# Geoengineering

Geoengineering refers to a set of emerging technologies that could manipulate the environment and partially offset some of the impacts of climate change. It could not be a replacement for reducing emissions (mitigation) or coping with a changing climate (adaptation); yet, it could supplement these efforts.

Geoengineering is conventionally split into two broad categories: The first is carbon dioxide removal (CDR). The other is ‘albedo modification’, often called solar radiation management (SRM) or ‘solar geoengineering’.

CDR aims to remove carbon dioxide from the atmosphere, which would address the root cause of climate change — the accumulation of carbon dioxide in the atmosphere. It may become an important part of addressing climate change. But it is currently still expensive and relatively slow.

Albedo modification seeks to reflect a small fraction of sunlight back into space to cool the planet. The principle is simple. It is the same reason we wear white in the summer and black in the winter. Lighter colors reflect sunlight and cool what’s underneath. Darker colors absorb light and heat. Albedo modification is no substitute for cutting carbon dioxide pollution. It is a potential supplement.

## Albedo Modification

There are several proposed albedo modification technologies. The two main ones are: marine cloud brightening and stratospheric aerosol injection. The first is just that: attempting to brighten marine clouds to reflect more sunlight back into space. The advantage: it appears to be a relatively innocuous methodology. The main minus: it could only be applied to around 10 percent of the globe, with spotty results and potentially large risks around disturbing regional weather patterns.

Stratospheric aerosol injection refers to technologies that could cool the planet by injecting tiny reflective particles, such as sulfate aerosols or even diamond dust, into the upper atmosphere. These particles could scatter a small fraction of sunlight back into space. They could essentially act like a very thin sunshade for the ground beneath.

We know from scientific research and from examples in our natural world that reducing sunlight reduces global average temperatures. We even see this with natural volcanic eruptions. When Mount Pinatubo erupted in 1991, for example, the earth cooled by 0.5° Celsius for more than a year because of the 20 million metric tons of sulfur dioxide that were released in the atmosphere and reflected sunlight back to space.

Albedo Modification could cool the planet in a similar way. In fact, we could cut the rate of global average warming in half with one quarter of the amount of sulfates as released by Mount Pinatubo.

In short, there is little doubt that albedo modification could reduce global average temperatures. The challenge is that there are uncertainties and risks associated with albedo modification’s effects on variables other than temperature like precipitation.

## Albedo Modification Benefits and Risks

Climate models have consistently shown that albedo modification, when used in moderation and combined with emissions cuts, has the potential to reduce climate changes around the globe. It could stop rising temperatures and keep the world below the 1.5° Celsius target agreed upon at the Paris climate talks — a goal that is extremely unlikely to be achieved by emissions cuts alone.

Albedo modification could also curb the rise in peak temperatures, which cause dangerous heat waves, and reduce extreme rainfall that often leads to flooding. Early evidence suggests it may even have the potential to slow sea-level rise, which threatens many coastal areas. Furthermore, albedo modification could achieve all of these results relatively rapidly (within years to decades) and inexpensively (with some estimates ranging from $1 to$10 billion per year).

However, these global benefits come with novel risks and significant uncertainty. Current climate science is not advanced enough to predict local impacts, which could be negative for some countries or regions, or to identify all possible effects that it could have on the Earth’s complex climate system. Yet, it is worth noting that to date, among the hundreds of peer-reviewed papers showing climate models, there is not a single climate model run that shows that moderate albedo modification would make any region worse off overall.

Another challenge relates to ocean acidification. Every year, the ocean absorbs about one-quarter of the CO2 we emit into the atmosphere, changing the chemistry of the oceans and harming marine ecosystems. Given that albedo modification strategies would not remove C02 from the atmosphere, but rather reflect sunlight back to space, it could do little to address this serious problem.

It is therefore clear that albedo modification could not counteract all negative impacts of climate change or eliminate the long-run risks of climate change, since it does not address the root cause — increased greenhouse gas concentrations in the atmosphere. Therefore, albedo modification has the potential only to supplement, but not substitute for, mitigation and adaptation strategies.

## Albedo Modification Research

U.S. National Academy of Sciences (2015)Research could reduce uncertainty about the technology’s potential benefits and risks, but, for decades, research in albedo modification has been limited because of a fear, or taboo, that it could lesson efforts to cut emissions. This taboo is weakening, with the U.S. National Academy of Sciences and major environmental groups such as the Environmental Defense Fund and the Natural Resources Defense Council now supporting research. Yet, there is still no U.S. government research program. In fact, the worldwide effort focused on improving albedo modification technology likely amounts to fewer than the equivalent of five full-time researchers.

Research on albedo modification offers an extraordinary social return-on-investment. If the technology proves workable, it might cut the negative global impacts of climate change in half, providing enormous welfare benefits of at least 1% of global GDP by mid-century, over \$1 trillion per year, and dwarfing direct costs to the tune of more than a thousand to one.

Furthermore, a modest research effort can yield rapid progress because the technical development of albedo modification would be largely an exercise in the application of existing tools from aerosol science, atmospheric science, climate research, and applied aerospace engineering; and governance research can build upon decades of climate policy work across fields as diverse as economics, international law, environmental ethics, and risk perception.

## Albedo Modification Research at Harvard

Our group is a fast-growing team of researchers focused on the science and public policy of albedo modification. We research the benefits and risks of different aerosols, the climate impacts of using the technology, and the broader economic, political, and governance risks.

Given the increasing interest in and need for research on this subject, we are working to build Harvard's Solar Geoengineering Research Program (SGRP), a broader program at Harvard that will bring together an interdisciplinary group of faculty from across the university to accelerate the understanding of the effectiveness and risks of solar geoengineering. The program will combine three key elements: research on solar geoengineering technologies, analysis of environmental risks, and a broad program of assessment and governance research.

Establishing programs for albedo modification research is essential. Over the coming decades, humanity will face hard decisions about climate change and albedo modification, whether we have research programs or not. However, if we establish robust albedo modification programs at Harvard and elsewhere, we expect those decisions will be better informed, and will thus lead to significantly better outcomes.