2018 was Earth's fourth-hottest year on record: Report

Earth experienced its fourth-hottest year in 2018 since global temperature records began, according to a report by NASA and the National Oceanic and Atmospheric Administration (NOAA) which found the trend of hotter-than-average annual temperatures continued last year.

Scientists at NASA's Goddard Institute for Space Studies (GISS) here found that global temperatures in 2018 were 0.83 degrees Celsius warmer than 1951 to 1980 mean.

Globally, 2018's temperatures rank behind those of 2016, 2017 and 2015. The past five years are, collectively, the warmest years in the modern record, NASA said in a statement.

NOAA's analysis found 2018 global temperatures were 0.79 degrees Celsius above the 20th-century average.

"2018 is yet again an extremely warm year on top of a long-term global warming trend," said GISS Director Gavin Schmidt.

Since the 1880s, the average global surface temperature has risen about one degree Celsius.

This warming has been driven in large part by increased emissions into the atmosphere of carbon dioxide and other greenhouse gases caused by human activities, according to Schmidt.

Weather dynamics often affect regional temperatures, so not every region on Earth experienced similar amounts of warming.

Warming trends are strongest in the Arctic region, where 2018 saw the continued loss of sea ice, NASA said.

In addition, mass loss from the Greenland and Antarctic ice sheets continued to contribute to sea level rise.

Increasing temperatures can also contribute to longer fire seasons and some extreme weather events, according to Schmidt.

"The impacts of long-term global warming are already being felt -- in coastal flooding, heat waves, intense precipitation and ecosystem change," said Schmidt.

NASA's temperature analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations.

These raw measurements are analysed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heat island effects that could skew the conclusions.

These calculations produce the global average temperature deviations from the baseline period of 1951 to 1980.

Since weather station locations and measurement practices change over time, the interpretation of specific year-to-year global mean temperature differences has some uncertainties.

Taking this into account, NASA estimates that 2018's global mean change is accurate to within 0.1 degrees, with a 95 per cent certainty level.

NOAA scientists used much of the same raw temperature data, but with a different baseline period and different interpolation into the Earth's polar and other data-poor regions.