HFC greenhouse gases: a factfile
Hydrofluorocarbon (HFC) gases are set to be phased out under a historic international deal that experts say could do a huge amount to curb global warming.
What are they?
HFCs are part of a family called F-gases, which have fluorine as a common component. They are mainly used in refrigeration, air conditioners and aerosols.
They are cousins of chlorofluorocarbons (CFCs) -- a notorious substance that depletes the ozone layer, the thin gaseous shield that protects life on Earth from dangerous solar rays.
Why are they being banned?
HFCs were brought in to replace CFCs, which were banned in 1992 under the 1987 Montreal Protocol to protect the ozone layer.
HFCs have done their part in the process to heal the ozone, but have become a big problem on their own: they are massively efficient at trapping heat from the Sun. As a result, they are major contributors to global warming.
A molecule of HFC can be nearly 15,000 times more effective at warming than a molecule of carbon dioxide, depending on the type. Most of the HFCs entering the atmosphere come from routine leaks in refrigeration and air conditioning.
How could the ban fight climate change?
Eliminating HFCs could reduce global warming by 0.5 C by 2100, according to a 2015 study by the Institute for Governance and Sustainable Development.
UN members, in the historic Paris Agreement sealed last year, set a goal of curbing global warming to less than two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels.
At present, Earth is on course for several degrees of warming by 2100, scientists say. This would doom many parts of the planet to worsening floods, droughts, desertification, rising seas and storms.
The Paris deal is voluntary and hedged with uncertainty as to whether countries will ratchet up their efforts to "decarbonise" their economies, moving away from polluting fossil fuels.
Scrapping HFCs would at the least buy some time to make the switch to cleaner sources and boost energy efficiency.
How many HFCs do we produce?
HFC emissions have been projected to grow from around one gigatonne (a billion tonnes) of carbon dioxide equivalent per year today, to between four and nine a year by 2050.
The increase is largely due to an expected huge rise in the use of air conditioners in developing countries in the coming decades.
The European Union introduced regulations to control HFCs from 2015 and encourage the use of safer alternatives such as ammonia, water or gases called hydrofluoroolefins.
Switching entails financial costs, which for India and some other developing countries was a sticking point in the negotiations.
What's in the deal?
The agreement takes the form of an amendment to the Montreal Protocol, already deemed one of the most successful environmental agreements ever.
Reached after seven years of negotiations among 197 parties, it sets down three pathways for eliminating HFCs.
Developed countries will start to phase down HFCs by 2019. Developing countries will follow with a freeze in consumption levels in 2024, with some other countries following suit in 2028.
By the late 2040s, all countries are expected to consume no more than 15-20 per cent of their baseline levels. The deal is legally binding, meaning those who break it could face punishment.
Countries also agreed to provide "adequate financing" for HFC reduction, the cost of which is estimated at billions of dollars globally, according to the UN Environmental Programme.
The exact amount of additional funding will be agreed at a meeting in Montreal in 2017. There will also be grants for research on affordable alternatives to HFCs.
SOURCES: Intergovernmental Panel on Climate Change Fifth Assessment Report; European Commission; UNEP