It's been called the greatest challenge in human history: curbing emissions of global warming gases so they don't cause catastrophic climate change—without wrecking the global economy and dooming billions to poverty in the process. Some say it will take breakthrough technologies and profound changes in how we live. Others argue we can make a major dent with existing technologies—if we get serious about acting now.
Join us for a live chat at 3 p.m. EST on Thursday, 17 January, on this page, with two scientists who have taken a careful look at what it will take to conquer climate change. Stephen Pacala is the lead author of an influential 2004 Science paper that argued that we can make progress now by launching seven major campaigns—known as "wedges"—to reduce emissions. Steven Davis is the lead author of a new paper that argues we need to do much more than that, and launch 19 to 31 wedge campaigns
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Steve Davis is an assistant professor in Earth system science at the University of California, Irvine. At UCI and previously as a postdoc at the Carnegie Institution for Science's Department of Global Ecology, his research has focused on carbon emissions embodied in international trade, the commitment to future warming represented by existing energy infrastructure, and the climate benefits of agricultural intensification.
Stephen W. Pacala
Stephen W. Pacala is the director of the Princeton Environmental Institute and The Frederick D. Petrie Professor of Ecology and Evolutionary Biology at Princeton University. He also co-directs the Carbon Mitigation Initiative, an effort to develop solutions to the greenhouse warming problem, and is a founder and Chairman of the Board of Climate Central, a nonprofit media organization focusing on climate change. His work focuses on problems of global change with an emphasis on interactions among the biosphere, greenhouse gases and climate.
Eli Kintisch is a contributing corespondent at Science and author of Hack the Planet  (Wiley, 2010). He is an MIT-Knight Science Journalism Fellow.