Increasing demand for home air conditioning driven by global warming, population growth and rising incomes in developing countries could increase the planet's temperatures an additional half a degree Celsius by the end of the century, according to a new report by the Rocky Mountain Institute.

The demand is growing so fast that a "radical change" in home-cooling technology will be necessary to neutralize its impact, writes RMI, an energy innovation and sustainability organization.

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The problem with air-conditioning comes from two sources: the amount of energy used, much of which is still powered by carbon-emitting coal, oil and gas generation, and the leaking of hydrofluorocarbon (HFC) coolants, which are short-lived climate pollutants many times more potent than carbon dioxide.

While international agreements like the recent Kigali Amendment to the Montreal Protocol are starting a global effort to phase down the use of HFCs, that alone won't be enough to keep cooling from contributing to the causes of global warming and fueling a vicious circle, the report's authors write.

Air conditioning, and homes themselves, will also have to become more energy efficient. To ramp up efforts to bring down emissions from cooling, RMI joined the government of India, British entrepreneur Richard Branson and other organizations on Monday in launching the Global Cooling Prize, an effort to spur development of highly efficient cooling technology to reduce further warming from the residential air conditioning sector.

The Problem with HFCs

Approximately 1.2 billion window-mounted air conditioning units and other small-scale, room-cooling devices are currently in use worldwide. By 2050, the figure is expected to increase to 4.5 billion, according to RMI.

Many of today's air conditioners use hydrofluorocarbons (HFCs), coolants that are short-lived climate pollutants that can leak into the atmosphere at the end of an air conditioner's useful life when the devices are destroyed. HFCs remain in the atmosphere for an average of 14 years and are approximately 1,000 to 3,000 times more potent than carbon dioxide as a greenhouse gas.

Less-damaging alternatives to HFCs exist, and several countries and states, including California and New York, have started efforts to phase out HFCs in air conditioning and other cooling equipment. India, where the growth of air conditioning is expected to surge, has committed to begin reducing its HFCs use by 2028. The Kigali Amendment, agreed to in 2016, commits countries to phasing down HFCs by more than 80 percent over the next 30 years.

Increasing Air Conditioner Efficiency

Energy demand is the other side of the residential cooling problem. RMI estimates that the amount of energy that will be required to power the 4.5 billion window air conditioners expected by 2050 is equivalent to the current electricity demand of the United States, Germany and Japan combined.

Growth in the demand for air conditioning is already outpacing growth in solar power, with new residential air conditioning units worldwide consuming approximately 100 GW of energy in 2017, compared to 94 GW of new solar energy generation.

"You can't build enough renewable energy fast enough to keep pace with the growth of air conditioning," said Iain Campbell, a senior fellow with RMI and lead author of the report.

RMI is partnering with the Indian government's Department of Science and Technology and others on the two-year, $3 million Global Cooling Prize competition to foster the development of air conditioners that have 80 percent lower greenhouse gas emissions because they use less energy and transition to coolants that aren't powerful greenhouse gases.

At least one company already sells an air conditioner with associated greenhouse gas emissions that are 71 percent lower than today's market average, Campbell said. The device, built by Indian manufacture Godrej Appliances, uses 60 percent less energy than other air conditioners and uses a coolant with a lower global warming potential.

The prize hopes to spur more companies to develop air conditioners with even lower climate-warming emissions that can compete with existing cooling systems.

Cost is important, particularly since the countries that are expected to see the greatest increase in home air conditioning demand in the coming decades are developing countries. With that in mind, the prize rules require that the cost of any new device must not exceed two times the cost of the current market average. A device that is twice as expensive but several times more efficient than existing air conditioners could pay for itself in less than four years through lower electricity bills, Campbell said.

The RMI report also describes other measures to shift to less polluting cooling, including improving energy efficiency in homes and buildings and providing financing, subsidies, and other financial incentives to reduce upfront costs for consumers.

Nikit Abhyankar, an engineer in the International Energy Studies Group at Lawrence Berkeley National Laboratory, said the changes will have to come quickly as the demand for air conditioning grows. "The scale of the problem is huge and is just going to explode," he said.