Last year was hottest on record globally - NASA
Last year's global average temperature was the hottest ever by the widest margin on record, two US government agencies say.
Data from NASA and the National Oceanic and Atmospheric Administration showed that in 2015, the average temperature across global land and ocean surfaces was 0.90°C above the 20th century average, surpassing 2014's previous record by 0.16 degrees.
During the final month, the December combined global land and ocean average surface temperature was the highest on record for any month in the 136-year record.
This was the fourth time a global temperature record had been set this century, the agencies said in a summary of their annual report.
"2015 was remarkable even in the context of the larger, long-term warming trend," said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies.
The sharp increase in 2015 was driven in part by El Nino, a natural weather cycle in the Pacific that warms the ocean surface every two to seven years. But scientists say human activities - notably burning fossil fuels - were the main driver behind the rise.
"We would not have seen the record warming without the long-term trend," said Mr Schmidt.
The latest El Nino started in late 2015 and will last until spring 2016. It is among the strongest ever recorded but Mr Schmidt and others said the weather phenomenon played just a supporting role in the earth's temperature rise.
The 2015 data underscores the urgency of cutting greenhouse gas emissions if the world is to hold temperature increases to well below 2°C, the target agreed to by more than 190 countries at climate talks in Paris last December.
Mr Schmidt said the fact that the world was now halfway to the UN goal has led many scientists to argue that even that target is too high and more stringent goals are needed.
NASA scientist Compton Tucker told RNZ the record breaking temperatures made it impossible to deny climate change. "We're starting to see the death of climate change denial ... the evidence is overwhelming," he said.
New Zealand climate scientist James Renwick said the rise in average temperature may not sound like a large difference, but in fact is a surprising increase.
"When you're looking at global average temperatures averaged over a whole year they don't change much, and normally the new record is four or five hundreths of a degree larger than the previous.
"This [is] twice the size of any previous jump and I think it's a real wake up call for anyone who's not sure about what's going on."
Leaders from around the world last month in Paris pledged to keep warming below 2°, and Dr Renwick said with the rate of warming the world was now experiencing "temperatures could go up by another half a degree in only another 30 years or so, so we really have to get on top of greenhouse gas emissions."
He said the global economy was built on fossil fuels and that could not be changed overnight.
"There are very rapid changed changes in renewable technologies, electric vehicles and so on and that's great, but to really change the direction of the global economy in terms of how energy's produced is a big ask and it will take time.
"The thing is, we really need to start."
Dr Renwick said New Zealand's emissions profile was unusual, with almost half coming from the agricultural sector, but the biggest growth areas for emissions came from the transport and energy sectors.
"We could make big moves there, if it was possible for the Government to incentivise the introduction of electric vehicles, to invest in public transport rather than building roads, just to move the economy, putting a price on carbon that would really help market mechanisms to move things in the right direction."
- RNZ / Reuters
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