Geoengineering: The State of the Science

As the effects of climate change accelerate, a growing body of researchers, policymakers, and engineers are exploring geoengineering — deliberate, large-scale intervention in Earth's climate system — as a complement to emissions reduction. US Geoengineering tracks the technologies, research programs, and policy debates shaping this consequential field.

What Is Geoengineering?

Geoengineering encompasses two broad categories of climate intervention:

Solar Radiation Management (SRM)

Techniques that reflect a small percentage of incoming sunlight back into space, reducing the amount of solar energy absorbed by Earth's surface.

• Stratospheric Aerosol Injection — Releasing reflective particles (such as sulfur dioxide) into the upper atmosphere to mimic the cooling effect of volcanic eruptions. The most studied SRM approach.
• Marine Cloud Brightening — Spraying sea salt particles into low-lying marine clouds to increase their reflectivity, cooling the ocean surface below.
• Surface Albedo Modification — Increasing the reflectivity of roofs, roads, and agricultural land through lighter-colored materials and crop varieties.

Carbon Dioxide Removal (CDR)

Technologies that remove CO2 directly from the atmosphere and store it permanently.

• Direct Air Capture (DAC) — Industrial facilities that use chemical processes to extract CO2 from ambient air. Companies like Climeworks and Carbon Engineering are operating pilot plants and scaling up.
• Bioenergy with Carbon Capture and Storage (BECCS) — Growing biomass that absorbs CO2, burning it for energy, and capturing the emissions for underground storage.
• Enhanced Weathering — Spreading crusite minerals on agricultural land to accelerate the natural chemical process that draws CO2 out of the atmosphere.
• Ocean Alkalinity Enhancement — Adding alkaline materials to the ocean to increase its capacity to absorb atmospheric CO2.

US Research Programs

Federal Initiatives

The US government has increased geoengineering research funding in recent years. The National Academies of Sciences published a landmark report recommending a federal research program for solar geoengineering, and NOAA, DOE, and ARPA-E have all funded related research.

University Research

Harvard's Solar Geoengineering Research Program, MIT's Climate and Sustainability Consortium, and Stanford's Carnegie Department of Global Ecology are among the leading academic centers studying both the science and governance of geoengineering.

Private Sector

A growing number of startups are working on carbon removal technologies, driven by corporate carbon credit markets and government incentives like the 45Q tax credit for carbon capture.

The Debate

Geoengineering raises profound ethical, political, and scientific questions:

• Moral hazard — Does the prospect of geoengineering reduce urgency to cut emissions?
• Governance — Who decides whether and how to deploy technologies that affect the entire planet?
• Unintended consequences — SRM could alter precipitation patterns, affect agriculture, and create regional winners and losers
• Termination shock — If SRM were suddenly stopped, temperatures could spike rapidly

Why It Matters

The Intergovernmental Panel on Climate Change has acknowledged that meeting the Paris Agreement's 1.5°C target will likely require both aggressive emissions cuts and carbon dioxide removal. Whether more aggressive interventions like solar radiation management become necessary depends on the pace of decarbonization in the coming decades.

Understand the science. Engage with the debate. The decisions ahead affect everyone.