Can global warming be mitigated by a technological fix such as injecting light-blocking particles into the atmosphere or chemically “scrubbing” excess greenhouse gases from the atmosphere? Department of Global Ecology scientist Ken Caldeira addressed this question in his testimony to the U.S. House of Representatives Committee on Science and Technology in a hearing titled“Geoengineering: Assessing the Implications of Large-Scale Climate Intervention” on November 5, 2009.

Caldeira testified that climate change poses a real risk to Americans and that the surest way to reduce this risk is to reduce emissions of greenhouse gases. But other options, such as geoengineering approaches, may also cost-effectively contribute to risk reduction in certain circumstances. 

Solar Radiation Management (SRM) approaches seek to reduce the amount of climate change by reflecting some of the sun’s warming rays back to space. Carbon Dioxide Removal (CDR) approaches seek to reduce the amount of climate change and ocean acidification by removing the greenhouse gas carbon dioxide from the atmosphere.

 The most promising SRM proposals appear to be inexpensive, can be deployed rapidly, and can cause the Earth to cool quickly. But they do not address the root causes of our climate problem or the problem of ocean acidification.  Examples of SRM include injecting particles into the atmosphere or whitening clouds over the ocean to reflect incoming solar radiation. While SRM approaches may reduce overall climate risk, they may also introduce additional environmental and political risk.

The most promising CDR approaches appear to be expensive (relative to SRM, but perhaps competitive to reducing emissions) and take a long time before they could cool the Earth. However, they address the root cause of the problem – excess carbon dioxide in the atmosphere. Examples include biological approaches such as planting forests and chemical approaches that extract carbon dioxide from the atmosphere or from emissions sources and store it underground.

Neither SRM nor CDR would be a climate cure-all, however. 

“The best, surest, and clearest way to reduce environmental risk associated with greenhouse gas emissions is to reduce greenhouse gas emissions,” said Caldeira in his written testimony. “If you take the risk of climate damage seriously, you want to take action to diminish risk by reducing greenhouse gas emissions, but you would not want to limit yourself to only one risk-reduction approach.”

Caldeira compared geoengineering approaches to seatbelts in automobiles. “Just because we wear seatbelts, that does not mean we will drive more recklessly,” he said. “Seat belts can remind us that driving is a dangerous activity.”

He stressed the need for a research program to uncover the limitations and potential pitfalls of geoengineering. “We do not want our seat belts to be tested for the first time when we are in an automobile accident. If the seat belts are not going to work, it would be good to know that now. If there is something really wrong with thoughtfully intervening in the climate system, we should try to find that out now, so that if a crisis occurs, policy makers are not put in the position of having to decide whether to let people die or try to save their lives by deploying, at full scale, an untested system.

“We need the research now to establish whether such approaches can do more good than harm,” he said. “This research will take time. We cannot wait to ready such systems until an emergency is upon us.”