Geo-engineering, or climate engineering, is still in its embryonic stage of development. Some of the ideas experts are discussing, such as putting lunar glass or metallic reflecting disks into space to reduce the amount of incoming solar radiation, sound like the stuff of science fiction. But proponents claim geo-engineering may be the planet's only hope against the most devastating effects of climate change.

The idea of manipulating environmental systems or weather patterns through drastic measures to prevent greenhouse gases from accumulating in the Earth's atmosphere has its detractors. Critics say geo-engineering could have potentially disastrous, unintended consequences. They contend that climate engineering could be a dangerous, perhaps permanent, manipulation of Earth's most basic systems and is therefore, fundamentally, unethical. They also say the idea is a distraction from real action on climate-change mitigation.

Others argue that more research should be done to show whether various geo-engineering strategies could work at all, particularly if climate-mitigation efforts are unsuccessful. It is too early to tell whether the technologies being discussed are feasible, proponents say. Jane Long, former associate director-at-large at Lawrence Livermore Laboratory and co-chair of the Bipartisan Policy Center task force on climate remediation, says, "A lot of the ideas that are out there right now haven't been researched very much. They might all turn out to be not very good ideas, and, furthermore, there might be a bunch of new ideas that people haven't come up with yet because there hasn't been anybody coherently thinking about it."

There are two basic types of geo-engineering: In solar-radiation management (SRM), systems are manipulated to reduce incoming solar radiation by making the Earth more reflective. The second type involves carbon management to reduce the amount of greenhouse gases in the Earth's atmosphere. One method to reduce carbon dioxide would add iron and other nutrients into the ocean to speed up the absorption of carbon sequestration from phytoplanktons.

A scientific team, led by Stephen Salter at the University of Edinburgh and John Latham at the University Corporation for Atmospheric Research, Colorado, is studying the potential of a cloud-brightening vessel that would shoot small sea-salt particles from an unmanned ship or aircraft into clouds to make them more reflective of the sun's radiation and cool the Earth's temperature.

Another type of SRM would shoot particulates into the stratosphere, mimicking the effects of a volcanic eruption.

Some in the scientific community worry that any major manipulation of the earth's environmental systems could create unintended consequences. Joe Casola, staff scientist with Climate and Energy Solutions, Washington, D.C., says that studies of volcanic eruptions have shown that volcanoes cause changes in precipitation patterns, particularly related to monsoon cycles. "If we're talking about doing something on purpose that affects the monsoon cycle, I think that is something that should give some serious pause and consideration, given the number of people that depend on monsoon cycles around the world," Casola says.