In what will be the world's biggest solar geoengineering program to date, U.S. scientists part of the $20 million Harvard University project are going to send aerosol injections 20km (~12.4 miles) into the earth's stratosphere "to establish whether the technology can safely simulate the atmospheric cooling effects of a volcanic eruption," The Guardian reports. From the report: Scientists hope to complete two small-scale dispersals of first water and then calcium carbonate particles by 2022. Future tests could involve seeding the sky with aluminum oxide -- or even diamonds. Janos Pasztor, Ban Ki-moon's assistant climate chief at the UN who now leads a geoengineering governance initiative, said that the Harvard scientists would only disperse minimal amounts of compounds in their tests, under strict university controls. Geoengineering advocates stress that any attempt at a solar tech fix is years away and should be viewed as a compliment to -- not a substitute for -- aggressive emissions reductions action. But the Harvard team, in a promotional video for the project, suggest a redirection of one percent of current climate mitigation funds to geoengineering research, and argue that the planet could be covered with a solar shield for as little as $10 billion a year. Some senior UN climate scientists view such developments with alarm, fearing a cash drain from proven mitigation technologies such as wind and solar energy, to ones carrying the potential for unintended disasters. If lab tests are positive, the experiment would then be replicated with a limestone compound which the researchers believe will neither absorb solar or terrestrial radiation, nor deplete the ozone layer.