GENEVA (REUTERS, NYTIMES) - Last year was the Earth's second-hottest since records began, and the world should brace itself for more extreme weather events like the bush fires ravaging much of Australia, the World Meteorological Organisation (WMO) said on Wednesday (Jan 15).
The Geneva-based WMO combined several datasets, including two from the US space administration Nasa and the UK Met Office.
These showed that the average global temperature in 2019 was 1.1 deg C above pre-industrial levels, creeping towards a globally agreed limit after which major changes to life on Earth are expected.
"Unfortunately, we expect to see much extreme weather throughout 2020 and the coming decades, fuelled by record levels of heat-trapping greenhouse gases in the atmosphere," said WMO secretary-general Petteri Taalas.
Australia had its hottest, driest year ever - a precursor to the bush fires.
Scientists say climate change is likely to have contributed to severe weather in 2019 such as a heat wave in Europe and the hurricane that killed at least 50 people when it barrelled through the Bahamas in September.
Governments agreed at the 2015 Paris Accord to cap fossil fuel emissions enough to limit global warming to 1.5 deg C above pre-industrial levels - after which global warming is expected to be so severe that it will all but wipe out the world's coral reefs and most Arctic sea ice.
However, the WMO has previously said that much greater temperature rises - of 3 to 5 deg C - can be expected if nothing is done to stop the rise in harmful emissions, which hit a new record in 2018.
The United States - the world's top historic greenhouse gas emitter and leading oil and gas producer - began the process of withdrawing from the Paris Agreement last year. US President Donald Trump has cast doubt on mainstream climate science.
On a conference call with reporters on Wednesday, however, US scientists said it was clear from the data that greenhouse gas emissions were warming the planet.
"We end up with an attribution of these trends to human activity pretty much at the 100 per cent level... All of the trends are effectively anthropogenic (man-made) at this point," said Dr Gavin Schmidt, director of Nasa's Goddard Institute for Space Studies.
The hottest year on record was 2016, when a recurring weather pattern called El Nino pushed the average surface temperature to 1.2 deg C above pre-industrial levels, the WMO said.
"In the future, we easily can expect warmer El Ninos than the previous ones," said WMO scientist Omar Baddour.
"We can raise a red flag now."
Since the 1960s, each decade has been warmer than the previous one, by significant amounts.
While the 2010s continued this trend, the second half of the decade was especially warm - the five hottest years ever have occurred during that span.
"We've entered a new neighbourhood in the last five years," said Mr Deke Arndt, chief of the monitoring branch of the National Centres for Environmental Information, which conducted separate analysis by the National Oceanic and Atmospheric Administration (NOAA), which also released its findings on Wednesday. NOAA also concluded that 2019 was the second-warmest year ever.
Nasa and NOAA do independent analyses but use most of the same temperature data, which is gathered at sea from ships and buoys and on land from tens of thousands of observing stations coordinated by government meteorological agencies.
This exhaustive data set is then combed for errors and less obvious factors - like the moving of a weather station from one year to the next - that might bias the analysis.
The studies take into account the contribution of natural influences, or forcings, on climate, like volcanic eruptions that can temporarily cool the atmosphere or regular changes in Earth's orbital cycle.
"We end up with a massive discrepancy," Dr Schmidt said. "That tells us the natural forcings are not capable of explaining the trends we've seen since the 19th century.
"These trends are the footprints of human activity stomping on the atmosphere," he said.
As in Australia, extreme heat in southern Africa has contributed to the region's worst drought in decades. Zambia and Zimbabwe are most affected, with millions of people suffering food shortages as production of maize and other grains declined by 30 per cent or more.
The countries' electricity supply is also at risk, as water levels along the Zambezi, one of Africa's major rivers, are exceptionally low. Under normal conditions, Zambia and Zimbabwe each get about half their electricity from separate hydroelectric plants at a dam on the Zambezi.
The reservoir behind the dam is currently at less than 20 per cent of capacity, meaning the plants cannot generate as much power.
In North America, record high temperatures were set across Alaska, including in Anchorage, the largest city.
The Bering Sea, off Alaska's north-west coast, was ice-free for much of last year. Satellite images taken in late March showed largely open water at a time when the sea is normally completely covered in ice.
The lack of ice is thought to have contributed to the increased warming across the state - a positive feedback loop in which warming creates conditions that lead to more warming.
