First half of 2016 warmest on record: NASA

The six-month period from January to June was the planet's warmest half-year on record, and also had the lowest Arctic sea ice extent since satellite records began in 1979, according to  National Aeronautics and Space Administration (NASA).

Two key climate change indicators — global surface temperatures and Arctic sea ice extent — have broken numerous records through the first half of this year, according to the US space agency's analyses of ground-based observations and satellite data.

Each of the first six months of 2016 set a record as the warmest respective month globally in the modern temperature record, which dates to 1880, according to scientists at NASA's Goddard Institute for Space Studies (GISS) in the US.

The six-month period from January to June was also the planet's warmest half-year on record, with an average temperature 1.3 degrees warmer than the late 19th century.

Five of the first six months of this year also set records for the smallest respective monthly Arctic sea ice extent since consistent satellite records began in 1979, according to analyses developed by scientists at NASA's Goddard Space Flight Centre.

The one exception, March, recorded the second smallest extent for that month.

While these two key climate indicators have broken records this year, NASA scientists said it is more significant that global temperature and Arctic sea ice are continuing their decades-long trends of change.

Both trends are ultimately driven by rising concentrations of heat-trapping carbon dioxide and other greenhouse gases in the atmosphere.

The extent of Arctic sea ice at the peak of the summer melt season now typically covers 40 per cent less area than it did in the late 1970s and early 1980s.

Arctic sea ice extent in September, the seasonal low point in the annual cycle, has been declining at a rate of 13.4 per cent per decade.

"While the El Nino event in the tropical Pacific this winter gave a boost to global temperatures from October onwards, it is the underlying trend which is producing these record numbers," GISS Director Gavin Schmidt said.

Previous El Nino events have driven temperatures to what were then record levels, such as in 1998.

However, this year, even as the effects of the recent El Nino taper off, global temperatures have risen well beyond those of 18 years ago because of the overall warming that has taken place in that time.

The global trend in rising temperatures is outpaced by the regional warming in the Arctic, said Walt Meier, a sea ice scientist at NASA Goddard.

"It has been a record year so far for global temperatures, but the record high temperatures in the Arctic over the past six months have been even more extreme," Meier said.

"This warmth as well as unusual weather patterns have led to the record low sea ice extents so far this year," he said.