Global warming from human cooling
The International Energy Agency estimated that greenhouse gas emissions from MAC systems globally were around 420 million metric tonnes of carbon dioxide equivalent in 2015. That was about 1 percent of global energy-related CO2 emissions that year. However, if not improved, MAC systems will become a larger share of the climate impacts of vehicles in the years ahead, as we decarbonize the fuels they run on and other components.
In recent decades, hydrofluorocarbon (HFC) refrigerants have been widely applied in vehicles because they offer good performance in terms of heat exchange and come at an affordable cost. However, pressure is mounting to move away from HFC refrigerants because their global warming potentials are higher than 1,000, meaning that they are more than 1,000 times more powerful than CO2 in their climate warming impacts.
The impacts come in two forms. Refrigerants leak into the atmosphere during assembly, vehicle maintenance, operation, and scrapping and recycling. Leakage of refrigerants is also referred to as direct emissions, and the IEA estimated that these account for about 30 percent of total GHG emissions from MAC systems. The remaining 70 percent are indirect emissions that come from the increased energy consumed to run MAC systems. While several studies have found that MAC systems account for 3 percent to 7 percent of total fuel consumption in passenger cars, that can go up to 20 percent in humid and hot climates. For heavier vehicles, the impact is even more severe. A report from the International Council on Clean Transportation found that in buses, about 30 percent of total energy is consumed by their MAC systems.
International efforts to phase down the use of harmful refrigerants go back to the 1980s and the Montreal Protocol. The European Union is leading the way and has banned refrigerants with global warming potential greater than 150 for all vehicles since 2017. The United States will ban the use of HFCs for transport beginning in 2025 and Canada banned refrigerants with a global warming potential higher than 150 in 2019.China ratified the Kigali Amendment in 2021 and the mandate will begin in 2024.
It’s important to overcome any challenges because the potential benefits of GHG reduction from MAC systems are substantial. A recent study by the ICCT found that improving MAC systems by adopting natural refrigerants would reduce direct emissions by 99 percent. Combining both direct and indirect emissions, the study found that cities with cool and warm climates can expect 60 percent and 45 percent less GHG emissions, respectively, from CO2-based MAC systems. Electric vehicles are considered more energy efficient than conventional internal combustion engine vehicles because they only lose about 15 percent to 20 percent of the energy they get from the grid when powering the vehicle; in contrast, conventional gasoline vehicles generally see a 70 percent loss from fuel to wheels. By applying a series of technologies that improve energy efficiency, MAC systems in electric vehicles can save more energy and therefore show greater GHG reduction benefits.