Ben and Ken: Thanks for offering many great questions, Redditers. We hope that our responses advanced the conversation about global climate change and possible solutions that include climate engineering. We certainly enjoyed this interaction. Signing off, Ken and Ben. Hi reddit! I’m Ken Caldeira and I work on a broad array of issues including the physical climate system, global energy systems, ocean acidification, and geoengineering. With the exception of the ocean acidifcation work, all of our research is based on performing simulations using computer models. Solar geoengineering involves trying to cool the Earth by deflecting some incoming sunlight away from our planet. Studies have shown that actions like putting small particles in the stratosphere could reflect some sunlight away from the Earth, potentially taking our climate back to a point similar to pre-industrial revolution. Of course, we know for sure about only one habitable planet, and toying around with this planet at the required scale would pose great risks – but allowing the Earth to warm from our greenhouse gas emissions also poses grave risks. Given that it is going to take time to transform our energy system into one that does not dump its waste in the atmosphere, what is the best path forward? I’m Ben van der Pluijm and I work in hazards geology and societal impacts of global change. The goal of 2016’s Paris Agreement to limit global warming to 2 degrees C (3.6 degrees F) is ideal, but unlikely from voluntary greenhouse gas emission reductions alone. Building on our remarkable history of engineering applications to overcoming societal challenges, climate engineering should be included as a viable solution for reducing the impacts of global warming. Climate engineering takes two approaches: (1) Carbon dioxide removal, and (2) solar radiation management. The former addresses the cause of climate warming by removing greenhouse gas from the atmosphere (“treat the illness”). The latter offsets the warming effects of greenhouse gases by allowing Earth to absorb less solar radiation (“treat the symptoms”). Given their worldwide impact, planning must occur on a global scale, involving all nations, large and small, rich and poor, and not be limited to a few technologically advanced, wealthy countries. We’re looking forward to answering questions about environmental change and dealing with the impacts for human society, and whether various geoengineering techniques could really be expected to reduce climate damage and decrease damage to both ecosystems and people. We were here from noon to 2 PM EST to answer your questions. Thanks for Asking Us Anything!