Unique analysis shows air-con heat relief significantly worsens climate change

(Press-News.org) Embargoed copy of the research paper available on request

While air-conditioning protects people from dangerous heat, it also significantly worsens global warming – by 2050 potentially producing more carbon dioxide than the current annual emissions of the United States, a new study reveals.

Scientists have combined climate science, energy modelling, and inequality analysis to create a unique framework using a set of well‑established global ‘storylines’ — Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP and RCP scenarios) — a set of ‘futures’ ranging from strong climate action to high emissions.

The study reveals that, by 2050 air-conditioning use will more than double. Electricity for cooling could reach 4,493 TWh under mid‑range scenarios, and much more in high‑emissions futures.  Emissions from air-conditioning could reach 8.5 GtCO₂‑eq per year in the worst‑case scenario — more the current annual emissions of the United States (5.9 GtCO₂‑eq).

Publishing their findings today (25 Feb) in Nature Communications, the international research group led by the University of Birmingham warns that most of this extra warming is caused by income-enabled growth in cooling consumption, more households adopting and using air conditioning, and not just rising temperatures.

Researchers estimate that air-conditioning use will add 0.03°C to 0.07°C of global warming by 2050, depending on the emissions pathway the world follows. This is the equivalent of around 74–183 billion transatlantic return flights. The predicted rise in temperature is a significant increase compared with the narrow margin left to keep warming below 1.5°C.

The paper also reveals a major global inequality - regions that need cooling the most, such as South Asia and Africa, have the least access to air-conditioning. Wealthier regions such as Europe and North America have lower cooling needs but higher air-conditioning usage.

Professor Yuli Shan from the University of Birmingham, the corresponding author, said: “Global warming is raising temperatures and causing more heatwaves, and as economic growth in some of the worst-affected countries means more people can offset extreme heat with air conditioning.

“As global temperatures rise, we risk being locked into an ‘arms race’ where defending ourselves against extreme heat is causing the issue to get worse. The world must transition quickly to cleaner, more efficient cooling technologies—while ensuring fair access to cooling, especially for vulnerable populations.”

As well as adopting a rapid transition to clean electricity, the research team recommends the fast adoption of low‑pollution cooling liquids in air-conditioning systems refrigerants and better building design – using insulation and shading more effectively. Researchers also advocate for behavioural changes such as turning the air-conditioning down and shifting cooling away from peak hours.

The study uncovers a fundamental development dilemma. Low-income limits regional access to cooling yet closing this gap to deliver equitable thermal comfort would generate substantial additional warming impact. Increasing demand resulting from rising incomes in low-income regions could have significant effects: an additional 94 million units at medium-income levels, 150 million units at high-income levels, and up to over 220 million units at the highest-income levels.

Dr Hongzhi Zhang, from Beijing Institute of Technology, the first author of this study, said: “The study reveals that if all low‑income regions gained the same access to air-conditioning as rich regions, related global emissions would jump dramatically - adding up to 0.05°C extra warming even in the most climate‑friendly scenario.”

Dr Hongzhi Zhang was a visiting PhD student at the University of Birmingham, supervised by Professor Yuli Shan.

Using their analysis framework, the researchers estimated how much cooling people will need as temperatures rise. They included humidity and weighted the results by where people live, as cooling needs matter more in areas with large populations.

They then fed these cooling‑need estimates into a global energy–economy model (GCAM) projecting how many air conditioners people will buy, how much electricity will be used, and how much greenhouse gas emissions the devices will produce.

The team ran GCAM under each of the five SSP‑RCP scenarios, so they could understand how air-conditioning use and emissions change in a sustainable world vs. a fossil‑fuel‑heavy world and how much warming comes specifically from air-conditioning use in each case. Researchers then compared regions by income and climate conditions, building an econometric model to reveal areas where people need air-conditioning but can’t afford it.

Finally, they measured how much extra warming AC emissions will cause, using a climate emulator called MAGICC, which estimates how emissions translate into additional warming.

Researchers at the University of Birmingham are using their wide-ranging pure and applied atmospheric research to provide solutions to the pressing problems of extreme weather and climate change which impact on our planet.

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‘Rising Air-Conditioning Use Intensifies Global Warming’ - Hongzhi Zhang, Yuli Shan, Ruoqi Li, Rui Xue, Junhua Ma, Jarmo Kikstra, Zongbo Shi, Zhaohua Wang, Bin Zhang, Bo Wang, Shuai Fang, Fan Yang, Klaus Hubacek is published by Nature Communications.

Notes for editors: 

Participating institutions include: University of Birmingham, UK; Imperial College London, London, UK; Beijing Institute of Technology, China; Digital Economy and Policy Intelligentization Key Laboratory of Ministry of Industry and Information Technology, Beijing, China; Nanjing University, China; Kunming University of Science and Technology, China; International Institute for Applied Systems Analysis (IIASA), Austria;  Soochow University, Suzhou, China; La Trobe University, Melbourne, Australia; Aalborg University, Denmark; and University of Groningen, the Netherlands. About the University of Birmingham

As well as being ranked among the world’s top 100 institutions, the University of Birmingham is the most targeted UK university by top graduate employers. Its work brings people from across the world to Birmingham, including researchers, educators and more than 40,000 students from over 150 countries.  

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