Nature | Editorial

The maximum climate ambition needs a firm research backing

We need to know what the 1.5 °C warming target will involve — even if we don’t reach it.

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The governments of the world have taken their time to tackle global warming. Now, at the request of those governments, the Intergovernmental Panel on Climate Change (IPCC) is assessing the impacts of 1.5 °C of warming, as well as ways to prevent temperatures from rising higher. Yet there is precious little science to assess, as a similar panel within the United Nations Framework Convention on Climate Change reported last year. The reason is simple: many scientists wrote off the chances of limiting warming to 1.5 °C years ago, and instead focused their energy on the still-aggressive goal of 2 °C.

This is understandable. The 2015 Paris climate agreement commits governments to keeping average global surface temperatures to between 1.5 °C and 2 °C above the preindustrial level. But warming has already passed the 1-degree mark, and some estimates suggest that even if current commitments are fully implemented, they would allow temperatures to rise nearly 3 °C. If the 2-degree goal seems implausible, given current politics, 1.5 °C is very nearly inconceivable.

Nevertheless, countries calling for more aggressive action — often those that have contributed the least to the problem and now have the most to lose — pushed for the 1.5 °C IPCC assessment. The deadlines are tight: scientists around the world now have roughly a year to run their models and submit papers to bolster the scarce body of literature surrounding the 1.5-degree goal. The IPCC will present its assessment in 2018, just before UN negotiators hold their first major meeting to assess progress under the Paris agreement and presumably to discuss ways to hasten action.

At a meeting in Oxford, UK, last week, researchers discussed the 1.5-degree agenda. There is plenty of work to be done. On the impacts side, for instance, scientists are planning to explore the probable increase in extreme weather using new tools to analyse global warming’s contribution to major storms and droughts that are already occurring. Further analysis will help to define how much those risks will increase as the world moves from 1.5 °C to 2 °C of warming. More generally, we need information about the progression of impacts on everything from coastlines and forests to human health, food and water supplies.

The mitigation agenda is more difficult. Scientists can and will run the numbers and chart theoretical pathways to 1.5 °C of warming, just as they have for 2 °C. But after more than quarter of a century of delay, there are no easy answers. Hitting either of these targets would require some extreme measures, such as wholesale abandonment of valuable fossil-fuel infrastructure or development of industrial-scale bio­energy systems that also pull carbon dioxide out of the atmosphere and sequester it underground, resulting in negative emissions. So daunting are the numbers that some researchers point to the emergency backstop of geoengineering, including strategies such as pumping aerosols into the atmosphere to block sunlight.

“After more than quarter of a century of delay, there are no easy answers.”

Unless the politics swirling around energy and climate policy change dramatically, the targets are clearly out of reach, but that does not mean that the IPCC’s latest research exercise is a waste of time. Regardless of any particular political target, the work can shed light on what deep decarbonization might mean for both human societies and the natural environment. That is information that policy­makers — particularly those pushing for aggressive action — can use. Each solution comes with its own challenges: technical, ethical, social and political. Ecologists and agronomists, for instance, need to explore the implications for land use and food production if bioenergy is scaled up with carbon-capture technologies. Social scientists need to engage on issues of equity, keeping in mind the parallel global goals of promoting sustainable development and eradicating extreme poverty across the planet. And governments have not exhausted their policy options. Political scientists and economists must continue to look for creative ways to break logjams at the national and inter­national levels.

One option, discussed at the International Conference on Fossil Fuel Supply and Climate Policy this week, also in Oxford, focuses on restricting the supply of fossil fuels coming onto the market. This wouldn’t staunch their use much unless all governments participated — which is hard to imagine — but in theory it could help to drive up the price of oil, gas and even coal, making renewable energies a bit more competitive. And if governments can determine what is taken out of the ground, could they also mandate what goes back in, requiring companies to bury emissions if they are to continue producing fossil fuels?

As it stands, there is minimal evidence that humanity will commit to its maximum climate ambition, but that could change as the impacts of global warming come into better focus. New technologies could also make it easier — and cheaper — to increase commitments. Scientists can help to provide a better basis for aggressive action when and if that happens.

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