The Earth’s carbon cycle is profoundly out of balance. After thousands of years of relative stability, modern human activities—primarily the burning of fossil fuels, large-scale deforestation, and intensive animal agriculture—have driven atmospheric carbon dioxide levels to heights not seen in millions of years. Rebalancing the carbon cycle is no longer a question of whether we can afford to act, but of how quickly and effectively we can intervene to restore a livable climate.
For decades, the climate conversation has been framed around one central task: reducing emissions. Every report, every international conference, every policy framework has revolved around cutting the flow of carbon dioxide into the atmosphere. And to be clear, this is essential. We must stop adding fuel to the fire. But as Peter Fiekowsky has argued with clarity and urgency, this is no longer enough. Fiekowsky is a physicist and author of Climate Restoration: The Only Future That Will Sustain the Human Race (2022).
What has received too little explicit attention is the fact that human activity is already a planetary-scale climate intervention. The accumulation of carbon dioxide, methane, nitrous oxide, and other greenhouse gases has altered Earth’s radiative balance. At the same time, sulfur and other industrial aerosols have masked a portion of that warming — a form of unintentional geoengineering driven by air pollution. In that sense, we are not “considering” geoengineering; we have been engaged in it for over a century.
The climate system is already destabilized. CO₂ levels today are above 420 parts per million—far higher than the 280 ppm baseline of pre-industrial times, and higher than at any point in human history. Even if we stopped emitting tomorrow, we would still be living in a climate defined by dangerous extremes: heatwaves, super-storms, accelerating sea level rise, and ecosystem breakdown.
The question, then, is not just how to slow the damage. It is how to restore a safe climate for ourselves and for generations to come.
Why Mitigation Alone Cannot Save Us
Think of it this way: reducing emissions is like slowing down a car that’s already speeding toward a cliff. It may keep us from going over quite as fast, but unless we steer away, the outcome is the same. The backlog of CO₂ already in the air—hundreds of billions of tons—will continue warming the planet for centuries.
But the problem is broader: the climate system now has a large positive energy imbalance—Earth is absorbing more solar energy than it radiates back to space because of human-induced greenhouse forcing. Recent work led by James Hansen shows that even with aggressive mitigation under current policy pathways, warming beyond 1.5 °C—and likely beyond 2 °C—this century is extremely likely unless the energy imbalance itself is addressed. This implies that limiting global warming within defined thresholds will require deliberate modification of Earth’s energy balance—a form of purposeful climate intervention.
Nature, however, has dealt with this problem before. Over millions of years, Earth has repeatedly drawn down atmospheric carbon through processes like photosynthesis and ocean sequestration. Forests, soils, plankton, and wetlands are the planet’s natural carbon pumps. Left to themselves, they work on geological time scales. But with human help, we can accelerate them.
This is the insight behind climate restoration: mitigation slows the damage, but restoration reverses it.
What Climate Restoration Means
Climate restoration is not a slogan. It is a measurable goal: bringing atmospheric CO₂ levels back to the safe range of 280–300 ppm and stabilizing the climate system.
That may sound ambitious—utopian, even. But as Fiekowsky reminds us, humanity has already undertaken massive global transformations before: ending ozone depletion through the Montreal Protocol, feeding billions with modern agriculture, and eradicating diseases like smallpox. The challenge now is to scale up the practices that nature already uses to store carbon and to complement them with safe technologies.
Climate restoration entails reducing atmospheric greenhouse gas forcing to levels consistent with a stable and safe climate. But current climate trajectories and energy imbalance science make clear that reducing emissions alone—or even drawing down carbon dioxide—may not be enough to avoid dangerous warming before irreversible impacts materialize. Therefore, restoring a stable climate must include purposeful research, governance, and, if responsibly and equitably governed, deployment of solar climate interventions such as stratospheric aerosol injection and marine cloud brightening. These are not fringe options; they are part of the set of tools required to manage the energy imbalance that humanity has already created.
