Climate change could have "potentially catastrophic effects" for human health, undermining all the health gains in the last half century, experts have warned.
But tackling climate change by cutting emissions from energy, transport and agriculture could provide a great global health opportunity, with benefits ranging from improved diets to fewer deaths and disease caused by air pollution.
Experts who contributed to The Lancet Commission on Health and Climate Change said funding to keep global temperatures from rising by more than 2C, seen as a threshold above which the worst impacts are expected, was a good investment.
They called on governments to phase out coal-fired power plants and improve cities to promote healthy, greener lifestyles, making them better places to walk and cycle to cut pollution and obesity, and boosting insulation to cut energy use and cold-related deaths and disease.
Politicians should also bring in carbon pricing to push up the price of high carbon goods and services to make people change their behaviour, while reducing the cost of other taxes such as VAT, boosting investment or cutting the price of low-carbon technology.
This could mean the cost of flying going up, perhaps with a hike in air passenger duty for flights after the first flight a person takes in a year, pushing up the prices of the "short hop, short-term, leisure travel, stag-parties in Barcelona".
Professor Paul Ekins, director of the Institute for Sustainable Resources, University College London, said: "That sort of thing could become quite a bit more expensive, such that people would think twice about doing that."
People would have more money in their pockets from cuts to other taxes and if they "really valued those stag nights in Barcelona, they can still do it but they'd have to give up more in order to have it", he suggested.
The health sector needed to take action too on clean energy, finding ways to deliver health services to patients without them having to drive to hospitals or switching asthma sufferers over to inhalers which do not use greenhouse gases, the commission said.
In a stark warning, the authors of the report published in the latest edition of The Lancet medical journal said the world was on track for 4C of warming, with many times more people at risk from a rise in extreme weather events .
Rising global temperatures would see health hit through storms, floods and droughts, starvation, migration and conflict, as well as other possible impacts including shifting patterns of infectious diseases such as malaria.
Commission co-chairman Professor Anthony Costello, director of UCL's Institute for Global Health, said: "On our current trajectory, going to 4C is somewhere we don't want to go, and that has very serious and potentially catastrophic effects for human health and human survival.
"It could undermine all the last half century gains.
"As such we see that as a medical emergency, as the action we need to do to stop that in its tracks and get us back on to a 2C trajectory or less requires action now, and action in the next 10 years otherwise the game could be over."
But he said: "It is a great global health opportunity. We're getting fatter, we're getting heart attacks, strokes, diabetes, respiratory ill health, depression, anxiety.
"All of the things we want to do to protect ourselves against climate change will improve our health, whether it's active transport, walking, cycling, eating healthier, sustainable, local diets or cutting air pollution.
"All of that will have a huge health dividend, health benefit and save a lot of money."
Prof Ekins said the main reason against action that climate deniers now gave was that it would be too expensive to do anything about it, something which he described as "simply wrong".
An estimated one trillion US dollars (£630 billion) would be needed each year up to 2050 to tackle climate emissions from energy, on top of the 105 trillion US dollars (£66 trillion) which would be required anyway for the energy system up to mid century.
But with people spending 6.8 trillion US dollars (£4.3 trillion) a year on health, and with the "kind of health risks coming down the line if we don't stick to 2C, that is a very good precautionary investment", Prof Ekins said.
Cutting air pollution as part of efforts to tackle climate change, for example by reducing transport emissions or coal-fired power stations, in the EU alone could save 38 billion euro (£27 billion) a year by 2050 due to reduced deaths, the report said.
And the experts warned climate change was not a distant problem that would happen somewhere else but an "immediate and grave threat" that, like a patient who was gravely ill, needed action straight away with the technology available.
Commission co-chairman Professor Hugh Montgomery, director of the UCL Institute for Human Health and Performance, said: "It's not our grandchildren, it's us and our children, and in this country as well as abroad."
The new Lancet report on health and climate change, which follows on from a previous commission convened on the issue in 2009, is published in the build-up to key United Nations talks in Paris in December on securing a new global climate treaty.
A Government spokesman said: "This Lancet report shows that as well as an economic opportunity, tackling climate change has major health benefits too.
"The Government has been clear on its commitment to climate change action – pushing for an ambitious global deal in Paris and driving innovation to build a low-carbon economy."