The NDC is dead; long live the NZT?

It’s all but impossible to keep up with the number of reports on climate change, even those published just this month. Close on the heels of the IPCC WG1 report, three noteworthy publications came out in September: Niklas Höhne et al’s Nature article Wave of net zero emission targets opens window to meeting the Paris Agreement; a climate change risk assessment published by Chatham House and written by Daniel Quiggin et al; and the UNFCCC’s synthesis report Nationally Determined Contributions under the Paris Agreement (advance version, Sept 17th). A fourth publication, the WMO’s United in Science 2021 provides a useful synthesis of climate analysis compiled from various other sources. In this post, I summarise some key messages – mainly for my own benefit, but you may find it useful too.

The first paper by Höhne et al, published in Nature on the 16th September, attempts to conjure optimism from – let’s face it – a pretty bleak outlook. It answers the question – how hot will it be in 2100 if countries fully meet their ‘current policies’, ‘current pledges’ (based on countries’ Nationally Determined Contributions) and ‘net zero’ targets. An optimistic note is struck by referring to the momentum or ‘wave’ of countries’ net zero targets. This wave, the authors argue, “could, if fully implemented, reduce best estimates of projected global average temperature increase to 2.0–2.4C by 2100, bringing the Paris Agreement temperature goal within reach”.

The study draws on methods used in UNEP’s Emissions Gap Report 2020 and Climate Action Tracker (CAT). Using the CAT method, the authors find that if net zero targets are fully implemented, then there would be a 66% chance of keeping warming below 2.2C. That compares favourably to countries’ current policies, which if implemented would gives us a 66% chance of keeping below 3.1C. Using the UNEP method, they found that net zero targets would give us a 66% chance of keeping warming below 2.5C, compared to 3.5C from implementing current policies. So you can see what difference it would make in terms of future warming if net zero targets were met – the authors inputted the same data using both CAT and UNEP methods and found roughly the same improvement (if you can call it that) of 0.8-0.9C less warming.

The Chatham House (CH) report was picked up widely by social media last week, possibly because of its doom-laden conclusion: “The risks are compounding, and without immediate action the impacts will be devastating”. The focus of the report is slightly different in as much as it pooh-poohs the net zero ‘pledges’ because they “lack policy detail and delivery mechanisms”. Instead, the focus in the CH report is firmly on countries’ nationally determined contributions (NDCs) (NB: there is an important distinction between NDCs and ‘current policies’ and, unfortunately, the CH report isn’t as clear as it could be in differentiating between them – see the UNEP 2020 Emissions Gap Report’s glossary for definitions of both terms).

The CH report begins with what we know already from UNEP, that there is a large gap between the emissions from countries’ NDCs and emissions required to keep below 1.5 and 2.0C. You can see the size of the gap in the image above (UNEP 2020). The emissions gap from NDCs is 12-15GtCO2 for 2.0C and 29-32GtCO2 for 1.5C. Personally, if you want to know about the emissions gap, I would recommend you read UNEP’s annual reports rather than the CH report.

I want to bring in the UNFCCC synthesis report here because it provides the very latest data on the NDCs. It also, I’m afraid to say, provides a damning, yet beautifully condensed, indictment of climate diplomacy. I recommend you read paras. 10-15 of the Executive Summary right now. But if you can’t, here’s a flavour:

Total global GHG emission level (without LULUCF), taking into account implementation of the latest NDCs of all Parties to the Paris Agreement, is estimated to be around 54.8 (52.8–56.8) Gt CO2 eq in 2025 and 55.1 (51.7–58.4) Gt CO2 eq in 2030,6 which are:
(a) In 2025, 58.6 per cent higher than in 1990 (34.6 Gt CO2 eq), 15.8 per cent higher than in 2010 (47.3 Gt CO2 eq) and 4.5 per cent higher than in 2019 (52.4 Gt CO2 eq);
(b) In 2030, 59.3 per cent higher than in 1990, 16.3 per cent higher than in 2010 and 5.0 per cent higher than 2019 (my emphasis).

UNFCCC, 2021 , para 10

If that’s not depressing enough, try para. 13 on for size. It points out that “taking into account implementation of all the latest NDCs” the total global GHG emission level in 2030 will be 16% above the 2010 level when, in order to be consistent with a 1.5C goal “with limited overshoot” we need to decline emissions by about 45% from 2010 levels by 2030.

Paragraph 14 is even worse:

In the context of the carbon budget consistent with 50 per cent likelihood of limiting
warming to 1.5 °C, cumulative CO2 emissions in 2020–2030 based on the latest NDCs would
likely use up 89 per cent of the remaining carbon budget, leaving a post-2030 carbon budget of around 55 Gt CO2, which is equivalent to the average annual CO2 emissions in 2020–2030.

UNFCCC, 2021, para 14

It’s worth re-reading paragraph 14 because it’s almost unbelievable. For 50/50 odds of keeping below 1.5C (not great odds) at our current rate of emissions, by 2030, we will have one year of carbon budget left. One year! Given this devastating news, what does UNFCCC conclude? Well, we have a choice: “either a significant increase in the level of ambition of NDCs between now and 2030 or a significant overachievement of the latest NDCs, or a combination of both” (para 15).

