Center of the National Oceanic and Atmospheric Administration (NOAA) said.
Senator Barbara Boxer, chairman of the Environment and Public Works Committee, said that the report should be an eye opener.
"The facts speak for themselves - whether it is NOAA's announcement on Wednesday that 2012 was the hottest year on record or the devastation caused by Superstorm Sandy, predictions of dangerous climate change impacts are coming true before our eyes," she said in a statement.
'We need to focus now on what we must do to address climate change so that we can protect our people, local communities, and the nation's economy," Boxer said.
According to NOAA, 2012 marked the warmest year on record for the contiguous United States with the year consisting of a record warm spring, second warmest summer, fourth warmest winter and a warmer-than-average autumn.
The US Climate Extremes Index indicated that 2012 was the second most extreme year on record for the nation.
The index, which evaluates extremes in temperature and precipitation, as well as land falling tropical cyclones, was nearly twice the average value and second only to 1998, it said.
"To date, 2012 has seen 11 disasters that have reached the $1 billion threshold in losses, to include Sandy, Isaac, and tornado outbreaks experienced in the Great Plains, Texas and Southeast/Ohio Valley," NOAA said.
On the national scale, 2012 started off much warmer than average with the fourth warmest winter (December 2011-February 2012) on record.
Winter warmth limited snow with many locations experiencing near-record low snowfall totals.
The winter snow cover for the contiguous US was the third smallest on record and snowpack totals across the Central and Southern Rockies were less than half of normal, it reported.
NOAA said spring started off exceptionally warm with the warmest March on record, followed by the fourth warmest April and second warmest May.
The season's temperature was 5.2°F above average, making it easily the warmest spring on record, surpassing the previous record by 2.0°F.