For decades, politicians have been debating how to prevent dangerous climate change. 2°C of global warming has often been used as a benchmark for danger. 2°C is somewhat arbitrary, though, and vulnerable countries have campaigned for a lower limit for many years: calling for “1.5°C to stay alive”.

In Paris last December, countries agreed to “pursue efforts” to limit to 1.5°C. This doesn’t sound like a particularly strong statement: ‘we’ll try?’. After all, the emission reduction pledges made in Paris could still leave us with as much as 3°C by 2100. But given the usual pace of international climate negotiations, even agreeing to try for 1.5°C demonstrates remarkable ambition, and many were surprised by the outcome.

Scientists were also a bit startled: they were invited to produce a special report about 1.5°C. Policy-makers want to know what the potential impacts of 1.5°C might be, and whether it can be achieved. Can we reduce our emissions that much? How much would it cost? What would be the impact of a 1.5°C warming? Would 2°C be that much worse?

Answering these questions is a big challenge for researchers. And, policy-makers want the answers quickly: by 2018.To give the scientific vehicle a jump start, the Environmental Change Institute decided to refocus its 25th anniversary conference on “1.5 Degrees: Meeting the challenges of the Paris Agreement”. In September, 220 delegates from around the world came together in Oxford to outline the key research questions; to figure out which ones we can already answer, and what we can do to quickly tackle the others.

Many of the discussions at the conference, and the media headlines that followed, focused on the feasibility of 1.5°C. In 2015, the global temperature reached 1°C above preindustrial levels, so by some measures we are already two thirds of the way there. Everyone agreed that limiting to 1.5°C would be extremely difficult, but some think it’s impossible, or not desirable. Staying below 1.5°C might require controversial actions such as sucking carbon out of the atmosphere, or reflecting the sun’s incoming radiation; raising important questions about governance that go way beyond physical science. What is clear, is that the less contentious and well proven measures, such as shifting to renewable energy, and improving energy efficiency, need to be implemented straight away. Researchers are now working to model all possible pathways to 1.5°C, to help policy-makers choose from the options available.

On other side of the coin is the impacts question: how would a 1.5°C world differ from a 2°C world, or an even hotter one? We know that limiting to 1.5°C will be hard, so is it worth it? Recent studies suggest important differences between 1.5°C and 2°C: half a degree could mean more heatwaves, higher sea levels, and the complete destruction of coral reefs. Now, scientists have a lot of work to do to figure out what other differences there might be, and how big they are. Climate modellers are already running new experiments at 1.5°C and 2°C.

New research won’t eliminate uncertainty: like all other aspects of looking into the future, we are not going to know for sure what a 1.5°C or 2°C world will be like unless we actually get there. But scientific estimates will help policy-makers to weigh up the true cost of emissions when they set the next climate change targets.