From the local paper to prestigious scientific journals, and from conversations in our living rooms to an Academy Award winning movie, we are all aware of the current discussion of the likelihood of human-induced changes to our planet’s climate.  We have all seen the Mauna Loa curves of increasing CO2 in the atmosphere, and compounded by other greenhouse gases we understand how the increased absorption of radiation in the atmosphere will lead to a warmer planet.  The planet is indeed getting warmer.  Summertime Arctic sea ice and year-round mountain glaciers are melting.  The potential for catastrophic change certainly exists.  Because of this potential danger, several well-respected scientists have begun to ask the question, “What can we do to offset this potential disaster?”  One suggestion has to do with aerosols. Aerosols are small liquid or solid particles suspended in the atmosphere, and like the greenhouse gases they interact in the Earth’s energy budget.  When aerosols are made from substances that do not absorb light they act to cool the planet. The suggestion is to artificially inject nonabsorbing aerosol particles into the stratosphere in order to scatter some of the incoming sunlight back to space in a way analogous to the injection of a major volcanic eruption like Pinatubo.  Such a suggestion, scientifically, becomes an interesting thought process that incites new research to answer the question, “What would be the consequences if we did?”  The real problem is that aerosols are extremely tricky creatures that we are only beginning to understand.  There are plenty that already exist in nature (sea salt, desert dust, biogenic particles), and human activity has inadvertently added a list of others (particles from agricultural burning and emissions from transportation and industry.)  We have studied aerosols enough to know that they both scatter and absorb sunlight, but we are still learning how to quantify the absorption and how to interpret its effect on climate.  We know that aerosols can affect cloud properties, but we are still learning how to fully characterize the aerosol-cloud interaction and how it affects cloud cover and precipitation.  We simply do not understand how aerosols are now affecting the Earth’s energy balance, the planet’s hydrological cycle, precipitation patterns and human health.  This lack of understanding makes prediction of either intentional or inadvertent changes to the global aerosol system extremely difficult.