April 29, 2015 — The best way to keep your floor dry is to avoid spilling a bucket of water onto the floor, rather than to deliberately tip the bucket and then develop technologies to dry the floor. The same is true of greenhouse gases: We need to prevent their emission now rather than focus on developing ever more complex and risky solutions to remove them from the atmosphere in the future.
Despite knowing what we need to do for well over 20 years, we have so far failed globally to reduce greenhouse gas emissions. The international goal of avoiding 3.6°F (2°C) of mean climate warming relative to the preindustrial era is becoming increasingly challenging. Recent modeling suggests that meeting this target may now require large-scale deployment of “negative emissions technologies” — NETs — which result in the net removal of CO2 and other greenhouse gases from the atmosphere.
Among the NETs that have been proposed:
- producing bioenergy with carbon capture and storage
- capturing CO2 from ambient air by engineered chemical reactions
- enhancing CO2-capturing natural weathering of minerals
- growing CO2-capturing forests in unforested areas
- boosting carbon uptake by the ocean by adding nutrients or increasing alkalinity
- changing agricultural practices to boost carbon capture (e.g., reducing soil disturbance or amending soils with biochar)
As part of a large team assembled under the auspices of the Global Carbon Project that analyzed the potential and limitations of a range of NETs, I know that, despite their significant mitigation potential, all of the NETs have limiting factors, such as cost and energy requirements (direct air capture), logistics of spreading materials over large areas (enhanced weather technologies), and potential competition for land and freshwater (afforestation and bioenergy with carbon capture and storage). While research and development may be able to overcome some of these limitations, none of the NETs offers an impact-free pathway to climate mitigation.
Perhaps the biggest downside of NETs, however, is this: they risk giving us a false sense of security that we will be able to engineer our way out of climate problems. In that case, people will likely continue to emit greenhouse gases and generate energy from greenhouse gas intensive fossil fuels, taking false comfort that technology will save us. The fact is that our ability to stabilize the climate declines as cumulative emissions increase. So the longer we continue with business as usual, the harder and more risky it becomes to take action. Therefore, while NETs may prove useful in climate regulation, emission reduction must remain the immediate priority for global climate policy.
More than ever, we need a global deal in Paris this year to limit greenhouse gas emissions, with binding targets for all countries. Without it, we are left on a path of continuing emissions, grasping at straws based on largely untested, future technologies. The simpler and less expensive solution of emission reduction has been staring us in the face for over 20 years, and we have failed to act. Let us make sure we act now. 
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If you are prone to stabbing yourself with sharp objects, it makes sense to 1) go see a therapist, but 2) stop the bleeding. The trick is to find a bandage that does more good than harm, and the natural solutions approach could very well be that bandage.