Limiting global temperature rise to 1.5C has long been the goal of developing countries and those most at risk from climate change. Since becoming enshrined in the Paris Agreement last December, the 1.5C goal has come under increased scrutiny and examination.
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?”
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:
Understanding the risk of half a degree of extra warming brings other scientific challenges, including the need to narrow the uncertainty over how much warming a given amount of carbon produces, known as the climate sensitivity, and the role of short-lived gases, such as methane.
Such questions are putting greater pressure on scientists to produce numbers, rather than to refine understanding, says Prof Ted Shepherd, Grantham professor of climate science at the University of Reading. He tells Carbon Brief:
“[T]he more I start to think about it, I think it will change what we do a lot…Now, all of a sudden, we’re forced to become much more quantitative…I think that’s going to force a paradigm shift in how we think about our research.”
A good example of this is the need to pin down the “threshold” for the Greenland ice sheet, says Gregory, who, as well as being a professor of meteorology at the University of Reading, is an expert in ice sheets and sea-level change. He tells Carbon Brief:
“[It] gives greater impetus to try to refine what we know about the future viability of the Greenland ice sheet. We are currently really quite uncertain, quantitatively, what will happen to it.”
Once global temperature change exceeds a certain point, the Greenland ice sheet would disappear, taking centuries, but, ultimately, raising global mean sea level by seven metres. The problem is that we don’t know where the threshold is exactly, Gregory tells Carbon Brief:
“[It] could be as low as 1C above preindustrial, which means that we’re in that range…Other studies suggest it might be 2C, or it might even be as far as 4C above preindustrial. So it could make a real difference to the Greenland ice sheet whether the temperature was held below 1.5C above preindustrial or 2C.”
A big question surrounding the IPCC’s special report on 1.5C is how much of the new wave of research will be ready in time? Any scientist wishing their research to be included will need to submit it to a peer-reviewed journal by October 2017, and have it accepted for publication by April 2018.
Such a short timescale is not unusual for very small questions, but this special report request is a different, says Dr Daniel Mitchell, a researcher in the University of Oxford’s Environmental Change Institute and the coordinator of the HAPPI project. He tells Carbon Brief:
“This is a question for the whole community on a global scale. [The UNFCCC] want to know everything there is to know about the feasibility, the impacts and, most importantly, for the policymakers, the cost-benefit [of a 1.5C limit].”
The urgency has caused some problems, not only with publication times, but also with getting the funding to do the work, Mitchell adds:
“Most of us are funded on projects that are not related to this so there has to be a lot of goodwill in terms of co-badging this science with our funded projects.”
Another option is to apply for new funding, but that, too, takes time. Shepherd tells Carbon Brief:
“The Natural Environment Research Council has just issued a call for proposals. But it just went out last month and it takes about six months to get the whole thing spun up.”
Though the wish list for potential topics to include in the special report is long, what gets discussed depends on what is published between now and the publication deadline, says Allen. This date is, he says, “frighteningly soon” from the point of view of an academic.
On that front, this week’s 1.5C conference in Oxford has a very clear objective, Allen tells Carbon Brief:
“We want to help the academic community to respond to this request from the UNFCCC…And we’re going to keep reminding people that just pontificating about 1.5C is not enough. They’ve got to get their thought down in published papers in short order.”
Academic research does not normally operate on a timescale, says Allen. But it’s not unwelcome.
“We’re very happy to be researching the difference between 2C and 1.5C. Most of us were expecting we’d be spending our time at the moment researching the difference between 2C and 4C or 5C…It brings new challenges for the research, but they’re challenges we’re happy to take on.”
The spotlight on 1.5C seems to have given the climate policy community a renewed vigour, as well as climate scientists, says Ajay Gambhir, a senior policy fellow in climate change mitigation at the Grantham Institute for Climate Change, Imperial College London. He tells Carbon Brief:
“What this has done is re-energised people to look more deeply at radical emissions reduction solutions…There’s a huge research agenda now as a result of Paris and, of course, that’s very exciting for scientists and researchers who are thinking about these issues.”
The need to remove carbon from the air using negative emissions technologies is a topic receiving quite a bit of attention since the shift to more ambitious climate targets. Gambhir explains:
“If we have relatively less ambition in the short term then that means we’re going to have to do very radical things in the medium and long term. What that means in terms of 1.5C is almost certainly a very, very large amount of negative emissions.”