Ok, so that’s bad. Let’s return to the Höhne et al paper for a moment. It begins by pointing out that “131 countries are discussing, have announced or have adopted net zero targets (NZT), covering 72% of global emissions”. The authors are also in no doubt about the deficiencies of the NDCs and countries’ ‘current policies’ in meeting the aims of the Paris Agreement, but they don’t dwell on it. Instead, they shift attention towards the net zero targets. The authors don’t say this, but – on reflection – could you regard the NZTs as an extension of the NDCs?

If so, there’s an obvious objection, which might go something like: Are you kidding! It’s taken 6 years for all signatories to commit to NDCs of such low ambition that the Paris targets will simply not be met. So, what makes you think most (not all – remember only 131 countries “are discussing, have announced or have adopted net zero targets, covering 72% of global emissions”) of these same countries will meet their NZTs? NZTs are simply kicking the proverbial can of emissions commitments 30 years down the road. Now that’s a worry.

Both the Höhne et al paper and the CH report share a similar assessment of the kind of temperatures we can expect by 2100 if we carry on at our current level of ambition. For Hohne et al, we’re looking at a 66% probability of keeping below 3.1-3.5C (that’s the median temperature btw) depending on which method one uses – CAT’s or UNEP’s. For the authors of the CH report, the indications are (at least in the energy sector) that we are tracking RCP4.5, which has a temperature associated with it of 2.7C by 2100 (and a 10% chance of reaching 3.5C). Take your pick – none offer a world we would want to live in/on/through.


Are you still here? Ok, so I have some issues with the CH report. I’m very happy to admit that they may be the result of my limited understanding of the topic. I am not, after all, a climate scientist.

On the plus side, the report provides “a granular examination of global progress towards decarbonisation of the energy sector” measured against 12 indicators which, the authors argue, most closely tracks RCP4.5. This is useful to know.

Furthermore, the report highlights “the risks and likely impacts if the goals set under the Paris Agreement are not met, and the world follows an emissions pathway consistent with recent historical trends”. Again, useful to know.

And it focuses not just on the high probability- low impact climate risks but the low-probability, high-impact ones too. Of itself, that’s fine. The recent IPCC AR6 report, for example, acknowledges what it calls ‘low likelihood-high warming storylines’ in its Technical Summary, noting that “a comprehensive risk assessment also requires considering the potentially larger changes in the physical climate system that are unlikely or very unlikely but possible and potentially associated with the highest risks for society and ecosystems” (TS p38, my emphasis). So the CH report is in good company here.

But I think that the CH authors are too quick to dismiss the net zero targets. It feels to me that these are both significant departures from ‘current policies’ and an important extension to NDCs. Personally, I think more weight could be given to the positive ‘wave’ of the net zero targets described by Hohne et al.  

I like the report’s Figure 1a. Here it is:

CPS: current policies scenario (IEA); SDS: sustainable development scenario (IEA)

On the one hand, it looks like good news in the sense that the pink line (indicator trends) peaks somewhere between 2020-30 and heads towards 2040 on a downward trajectory. It compares favourably to the green line (current policies scenario), which is very closely following RCP4.5. But on the other hand, it’s also bad news in as much as the trend is nowhere near either the sustainable development or RCP2.6 scenarios. The authors choose to call the pink line (indicator trends) trajectory an “RCP4.5-like trajectory”, and (as noted above) the associated median temperature by 2100 of emissions concentrations implied by RCP4.5 is 2.7C, with a 10% chance of 3.5C. Looking at the graph, though, you could argue that the indicator trends trajectory isn’t really shadowing RCP4.5 and, by 2050 say, could be closer to RCP2.6?

I’m also not sure how helpful it is for the report to remind its readers what would happen if decarbonisation plans were to halt completely – because that seems very unlikely to the point of not ever happening. But the report does do that, pointing out that in that scenario there would be a 90% chance of hitting 4C, and a 10% chance of hitting 7C (with a median of 5C). You mention 7C in any report – especially one from an authoritative institution like Chatham House – and the cranks are going to hit on it. And sure enough, they did.

The authors then explore the direct impact on societies from climate hazards we might expect from concentrations of CO2 that track RCP4.5. They refer to the SSPs – five shared socio-economic scenarios – and choose SSP2 as the one that “represents a similar trend in decarbonisation action that the emissions trajectory indicates”. I don’t really understand this. Each SSP, as Zeke Hausfather explains, “has a baseline scenario that describes future developments in the absence of new climate policies, beyond those already in place today” (my emphasis). The energy use for each SSP is presented below:

SSP1, Hausfather notes, would result in warming by 2100 of 3-3.5C, which is a bit above the temperature the CH report warns us of (2.7C with an outside chance fo 3.5C). SSP2 would result in 3.8-4.2C of warming by 2100, which is way above RCP4.5. So I’m not sure what’s going on here. Have the authors hit upon the right SSP? And anyway, these baselines proceed “in the absence of new climate policies”. By way of contrast, the net zero targets, while not always fully fledged into policy, suggest a move in the direction of new climate policies, don’t they? So, to return to a point made above, I’m not sure why the net zero targets are treated with such scepticism by the authors. Or, rather, I can see why there are grounds for scepticism; I just wouldn’t write a risk assessment that ignored them.

Note: I’d be really interested to discuss this further with the authors. They are the experts, I’m just that annoying back seat driver.

Published by andrew

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