Scientists Warn: Carbon Removal Won’t Save Us—Cutting Emissions Is Our Only Hope

A new APS report highlights the immense challenges of large-scale carbon dioxide removal (CDR) and emphasizes that cutting emissions is far more efficient. While technologies like direct air capture and enhanced rock weathering exist, they require massive energy and resources to make a significant impact. The report urges policymakers to focus on reducing emissions first while cautiously investing in CDR research for future needs.

CONTENTS:

• Key Findings on Carbon Removal Challenges
• Policy Recommendations
• The Bigger Picture

Scientists Warn: Carbon Removal Won’t Save Us—Cutting Emissions Is Our Only Hope

For nearly two million years, humans have used fire as a tool, first for warmth and cooking, and later for energy production. About 4,000 years ago, coal was discovered in northern China, marking the beginning of fossil fuel consumption. Today, humanity burns around 8.8 billion metric tons of coal annually, releasing vast amounts of carbon dioxide (CO2) that had been stored in Earth’s crust for millions of years. This accumulation of CO2 is driving climate change, intensifying hurricanes and heat waves, and accelerating the melting of glaciers and sea ice.

As nations strive to achieve net-zero emissions by 2050, the challenge remains: What can be done about the 1.5 trillion metric tons of CO2 already in the atmosphere? On January 27, 2025, the American Physical Society (APS) released a report titled “Atmospheric Carbon Dioxide Removal: A Physical Science Perspective.” The report, authored by Washington Taylor (MIT), Jonathan Wurtele (UC Berkeley), Bob Rosner (University of Chicago), and Brad Marston (Brown University), evaluates current CO2 removal (CDR) technologies and advises policymakers on the complexities of large-scale carbon removal.

Key Findings on Carbon Removal Challenges

Every year, human activities release approximately 35 billion metric tons (gigatons) of CO2. Removing even one gigaton is a formidable challenge. According to Marston, the energy required for large-scale CDR would compete with efforts to expand renewable energy, making the process a major logistical hurdle.

The report categorizes carbon removal technologies into two approaches: cyclic and once-through. Cyclic processes, like chemical direct air capture (DAC), use solvents or sorbents to capture CO2, which is then compressed and stored underground. Because atmospheric CO2 is dilute—comprising only 420 molecules per million—the process requires substantial energy just to concentrate the gas. Marston compares it to operating all the world’s air conditioners for a year just to remove 3% of annual emissions. Moreover, scaling up DAC would consume a significant portion of the total power output of the United States.

Once-through methods, such as enhanced rock weathering and ocean alkalinity enhancement, involve spreading finely ground minerals on land or in the ocean to accelerate natural CO2 absorption. Unlike DAC, these methods do not require additional energy to capture CO2. However, their large-scale implementation would demand an enormous amount of material—comparable to the global cement industry’s production levels.

Ecosystem-based strategies, including reforestation and soil carbon sequestration, are also considered. These approaches offer cost-effective benefits, including improved biodiversity and air quality. However, they come with risks, as stored carbon can be released by wildfires and other environmental disturbances.

Policy Recommendations

Despite the high energy costs, the report acknowledges that CDR may be necessary in the future. However, it advises selective investment in research and development rather than full-scale implementation at this stage.

Marston cites Climeworks’ DAC plant in Iceland as an example. Although heralded as a major achievement, it would take one million similar plants to offset annual global emissions—a scale that seems impractical. Thus, reducing emissions remains the most effective solution.

Ecosystem-based approaches, while limited in their potential, could play a crucial role in carbon management. However, land-use conflicts and unpredictable events like wildfires pose challenges. Additionally, any large-scale carbon removal strategy would require a massive increase in carbon-free energy production, such as solar or nuclear power.

The report also highlights the need for rigorous measurement, reporting, and verification systems to ensure the effectiveness of CDR initiatives. Given the complexity of tracking CO2 absorption in open systems like oceans, robust international standards are essential.

The Bigger Picture

Physicist Washington Taylor, who contributed to the report, recalls that in 2006, the full scope of climate change was not widely understood. By 2021, his interest in the issue led him to join the APS Panel on Public Affairs (POPA). Marston, who became involved in 2022, notes that APS had previously studied carbon capture, but given the rapid evolution of the field, another review was warranted.

Marston traces his awareness of climate science back to NASA scientist James Hansen’s 1988 testimony before Congress, where Hansen warned of global warming based on meteorological data. The United Nations responded by forming the Intergovernmental Panel on Climate Change (IPCC) in 1989. The predictions made in the IPCC’s first report in 1990—including stronger hurricanes, heat waves, and rising sea levels—have all materialized.

The evidence suggests that global action is still too slow to prevent worsening climate impacts. Taylor stresses the importance of continued scientific research, as informed decision-making is critical for addressing the climate crisis. The APS report underscores that large-scale CDR would require immense resources, making immediate emission reductions the most viable path forward. Ultimately, while scientists understand the problem, the real challenge lies in securing global cooperation and investment in effective solutions.

Without decisive action, Marston warns, the extreme weather events seen in recent years are only a preview of what’s to come.