Climate restoration does not mean “geoengineering the Earth into submission.” It means aligning our economic systems and political will with the regenerative capacities of life itself. At the same time, we may need some forms of geoengineering, such as solar radiation management (SRM), to reduce heating in the short term, to give us time for more permanent measures.
Critics of SRM often raise valid concerns: about moral hazard, governance, regional climate disruption, and the potential to delay more fundamental transitions away from fossil fuels. And yet, as Dr. Mike MacCracken contends, dismissing these approaches outright may be as dangerous as the climate impacts we seek to avoid. In a world already locked into 1.5°C of warming and headed rapidly toward 2.5°C or beyond, where ice sheets are melting faster than anticipated and extreme weather is becoming the norm. He asks: What happens if we do nothing but reduce emissions, and it turns out to be too little, too late?
Solar climate interventions—including stratospheric aerosol injection and other forms of solar radiation modification—are not replacements for emission cuts or carbon removal. They address the energy imbalance we have already engineered into the climate system and can reduce peak warming on timescales too short for mitigation alone. Responsible governance frameworks, global cooperation, and ethical safeguards are essential. Research, transparency, and equitable decision-making must precede any deployment — but research and planning cannot wait for warming to overtake humanity’s capacity to cope.
In this light, solar geoengineering is not proposed as a substitute for cutting emissions or removing carbon, but as a potential temporary measure—a climate bridge—that might help lower peak temperatures while longer-term solutions scale up. MacCracken envisions a research agenda grounded in transparency, global cooperation, and robust ethical frameworks. He emphasizes that we have a responsibility to future generations not only to act but to be prepared—by understanding the full range of tools at our disposal, including those that might one day be needed to prevent the most catastrophic outcomes.
This perspective does not come without conflict. Other respected scientists, such as Professor Raymond Pierrehumbert, offer strong critiques, warning that SRM could be a slippery slope, masking the symptoms without addressing the cause. The tension between these views underscores a critical truth: there is no perfect solution, only difficult trade-offs. The planet’s carbon imbalance, once set in motion, cannot be neatly reversed. But if we are to maintain a habitable world, we must be willing to face the complexity of our predicament with courage and intellectual honesty.
While geoengineering approaches have raised concerns in some quarters, those concerns largely stem from outdated framings that treat geoengineering as an optional “Plan B” rather than an inevitable outcome of the climate forcings already in place. The debate should not be framed as whether humanity will intervene at the planetary scale—because we already do—but how we can govern that intervention responsibly. James Hansen and colleagues argue that acknowledging our existing climate engineering via greenhouse gases and aerosols is essential to responsibly addressing the climate emergency, and that purposeful solar climate modification may be necessary to avoid the worst outcomes of an unchecked energy imbalance.
In the end, rebalancing the carbon cycle will require a portfolio approach—one that includes rapid decarbonization, large-scale ecosystem restoration, carbon dioxide removal technologies, and yes, the careful study of solar climate interventions. MacCracken’s appeal is not for reckless experimentation, but for responsibility: the responsibility to prepare for a world where climate damages mount faster than our best intentions can contain.
It is a call to humility, but also to agency. And perhaps the most sobering part of his argument is this: it’s not just about whether SRM works in a lab, or in a model—it’s about whether we will wish we had better understood it when the next tipping point comes.
Sea-Level Rise: An Escalating Threat
Dr. Mike MacCracken emphasizes that sea-level rise is not a distant concern but a present and accelerating reality. He points to the increasing rates of sea-level rise over the past century, attributing this trend to the melting of glaciers and ice sheets, as well as thermal expansion of seawater due to global warming. This ongoing rise poses significant risks to coastal communities, ecosystems, and infrastructure.
MacCracken underscores the importance of understanding and addressing the mechanisms driving sea-level rise. He advocates for comprehensive monitoring and modeling to predict future changes and inform adaptation strategies. By highlighting the tangible impacts already being observed, MacCracken calls for urgent action to mitigate further sea-level rise through emission reductions and other climate interventions.
