It is clear that climate change is happening now. The observed climate changes we report are not opinions to be debated, they are facts to be dealt with...This is a dynamic process. We know it is moving rapidly, the sooner we act, the better.

—Dr. Jerry Melillo, Director of the Ecosystems Center at the Marine Biological Laboratory in Woods Hole, Mass, a lead author of the report

The report, which confirms previous evidence that global temperature increases in recent decades have been primarily human-induced, incorporates the latest information on rising temperatures and sea levels; increases in extreme weather events; and other climate-related phenomena. Adding to its practical value in the realm of policy and planning, it is the first such report in almost a decade to break out those impacts by US region and economic sector, and the first to do so in such great detail.

This report demonstrates, provides the concrete scientific information, that climate change is happening now, happening in our own backyard, affecting the kinds of things that people care about. This is science that will inform policymaking—it doesn’t dictate any particular solution.

—Dr. Jane Lubchenco, Under Secretary of Commerce for Oceans & Atmosphere and NOAA Administrator

The report is not intended to direct policy makers to take any one approach over another to mitigate climate change or adapt to it. But it emphasizes that the choices we make now will determine the severity of climate change impacts in the future.

Implementing sizable and sustained reductions in carbon dioxide emissions as soon as possible would significantly reduce the pace and the overall amount of climate change and would be more effective than reductions of the same size initiated later.

—Global Climate Change Impacts in the United States

Findings. The study finds that Americans are already being affected by climate change through extreme weather, drought and wildfire trends and details how the nation’s transportation, agriculture, health, water and energy sectors will be affected in the future. The study also finds that the current trend in the emission of greenhouse gas pollution is significantly above the worst-case scenario that this and other reports have considered.

Among the key findings are:

1. Global warming is unequivocal and primarily human-induced. The emissions responsible for human-induced warming come primarily from the burning of fossil fuels (coal, oil, and gas) with additional contributions from the clearing of forests and agricultural activities.

2. Climate changes are underway in the United States and are projected to grow. These include increases in heavy downpours, rising temperature and sea level, rapidly retreating glaciers, thawing permafrost, lengthening growing seasons, lengthening ice-free seasons in the ocean and on lakes and rivers, earlier snowmelt, and alterations in river flows. These changes are projected to grow.

   US average temperature has increased by about 2º F over the past 50 years, which is more than the global average temperature increase. In the next couple of decades, another degree or so of temperature rise is projected.

3. Widespread climate-related impacts are occurring now and are expected to increase. Climate changes are already affecting water, energy, transportation, agriculture, ecosystems, and health. One example is that warming will be accompanied by decreases in demand for heating energy and increases in demand for cooling energy. The latter will result in significant increases in electricity use and higher peak demand in most regions.

   Another is that energy production and delivery systems are exposed to sea-level rise and extreme weather events in vulnerable regions. Climate change is also likely to affect some renewable energy sources across the nation, such as hydropower production in regions subject to changing patterns of precipitation or snowmelt.

   Sea-level rise and storm surge will increase the risk of major coastal impacts, including both temporary and permanent flooding of airports, roads, rail lines, and tunnels.

   These impacts are different from region to region and will grow under projected climate change.

4. Climate change will stress water resources. Water is an issue in every region, but the nature of the potential impacts varies. Drought, related to reduced precipitation, increased evaporation, and increased water loss from plants, is an important issue in many regions, especially in the West. Floods and water quality problems are likely to be amplified by climate change in most regions. Declines in mountain snowpack are important in the West and Alaska where snowpack provides vital natural water storage.

5. Crop and livestock production will be increasingly challenged. Agriculture is considered one of the sectors most adaptable to changes in climate. However, increased heat, pests, water stress, diseases, and weather extremes will pose adaptation challenges for crop and livestock production.

6. Coastal areas are at increasing risk from sea-level rise and storm surge. Sea-level rise and storm surge place many US coastal areas at increasing risk of erosion and flooding, especially along the Atlantic and Gulf Coasts, Pacific Islands, and parts of Alaska. Energy and transportation infrastructure and other property in coastal areas are very likely to be adversely affected.

7. Threats to human health will increase. Health impacts of climate change are related to heat stress, waterborne diseases, poor air quality, extreme weather events, and diseases transmitted by insects and rodents. Robust public health infrastructure can reduce the potential for negative impacts.

8. Climate change will interact with many social and environmental stresses. Climate change will combine with pollution, population growth, overuse of resources, urbanization, and other social, economic, and environmental stresses to create larger impacts than from any of these factors alone.

9. Thresholds will be crossed, leading to large changes in climate and ecosystems. There are a variety of thresholds in the climate system and ecosystems. These thresholds determine, for example, the presence of sea ice and permafrost, and the survival of species, from fish to insect pests, with implications for society. With further climate change, the crossing of additional thresholds is expected.

10. Future climate change and its impacts depend on choices made today. The amount and rate of future climate change depend primarily on current and future human-caused emissions of heat-trapping gases and airborne particles. Responses involve reducing emissions to limit future warming, and adapting to the changes that are unavoidable.

Resources

• Global Climate Change Impacts in the United States