updated 12/6/2010 2:46:07 PM ET 2010-12-06T19:46:07

Once more, as they've done each year for two decades, parties to the 193-nation U.N. climate treaty have been meeting to debate what to do about global warming.

The global negotiations have bogged down in part because the U.S. refused to join the 1997 Kyoto Protocol mandating reductions in industrial, transport and agricultural gases blamed for global warming.

The usually cautious U.S. National Academy of Sciences uncharacteristically urged the U.S. government to take action, raising the cost of the use of fossil fuels to rein in usage.

"The longer the nation waits to begin reducing emissions, the harder and more expensive it will likely be to reach any given emissions target," the academy said in a report last May.

"Climate change is occurring, is caused largely by human activities, and poses significant risks for — and in many cases is already affecting — a broad range of human and natural systems," the academy concluded in its report.

Some of those impacts:

TEMPERATURES: Scientists expect the year to end tied with 1998 and 2005 as the hottest on record, after a decade — 2000-2009 — that was the hottest ever.

SEA-LEVEL RISE: The warming ocean is rising at twice the rate of the 20th century, as waters expand from the heat and from the runoff of melting land ice.

GREENLAND: "There is now no doubt that Greenland ice losses have not just increased above past decades, but have accelerated," the U.S. National Oceanic and Atmospheric Administration reports. It says Greenland's capital, Nuuk, has experienced the warmest year on record, and glacier area loss was exceptional, including the breakaway of a 110-square-mile  chunk from the Petermann glacier in the far northwest.

ARCTIC OCEAN: The four greatest summer melts of the Arctic Ocean ice cap have occurred in the past four years, NOAA says. Some experts believe the Arctic summer may be ice-free within this decade.

ACIDIC OCEANS: Excess carbon dioxide absorbed by the oceans is turning them more acid. That will harm coral, oysters and other marine life dependent on carbonate to form shells. British researchers believe changes in the carbonate chemistry of the deep ocean may exceed anything seen in the past 65 million years.

PLANKTON: Worldwide levels of phytoplankton, at the base of the marine food chain, are down 40 percent since the 1950s, Canadian scientists say. Although acidity will also harm plankton, these experts blame warming of the waters for this half-century decline.

CORAL: Likewise, researchers blame warmer waters for the highly damaging bleaching this year of coral reefs in the southern Caribbean Sea and across the Indian Ocean. Bleaching occurs when essential micro-organisms leave the coral, and it often leads to the reef's death.

SPECIES: Scientists long have warned that climate change would accelerate the extinction of species unable to adapt to new conditions. Researchers, in a report in a British Royal Society journal, now say, "There are very strong indications that the current rate of species extinctions far exceeds anything in the fossil record."

AGRICULTURE: Wheat farmers in northern India report — and scientists confirm — that warmer temperatures in recent years have cut sharply into their grain yield, as the crop matures too quickly.

U.S. DROUGHT: As climate zones shift, severe and prolonged drought will afflict much of the western two-thirds of the U.S. by 2030, the U.S. National Center for Atmospheric Research says.

WEATHER DISASTERS: Late in a year when a historic heat wave and wildfires struck Russia, nationwide floods devastated Pakistan and the worst flooding and landslides in decades hit China, the Munich Re reinsurance company said climate change seems to be "the only plausible explanation" for the "exceptionally high" number of weather-related catastrophes.

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