Bringing Climate Change Home: New Assessment of U.S. Climate Impacts

The world is a big place, and when a group called the “Intergovernmental Panel on Climate Change” puts out a report on the global effects of climate warming, a natural question is: “So, what does this mean for me?” This week brings us an answer, in the form of the no less ambitious but decidedly more local “National Climate Assessment.”

Thirteen federal agencies and over 300 authors teamed up to produce the Third National Climate Assessment (NCA), as mandated by a 1990 law called the Global Change Research Act. While its methodologies and conclusions are similar to that of the IPCC’s work, it also comes with an important difference, namely, its focus is entirely on what the warming climate means for the United States. Even more importantly, the NCA delivers its information in a manner more relevant to American decision-makers, by breaking its results down by region and by sector (agriculture, infrastructure, health, etc.)

Climate change is affecting the migration patterns of migratory birds like these red knots, shown here in Delaware Bay.

The NCA is pretty blunt in its main findings: “Global climate is changing and this change is apparent across a wide range of observations. The global warming of the past 50 years is primarily due to human activities. Global climate is projected to continue to change over this century and beyond. The magnitude of climate change beyond the next few decades depends primarily on the amount of heat-trapping gases emitted globally, and how sensitive the Earth’s climate is to those emissions.”

Some of the NCA’s a key findings include important warnings about the effect of climate change on ecosystems and biodiversity: “In addition to climate changes that directly affect habitats, events such as droughts, floods, wildfires, and pest outbreaks associated with climate change are already disrupting ecosystem structures and functions in a variety of direct and indirect ways. These changes limit the capacity of ecosystems such as forests, barrier beaches, and coastal- and freshwater- wetlands to adapt and continue to play important roles in reducing the impacts of these extreme events on infrastructure, human communities, and other valued resources.”

In particular, the NCA found that:

1. “Climate change impacts on ecosystems reduce their ability to improve water quality and regulate water flows.”  Warmer air and water temperatures, changing precipitation patterns and decreased snowpack all exacerbate water pollution problems—resulting in higher levels of nutrients that lead to toxic algal blooms and pathogen outbreaks, and lower levels of oxygen. The result could be loss of aquatic ecosystems and species, like the iconic trout streams of the West.

2. “Climate change, combined with other stressors, is overwhelming the capacity of ecosystems to buffer the impacts from extreme events like fires, floods, and storms.” For instance, as rising sea levels chip away at coastal salt marshes, mangroves and barrier islands, communities inland become more vulnerable to hurricanes and other storms. And stress to forests from heat, drought and insect outbreaks means that houses near the urban-wildland interface are more at risk from major fires.

3. “Landscapes and seascapes are changing rapidly, and species, including many iconic species, may disappear from regions where they have been prevalent or become extinct, changing some regions so much that their mix of plant and animal life will become almost unrecognizable.”  From wildfires burning on previously frozen Arctic tundra, to species shifting their ranges northward and upward, to a proliferation of invasive species, our ecological communities are changing, and fast. If species and communities can’t keep pace with the rate of change, species declines and even extinctions will result.

Climate change can create mismatches between the emergence of pollinators like honeybees and the flowers they depend on. This could have serious consequences for both bees and flowers, which need the bees to fertilize them.

4. “Timing of critical biological events, such as spring bud burst, emergence from overwintering, and the start of migrations, has shifted, leading to important impacts on species and habitats.” In many places, the signs of spring are coming earlier—the budding of trees, blossoming of flowers, or the emergence of animals from migration. Since some aspects of life cycles are governed by day length and others by temperature, the shifting of some temperature-governed spring events earlier may lead to “mismatches” between predators and prey, or flower and pollinator, that could negatively affect survival.

5. “Whole system management is often more effective than focusing on one species at a time, and can help reduce the harm to wildlife, natural assets, and human well-being that climate disruption might cause.” Key to protecting both wildlife and human communities will be a suite of approaches, like being ready to respond to new threats, and protection and restoration of ecosystems, especially coastal and riparian habitats and corridors for species movement.

Communities, wildlife managers, and other decision-makers need accurate, relevant, local-scale information in order to make the right choices to reduce our vulnerability to climate change. The National Climate Assessment is the tool that many have been waiting for.

Aimee Delach, Senior Policy Analyst, Climate Adaptation