U.S. Climate Change Moving from Future into Present

May 2014

By Silke Schmidt

This month saw the publication of the third National Climate Assessment report, a combined effort by a large committee of scientists overseen by the federal government. Its scope is similar to that of the United Nations’ Intergovernmental Panel on Climate Change (IPCC), but it focuses on the scientific evidence for, and already visible consequences of, human-induced climate change in the United States.

Temperature Changes Across the United States. Source: National Climatic Data Center.
Temperature Changes Across the United States: 1991-2012 average temperature compared with 1901-1960 average. Source: National Climatic Data Center.

Compared to the previous two reports, this year’s is “by far the most urgent in tone”, according to New York Times reporter Justin Gillis. In the words of the scientists who co-authored the report, “climate change, once considered an issue for a distant future, has moved firmly into the present.”

Following the report’s release on May 6, 2014, President Barack Obama gave a series of interviews to local and national weather broadcasters; opinion polls indicate that they are among the most trusted sources of information in the country. The President made an effort to connect global warming as a problem affecting the entire planet to specific, well-documented consequences at the regional level.

In the Northeast, the already observed increase in the frequency of torrential rains was particularly striking: over the past half-century, the report found that the proportion of precipitation that is falling as very heavy rain increased by 71 percent in the Northeast, compared to 37 percent in the Midwest and 27 percent in the South. Examples of the devastation caused by such floods include Nashville in 2010, Colorado in 2013 , the Florida Panhandle earlier this year, and, worse yet, the flooding caused by Hurricane Sandy in 2012 . Heavy rains are more likely when a warmer ocean surface produces more evaporating water, and a warmer atmosphere has a greater ability to hold this excess vapor, until it is eventually released in a torrential downpour.

In the Midwest, an initial benefit from climate change may manifest itself in the form of longer growing seasons; however, in the long term, this benefit will be outweighed by crop damage due to more frequent extreme weather events, resulting in decreased agricultural productivity. In the Great Lakes, climate change will exacerbate already existing problems with invasive fish species, harmful algae blooms, and declining beach health.

In the Southwest, extreme weather will bring about more dramatic and prolonged water shortages. According to the report, “severe and sustained drought will stress water sources, already overutilized in many areas, forcing increasing competition among farmers, energy producers, urban dwellers and plant and animal life for the region’s most precious resource.”

In the American and Canadian Northwest, insects and wildfires will be among the most pressing problems. An outbreak of mountain pine beetles that began in 1996 has already devastated millions of acres of pine forest in that part of the country. The beetles benefit from warmer winters and longer summers, which allow them to reproduce at exponential rates. With the beetles killing huge numbers of trees, a forest is essentially converted from a net carbon sink to a net carbon source. The increasing frequency of wildfires has two particularly dire consequences: additional tree loss, and shortfalls in the budgets for fighting the fires.

At the other side of the country, the entire East Coast will have to deal with sea levels rising at a rate that is likely to exceed the global average published by the United Nations’ IPCC last September. While global sea levels are predicted to rise up to three feet by the end of the century, the number could be as high as five or six feet along the East Coast, because some degree of land sinking is going on all the way from southern Maine to northern Florida.

In Alaska, climate change is already being felt intensely through its effect on glaciers and winter sea ice. Fragile coastlines that used to be protected by sea ice are increasingly exposed to hurricane-force winter storms. This has already caused the displacement of several Alaska Native communities, who have to flee inland from their coastal villages. The most pressing climate change concerns and challenges for Hawaii and the Pacific Islands include damage to coral reefs, decreasing freshwater supplies, and greater stress on native marine and land-based ecosystems.

The wide variation in the impact of climate change across the U.S. illustrates an important point for Americans to remember: global warming does not happen at a steady pace throughout the country. Exceptions to the overall trend, such as the brutally cold winter of 2013/14 in much of the Midwest, should not be interpreted as evidence that climate change is not real.

The report emphasized the need for the U.S. to move forward with comprehensive climate legislation: efforts toward greenhouse gas emission reductions at the level of individual states and cities were considered a step in the right direction, but ultimately inadequate. According to the scientists, “harm to the nation will increase substantially in the future unless global emissions of heat-trapping gases are greatly reduced.”

The U.S. National Climate Assessment has been released in an interactive, mobile-device-friendly, digital format that can be found here. The full report, or individual chapters, can be downloaded here.


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