Heatwaves in the UK are forecast to become more frequent
The NHS - one of the world's largest public bodies - has been urged to cut its greenhouse gas emissions.
Each year, the UK's health service spent £400m on energy and emitted about one million tonnes of carbon, think tank New Economics Foundation said.
Its NHS Confederation-commissioned report said 5% of UK road transport emissions were from NHS-related trips.
The authors also warned that a more variable climate could see an increase in heat-related deaths and diseases.
The report - Taking the Temperature: Towards an NHS Response to Global Warming - says staff, patients and visitors travelled almost 25 billion passenger miles in 2001, predominately by cars and vans.
Waste was also an area for concern: "One in every 100 tonnes of domestic waste generated in the UK comes from the NHS, with the vast majority going to landfill."
It added that the NHS would have to cut its carbon dioxide (CO2) emissions by at least 600,000 tonnes if it was to meet the government's target of cutting CO2 by 60% from 1990 levels by 2050.
As the UK's largest public body, employing 1.3 million people, the NHS was ideally placed to offer advice to people about the health effects of a changing climate, said Andrew Simms, the think tank's policy director.
"The NHS will be working on the front line as climate change hits the UK," he predicted.
"The lethal heatwave that hit Paris not long ago shows the kind of thing that we can expect to become more common."
The 2003 heatwave was blamed for more than 14,000 additional deaths in France and 2,000 in England.
Cases of food poisoning, skin cancer and major emergencies were also likely to increase over the decades, the report suggested.
"As our climate health check of the health service shows, an NHS braced for a warming world can play a vital double role," Mr Simms explained.
"First, it can help the nation to cope and adapt, and its contact with over one million patients every 36 hours creates huge potential for promoting positive action.
"Second, it can lead the way by showing how large organisations can radically cut their greenhouse gas emissions."
Dr Gill Morgan, chief executive of the NHS Confederation, which represents more than 90% of NHS organisations, welcomed the findings.
"Our members understand their responsibility to tackle climate change," she said.
"By addressing some key aspects such as energy use, transport and waste, the NHS can not only have a considerable impact on reducing its carbon footprint but also its costs.
Dr Morgan said the organisation could save £50m each year if it cut energy consumption by 15%.
In February, the Department of Health launched software designed to assess the impact of healthcare facilities on the environment.
The NHS Environmental Assessment Tool (Neat) aims to raise environmental awareness, estimate the environmental impact of its activities and develop a strategy to improve its performance.
A number of measures have already been adopted by healthcare trusts, including installing solar panels, sourcing locally produced food and introducing park-and-ride schemes.