The Albedo Trap

Enhanced rock weathering spreads crushed silicate minerals across agricultural land to accelerate the natural process by which CO₂ is absorbed into carbonate minerals. Marine carbon dioxide removal dissolves alkaline materials in the ocean to increase its CO₂ uptake. Both are proposed as large-scale negative emissions technologies. Both require covering enormous surface areas.

Marston and Ibarra (arXiv:2501.01885) show that both approaches change Earth’s albedo — the fraction of sunlight reflected back to space — and the albedo change can overwhelm the radiative forcing from the CO₂ removed.

The mechanism is straightforward. Spreading light-colored crushed rock over dark agricultural soil increases land albedo, producing a cooling effect independent of any carbon removal. Conversely, changing ocean surface chemistry can alter ocean albedo. The radiative impact of even parts-per-thousand changes in albedo across millions of square kilometers is comparable to removing substantial quantities of atmospheric CO₂.

The problem: the albedo effect operates immediately, while the CO₂ removal effect accumulates slowly. In the early years and potentially decades of deployment, the albedo change dominates the total radiative balance. For some configurations — particularly land-based enhanced weathering in certain regions — the net effect can be warming, not cooling. You deploy a carbon removal technology and the planet gets warmer.

The structural insight: large-scale surface modifications cannot be evaluated by their intended mechanism alone. Any technology that covers millions of square kilometers of Earth’s surface is, whether it intends to be or not, a geoengineering intervention with albedo consequences. The carbon removal is one effect among several, and it may not be the largest one.

Marston & Ibarra, “Removing Atmospheric Carbon Dioxide Using Large Land Or Ocean Areas Will Change Earth Albedo And Force Climate,” arXiv:2501.01885 (2025).