Abstract

A 450-ppm equivalent CO2 target by 2050 is an often-proposed goal under a future global emissions agreement, but there is considerable high side risk in global-warming models due to cloud formation, feedbacks in dissolved organic carbon from peat bogs in polar regions, and unaccounted solar dimming by particulates. The 450-ppm figure is predicated on absorption of some CO2 by oceans, but increasing acidification may dictate that CO2 produced during the next 50 years may have to be reduced further to preserve species diversity in the oceans. By consideration of industry capability, a 400-ppm target is shown to be affordable and achievable by renewables using 2/3 direct solar electricity by 2050 with technology currently being proven, together with aggressive energy efficiency. Sequestration of liquid CO2 under pressure in enormous continually excavated caverns at 2-km depth is technically much less certain and later in development.