COP26: What does the 1.5°C warming target mean?

  01 Nov '21   |  Posted by: Birlinn

Today marks the beginning of formal discussions between world leaders at the COP26 climate change conference being hosted in Glasgow. In yesterday’s opening speech, COP26 president Alok Sharma said the ‘window is closing’ on meeting the 1.5 degree warming target. But what does this really mean? Alastair McIntosh’s Riders on the Storm weaves together science, politics, and spirituality to offer a illuminating discussion of what has gone wrong, and what we can do to change things. In this extract, the writer and broadcaster offers a succinct explanation of the Paris Agreement, what 1.5 degrees of warming really looks like, and what we can do to achieve this goal.

Extract from Riders on the Storm by Alastair McIntosh

The benchmark for climate action targets through this century is the Paris Agreement, being the outcome of the 21st Conference of the Parties, attended by the governments that are members of the United Nations Framework Convention on Climate Change. COP 21 took place in Paris at the end of 2015. By early 2020 it had been ratified by 189 of the 197 parties. Signatories include China, Russia, India and the countries of the EU. Non-signatories are a mixed bag of high emitters and failed states. Although the US was a signatory at the time of writing, President Trump signified his intention to withdraw in November 2020 in furtherance of his America First doctrine. As he put it: ‘I was elected to represent the citizens of Pittsburgh, not Paris.’

‘Paris’, as the agreement gets known, lacks any binding enforcement mechanism. Although it has the status of a UN treaty its pledges are aspirational. Nevertheless, this standing gives it leverage in international relations. As laid down in Article 2A, the primary objective is: ‘Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.’

Special Report: Global Warming of 1.5°C
Global Warming of 1.5°C, abbreviated to SR1.5, was released by the IPCC in October 2018 at the request of the UN’s Framework Convention to explore how to fulfil the Paris Agreement. It examined around 6,000 recent scientific studies, was compiled by more than 200 authors from all over the world and scrutinised by some 1,100 peer reviewers. In generating media reports and headlines internationally, it bolstered the work of scientists, policy officials and concerned politicians, and helped fuel a rising new wave of climate activism that spanned the ‘Fridays for Future’ school climate strikes associated with Greta Thunberg, the demands of Extinction Rebellion and many other endeavours less prominent in the public eye.

The IPCC’s remit was: ‘. . . to provide a Special Report in 2018 on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emissions pathways.’ In conceding the possibility – most would say a foregone conclusion – of a target overshoot approaching 2°C, SR1.5 includes models showing how temperatures might be brought back down to 1.5°C again by more stringent measures taking effect later in the century.
It therefore set itself a dual target, whereby:

“In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030, reaching net zero around 2050. For limiting global warming to below 2°C, CO2 emissions are projected to decline by about 25% by 2030 in most model pathways and reach net zero around 2070.”

The starting point of SR1.5 was the baseline that the world had already warmed by 1°C by 2017. It anticipates that, in the absence of rapid and effective action, the combination of existing carbon concentrations and new emissions added all the time are likely to raise world temperatures to 1.5°C above pre-industrial levels sometime between 2030 and 2052. By ‘net zero’, it means that any further CO2 emissions in one context are offset by an equal compensating level of removal in another. An example is offsetting the carbon cost of a flight by paying to plant trees to soak up CO2 – a practice based on the questionable assumption that any trees planted will be cared for, and never burnt or felled and allowed to decompose back to atmospheric carbon gases.

Why did the Paris Agreement choose 1.5°C as a relatively safe threshold? One answer found in SR1.5 is that here the earth will have reached its ‘limits to adaptation and adaptive capacity for some human and natural systems’, and that if the warming overshoots towards 2°C, then with high confidence some ecosystems will be irreversibly damaged or lost. A harbinger of such an occurrence would be the Australian forest fires of 2019–20. On preliminary estimates, these destroyed half of the remaining 40 million-year old Gondwana rainforest in such regions as the Blue Mountains and the world heritage Nightcap National Park, including parts that had never before been logged or burned.

If temperatures can be constrained or brought rapidly back down to 1.5°C, then the projections for global sea level rise for the period spanning the turn of the twentieth century to the end of the twenty-first should be within 0.26–0.77 metres. An overshoot to 2°C raises this to 0.35–0.93 metres. As the mid-points of these ranges are 0.51 and 0.64 metres respectively, one way of looking at it in round figure terms is that the difference between 1.5°C and 2°C is half a metre and two-thirds of a metre by the century’s end, which is to say within a single human lifetime. On top of that, SR1.5 reminds us that polar ice sheet instability is more likely to be triggered above 1.5°C.

