When the book discussed geoengineering through The Day After Tomorrow, it was largely a theoretical conversation — the kind of extreme intervention that might become necessary if climate change progressed unchecked. Since 2018, that conversation has become concrete. Companies and researchers are actively experimenting with altering the atmosphere, and the governance frameworks to manage these interventions do not exist.
The book's Geoengineering page covered the concepts — solar radiation management, carbon capture, stratospheric aerosol injection. What has changed is that some of these are no longer concepts.
Stratospheric aerosol injection — releasing reflective particles into the upper atmosphere to reduce incoming solar radiation — has moved from computer models to real-world proposals and small-scale experiments. Harvard's SCoPEx project planned to release small amounts of calcium carbonate into the stratosphere to study the effects, though it faced significant opposition and delays. More controversially, a startup called Make Sunsets began releasing sulfur dioxide particles from weather balloons in 2022, essentially conducting unilateral geoengineering experiments without scientific oversight or international coordination.
Marine cloud brightening — spraying sea salt particles into low-lying clouds to make them more reflective — has advanced to outdoor experiments. Researchers at the University of Washington conducted tests off the coast of California, studying whether the technique can cool local ocean temperatures to protect coral reefs.
Enhanced weathering — spreading crusite rock dust on agricultural land to accelerate natural chemical processes that absorb carbon dioxide — is being trialed at scale by companies like Lithos and UNDO, with farmers spreading basalt dust on their fields.
The governance void is the most alarming dimension. No international framework exists for who gets to alter the Earth's atmosphere. The effects of stratospheric aerosol injection would be global and unevenly distributed — potentially benefiting some regions while causing drought or disrupted monsoons in others. A decision that affects every person on Earth is being made by researchers, startups, and national governments acting unilaterally. This is the book's Could We? Should We? question at planetary scale.
The moral hazard concern is significant. If geoengineering appears to offer a "plan B" for climate change, it could reduce the political urgency of cutting emissions — which remains the only durable solution. The book's Complexity and Unintended Consequences framework warns against the assumption that we can engineer our way out of complex systems problems with simple interventions. Climate is the most complex system there is.
Intergenerational Responsibility — one of the book's most powerful ethical threads — applies with particular force. Once stratospheric aerosol injection begins, it cannot easily be stopped: abrupt termination would cause rapid warming ("termination shock"), committing future generations to maintaining an intervention they did not choose. See Should anyone have the right to alter the Earth's atmosphere on purpose? and What do we owe people who haven't been born yet?