Water is growing scarcer in dry regions. Torrential rains are increasing in wet regions. Heat waves are becoming more common and more severe, and wildfires are getting worse. Forests are dying under assault from heat-loving insects.
Scientists say that there are sweeping changes taking place in our world and that they have been caused by an average warming of less than 2 degrees Fahrenheit over most U.S. land areas in the past century. If greenhouse gases such as carbon dioxide and methane continue to escalate at a rapid pace, they said, the warming could exceed 10 degrees by the end of this century.
Climate change, once considered an issue for a distant future, has moved firmly into the present, the scientists declared in a major new report assessing the situation in the United States.
Summers are longer and hotter, and extended periods of unusual heat last longer than any living American has ever experienced, the report continued. Winters are generally shorter and warmer. Rain comes in heavier downpours. People are seeing changes in the length and severity of seasonal allergies, the plant varieties that thrive in their gardens, and the kinds of birds they see in any particular month in their neighborhoods.
The report is the latest in a series of warnings about global warming. Its region-by-region documentation of changes that are occurring in the United States, and of future risks, indicates that few places will be unscathed and some, such as northerly areas, are feeling the effects at a swifter pace than had been expected.
Alaska in particular is hard-hit. Glaciers and frozen ground in that state are melting, storms are eating away at fragile coastlines no longer protected by winter sea ice, and entire communities are having to flee inland a precursor of the large-scale changes the report foresees for the rest of the United States.
The study, known as the National Climate Assessment, was prepared by a large scientific panel overseen by the government and received final approval at a meeting Tuesday.
The White House, which released the report, wants to maximize its impact to drum up a sense of urgency and build political support for a contentious new climate change regulation that President Barack Obama plans to issue in June.
But instead of giving a Rose Garden speech, Obama spent Tuesday giving interviews to local and national weather broadcasters. The goal was to tell Americans that global warming caused by carbon emissions is linked to the changing conditions in their own backyards.
Speaking to Al Roker of NBC News, in an interview scheduled to be shown Wednesday morning on the Today show, Obama said: This is not some distant problem of the future. This is a problem that is affecting Americans right now. Whether it means increased flooding, greater vulnerability to drought, more severe wildfires all these things are having an impact on Americans as we speak.
In the Northeast, the report found a big increase in torrential rains and risks from a rising sea that could lead to a repeat of the kind of flooding seen in Hurricane Sandy. In the Southwest, the water shortages seen to date are likely just a taste of the changes to come, the report found.
In that region, the report warned, 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 regions most precious resource.
The report did say that in the short run, climate change has helped some in the Midwest, with a longer growing season for crops and a longer shipping season on the Great Lakes.
The new report emphasized that people should not expect global warming to happen at a steady pace, nor at the same rate throughout the country. Bitterly cold winters will continue to occur, the report said, even as they become somewhat less likely.
Warming, too, will vary. While most of the country has warmed sharply over the past century, the Southeast has barely warmed at all, and a section of southern Alabama has even cooled.
The report cited the likely role of global warming in causing an outbreak of mountain pine beetles that has devastated millions of acres of pine forest across the American West and the Canadian province of British Columbia; warmer winters and longer summers have let more of the beetles survive and reproduce at an exponential rate.
And the report warned of severe, long-lasting heat waves. For instance, it cited research saying the type of record-breaking heat that scorched Texas and Oklahoma in 2011 had become substantially more likely because of the human release of greenhouse gases.
On rising sea levels, the new report went beyond warnings issued in September by the United Nations Intergovernmental Panel on Climate Change, which said that by the end of the century, sea levels could rise by as much as 3 feet globally if emissions continue at a rapid pace.
The U.S. scientists said the rise could be anywhere from 1 to 4 feet, and even said that 6 feet could not be ruled out.
Along much of the East Coast, the situation will be worse than the global average because the land there is sinking, scientists claimed.