It is all very well to say ‘build walls and raise everything up’, but consider just one small example, again from a well-documented part of the world from where these types of stories more readily emerge. Officials in the Florida Keys, a string of islands linked by causeways off the American coast, have found that to keep a threatened three-mile stretch of road dry in 2045 would mean elevating it by 2.2 ft – that’s two-thirds of a metre. This would cost $128 million, and some 300 miles of similar stretches of road also need raising. Multiply that up for a crude estimate, and you hit $12.8 billion. The county can’t afford it, the taxpayers won’t bear it and the mayor fears a string of lawsuits from irate householders who claim the law entitles them to have such lifeline links maintained.

‘What is government for? They’re supposed to protect your property,’ insisted one resident.

‘Maybe we should think about stopping, or trying to stop, the cause of the water rising,’ said another. ‘At what point will the road be high enough?’

‘We’ve Only Twelve, Eleven, Ten . . . Years Left’
To turn that round another way, at what point does the world run out of ‘carbon budget’ to keep within the 1.5°C threshold? From where did climate change derive the slogan, as it was when SR1.5 came out, ‘We’ve only got twelve years left,’ and counting down progressively since then, as if the next space shot is heading off to colonise Mars courtesy of Elon Musk?

The twelve-year countdown is never mentioned by the IPCC, but the calculus based on SR1.5 looks like this. Since the industrial age began and through until the end of 2017, anthropogenic emissions have accumulated 2,200 billion tons (or gigatons) of CO2 in the atmosphere. To have medium confidence of a 50:50 chance of containing global warming to within 1.5°C of pre-industrial temperatures, only an estimated 580 billion tons of capacity remain. If we want to raise the confidence level to a 66 per cent chance, we should think of it as only 420 billion tons remaining of the so-called ‘carbon budget’.

How long will that last us? Well, annual CO2 emissions for 2017 were running at 42 billion tons. Average out those two budget figures, divide by forty-two, and there’s your twelve years, starting in 2018 and lasting through to 2030. I’m guessing that’s how, in rough and- ready terms, somebody somewhere came up with that date and caption. Reasonably enough, it caught on. What’s unhelpful is that we’ve had a string of ‘Only so-many years left . . .’ warnings going back to the 1990s, the vagueness and inflexibility of which left hostages to fortune. But what’s helpful this time is that it’s grounded in measurable science. It passes a key, if sometimes glib, acid test of scientific method: ‘If you can’t count it, it doesn’t count.’ And for campaigning purposes, that brings to life the urgency of the primary Paris target. It shows why it matters that we cut emissions first by 45 per cent by 2030, and then on down to net zero by 2050.

But how? What does it mean the governments of the world must do? And what in a context where SR1.5 states that the national mitigation ambitions that have so far been submitted to the UN under the Paris Agreement ‘would not limit global warming to 1.5°C’? In fact, with medium confidence, they point more towards 3°C by 2100. In other words, we’re already failing by a factor of at least 100 per cent. To get to grips with what needs doing, SR1.5 maps out four Illustrative Model Pathways for differing mitigation action strategies. Here is yet another set of models, overlapping with, but not identical to, the two sets of models that we have previously touched on – the RCPs and the SSPs. One can almost sense the fun draining from the hard realities as SR1.5 avoids the acronym IMP for its Illustrative Model Pathways, naming them just pathways P1, P2, P3 and P4. Here we need not enter into detail. Suffice to say that each explores a different CO2 mitigation option showing how, through to 2100, it would be technically possible in principle to limit global warming to 1.5°C with no or limited overshoot up to 2°C.

The framing here is crucial to understand. In order to work within what could make Paris possible, all four pathways assume a commitment to low emissions scenarios as their baseline. Two assumptions here are worth highlighting. Quantitatively, that there will be investment in the world energy system of around $2.4 trillion between 2016 and 2035 – that is, about 2.5 per cent of global GDP. And qualitatively, a recognition that ‘social justice and equity are core aspects of climate-resilient development pathways’ that could slow warming to 1.5°C, and this so that the ‘inevitable trade-offs’ of decarbonisation can be undertaken ‘without making the poor and disadvantaged worse off ’.

Within that hopeful framing, the pathways vary in their assumptions about levels of technological innovation, decarbonisation of the energy supply, downsizing energy demand, the degree of international cooperation and social shifts towards sustainable and healthy consumption patterns. All four scenarios would entail ‘rapid and far-reaching transitions’ in how we live. All require a global transformation of energy production, transport, agriculture, the built environment and industrial processes. Not for nothing does SR1.5 invoke the word ‘unprecedented’ twenty-eight times.

  • Share: