How do climate impacts at 1.5C and 2C compare? How fast would the global economy need to decarbonise? Is the amount of “negative emissions” required for either limit feasible? Expectation is heavy that a special report by the Intergovernmental Panel on Climate Change (IPCC), due in 2018 at the behest of the United Nations, will answer all these questions.
So is the scientific community rising to the challenge or feeling the pressure?
Ahead of a major conference in Oxford this week, Carbon Brief has been talking to climate scientists, economists and public health experts about how the spotlight on 1.5C has changed the way they work.
Degrees of separation
Back in August, the chair of the IPCC, Dr Hoesung Lee, told scientists at a meeting in Geneva that they bore a “great responsibility” in making sure the special report on 1.5C meets the expectations of the international climate community.
Dr Rachel James, a research fellow at the University of Oxford’s Environmental Change Institute, explains how this has been interpreted by scientists. She tells Carbon Brief: “Part of it is about how we get to 1.5C and part of it is about impacts at 1.5C, and really balancing those. Is it possible to get to 1.5C? And are the impacts at 1.5C and 2C different enough that it’s worth pushing for 1.5C?”
What we’re really trying to assess is, what can we say about an extra 0.5C of warming?
Rachel James, research fellow, Environmental Change Institute, University of Oxford
The comparison with 2C is not technically what the Paris Agreement called for, even though that’s how it has been perceived, says Prof Myles Allen, professor of geosystem science at the Environmental Change Institute and a convenor of this week’s conference. He tells Carbon Brief: “The Paris Agreement was very clear…[parties] are interested in the impacts of 1.5C of warming. They didn’t say ‘versus 2C’, or anything else in particular. But, obviously, because the focus was on 2C up until then, a lot of people have interpreted this as what’s the relative impact of 1.5C versus 2C.”
Comparing impacts for crop production, extreme weather and sea level rise, for example, at different global temperatures means flipping on their head the way climate projections are traditionally constructed. Picking a “tolerable” temperature limit first and investigating impacts and pathways later isn’t how scientists have always done things, says Prof Jonathan Gregory, professor of meteorology in the National Centre for Atmospheric Science at the University of Reading.
He tells Carbon Brief: “Previously they did it the other way round. They said, let’s imagine various stories about what future technological and demographic development there would be and [then they asked], what does that mean for CO2 emissions and [global] temperatures?”
Understanding the effect of half a degree extra warming presents a specific challenge, says Allen. He tells Carbon Brief: “We’re talking about relatively subtle levels of warming, where we have to really think much harder about natural variability and so forth to take that into account when we’re talking about the risks at these different levels of warming.”
With their group at Oxford University, Allen and James are working on a new project dedicated to tackling these new questions. The HAPPI project (Half a degree Additional warming, Prognosis and Projected Impacts) is an international effort, listing more than 35 different institutions worldwide as collaborators.
James tells Carbon Brief: “What we’re really trying to assess is, what can we say about an extra 0.5C of warming?…One of the things that it highlights is that using existing modelling experiments, from CMIP3 and CMIP5, is it’s quite difficult to identify those differences.”
Another shift within the climate change research community is that, until recently, most work has been looking at impacts at higher levels of warming. James tells Carbon Brief: “Looking at the research that has been done to identify impacts at specific degrees of warming, most of it has been at 2C or at 4C. It’s quite interesting that we’re having the 1.5C conference in Oxford because in 2009, we had a “4C and beyond” conference.”