The unusually warm winter, the warmest on record, puts species and crops in danger, with ski resorts suffering from lack of snow and animals unable to hibernate, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

Record temperatures in January helped push up the combined winter temperature, the agency reported. The combined land and ocean temperatures from December to February were 1.3 degrees Fahrenheit above average for the period since record keeping began in 1880.

The report noted that in the Northern Hemisphere the combined land and water temperature was the warmest ever at 1.64 degrees Fahrenheit above average.

"Contributing factors were the long-term trend toward warmer temperatures as well as a moderate El Niño in the Pacific," Jay Lawrimore from the NOAA's National Climatic Data Center told Reuters.

The climatic phenomenon known as El Niño is a periodic warming of the tropical Pacific Ocean. It was particularly strong in January - the warmest January ever - but the ocean surface had since begun to cool.

The researchers cautioned against over-interpreting the new report. "We don't say this winter is evidence of the influence of greenhouse gases," Lawrimore said.

The Washington report comes just over a month after the Intergovernmental Panel on Climate Change said global warming was very likely caused by human actions and is likely to be seen as further evidence for global warming.