<p>Humans may have changed the Earth's climate ever since they
began using "slash and burn" tactics to clear forests for
growing crops. But today's civilizations must deal with the
industrial revolution's contribution to a warming planet and the
choice of trying to reverse or balance out such climate change
with new geoengineering tactics.</p> <p>Geoengineering ideas
typically aim to stop the warming of the Earth's climate by
removing the greenhouse gas carbon dioxide (CO2) or by
reflecting more sunlight back into space. Many mimic natural
processes such as the cooling effect of volcanic eruptions or
boosting the CO2-absorbing effect of forests. But the idea of
humans intentionally engineering the Earth's climate on a grand
scale still attracts plenty of controversy as well.</p> <p>Here
you can take a look at ratings for some of wildest
geoengineering ideas described in a 2009 report by the UK's
Royal Society. The British study has been cited in later U.S.
reports by the U.S. National Academy of Sciences (201