"The start of 2018 has continued where 2017 left off – with extreme weather claiming lives and destroying livelihoods"

* 2015-17 were warmest years on record - UN weather agency

* Weather extremes extend into 2018 from Arctic to Australia

By Alister Doyle

OSLO, March 22 (Reuters) - The past three years were the hottest on record and heat waves in Australia, freak Arctic warmth and water shortages in Cape Town are extending harmful weather extremes in 2018, the United Nations said on Thursday.

Atlantic hurricanes and monsoon floods in India contributed to make 2017 the most costly year on record for severe weather and climate events, the U.N.'s World Meteorological Organisation (WMO) wrote in its annual report on the global climate.

"The start of 2018 has continued where 2017 left off – with extreme weather claiming lives and destroying livelihoods," WMO Secretary-General Petteri Taalas wrote in the report.

The study confirmed a provisional finding that 2016 was the warmest year in records dating back to the 19th century, with 2017 and 2015 tied for second place in a warming trend the WMO blames on man-made emissions of greenhouse gases.

Last year was the hottest year without an extra boost from an El Nino event that releases heat from the Pacific Ocean.

Talaas said unusually high temperatures in the Arctic in 2018 contrasted with bitter winter storms in Europe and North America.

Also so far in 2018, "Australia and Argentina suffered extreme heat waves, whilst drought continued in Kenya and Somalia, and the South African city of Cape Town struggled with acute water shortages," he said.

The report said that German reinsurer Munich Re estimated total disaster losses from weather and climate-related events in 2017 at $320 billion, a record after adjustment for inflation.

In 2015, almost 200 nations agreed to shift the global economy away from fossil fuels this century as part of the Paris climate agreement.

U.S. President Donald Trump, who doubts that man-made greenhouse gas emissions are the prime cause of warming, has said he will withdraw from the pact, and instead promote domestic coal, gas and oil.

The WMO said that levels of carbon dioxide were now above 400 parts per million of the atmosphere - far above natural variations in the past 800,000 years and backing up mainstream scientific findings that mankind is the cause.

Carbon dioxide "will remain above that level for generations to come, committing our planet to a warmer future, with more weather, climate and water extremes," Talaas said. (Reporting By Alister Doyle, editing by Pritha Sarkar)

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