The Climate Change Commission's budgets would see New Zealand make shallower cuts to emissions over the next decade than may be consistent with limiting global warming to 1.5 degrees, Marc Daalder reports
ANALYSIS: One of the main authors of a groundbreaking 2018 report on what is needed to limit global warming to 1.5 degrees above preindustrial levels has told Newsroom that the Climate Change Commission made an error when asserting its recommended emissions budgets were consistent with that goal.
Joeri Rogelj is a lecturer in climate change at the Imperial College London and was coordinating lead author on the section of the landmark Intergovernmental Panel on Climate Change (IPCC) report that dealt with emission reduction pathways compatible with 1.5 degrees. After a Newsroom analysis raised questions about the commission's efforts to show its budgets are consistent with those pathways, he confirmed to Newsroom that the commission's calculations involve a fundamental error, "comparing apples with oranges".
The news comes as a non-profit coalition of more than 300 lawyers filed proceedings in the High Court against the commission and Climate Change Minister James Shaw, alleging similar "logical errors" mean the commission's final advice on emissions budgets and New Zealand's Paris target are not consistent with 1.5 degrees, the Paris Agreement or the Zero Carbon Act.
Newsroom's analysis of the commission's budgets raises additional questions about whether the domestic carbon dioxide reductions it called for are aligned with the IPCC's pathways. This in turn could challenge the budgets' consistency with 1.5 degrees, as the IPCC pathways are widely recognised (including by the commission) as some of the most authoritative indicators on this matter.
According to the Zero Carbon Act, the budgets are required to be set with (among other things) "a view to meeting the 2050 target and contributing to the global effort under the Paris Agreement to limit the global average temperature increase to 1.5° Celsius above pre-industrial levels". But after adjusting for the commission's "apples and oranges" accounting method, net CO2 will fall to just 29 percent below 2010 levels by 2030, when the IPCC envisioned a 40 to 58 percent reduction. Steeper cuts later in the 2030s could make up the difference, however.
Speaking to Newsroom prior to the filing of the lawsuit last week, Shaw said he would have to receive advice on the numbers before he could comment fully. He did however say that officials were still working up their advice on whether and how he should accept the commission's recommendations - and that the "burden of proof" for deviating from the recommendations was high.
For its part, the commission insists its work holds up to scrutiny. Policy advisors at the commission interviewed before the launch of court proceedings last week said they maintain that the budgets are consistent with the IPCC pathways and with limiting warming to 1.5 degrees.
IPCC pathways
About halfway through its 419-page report, the commission outlines why it thinks its budgets are consistent with 1.5 degrees. This argument relies on two premises: That the budgets are compatible with meeting New Zealand's 2050 net zero and biogenic methane targets and, as an "additional consideration", that the budgets are aligned with the IPCC pathways.
Those pathways come in three forms, depending on the degree to which 1.5 degrees is briefly overshot. For carbon dioxide, the most important greenhouse gas, the IPCC looked at five pathways where there was no overshoot, 37 where temperatures rise above 1.5 degrees in a "limited" manner and 36 with "high" overshoot. All of these scenarios resulted in a 50 to 66 percent chance of achieving the stated outcome (no, low or high overshoot and otherwise keeping warming at 1.5 degrees) and many of them relied on carbon capture and storage technology which is not yet proven at scale.
Among the no and low overshoot pathways, the middle 50 percent (also called the interquartile range) require reducing net CO2 emissions by 40 to 58 percent below 2010 levels by 2030 and by 94 to 107 percent by 2050.
In its report, the commission identified this interquartile range as the target to aim for.
"We have used the ‘interquartile range’ of the IPCC’s pathways," the commission wrote. "This gives a more conservative, but also more likely, range for the emissions reductions that are needed."
The commission said in its report that by 2030, its pathway would see New Zealand's agricultural nitrous oxide emissions fall just within the necessary range and agricultural methane fall just outside (an 8 percent reduction, compared to the IPCC range of 11 to 30 percent). Fortunately, it would make up the difference with CO2, which would fall 55 percent from 2010 levels.
