In a move long expected, the U.S. National Academy of Sciences has called for research into solar radiation management (SRM), the brand of geoengineering that involves blocking a fraction of the sun's rays to cool the planet. From the America's Climate Choices report, out today:
Although few, if any, voices are promoting SRM as a near-term alternative to GHG emission reduction strategies, the concept has recently been gaining more serious attention as a possible "backstop" measure, because strategies attempted to date have failed to yield significant emissions reductions and climate trends may become significantly disruptive or dangerous. Further research is necessary to better understand the physical science of the impacts and feasibility of SRM as well as issues related to governance, ethics, social acceptability, and political feasibility of planetary-scale, intentional manipulation of the climate system.
While these [geoengineering] proposals merit further research, their efficacy and environmental consequences are not currently well understood.
The report goes on to mention the need for more research in modeling geoengineering schemes, the challenge of collecting data for field tests, and governance and ethical issues. An academy report in 1992  included a chapter called "Geoengineering," which provided a similar review of research questions related to the topic. But the chapter attracted little attention.
This chapter is expected to make a bigger splash. Along with statements by the American Geophysical Union and the U.K.'s Royal Society, it could help advocates who want the U.S. government to support research in this emerging and controversial area.