(CNN) Climate change is already affecting the health of populations around the world, but things are set to get worse if adequate changes aren't made, according to an international consortium of climate experts.

Fueling the impact is the fact that more than 2,100 cities globally exceed recommended levels of atmospheric particulate matter -- particles emitted when fuels, such as coal or diesel, are burned and are small enough to get into the lungs -- says a report published Monday in the medical journal The Lancet

In the UK alone, 44 cities exceeded levels recommended by the World Health Organization.

Since 1990, exposure to fine particulate matter -- smaller than 2.5 micrometers in diameter -- increased by 11.2%, the report states, aided by a slow transition away from fossil fuels.

Climate change "is the major health threat of the 21st century," said Hugh Montgomery, co-chairman of The Lancet Countdown on health and climate change and director of the Institute for Human Health and Performance at University College London in the UK. "There's an urgent need to address it."

The latest report highlights multiple health, weather and economic consequences that need immediate attention.

Poor air quality

"Air pollution is one of the leading causes of premature mortality globally," said Paul Wilkinson, professor of environmental epidemiology at the London School of Hygiene and Tropical Medicine, who co-authored the report.

More than 803,000 deaths across 21 Asian countries in 2015 were attributable to pollution from coal power, transport and the use of fossil fuels at home, the report states.

But there are "some glimmers of hope," he said, such as the fact that coal power peaked in 2013 and is now showing evidence of a decline.

Investment in coal also declined from 2013, Wilkinson said, but this "will take a couple of generations to realize."

Wilkinson urges governments to prioritize moving away from fossil fuels, as their harms to the environment and human health have long been known. But 71% of 2,971 cities in the WHO's air pollution database exceed the organization's annual exposure guideline for particulate matter.



Increased disease

"Cases of dengue fever have doubled every decade since 1990," Montgomery said. More people are getting it due to climate change, he said, and "it's going to go up."

Dengue is a virus spread by mosquitoes and can result in fever, headaches and pain. Severe cases can bring a multitude of symptoms including bleeding, shock, organ failure -- and potentially death. There is no treatment or vaccine.

Changes in global temperatures, specifically higher temperatures, have increased the range of countries where the mosquitoes carrying the virus can thrive.

The WHO estimates that 390 million dengue infections occur globally each year. Deaths from dengue have increased worldwide, particularly in the Asia-Pacific, Latin America and Caribbean regions, the report states.

Heat waves: Increased risk of death, decreased labor

Between 2000 and 2016, temperatures rose by 0.9 degrees Celsius where people are living, said Peter Cox, professor of climate system dynamics at the University of Exeter, who also co-authored the report.

"The land is warming much quicker than the ocean," he said, highlighting the increased number of heat waves people experience today and the extreme vulnerability of older people. With populations now living longer, the numbers of those vulnerable to heat stresses will only go up.

During that same time frame, the number of older people exposed to heat waves increased by roughly 125 million, and the the ability of people to work -- namely to do physical or manual work outdoors -- fell by 5.3%, Cox said, resulting in economic losses for countries.

The need to adapt and become resilient

Addressing climate change will result in benefits and improvements to public health, but governments are too slow to address the problem, the authors agreed.

Although an increasing number of countries started to develop plans and strategies to reduce the impact of climate change, the majority are high-income nations, the report shows.

"Less than a third of countries have done anything so far," said Georgina Mace, head of the Center for Biodiversity and Environment Research at UCL, who was also involved in the report. "In low-income countries in particular, there is low expenditure on adaptation."

Countries can prepare for changes in infrastructure such as transport, electricity and health care supplies, which can be affected by extreme weather events.

In addition, policies to reduce use of fossil fuels and entice people toward electric vehicles and renewable energy sources can be prioritized. The report shows that while sales of electric cars have risen to 77 million per year, this is easily lost next to the figure of 1.2 billion: the total number of regular gas- and diesel-fueled cars being driven.

Not enough is being done, Mace said.

"Adaptation is going to become more important in the future," she said. "The impact is going to get a lot worse."

"The indicators reflect the breadth of the transformation that is required to address these public health issues by not only considering the direct and indirect impacts of climate change on health but also considering adaptation and mitigation issues, as well as economic and finance issues as the world moves from a fossil-fuel driven to a low-carbon economy," said Clare Goodess, senior researcher at the Climatic Research Unit at the University of East Anglia, who was not involved in the report.

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Goodess said more work is needed to improve the attribution of these observations to climate change, a point on which the authors of the report agree.

"Many of the most dramatic trends in health impacts are related to rising temperature and more frequent high-temperature extremes," Goodess said. "The attribution of these temperature trends to human activities is now unequivocal so the urgency of addressing the issues raised by this report is not in doubt."