And deeper cuts in some areas would be needed to make up the difference for failing in others, Rogelj told Newsroom.
"Being at the high end of this range, i.e., not so deep methane emissions [cuts], means that you need to do more on CO2."
Gross-net accounting
But is the commission's pathway really doing more on CO2. A closer look at the table shows that it expects net CO2 levels in 2030 - which include the carbon-sucking impact of forestry - to be 55 percent below gross CO2 levels in 2010. While New Zealand uses this gross-net accounting to set and measure progress against certain targets, it wouldn't appear to be useful for asserting compatibility or alignment with the IPCC pathways, which were calculated in a net-net manner.
"Net-net should absolutely be compared, gross-net absolutely not," James Every-Palmer, the treasurer of Lawyers for Climate Action New Zealand, told Newsroom.
"Their question is, what does the special report require of us? They correctly identify that -40 to -58 percent reduction on 2010 levels by 2030 for net carbon dioxide. Then what they should do is take our 2010 net CO2 and apply those reductions. The mistake that they've made is that they apply those reductions to net CO2 from gross CO2. That's just a mathematical error."
He also points to Stats NZ, which uses a net-net approach for its own representation of New Zealand's progress against the IPCC pathways.
Matt Smith, a principal analyst at the commission, said there was some consideration as to whether a net-net or gross-net framing would best suit this comparison. However, he said, the commission ultimately chose to follow a gross-net approach based on international guidance - like the rules for setting targets in the Kyoto Protocol.
"We considered that what the IPCC have said about net emissions made sense in a global context but didn't make sense in a New Zealand context," he said. Because forests store a stock of carbon (a limited amount) while annual emissions represent one slice of a flow (an ongoing amount), counting forestry removals in the 2010 base year would require maintaining those removals indefinitely.
"The net-net comparison that the IPCC did said that land sector emissions need to be reduced like any other emissions. It didn't say that you need to plant forests forever to maintain the same level of removals that you had in 2010."
Stephen Walter, the commission's general manager for emissions budgets, adaptation and markets, agreed, saying the issue was around the differing roles of the land sector in different countries.
"Basically, what the [international] rules state is that if the land sector is a net source of emissions, then net-net is the appropriate methodology. If it's a net sink, then gross-net is the appropriate methodology. Globally, the land sector is a source, but in New Zealand, it's a sink. And so that's why, globally it's appropriate for the net-net and for New Zealand to be gross-net," he said.
Experts disagree
Luke Harrington, a senior research fellow in climate science at Victoria University of Wellington, told Newsroom he agreed with the commission's position.
"I would agree with the commission's point ... that there's a risk that if you had a net-net consideration of changes since 2010, there's a potential to witness artificial success or failure depending on whether there had been a lot of forestry cut down just before 2010, or immediately afterwards," he said.
However, Harrington also said that cumulative emissions were more important than hitting a point-year target.
"There is far too much of an opportunity to cherry pick start and end years to make claims that we are doing far more, or far less than we should be (and even more so when integrating volatile emissions land use change into the GHG profile)."
Other climate scientists who spoke to Newsroom said the commission erred in comparing results of two different accounting methods.
"The IPCC reports emissions for the pathways it assesses most closely in net-net terms. Comparing with these global pathways using different accounting conventions is thus indeed comparing apples with oranges," Rogelj said. He added that even net-net comparisons might have been produced by different accounting methods and could easily offer "a too rosy picture" of ambition and feasibility.
Sam Dean, the principal scientist on climate issues at NIWA, also said the two figures shouldn't be compared.
"While a net-to-net comparison has a strong relationship to temperature change, comparing net-to-net with a gross-to-net comparison is not straightforward," he said.
If the commission's pathway to 2030 was evaluated against IPCC pathways to 2030 on a like-for-like basis, net CO2 emissions fall only 29 percent. That sits outside the interquartile range, which requires a minimum reduction of 40 percent from 2010 levels. In fact, the commission's net-net pathway to 2030, when compared with the 42 limited or no overshoot IPCC scenarios on a percentage basis, falls outside not only the interquartile range but outside even the least ambitious overall.
