"Reducing Short-Lived Climate Pollutants (SLCPs) Is an Essential Action, in Addition to CO₂ Reduction, for Saving the World by 2050" Interview with Prof. Ramanathan, Winner of the 2021 Blue Planet Prize

Professor Veerabhadran Ramanathan of the Scripps Institution of Oceanography, University of California, San Diego (USA) is one of the two winners of the 2021 Blue Planet Prize. He discovered substances that have a negative impact on global warming in much the same way as carbon dioxide (CO₂) does, and has continued to study such substances.

"When we talk about global warming, the only thing people immediately think about is carbon dioxide from fossil fuel combustion. In fact, until 1975, all the scientists also thought that the emission of carbon dioxide was the only thing we needed to worry about. In 1975, when I was just fresh out of graduate school, I discovered that there were other gases heating the planet. What I identified at the time was chlorofluorocarbons. Some of them are called CFC-11 and CFC-12, whose trade names are Freon 11 and Freon 12."

Chlorofluorocarbons (CFCs) are chemical compounds containing atom(s) of carbon, chlorine, and fluorine. They are artificial substances that do not exist in nature, and were developed in 1928 as ideal refrigerant gases for use in refrigerators. Because of their properties of being oil-soluble, volatile, nonflammable, and non-toxic to humans, they were used in insulating material, in spray cans or for precision cleaning, in refrigerators as refrigerants and were consumed in large amounts during the 1960s through the 1980s, mainly in developed countries.

"At that time, most of the released CFCs came from spray cans and from refrigerators. One year before the publication of my paper, two atmospheric chemists, Sherwood Rowland and Mario Molina, concluded that CFCs, through chemical reactions, would lead to the destruction of the ozone layer," said the professor.

"The new finding of my research, published a year later in 1975, was that CFCs can also trap enormous of infrared heat within the planet, which is a totally different effect from the chemical effect on the ozone layer. The trapping of infrared heat arises from the configuration of the CFC molecule, basically due to the physics of CFCs. What I found was that one metric ton each of CFC-11 and CFC-12 in the air traps more heat than 10,000 tons of carbon dioxide. This was a bombshell to the science community. Many scientists had a hard time believing that, and it took few years for them to confirm my findings."

Later, the production, consumption, and trade of CFCs were regulated internationally by the Montreal Protocol, adopted in 1987. The Montreal protocol was enacted because of the effect of CFCs on the ozone layer. However, it is now recognized as the most successful climate action so far, because of my finding about the heat trapping effect of CFCs.

Right now, we know that in addition to CFCs, there are other substances with a global warming potential. Among them, those with a relatively short residence time in the atmosphere are called short-lived climate pollutants (SLCPs), namely methane (CH4), hydrofluorocarbons (HFCs^*1), tropospheric ozone (O₃), and black carbon (BC, so-called soot). The first three are gases, and black carbon is a particle, called aerosols. The SLCPs stay in the atmosphere for less than a few weeks (black carbon) to about a decade (methane and HFCs). In contrast, CO₂ is referred to as a long-lived climate pollutant because after it is emitted into the atmosphere, about 50% of it stays for a century, and about 20% stays for 1,000 years.

Professor Ramanathan described the relationship between CO₂ and SLCPs and compared the way these substances heat the planet to "a blanket on a cold winter night that keeps you warm."

"When you put the blanket over you, it traps your body heat and prevents it from escaping. In the same way, these substances cover the entire planet like a blanket, and slow down the rate at which the heat escapes, so the planet heats up. While it was already known that CO₂ functions as a long-lasting blanket, my research revealed that there were other blankets."

"The average lifetime of HFCs, which replaced CFCs, is a decade. The average lifetime of methane is about 11 years, and that of ozone is about a few months. Because black carbon is not a gas but is a particle, it does not trap the planet's heat. Instead, it traps the sun's heat and promotes global warming. Black carbon has a lifetime of a few weeks or less, and it is a major air pollutant leading to millions of premature mortalities every year. Substances that stay in the atmosphere for less than about a decade are called short-lived climate pollutants (SLCPs). In a paper published in 2010, I showed that the reduction of SLCP emissions, in addition to reducing emissions of CO₂, is a key to solving the climate change problem. The heat trapping by black carbon will disappear within weeks and that of methane and HFCs within a few decades. So we have an opportunity to cut down the warming much faster."

*1   Hydrofluorocarbons (HFCs) are general terms for compounds containing atom(s) of carbon, hydrogen, and fluorine. As of 2021, the reduction of CFC alternatives is an international issue, and there is a pressing need to shift to clean refrigerants, or non-CFCs, which do not use CFCs.

Professor Ramanathan continues to sound an alarm about the situation where the focus is only on CO₂ as an issue of global warming. CO₂ is the major global warming agent but SLCPs have a short lifetime and an extremely high global warming potential. Compared with the global warming potential of CO₂, methane is 25 to 100 times more potent, black carbon is 500 to 2,000 times more potent, and HFCs, which are used as refrigerants, are 2,000 times more potent, according to the professor. Reducing SLCP emissions would not only curb global warming immediately, but would also sharply reduce the amount of energy absorbed in the atmosphere.

