Worsening heatwaves are taking a heavier toll on rich as well as poor countries, according to an annual ranking that measures the damage done by extreme weather to human life and economies.
The Global Climate Risk Index, published on Wednesday by environmental think-tank Germanwatch, rated Japan as the most-affected country in 2018, while Germany was in third position.
Both of the industrialised nations were hit hard by heatwaves and drought that year, as was India - in fifth position - which suffered water shortages, crop failures and riots, Germanwatch said in a report.
"Recent science has confirmed the long-established link between climate change and the frequency and severity of extreme heat," it added in a statement.
In 2018, a severe summer heatwave in Japan killed 138 people and caused more than 70,000 people to be hospitalised with heat stroke and exhaustion, the report said.
And in Germany, the period from April-July 2018 was the hottest ever recorded in the country, leading to the deaths of more than 1,200 people.
Across Europe, extreme heat spells are now up to 100 times more likely than a century ago, according to the report. It noted that the impact of heatwaves on African countries may be under-represented due to a lack of data.
Powerful storms also left a trail of destruction in 2018, with the Philippines second in the climate risk index due to large losses when it was battered by top-strength Typhoon Mangkhut.
Madagascar was the fourth most weather-affected country as two cyclones killed about 70 people and forced 70,000 to seek refuge.
In Kenya and Rwanda - seventh and eighth in the index - seasonal rains were much heavier than normal, causing floods that destroyed homes and livestock and fuelled diseases.
Laura Schaefer, a policy advisor with Germanwatch, told journalists at the UN climate talks in Madrid that the index results showed that the "signs of climate crisis", on all continents, could no longer be ignored.
"But climate impacts most existentially hit developing countries and communities around the world - and create a real climate crisis for millions of people," she said, adding that the poor had the fewest resources to cope.
Between 1999 and 2018, seven of the 10 countries most affected by extreme weather were lower-income developing countries, with Puerto Rico, Myanmar and Haiti at the top.
In the past 20 years, nearly half a million deaths were directly linked to more than 12,000 extreme weather events worldwide, while economic damages exceeded $3.5 trillion, the report said.
Germanwatch joined developing states and aid agencies in urging UN negotiators to set up a system to regularly assess the needs of vulnerable countries in addressing "loss and damage" caused by climate change, and to provide new funding to repair it.
Wealthy nations have long resisted pressure to stump up such finance, beyond expanding insurance programmes. But as the cost of extreme weather increases globally and planet-heating emissions continue to rise, that pressure is growing.
Renato Redentor Constantino, of the Institute for Climate and Sustainable Cities in the Philippines, said it was "plainly unacceptable" that those suffering the most had done the least to cause the problem, given their historically low emissions.
"The extreme weather events we have been facing are a result of emissions that the world failed to eliminate," he said. (Reporting by Megan Rowling @meganrowling; editing by Laurie Goering. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, climate change, women's and LGBT+ rights, human trafficking and property rights.