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Paris targets ‘more readily achievable’, Canadians say

23 Apr 2018
RCP phase space
RCP phase space.

The targets for climate change outlined in the Paris Accord are easier to achieve than commonly thought. That’s the claim of researchers in Canada, who have defined climate outlooks in a way that is both simple and easier to analyse.

The new definition relies on just two parameters – total energy use this century, and the carbon intensity of that energy – that can be mapped onto a phase-space diagram. By data-mining that phase space, the researchers found that current “business as usual” scenarios given by the Intergovernmental Panel on Climate Change (IPCC) assume increasing carbon intensity, or so-called re-carbonization – contrary to recent trends.

“By thinking that we’re definitely heading in a direction of re-carbonization before we institute climate policies, it makes climate policy that aims for de-carbonization look overly difficult,” said Justin Ritchie of the University of British Columbia. “If we update our outlook for business-as-usual, the necessary climate policies to guide a low-carbon transition appear far more achievable than previously thought.”

The creation of future climate scenarios is a complicated business. For many years, they have been based on integrated assessment models (IAMs) – computer models that explore the projected interplay of population, economics and energy use up to the year 2100.

Since the IPCC’s Fifth Assessment report in 2014, two more layers have been added. Above IAMs are shared socio-economic pathways (SSPs), which describe possible socio-economic developments; while the layer above SSPs consists of representative concentration pathways (RCPs), which define the levels of greenhouse gases that could ensue from the different underlying scenarios. RCP8.5 is the oft-called business-as-usual scenario, in which no strong policy action on climate change is taken.

The problem with this approach, according to Ritchie, is that the underlying IAMs are very time-consuming to run. “If they are used to map all the possible future developments based on different scenarios of population, GDP and energy use, it can get quite unwieldy,” he explained. “For example, there were 1,184 scenarios produced by about 20 different IAMs for the IPCC’s Fifth Assessment, and managing all those model outputs is a growing challenge… Further, most of those scenarios were based on a common set of population and socioeconomic projections, so while their number is quite large, they are actually surprisingly narrow in scope.”

Instead of this top-down approach, Ritchie and colleague Hadi Dowlatabadi, also from the University of British Columbia, generated climate outlooks the other way around, mapping out all the combinations of carbon intensity and energy use that could generate a certain level of carbon emissions as given by the RCPs.

Doing it this way reveals the full range of possibilities without resorting to complex simulations, says Ritchie. It “allows us to see that integrated assessment models may be too narrowly focused”.

Indeed, Ritchie and colleagues’ method revealed that RCP8.5 is mostly depicting a world in which coal remains the cheapest form of energy and outcompetes other types of energy generation.

“Since that looks increasingly unlikely, it means they are likely overestimating how difficult it will be to develop along technology pathways that lead to 2˚ of warming or less, in line with the Paris Agreement,” Ritchie said. “Renewables, energy-efficiency and oil and gas technologies have proved far more dynamic than anticipated. Thus, coal has been losing global market share for a long time.”

The team published the study in Environmental Research Letters (ERL).

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