u.s. climate has already changed...,

NYTimes |  The effects of human-induced climate change are being felt in every corner of the United States, scientists reported Tuesday, with water growing scarcer in dry regions, torrential rains increasing in wet regions, heat waves becoming more common and more severe, wildfires growing worse, and forests dying under assault from heat-loving insects.

Such sweeping changes have been caused by an average warming of less than 2 degrees Fahrenheit over most land areas of the country in the past century, the scientists found. If greenhouse gases like carbon dioxide and methane continue to escalate at a rapid pace, they said, the warming could conceivably 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 dire warnings about how the effects of global warming that had been long foreseen by climate scientists are already affecting the planet. Its region-by-region documentation of changes occurring in the United States, and of future risks, makes clear that few places will be unscathed — and some, like 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 among Americans about climate change — and thus to build political support for a contentious new climate change regulation that President Obama plans to issue in June.