Attempts to curb climate change by capturing carbon underground or geo-engineering to help the Earth better reflect incoming sunlight are nowhere near ready for use, a US panel of scientists said.
"There is no substitute for dramatic reductions in greenhouse gas emissions to mitigate the negative consequences of climate change," said the National Research Council in a two-part report on proposed climate-intervention techniques.
"If society ultimately decides to intervene in Earth's climate, any actions should be informed by a far more substantive body of scientific research, including ethical and social dimensions, than is presently available."
The panel urged against "albedo-modification technologies, which aim to increase the ability of Earth or clouds to reflect incoming sunlight," saying they "pose considerable risks and should not be deployed at this time."
Such techniques "would only temporarily mask the warming effect caused by high CO2 concentrations, and present serious known and possible unknown environmental, social, and political risks, including the possibility of being deployed unilaterally," said the report.
Carbon dioxide removal is better understood "but current technologies would take decades to achieve moderate results and be cost-prohibitive at scales large enough to have a sizeable impact," it added.
"Direct air capture of carbon is an immature technology with only laboratory experiments carried out to date and demonstration projects in progress," the report said.
"Technologies for storing the captured carbon are at an intermediate stage, but only prototypes exist and are not at the scale required for significant sequestration."
Other techniques such as forest restoration and low-till agriculture are "mature, readily deployable technologies with well-known environmental consequences," the report said.
It also warned against ocean-based approaches to accelerate natural removal of carbon dioxide, saying they "carry significant environmental and socio-political risks."
The study was sponsored by the National Academy of Sciences, the US intelligence community, the US space agency NASA, the National Oceanic and Atmospheric Administration, and the Department of Energy.