Solar Geoengineering: Ineffective, Risky, and Unnecessary
Some people are proposing to counteract climate change by artificially dimming the Sun. But it’s largely ineffective. It’s potentially risky. And it’s unnecessary. Instead, we should focus on real-world solutions that work.
Stopping climate change is relatively straightforward. We already know what to do. We just have to do it.
Mostly, we need to halt the emissions of greenhouse gases — which stem from the world’s energy use, land use and agriculture, and exotic materials — as soon as possible. There are already many opportunities to cut emissions from electricity, food and agriculture, industry, transportation, and buildings.
There are also opportunities to support and enhance natural carbon sinks that can help remove greenhouse gases we have already emitted. And there are ways to improve society that have additional climate benefits.
At Project Drawdown, we outline dozens of opportunities to reduce emissions, support carbon sinks, and improve society — keeping the world from heading towards uncontrolled climate change.
The essential solutions are right in front of us. Our job is to bring them to scale as quickly, safely, and equitably as possible.
But some people seem unwilling to accept this and are proposing to deploy hair-brained ideas to counteract climate change instead of addressing its underlying causes.
Enter the concept of “solar geoengineering”.
What is Solar Geoengineering?
The basic idea is to manipulate the amount of sunshine hitting the Earth, reflecting some of it back to space. This is supposed to cool the planet just enough to counteract the warming effects of rising greenhouse gases.
There are several ways to reflect sunlight. We could place big mirrors in orbit or in a stable position between the Earth and the Sun. But the most frequently discussed option is to inject aerosols into the stratosphere, the layer of air that resides about 10 to 50 kilometers above the surface. These aerosols would scatter some sunlight striking the Earth, reflecting it to space.
There’s already a natural layer of sulfate aerosols in the stratosphere, with sulfur originating from strong volcanic emissions and other natural sources. It varies in thickness from year to year, especially after large volcanic eruptions. Solar geoengineering would make this layer thicker, reflecting more sunlight, thereby cooling the planet.
At first glance, this might sound reasonable. Why can’t we just scatter a bit of sunshine, and cool the planet a bit? Couldn’t this nicely counteract the effects of global warming?
No. Not exactly.
It Won’t Conveniently Counteract Greenhouse Warming
While it might sound reasonable to cancel out greenhouse warming with solar geoengineered cooling, it isn’t that simple. The ways greenhouse gases warm the planet are very different from how solar geoengineering might cool it. One doesn’t directly cancel out the other.
By effectively “trapping” some of Earth’s outgoing infrared radiation, greenhouse gases warm the planet in a particular way. First of all, rising greenhouse gases cause the planet to warm more at night than during the day — a pattern observed across much of the world. They also warm the planet more in the high latitudes, especially in the northern hemisphere, than the equatorial regions. And they usually cause more warming in the winter months than in the summer.
Injecting aerosols into the stratosphere would cool the planet — but in a different way. Because aerosols reflect solar radiation, they are more effective during the day, during the summer, and in the equatorial zone. In other words: The opposite pattern of greenhouse warming.
So this kind of solar geoengineering would not conveniently counteract the warming caused by greenhouse gases. It tends to cool in the wrong places, at the wrong times, to be a perfect antidote to greenhouse warming.
Simply put, it doesn’t provide an easy solution to greenhouse warming.
An analogy comes to mind: If your hair is on fire, sticking your feet in ice water won’t help.
An analogy comes to mind: If your hair is on fire, sticking your feet in ice water won’t help.
Not only is solar geoengineering largely ineffective, it could be dangerous. The combined effect of greenhouse gases and solar geoengineering could create a real mess — potentially destabilizing weather and climate patterns in unforeseen ways. That could make things even worse.
It Has Other Risks
If the effects of solar geoengineering on climate alone don’t worry you — and they should — there are a suite of other impacts to consider.
Potentially the most serious is how changing the nature of sunlight around the Earth would affect photosynthesis, the very foundation of the biosphere. By reducing the amount of sunlight striking the Earth’s surface, and changing the balance of “direct” and “diffuse” sunlight (effectively making the sky look more hazy), solar geoengineering could have a profound impact on ecosystems and crops.
Also, fundamentally changing the nature of the stratosphere — for decades to come — could have profound impacts on the physics, chemistry, and circulation of the upper atmosphere. The long-term environmental effects of this are still poorly understood, but one worry is it could harm the stratospheric ozone layer.
