Global temperatures could rise by 3-5 degrees Celsius (5.4-9.0 degrees Fahrenheit) in the next eight decades if greenhouse gas concentrations in the atmosphere increase at the current rate, the UN's World Meteorological Organization (WMO) said on Thursday.

In the WMO's annual statement on the state of the climate, Secretary-General Petteri Taalas said that the rise would be "considerably higher" than that if all known fossil fuel resources were exploited.

The report also said that 2018 was "on course to be the 4th warmest year on record," the other three being 2015, 2016 and 2017. All the 20 warmest years on record have been in the past 22 years, the WMO said.

The predicted 3-5 degree rise far exceeds the target of 2 degrees Celsius above pre-industrial levels that was set by the world's countries at the 2015 Paris climate conference. Even that goal would require a drastic reduction in the use of the fossil fuels that create many of the greenhouse gases behind global warming.

According to scientists, the 2-degree limit is essential if humankind is to avert even partially the ill effects of climate change, including extreme weather conditions such as hurricanes and droughts.

Read more:Far-right populists and climate policy: an attempt to move the goalposts 

Major conference

The WMO's warning comes ahead of the most important UN climate conference since that in Paris, which will open in Katowice, Poland, on Sunday.

The meeting aims to produce a "rule book" for implementing the measures agreed on in Paris. The conference is taking place under the shadow thrown by the withdrawal from the Paris Agreement by the United States, the world's largest per-capita polluter.

Read more: Can Poland end its toxic relationship with coal?

Heatwave risk to vulnerable people

Adding weight to the WMO's assessment is another climate study released on Thursday by The Lancet Countdown on Health and Climate Change.

The study, carried out by experts from 27 institutions worldwide, warned that climate change posed an unprecedented health risk for the entire world and particularly for Europe, where rising temperatures and an aging population combined to form a "perfect storm" of risk factors.

More than 150 million vulnerable people worldwide were affected by potentially dangerous heatwaves last year, it said, while a total of 153 billion work hours were lost owing to unusually hot weather.

The executive director of The Lancet Countdown, Nick Watts, said the negative effects of climate warming were being felt right here and now, and not in the distant future.

"For a very, very long time we have thought about climate change as something that affects the environment some time in 2100," he told the news agency AFP.

But now, he said, it was not "just affecting polar bears or rainforests; it's something that affects communities, children, families in the UK and Europe and around the world."

Read more: Great Barrier Reef: "last-chance" tourists flock to world wonder as coral disappears 

tj/rt (Reuters, AFP)

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