'You haven't seen anything yet': Scientists warn of hotter temperatures to come as 2010s named hottest decade ever

Scientists have declared the 2010s the hottest decade since measurements began - inevitably, with nine of the hottest years on record having come since 2010.

And the rate of warming is speeding up.

"If you think you've heard this story before, you haven't seen anything yet," said NASA's Gavin Schmidt. 

NASA and fellow US agency the National Oceanic and Atmospheric Administration (NOAA) this week said 2019 was the second-hottest year worldwide at 14.85C on average - 0.95C hotter than the 20th century average, and 1.16C hotter than the late 19th century, when fossil fuels started to be used in large amounts.

Alaska was more than 3.4C above average, the first time it's ever averaged above freezing, and ice levels in the Arctic and Antarctic were at their second-lowest on record.

"This is going to be part of what we see every year until we stabilise greenhouse gases" from the burning of coal, oil and gas, said Dr Schmidt.

"This shows that what’s happening is persistent, not a fluke due to some weather phenomenon: we know that the long-term trends are being driven by the increasing levels of greenhouse gases in the atmosphere."

2019 was only marginally behind 2016, the hottest year on record thanks to a strong El Nino weather variation, which warmed up the Pacific Ocean. 

Dr Schmidt said it's likely the 2010s were the hottest decade since civilisation began, he and other scientists pouring cold water on hopes warming could be kept below 1.5C, with emissions hitting a new record in 2019. The rate of warming is double now what it was in 1981. 

"Every decade since the 1960s clearly has been warmer than the one before."

Earlier this week scientists said the world's oceans hit new highs in 2019. It's not just melting ice caps that could make sea levels rise, with the oceans themselves undergoing thermal expansion thanks to the heat.

2019 was New Zealand's fourth-warmest year on record, according to the National Institute of Water and Atmospheric's (NIWA) annual climate summary, released last week. Not a single month was below average in temperature.

NASA and NOAA's report matches one released by European scientists last week, which also found 2019 was the second-hottest year on record.

The only year that features in the top 10 hottest-ever that didn't happen in the 2010s was 2005. 2019's entry at number two pushes the hottest year from the 20th century - 1998 - into 11th place.