Stratospheric Particle Injection for Climate Engineering (Spice) project (see Skyhook to Save the Climate? ) was cancelled after public outcry. But there are good reasons why geoengineering should not be considered. Why not to geoengineer The obvious way to combat climate change is to cool the planet by reducing emissions of greenhouse gases and removing them from the atmosphere. That means using less energy, replacing fossil fuels by renewables, halting deforestation, and adopting sustainable farming practices. As documented in two major reports published by ISIS Food Futures Now: *Organic *Sustainable *Fossil Fuel Free , Green Energies - 100% Renewable by 2050 , all the necessary technologies are available and getting better and cheaper every day, only the political will is missing. Geoengineering offers an alternative quick fix, which is to reduce the amount of radiation reaching Earth's surface in the first place.  There are several suggestions about how this might be done, for example, by putting mirrors into space or sulphur particles into the stratosphere, or by increasing the brightness of clouds by spraying sea salt into them (see GeoEngineering A Measure of Desperation , SiS 41). Geoengineering involves making changes on a planetary scale . A major drawback of geoengineering, whether it involves solar radiation management (SRM) or other measures such as fertilizing the oceans in the hope of increasing the absorption of carbon by phytoplankton, is that it is likely to be very difficult to reverse.  If we sent small particles into the stratosphere what could happen if