The physical signs and socio-economic impacts of climate change are accelerating as record greenhouse gas concentrations push temperatures to dangerous levels, the World Meteorological Association says.

The State of the Climate report warns climate change threatens to reverse gains made tackling malnutrition. World hunger is rising after a prolonged decline, with the number of undernourished people increasing to 821 million in 2017 due to severe droughts.

The number of people exposed to heatwaves increased by 125 million between 2000 and 2016. The average duration of heatwaves is now 0.37 days longer than between 1986 and 2008.

Key climate change indicators – rising sea levels, shrinking sea ice and extreme heatwaves – are becoming more pronounced. Carbon dioxide levels keep rising and greenhouse gas concentrations are expected to increase further this year.

Last year was the fourth-warmest on record, with the past four years comprising the top four.

The global mean sea level was 3.7mm higher than in 2017, mainly due to loss of mass from sea ice.

Most natural hazards last year – affecting 62 million people – were associated with extreme weather. Floods hit more than 35 million people.

The west coast of New Zealand’s South Island took almost a year’s rainfall over two days last month, in a storm the Insurance Council of New Zealand says was likely influenced by climate change.

New Zealand’s MetService attributes the storm in part to warm marine weather, which will become increasingly common as climate change progresses.