People's health is being damaged today by climate change through effects ranging from deadly heatwaves in Europe to rising dengue fever in the tropics, according to a report.
Billions of hours of farmwork have been lost during high temperatures and global warming has damaged the ability to grow crops, it said.
The Lancet Countdown on Health and Climate Change was produced by 150 experts from 27 universities and institutions including the World Health Organization and the World Bank.
"The findings are clear and the stakes could not be higher," said Tedros Adhanom Ghebreyesus, the director-general of the WHO. "We can not delay action on climate change. We can not sleep through this health emergency any longer. "
The report sets out the impacts of global warming on health in stark terms. "A rapidly changing climate has dire implications for every aspect of human life, exposing vulnerable populations to extremes of weather, altering patterns of infectious disease, and compromising food safety, safe drinking water and clean air," he said.
Nick Watt, the executive director of the Lancet Countdown, said: "These are not things happening in 2050 but are things we are already seeing today. We think of these as the canary in, ironically, the coalmine. "
On Tuesday the UN said action to cut carbon emissions must be tripled to avoid catastrophic warming. International climate change negotiations were due to resume on Monday in Poland.
The Lancet report said the lack of progress "threatens both human lives and the viability of the national health systems they depend on, with the potential to overwhelm health services."
A survey in the report of leaders of almost 500 global cities found half expected their public health infrastructure to be seriously compromised by climate change, meaning failures system such as shutting down hospitals.
A heatwave in Europe this summer was linked to hundreds of premature deaths in the UK alone. MPs said in July that the UK was "woefully unprepared" for heatwaves.
The Lancet reports that populations in Europe and the Eastern Mediterranean are at a higher risk than those in Africa and Southeast Asia because of the high proportion of vulnerable and older people living in cities.
Temperatures rise across the world, the report says 157 million more vulnerable people were subjected to heatwave in 2017 than in 2000. Hot conditions directly damage health via heatstroke, but dehydration and exacerbation of conditions such as heart disease are also very dangerous. Heat also worsens air pollution and mental health problems.
Prof. Kristie Ebi, of the University of Washington, said: "Increased mortality in extreme heatwaves is happening now [but] there is abundant evidence that communities are not prepared for the ongoing increases in the frequency, intensity and duration of heatwaves. "
The Lancet report said 153bn hours of work were lost in 2017 due to extreme heat, 80% of it in agriculture. Almost half of the losses were in India, equivalent to 7% of its total working population, while China lost the equivalent of 1.4% of its workers. "This has led to vast losses for national economies and household budgets," said Prof. Joacim Rocklöv of Umeå University in Sweden.
Relatively small changes in temperatures and rainfall could cause large changes in the transmission of infectious diseases spread through water and mosquitoes. The ability of the dengue fever virus to be transmitted – its "vector capacity" – reached a record high in 2016, according to the report, 10% above the 1950s baseline. The danger from cholera risk was also rising in regions such as the Baltic states where the sea has been warming up rapidly.
Doctors not involved in the report said they presented convincing evidence. "It is clear that climate change is directly impacting our health," said Howard Frumkin, head of the Wellcome Trust's Our Planet, Our Health program. "All sectors must prioritize action on climate change if we are to significantly reduce the potentially devastating impact on our planet and our health, affecting generations to come."
Prof. Paul Ekins, of University College London, said the health benefits of tackling climate change had long been underestimated, with just 5% of funding for adaptation to the global warming being spent on health.
"These benefits are enormous, near-term and affect our health immediately," Ekins said. "If you factor in these benefits, cutting emissions to [keep the temperature rise below] 1.5C is going to be a net benefit to humanity in monetary terms. "
The Lancet report noted some promising trends, such as the phase-out of coal and the growth of electric cars.
Prof. Hilary Graham, of the University of York and part of the Lancet Countdown team, said linking health and climate change could help spur further action. "Health is what people feel. It makes a direct connection with their lives and the lives of people they care about like their children and grandchildren. "