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Dr. Peter DeCarlo is an associate professor of environmental health and engineering at Johns Hopkins Whiting School of Engineering. He studies atmospheric air pollution with applications to ambient air quality, including atmospheric aerosols and emissions from anthropogenic activities including natural gas development.
Dr. DeCarlo has published extensively in the areas of atmospheric aerosols (particulate matter), air quality, and climate. He has performed air quality measurements all over the world and visited many Congressional offices to discuss climate change and air quality issues. He received his PhD in atmospheric science from the University of Colorado. He earned a postdoctoral fellowship at the Paul Scherrer Institute in Switzerland and an AAAS Science Policy Fellowship in Washington DC.
“Solar radiation management is really just energy management,” Dr. DeCarlo says. “We’ve added excess energy into the climate system through the addition of greenhouse gasses, and now we’re trying to figure out ways to offset that.”
Solar radiation management aims to prevent some amount of solar radiation—sunlight—from coming into the Earth’s atmosphere and staying there. And, like other forms of climate engineering, it largely seeks to mimic natural processes. But it also seeks to mimic and repurpose observed processes: the way we’ve polluted the planet over the last 200 years has provided clues as to how we might meddle with the environment in positive ways.
Bright, reflective areas—deserts, ice caps, and clouds—bounce solar radiation out, so one form of solar radiation management, known as marine cloud brightening, seeks to make clouds more reflective and more long-lasting. Some scientists have even proposed injecting large amounts of sulfur dioxide into the atmosphere to mimic a volcanic eruption, which would, in theory, reflect more solar radiation back into space. But whether these forms of solar radiation management would do more harm than good is a source of continued debate.
“We’ve been engineering the climate since the Industrial Revolution, inadvertently at first, and now full knowledge of what we’re doing,” Dr. DeCarlo says. “We have to be really careful about these sorts of interventions and their potential side effects.”
Even if some solar radiation management applications successfully achieve their initial goals, they can still carry weighty concerns. Once started, climate interventions will need to be monitored and maintained for decades or centuries; abruptly terminating them could lead to a climate shock and worsen conditions even beyond their starting point.
“Understanding that the solar radiation management techniques aren’t forever and that they don’t have the same lifetime as the greenhouse gasses that we’re putting into the atmosphere, is a really important piece of the discussion,” Dr. DeCarlo says. “If we do go down this path, and I’m not saying that we should, we’d have to invest in long enough time scales to keep that offset going.”
By altering the climate, solar radiation management could come with unforeseen negative side effects, much like the rapid period of industrialization did. And, as in the past, it’s likely that the negative consequences would disproportionately affect the less wealthy parts of the world. Without massive global cooperation—cooperation of the type that’s not yet been achieved in any other climate goals—solar radiation management could repeat those past mistakes.
“Any undertaking of solar radiation management would, almost by definition, impact the globe,” Dr. DeCarlo says. “But the upfront costs don’t make it accessible to every country. As a result, without some type of international consensus, there are going to be winners and losers. We’re seeing this already with climate change.”
Solar radiation management is also controversial because it can pull away research and resources from more practical approaches. At its root, it does not address the main cause of climate change: the world’s reliance on fossil fuels. There may yet be a way to utilize solar radiation management effectively. It would need to start small and be monitored carefully, working in tandem with broader climate solutions.
The future of the fight against climate change requires a sober mix of practicality and optimism. Dr. DeCarlo notes that COP 28 signifies 28 years of formal discussion around mitigating the effects of climate change. The graph of greenhouse gas emissions over those 28 years does not inspire confidence in those talks’ effects: emissions dipped during Covid-19, but have since recovered, and are now going up again.
“Generations of climate scientists before me have been talking about climate change,” Dr. DeCarlo says. “They were right, but people didn’t take them seriously. And I would argue that maybe the science is being taken more seriously now, but the actions to stop what’s going on aren’t being pursued as actively, and I think there’s a lot of lip service to those actions.”
For engineers working to fight against climate change, it can be frustrating to wait for political will to catch up to the scientific reality. And the effects of one’s labor aren’t always immediately visible, as impacts on climate may take years to manifest. But the world needs engineers—especially their curiosity and ingenuity—to build a future less reliant on fossil fuels. That future is more possible now than it was in decades prior, thanks to renewable energy systems and more environmentally friendly forms of energy storage.
“I think we can be hopeful about those types of breakthrough technologies that move us beyond the need for burning carbon,” Dr. DeCarlo says.
More than giant mirrors in space, what’s needed is an engineering mindset in climate decision-making. Dr. DeCarlo notes that most politicians don’t have science or engineering degrees, yet they face many policy questions that are deeply intertwined with science and engineering topics. But even without a STEM background, it’s possible to adopt an engineering mindset that is quantitative, specific, and methodical in its approaches.
“Having that critical ability to look at a problem and think about ways to solve it quantitatively is really important, and it’s something we need in the political space,” Dr. DeCarlo says.
A quantitative process can still leave room for hope. And solar radiation management is, at its core, a hopeful idea. While the world waits for its governments to align on basic climate measures, its scientists and engineers will continue to dream up ways to change things for the better.
“We got to where we are because of fossil fuels,” Dr. DeCarlo says. “But that doesn’t mean we have to stick with them. We can move beyond them. We need that evolution. And we need to think about how to keep taking those steps forward."
Matt Zbrog is a writer and researcher from Southern California. Since 2018, he’s written extensively about a wide range of engineering disciplines, with a particular focus on the potential impacts of major technological breakthroughs. His work largely centers around conversations with engineering faculty at top universities, highlighting their research in areas such as nuclear power, artificial intelligence, soft robotics, and semiconductor design. He’s also worked with leaders and subject matter experts at the Institute for Electrical and Electronics Engineers (IEEE), the California Department of Water Resources (DWR), the National Society of Professional Engineers (NSPE), and the Society of Women Engineers (SWE).
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