While the need for negative emissions has got more airtime since Paris, some scientists have been talking about the largely theoretical technologies for a long time, says Allen. They have always been necessary if we wish to stabilise global temperature at any level, he notes.
“To get net emissions to zero, you’re still going to need to compensate for some residual emissions somewhere. There’s no real way around that…The question is how big can we make that process, how fast can we get CO2 out of the atmosphere without imperilling other things that we need, such as producing food, for example.”
Is the 1.5C goal feasible, given the amount of negative emissions required? Yes, says Allen, but it comes with a long list of boxes that need ticking all at the same time. He tells Carbon Brief:
“It’s certainly not out of the question. That’s actually a really important point for people to take on. But, of course, it will require totally unprecedented rates of change in the globally energy system if it’s actually going to be achieved.”
With such a huge caveat, is this a useful definition of “feasible”? Gambhir’s work involves coming up with various different metrics for expressing “feasibility”. He tells Carbon Brief:
“It’s fair to say that a lot of feasibility work we did over the last couple of years suggested that 2C is pushing the boundaries of feasibility across a number of measures and that gives us an early signal about how hard 1.5C would be.”
Carbon Brief analysis suggests there are about five years’ worth of current emissions left before the budget for 1.5C is blown, meaning that never crossing the 1.5C threshold is now nigh-on impossible. But this isn’t a reason not to try, thinks Mitchell says. He tells Carbon Brief:
“Personally, I don’t know if 1.5C is achievable – a lot of my colleagues seem to think it is. But I think if we aim for 1.5C and get to 2C, then that’s a good end result. I think we’re going to overshoot, whichever we aim for. So we may as well aim for the lower one.”
As well as technical constraints, there are, of course, social and political aspects of feasibility, too. Gambhir says:
“We do need a sense of how viable rapid transitions are, what they might lead to in terms of political backlash, in terms of social inertia, before we can have a really confident sense of how fast we can go.”
The question of how fast a transition society could tolerate is important in public health, too, says Nick Watts , executive director of the Lancet Countdown to 2030: Public Health and Climate Change. The focus on 1.5C has prompted mixed reactions in the medical community, he tells Carbon Brief:
“On the one hand, that renewed ambition, that renewed drive to reconsider whether 2C is doing enough to protect the public’s health is a good thing. On the other hand, there is a need to look at what the implications of that are.”
While past studies show the benefits for public health of climate mitigation, they haven’t necessarily looked at the difference of an extra 0.5C. He tells Carbon Brief:
“It’s entirely possible, probable, that you’re going to see just as many of those positive benefits [of mitigation] come through. But I think as health professionals and any doctor or nurse would say, they want to see the evidence first before they try the treatment out on the patient.”
With so much to do and a short timeline to do it in, is there a risk the IPCC’s special report will be incomplete? That’s not a risk, it’s a certainty, say Allen. He tells Carbon Brief:
“I think everybody has to accept that we won’t have the definitive answer about the difference between 1.5C and 2C done on that timeframe.”
The challenge for scientists is to answer the question as best they can in the time frame they have been given. But it will be important to be upfront about what’s left unanswered, says Mitchell. He is hoping the level of “quality control” doesn’t drop in the haste to get more papers submitted. He tells Carbon Brief:
“I’m hoping that people won’t try to do five or six papers, that they’ll try to do one good study…You can do one good study on that timescale.”
In other words, scientists are mindful of the careful balance between being fast in order to be policy-relevant and not compromising their scientific integrity. But whatever the eventual scope of the IPCC special report, the future of the 1.5C goal won’t be decided on the strength of it alone, says Shepherd. Past lessons teach us that much, he tells Carbon Brief:
“The Montreal Protocol was the first agreement, but actually that didn’t really control things. It took various amendments after that…The [1.5C] evidence report will be important, but I’m sure there will be more information in the coming years. It isn’t like that will be the final word.”
Any research that doesn’t make it in time for the special report will be hoovered up by the IPCC’s next big assessment report, due in 2021. As with other reports and other topics, this will essentially update and refine the last instalment with new knowledge. So while the 1.5C special report is undoubtedly important and science is bending as best it can to meet its demands, simple logistics mean it’s unlikely to tick all the boxes.
Carbon Brief journalists will be covering the 1.5C conference in Oxford this week. Follow us on Twitter for updates, or email us via [email protected] if you have any questions you would like us to put to the attendees.