"This could certainly be interpreted as meaning that the climate commission pathway is in fact not consistent with the central 50 percent of the indicative IPCC pathways with no overshoot between 2010 and 2030," Dean said. However, he too stressed that cumulative emissions were key and that he suspected the commission's pathway would fall back within the IPCC bounds from that perspective.
The area under the curve
Further analysis of the commission's figures indicates this could well be the case.
Although the net CO2 cuts in the 2020s are relatively shallow, they grow much steeper in the 2030s and reach net zero by 2038. By comparison, the IPCC special report said net CO2 emissions would need to reach zero between 2040 and 2055, globally.
"The commission demonstration pathway involves very strong CO2 reductions from 2025 onwards, reaching net zero by 2038, with negative emissions after that. As the IPCC makes clear it is the cumulative emissions of CO2 that control the likelihood of a temperature overshoot. This means that with regard to the likely total net CO2 emissions over the timeframe to 2050 that the demonstration pathway is almost certainly consistent with a global effort to limit warming to 1.5 degrees with a low risk of overshoot," Dean said.
"In a nutshell, the pathway has higher net emissions in the early period and gets to negative emissions faster compared to the indicative IPCC scenarios. Following such a pathway is consistent with the intention of the IPCC to provide indicative global scenarios, not regional prescriptions."
By 2038, New Zealand will have cut net CO2 by a greater percentage from 2010 levels than any of the IPCC scenarios envisaged. If those percentage reductions were applied to global emissions in 2010, the commission's pathway would see lower cumulative emissions between 2018 and 2050 than would all but three other pathways.
Does that close the book? Are the commission's pathways consistent with 1.5 degrees because of those steeper, later cuts, even if they don't fall within the IPCC interquartile range out to 2030?
Not quite, says Every-Palmer.
"First, we have a history of kicking the can down the road on taking serious climate action. That is, we keep saying 'We’ll do something next decade' while our net emissions keep rising," he said.
"A large motivation for our judicial review claim is to increase the pace of change – we see taking action in the present decade as crucial to limiting global warming to 1.5 degrees. The time has come for rapid decarbonisation of the economy."
The IPCC report also found that emissions need to fall more steeply in the next decade than in the decades afterwards to best limit the chance of overshoot. That's because the 1.5 degree threshold could be crossed as soon as 2026 - just as New Zealand embarks on achieving its second emissions budget. So while the commission's pathway is likely to be consistent with limiting warming to 1.5 degrees, its reliance on steeper cuts later could contribute to greater temporary overshoot.
Net zero 2038?
But the commission still says its pathway is compatible with the IPCC ranges.
"Part of that slower start ... is the consequence of actions or inactions from the past. We haven't tackled gross emissions," Grant Blackwell, the commission's chief scientist, told Newsroom.
"When we look at the types of reductions that we're making or the pathways signify, then we are confident that they are taking a wee while but then dropping all the way down and are compatible with the sorts of reductions and models the IPCC looked at."
Smith, the commission's principal analyst, added that the pathway would cross that 40 percent lower bound of the IPCC range in 2032, just two years after it was meant to.
There's also the question of how realistic those later cuts are. The ones which come after 2035 won't have been put to the same depth of scrutiny as the emissions budgets themselves.
"Any projections beyond the 5-10 years have to be taken with a grain of salt. They are too far ahead to rely on with any confidence or to justify a lack of urgent action now," Every-Palmer said.
Blackwell said those projections were not just based on hypothetical future policies enacted in the 2030s, but represented the payoff from long-view policies implemented today.
"If the Government acts now and sets those things in motion, you see those actions really accelerating and coming to fruition. The actions that lead to those first three budgets, in our expectation and in our approach, is that they build and accelerate so that you get those continuing, accelerating reductions," he said.
"The really critical thing is action now."
