrastructure (NNBI), which focuses on restoring or creating coastal ecosystems like salt marsh, mangroves, oyster or coral reefs, beaches, and dunes to capitalize on the natural protection from waves and erosion provided by these systems, may be more effective at withstanding extreme events. Finally, switching focus from short-term planning based on historical information to long-term strategies developed using historic and future data from climate model projections may increase both environmental and human system resilience to these climate-induced impacts.

For a copy of this article, please email Sarah Weiskopf at sweiskopf@usgs.gov.