Diverging Perspectives on Solar Radiation Management
The debate over SRM reflects a broader discourse on how best to address the climate crisis.
Dr. Mike MacCracken’s Position:
MacCracken views SRM as a potential interim measure to reduce global temperatures while long-term solutions, such as transitioning to renewable energy and enhancing carbon sinks, are implemented. He argues that, given the accelerating impacts of climate change, including sea-level rise, it is prudent to research and understand all possible tools that could mitigate these effects. MacCracken emphasizes that SRM should not replace emission reductions but could serve as a complementary strategy to buy time and prevent the most catastrophic outcomes.
Professor Raymond Pierrehumbert’s Counterpoint:
In contrast, Professor Raymond Pierrehumbert expresses strong reservations about SRM. He cautions against the moral hazard it presents, where reliance on technological fixes might detract from efforts to reduce greenhouse gas emissions. Pierrehumbert also raises concerns about the potential for unintended consequences, such as changes in precipitation patterns and impacts on regional climates. He advocates for focusing resources on proven mitigation strategies and warns that SRM could introduce new risks without addressing the root causes of climate change.
Navigating the Path Forward
The contrasting views of MacCracken and Pierrehumbert highlight the complexity of climate intervention strategies. While MacCracken urges the exploration of all options, including SRM, to address immediate threats like sea-level rise, Pierrehumbert advises caution, emphasizing the need to prioritize emission reductions and avoid potential pitfalls of untested technologies.
This dialog underscores the importance of informed, multidisciplinary approaches to climate policy, where diverse perspectives contribute to robust decision-making. As the climate crisis intensifies, balancing immediate needs with long-term sustainability remains a central challenge.
Given this, here are some climate restoration pathways that Peter Fekowsky and others urge us to consider:
- Ocean Fertility
Tiny plankton in the ocean absorb vast amounts of CO₂ through photosynthesis, transporting carbon to the deep sea when they die and sink. Ocean iron fertilization—adding trace amounts of iron to stimulate plankton blooms—could safely accelerate this natural pump. Careful governance and monitoring would be required, but the potential is enormous. - Enhanced Land Photosynthesis
Expanding and protecting forests, rewetting peatlands, restoring prairies, and investing in regenerative agriculture all pull carbon from the air while revitalizing biodiversity, water cycles, and soils. Biochar, a stable carbon form created from biomass, can lock carbon away for centuries while improving soil fertility. - Technological Capture
Direct air capture (DAC) and other industrial methods remain expensive today, but they will likely play a role at scale—especially for sectors that are hard to decarbonize. Fiekowsky suggests we should see these as complements, not competitors, to natural solutions. - Ecosystem Regeneration as Climate Restoration
Beyond carbon, restoring ecosystems helps reset the hydrological cycle, moderates regional climates, and creates more resilient landscapes. A bioregional approach—rooted in the unique patterns of place—can scale this work across the globe.
The lesson is clear: climate restoration cannot be left to technocrats or corporations alone. It requires democratic oversight, Indigenous leadership, citizen participation, and international cooperation.
From Net Zero to Safe Climate
The dominant global framework—“net zero by 2050”—is not enough. It stabilizes emissions at dangerous levels but does not restore a livable climate.
Instead, we must shift the goalposts: not just slowing the damage, but restoring the conditions in which human societies and ecosystems can thrive. That means financing climate restoration at scale, supporting innovations and community projects alike, and insisting on policies that make restoration as urgent as mitigation.
The climate crisis is often framed as a narrowing corridor of diminishing options. But climate restoration opens the frame again. It says: our choices matter. We can aim higher than mere survival. We can aim for a habitable, flourishing planet.
As Fiekowsky insists, climate restoration is not utopia—it is necessity. It is also possibility, if we mobilize the will, the resources, and the imagination to act.
The next part of this book will explore what that mobilization looks like: the pathways—technological, political, cultural, and ecological—that can take us from where we are to where we need to be.