Solar geoengineering does nothing for the non-climatic effects of increasing carbon dioxide. Even if it could counteract global warming, it would do nothing about ocean acidification. This alone takes it out of contention as a serious solution.
Mostly, I worry about the moral hazard of solar geoengineering — distracting us from the real work of addressing climate change. Instead of spending time, attention, and money on fantasies, let’s focus our attention on reducing the world’s greenhouse gas emissions, supporting nature’s carbon sinks, and improving the foundations of society.
Despite Mistaken Headlines, Scientists are Not Endorsing the Idea
Solar geoengineering has gained attention recently because the National Academy of Sciences, a respected advisory body to the U.S. government, proposed a limited research program on it.
It did not endorse the concept, as some media outlets erroneously reported. It merely proposed a research effort to examine the concept, including its potential dangers. That’s a reasonable course of action.
But don’t mistake this call for study as an endorsement of solar geoengineering by serious climate scientists. That’s not the case.
It’s Unnecessary
One last argument you hear from proponents of solar geoengineering is that we may need it as an emergency measure to “tap the brakes” on climate change — if we don’t act in time.
That’s an ironic position to take since solar geoengineering diverts attention from effective climate action.
But it’s also wrong for another reason: We have other tools to “tap the brakes” on the climate system. And these aren’t a dangerous distraction from stopping climate change. In fact, they’re part of the solution.
Global warming is caused by multiple gases — not just carbon dioxide. Each gas has its own characteristics. Some trap more heat, molecule for molecule, than others. And some last longer in the atmosphere than others.
To quickly slow climate change, and buy time for us to make other emissions reductions, we can focus on short-lived, powerful greenhouse gases like methane, carbon monoxide, and “black carbon”.
To understand how this might work, let’s look at “pulse-response” diagrams of how greenhouse gases affect climate. We see how a single year of emissions (based on the mix we emit today) would warm the planet over the subsequent decades. In other words, we can estimate how a single year’s “pulse” of greenhouse gases causes a warming “response” in future decades.
In this example, adapted from the IPCC Fifth Assessment Report, we can see how the planet warms (in mK, or thousandths of a ˚C) over time from a single year’s emissions.
First we see how the planet would warm from a single year’s emission of carbon dioxide (CO2) and nitrous oxide (N2O) — two greenhouse gases that live in the atmosphere for hundreds of years.
Then we add “short-lived” warming agents, including methane (CH4), carbon monoxide (CO), and black carbon (BC) which have a profound warming impact for a few decades, but then disappear.
We can then separate the effects of short-lived warming agents (black carbon, methane, and carbon monoxide) and long-lived ones (carbon dioxide and nitrous oxide).
These curves illustrate how we can have a profound and immediate impact on climate change by redoubling our efforts on short-lived warming agents — primarily methane, carbon monoxide, and black carbon. This is how we can “tap the brakes” on climate change without the failures and unnecessary risks solar geoengineering.
We need to reduce all greenhouse gas emissions as quickly as possible, of course. Still, a redoubled effort on methane, carbon monoxide, and black carbon could have an immediate impact on climate change in the coming decades, giving us time to deploy longer-term climate solutions.
Stopping climate change requires us to focus on the job at hand, not getting distracted by science-fiction ideas that won’t really work, pose considerable risks, and only delay us from effective action.
While there are many “non-solutions” in circulation these days, solar geoengineering is the most bizarre. It’s largely ineffective at countering greenhouse warming and poses significant risks to the planet.
If you’re thinking solar geoengineering sounds a bit like using smoke and mirrors to address climate change, I don’t blame you. You’re not far off.
If you’re thinking solar geoengineering sounds a bit like using smoke and mirrors to address climate change, I don’t blame you. You’re not far off.
It’s time to move away from fantasies and get back to the work of reducing emissions, supporting nature’s carbon sinks, and improving the condition of people around the world. Those are the foundations of addressing climate change, and anything else is a distraction that we can no longer afford.
Dr. Jonathan Foley (@GlobalEcoGuy) is a climate & environmental scientist, writer, and speaker. He is also the Executive Director of Project Drawdown, the world’s leading resource for climate solutions.
These views are his own.
Copyright © 2021, Jonathan Foley. All rights reserved.
4/5/2021: Post updated for clarity, including adding “to deploy” to the following sentence, to avoid potential confusion with those who wish to research solar geoengineering further: “But some people seem unwilling to accept this and are proposing to deploy hair-brained ideas to counteract climate change instead of addressing its underlying causes.”
