Could solar geoengineering cool the planet? The US is serious about finding out | Science

Any work on solar geoengineering – the idea of ​​artificially making the atmosphere more reflective to cool an overheated planet – is fraught with controversy. Last year, for example, a tech entrepreneur claimed he launched two weather balloons from Baja California into the stratosphere, where they may have released a cloud of sulfur dioxide resulting in a small patch of reflective sulfate particles. The stunt drew widespread condemnation. But the question for researchers was: If a renegade actor had made a major release, would they have been able to spot her — or know with certainty what she would do?

The US National Oceanic and Atmospheric Administration (NOAA) is venturing into the fray to answer these questions with the aim of understanding the types, amounts and behavior of particles naturally present in the stratosphere. Unlike Mexico, the program’s balloons and high-altitude aircraft do not release particles or gases. But the large-scale field campaign is the first the US government has ever conducted related to solar geoengineering. It’s very basic research, says Karen Rosenlof, an atmospheric scientist at NOAA’s Chemical Sciences Laboratory. “You have to know what’s there before you can start with it.”

Research into solar geoengineering — also known as solar radiation management — has long been anathema to some climate scientists and activists. They fear it could distract from emissions cuts, pose unforeseen risks and fail to address some impacts of rising carbon dioxide, including ocean acidification. Federal agencies have largely stayed away from the work even after a National Academies of Sciences, Engineering, and Medicine (NASEM) report recommended a $200 million research program in 2021.

But in an unusual move, Congress directly directed NOAA to develop a program in a 2020 spending bill. Support for the program, innocently dubbed Earth’s Radiation Budget, has grown to nearly $10 million annually. SilverLining, an organization that supports solar geoengineering research, has championed it and garnered the support of key lawmakers, says Kelly Wanser, Executive Director of SilverLining, who came from a career in technology to climate advocacy. She said she’s told lawmakers the emissions cuts aren’t happening fast enough and that solar geoengineering may – or may not – be needed to reduce the impact over the next 40 years. “What do we need to know in order to evaluate these things very strictly and honestly with ourselves?” asks Wanser. “I want to know it.”

A focus of the NOAA program is sulfates, the reflective particles that would be flung into the stratosphere in many solar geoengineering proposals. Volcanoes and industrial emissions are the main natural sources of sulfur dioxide, a precursor to sulfates; Carbonyl sulfide, a gas given off by microbes in the oceans, is another. The updrafts in severe storms in the tropics are believed to pump the gases into the stratosphere, but massive wildfires are emerging as another important mechanism to lift them.

Because the stratosphere has no weather, sulfate particles linger there for years, encouraging geoengineering advocates. But researchers need a clearer picture of natural stratospheric particles before they can consider artificially supplementing them, says Gregory Frost, NOAA’s atmospheric chemist who oversees the program.

In 2020, NOAA began periodically launching sensor-equipped weather balloons to collect baseline data on particle size and concentration. The record should allow NOAA to detect shifts in particle distribution that could indicate a new source, such as B. an outbreak – or a secret geoengineering intervention, says Frost.

The measurements could also help climate modelers to represent stratospheric particles more realistically. “The only way to know if our models are doing the right thing is to have data to evaluate them,” says Simone Tilmes, a modeler at the National Center for Atmospheric Research (NCAR). At the moment, most models treat particles roughly, categorizing them into some arbitrary size ranges. Now, with NOAA funding, Tilmes’ team has upgraded NCAR’s flagship climate model with 40 possible bins for sulfate magnitude, and so far it appears to be more accurate at capturing events like the 1991 sulfur-rich Mount Pinatubo eruption.

Now the project is embarking on its next phase, the largest stratospheric aircraft campaign in the past two decades, “if not ever,” says Frost. One of NASA’s WB-57 research jets – a heavily modified 1960s bomber – has been outfitted with 17 instruments, many of which have never flown into the stratosphere before. One can measure sulfur dioxide levels down to 2 parts per trillion, and another can distinguish different particles based on their chemical composition.

Next week flights will begin from Houston, Texas at altitudes of up to 12 miles, and later this month the team plans to move to Fairbanks, Alaska, where they will fly through the end of March. At this time of year, air that had entered the stratosphere half a decade earlier in the tropics is descending in the Arctic. “We’re going to be diving into really old stratospheric air,” says Troy Thornberry, NOAA’s atmospheric chemist who directs the flights. By studying aging sulfate particles, the team hopes to witness the chemical reactions that break them apart and release sulfur at the end of their lives. They want to investigate how such sulfur interacts with organic particles such as soot and meteorite dust. Rosenlof says they will also study how soot absorbs heat from the sun, causing air parcels to rise and increasing the lifespan of particles in the stratosphere.

Further flights to Costa Rica in 2024 and to the southern hemisphere in 2025 are planned. In the meantime, however, the team is open to missions with opportunities. When there’s a massive volcanic eruption, they’ve assembled the perfect payload to study its impact, Frost says. “That would be an event that we want to study if possible.” The same applies to all wildfires, which were similar in size to those in Australia in 2020.

Some researchers want the US government to embark on a major solar geoengineering research program. While the NOAA program is well designed, it’s just one small piece of the puzzle, says Chris Field, a climate scientist at Stanford University and chair of the NASEM report. “It’s really important to find a way to ask bold questions where something unexpected might go wrong.” In March 2022, Congress mandated the White House Office of Science and Technology Policy to develop such a plan, but it was still not published. “Government-funded research is a very good idea – and this is the only way this work should ideally be funded,” says Sikina Jinnah, who studies geoengineering governance at the University of California at Santa Cruz.

Though some climate scientists disagree that such research should continue, or have even called for it to be banned, stopping it would be a mistake, says James Hurrell, a climate scientist at Colorado State University who previously led NCAR. “If we could help avoid the worst of the effects [of climate change] and buy the world more time to reduce concentrations, don’t we want to know?” And if it’s a bad idea, he adds, “the best way to prove it is through research.”

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