The 2-degree Fahrenheit increase in global temperatures since the end of the 19th century is largely driven by rising carbon dioxide and other greenhouse gas emissions from human activity, says Institute Director Gavin Schmidt.
The conclusion confirms NASA's well-established finding that man-made emissions are driving climate change, as President Donald Trump and some senior officials often challenge.
In both agencies' actions, the Earth has now recorded its five hottest annual average temperatures over the past five years.
"2018 is once again an extremely hot year on top of a long-term global warming trend," Schmidt said in a press release.
The strongest warming trends occur in the Arctic, where the loss of ice sheets continues to contribute to sea level rise, NASA says. The amount of sea ice covered by sea ice amounted to about 4 million square miles in 2018, the second smallest annual average on record since 1979, NOAA reports.
"The effects of long-term global warming are already being felt – in coastal floods, heat waves, intense rainfall, and ecosystem change," Schmidt said.
In the United States, much of the lower 48 was warmer than average, NOAA reports. The largest divergence from the average occurred west of the Rockies and in the southeast, and 14 states saw annual temperatures among the highest on record.
Arizona topped the list with the second hottest year on record, followed by New Mexico and California with their third and fourth warmest years, respectively. South Dakota and Nebraska were the only two states to record temperatures below the average of the 20th century, the first time since 2014, all states have experienced cooler years.
The United States also experienced its wettest year for 35 years and the third highest rainfall dates back to 1895. National average rainfall was 34.63 inches or 4.69 inches above average.
The nation's $ 1 billion disasters included hurricanes Florence and Michael and Western fires that unfolded over months. These three events amounted to $ 73 billion of the 14 events totaling $ 91 billion in costs. The events together claimed 247 lives.
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