As the diagram above shows, we have to bend the warming curve quickly before 2050, then flatten it and finally, by 2100, bend it downwards below 1.5°C. If we start mitigating SLCPs and CO₂ now, SLCPs will bend the warming curve within 10 years and cut the rate of warming from now until 2050 by half; CO₂ reduction, if begun now and approach zero emissions by 2050, will flatten the curve by the latter half of this century. These are the two levers we have to pull as hard as we can now. We need to pull on a third lever, which concerns extracting the CO₂ from the air, as much as 250 billion tons of CO₂ has to be taken out by the 2070s. This step will bend the curve down to below 1.5°C by 2100. This is the three-lever strategy advocated by Professor Ramanathan for the last 10 years.

"If we don't do anything, the average temperature will rise by more than 2°C by 2040. Then, what happens if we start reducing CO₂ emissions now and aim to achieve carbon neutral by 2050? Even so, the projected curve of temperature will continue to go upward, not downward, for the next 30 years. You may wonder why the temperature rises even when we reduce emissions. The important thing to remember here is that CO₂ has a long lifetime. We have already emitted more than two trillion tons of CO₂ and about half of it has accumulated in the air. There is about 1.1 trillion tons of CO₂ in the air as of today. Even if we cut down the emissions today, the 1.1 trillion metric ton blanket will stay there for at least a hundred years, and it will keep heating and heating."

"In contrast, if we reduce SLCP emissions starting from 2021, the change will be noticeable because the amount of SLCPs in the atmosphere will quickly decrease. We can curb the temperature rise within five to ten years," Professor Ramanathan said.

"The problem with the current approach is that the focus is only on CO₂. This approach alone will not prevent a looming catastrophe. The temperature will rise by more than 1.5°C over the next 10 years, and by more than 2°C over the next 25 years. The only way to keep the temperature rise below 2°C over the next 30 years is to cut both CO₂ and SLCP emissions to zero."

In order to simultaneously reduce CO₂ and SLCP emissions, Professor Ramanathan pointed out several key issues.

"The first point is to move away from fossil fuels, which are a source of not only CO₂ but also SLCPs. Natural gas, whose main component is methane, is sometimes considered to have a lower environmental impact than petroleum. According to the professor, 10 to 15 percent of methane emissions come from leaks in natural gas piping. Moreover, diesel vehicles burn fossil fuel and emit black carbon, which pollutes the atmosphere and contributes to global warming."

"You need targeted measures. For example, the poorest three billion people, who make up 40 percent of the world's population, either have no access to fossil fuels or cannot afford them; and live by burning firewood, dung, and coal. Incomplete burning of fossil fuels produces black smoke, or soot, which contains black carbon. According to a report from the United Nations Environment Programme (UNEP)^*2, low-quality used cars exported from developed countries to developing countries are causing air pollution and hindering efforts to mitigate climate change. Once people stop using fossil fuels and give the poorest 3 billion financing for cleaner as well as affordable energy, black carbon will be gone," Professor Ramanathan said.

Recently, Professor Ramanathan has also been focusing on the issue of health. "We should focus on people's health first, and then the health of the planet. Fossil fuels cause air pollution and kill about 4 million to 10 million people every year. Japan, China, and the United States have begun to take action on air pollution, not to protect the planet or glaciers, but to protect our lungs. What we have done is to let the fossil fuels burn and just put filters as a temporary fix. If we fundamentally switch to renewables, air pollution will soon disappear."

Although Professor Ramanathan has been studying SLCPs for more than 50 years, he strongly feels the need for scientists to speak directly to people about the situation, where measures against SLCPs are lagging behind in combating global warming. He was able to engage with a variety of faith leaders, including Pope Benedict and now Pope Francis, the 14th Dalai Lama, and India's spiritual leader Amma, to give them some scientific support. He himself is a Hindu, but he says religious differences pose no problem when he talks to people of other religions.

"It is not that I persuaded them, but everyone I talked to were surprised to know that there is so much scientific evidence. I am beginning to think that it is necessary to be actively involved in forming alliances with faith leaders for the fight against climate change. We as scientists can make a difference by speaking directly to people who are constantly being told that climate change is flawed and uncertain science and there is no need to worry about it."

At the end of the interview, we asked the professor for his message to the younger generation.

"The brightest spot I see in climate change is how the youth are rising up to take action. My generation will work to protect you, but you have to shout out and make sure your voice is heard. At the same time, you have to educate yourself. I have recently started an education program for learning about climate change, protecting nature, respecting nature, and loving nature. I know that we are going to solve this problem. But you children have to play a part. You cannot just sit there. We all need to do it together."

This article is based on a video interview with Professor Ramanathan, which was released on the commendation special website for the 2021 Blue Planet Prize. Please watch and enjoy his video interview as well.
Special website for the 2021 Blue Planet Prize: https://www.af-info.or.jp/en/blueplanet/special2021/

*2   Released by the United Nations Environment Programme on October 26, 2020: https://www.unep.org/news-and-stories/press-release/new-un-report-details-environmental-impacts-export-used-vehicles