The use of negative emissions technologies, such as those that can remove carbon dioxide from the atmosphere, to limit global warming to less than 2°C in the coming century is likely unfeasible according to a study published in Nature Communications this week. The findings show that, in all but the most optimistic conventional climate mitigation scenarios, the negative emissions requirements are beyond the capabilities of current technologies.

Negative emissions technologies include the capture of human-produced carbon dioxide at the site of production, direct removal of carbon dioxide from the atmosphere, and engineered enhancement of natural carbon sinks, and are increasingly invoked as a requirement to limit global warming to less than 2°C above preindustrial levels and to avoid dangerous climate change. However, these technologies are not yet developed and the level of negative emissions necessary to stay below the 2°C limit remains unclear.

Thomas Gasser and colleagues use state-of-the-art carbon-climate models to quantify the trade-off between conventional mitigation strategies (consumption of fewer fossil fuels) and negative emissions required to reach the 2°C target under the Intergovernmental Panel on Climate Change’s RCP2.6 warming scenario. This is an optimistic scenario that assumes emissions will peak between 2010 and 2020, requiring lower levels of mitigation and negative emissions than other possible scenarios. The authors conclude that even under very aggressive mitigation scenarios, negative emissions of 0.5-3 Giga-tonnes of carbon per year and a storage capacity of 50-250 Giga-tonnes of carbon are required, and that negative emissions alone, in the absence of conventional mitigation, are unlikely to achieve the 2°C goal.