The forthcoming Intergovernmental Panel on Climate Change (IPCC) special report on 1.5°C will suggest a significant "carbon budget" for the 1.5°C climate warming target, in a political fix that will further undermine the organisation's credibility.
The report will use unwisely low assumptions about the Earth's climate sensitivity to pull a rabbit out of a hat: a carbon budget that from any sensible risk-management perspective simply does not exist. The political effect will be to say that the climate crisis is less bad than it is, and that we can "allow" more fossil fuel emissions.
In fact, recent research shows that climate sensitivity is higher that the median used in recent IPCC reports, but now the 1.5°C report will go in the opposite direction. The final report will likely have an even higher 1.5°C "carbon budget" figure than in the drafts leaked in recent months.
This is a scandalous outcome that may finish the IPCC as a credible and dispassionate compiler of climate science research. A report we will release on 20 August, What Lies Beneath: The understatement of existential climate risk, will show that IPCC reports tend toward reticence and caution, erring on the side of “least drama”, exhibiting a preference for conservative projections and scholarly reticence, and downplaying the more extreme and more damaging outcomes, such they are now becoming dangerously misleading with the acceleration of climate impacts globally.
Oliver Gedden, head of the EU Research Division at the German Institute for International and Security Affairs in Berlin, warned in 2015 that climate scientists and economists who counsel policymakers are being pressured to extend their models and options for delivering mitigation later, which has “introduced dubious concepts, such as repaying ‘carbon debt’ through ‘negative emissions’ to offset delayed mitigation — in theory”. He says that climate researchers who advise policymakers feel that they have two options, to be pragmatic or be ignored. “Many advisers are choosing pragmatism… Each year, mitigation scenarios that explore policy options for transforming the global economy are more optimistic — and less plausible… The scientific community must defend its independence from outside interference."
Gedden's comments about pragmatism and plausibility are particularly apt in the case of the 1.5°C report.
The 1.5°C report
In October this year, the Intergovernmental Panel on Climate Change (IPCC) will release a special report on the impacts of global warming of 1.5°C and emission pathways to achieve this goal.
The 2015 Paris climate policymaking conference (COP21) set a goal of limiting the global average temperature increase to “well below 2°C above pre-industrial levels and to pursue efforts to limit the increase to 1.5°C”. The 1.5°C was included as a COP outcome for the first time to pacify growing anger from the small-island states and least-developed countries about the low ambition of the international policymaking process. COP21 requested the IPCC to report on how to achieve the goal.
The Paris Agreement was a political fix in which grand words masked inadequate deeds. The UN Environment Program says that current pledges from governments represent only about half of what would be required to avoid a 2˚C temperature rise, and just a third of what’s required to limit warming to 1.5˚C.
The voluntary emission reduction commitments made by nations since Paris put the world on a path of more than 3°C of warming by 2100, and up to 5°C if high-end risks including carbon-cycle feedbacks are taken into account. Warming in the zone of 3–5°C is an existential risk to human civilisation.
What will the 1.5°C report say?
If previous IPCC reports, and recent leaks, are any guide, the October report will understate the risks and hence also understate the actions required. Leaks of drafts suggest it will include:
- At current emissions rate, human-induced warming will exceed 1.5°C by around 2040.
- A carbon budget exists for 1.5°C.
- Governments can still cap temperatures below the 1.5°C ceiling only with "rapid and far-reaching" transitions in the world economy and deep reductions in all emission sectors.
- How impacts across the climate system and society will be less severe at 1.5°C than at 2°C.
Contrary to the leaked report, there is credible evidence that Earth’s warming since the late-19th century will hit 1.5°C about a decade from now. For example, Melbourne-based researchers say the global temperature increase will likely exceed 1.5°C between 2026 and 2031. Other scientists have made similar projections.
Is there a carbon budget remaining for 1.5°C?
No, from a sensible risk-management viewpoint, there is no carbon budget for 1.5°C without including a lot of “negative emissions”, that is, drawing carbon dioxide (CO2) from the atmosphere to reduce the warming.
“We have no carbon budget left for the 1.5°C target and the opportunity for holding to 2°C is rapidly fading unless the world starts cutting emissions hard right now,” says Prof Michael Mann. Prof. Stefan Rahmstorf of Germany’s Potsdam University considers that we are now “in a kind of climate emergency” and that at least 1.5°C is “locked in”. (“Locked in” means that the warming will occur for the present level of emissions in the absence of large-scale carbon drawdown and/or solar radiation management.) Three other senior Australian scientists to whom I have spoken agree with the 1.5°C figure articulated by Mann and Rahmstorf. Some think it is likely to be somewhat higher.
So for a 1.5°C goal, humans need to draw back down every ton of emissions from now on, and more. In other words, what goes up must come down. Yet, extraordinarily, the more recent leaks of the draft IPCC report have actually increased the carbon budget for 1.5°C, and dropped references to it being “already out of reach” for a 66% chance of not exceeding the target.
How can there be an emissions path for 1.5°C?
The emission scenarios associated with the 1.5°C goal are based on “overshooting” or exceeding the 1.5°C target by up to half a degree — getting towards 2°C — before cooling back to the target by century’s end with carbon drawdown. Because the Paris Agreement does not encompass the steep emissions reductions required, many of the emission scenarios rely unduly on an unfeasible amount of drawdown in the second half of the century using a technology — Bio-Energy with Carbon Capture and Storage (BECCS) — which is unproven at scale. This is a dangerous path, and there is growing alarm amongst scientists about BECCS being a political fix in order to avoid stronger action right now, for example here, here and here.
What are the risks with “overshoot”?
On the present high-emissions path, warming will not only pass 1.5°C but hit the 2°C level by the mid-century. Large reductions in CO2 emissions will not by themselves significantly delay this timing. The dangers in overshooting increase with the duration and the magnitude of the overshoot. In a period of rapid warming, most major tipping points once crossed are irreversible on human timeframes, yet some of those tippings points are likely in the 1.5–2°C range.
Thus “overshoot scenarios”, which are now becoming the norm in policymaking circles, hold much greater risks, specifically that overshoot up to 2°C for up to half a century may trigger events and activate tipping points that cannot be reversed even with significant cooling.
Coauthor of the recent "hothouse" paper, Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research, says: “What we do not know yet is whether the climate system can be safely ‘parked’ near 2°C above pre-industrial levels, as the Paris Agreement envisages. Or if it will, once pushed so far, slip down the slope towards a hothouse planet. Research must assess this risk as soon as possible.”
In other words, the levels of "overshoot" likely to be central to the emissions reduction scenarios in the 1.5°C report may allow such a level of feedbacks that humans would lose the capacity to get warming back to survivable levels, let alone a safe climate.
What would hitting 2°C or more mean?
James Hansen, former NASA climate science chief and perhaps the world’s best known climate expert, says getting to 2°C or more would be a “prescription for disaster”, triggering tens of metres of sea-level rise and passing tipping points which could not be reversed on human timescales. In fact, if today’s CO2 level was maintained, it would produce a lot more warming than 1.5°C in the longer term. In the early- to mid-Pliocene 3–4.5 million years ago, CO2 levels were similar to today but temperatures were 3–4°C warmer than pre-industrial values.
What are the tipping points?
Tipping points have very likely already been passed for summer sea-ice free Arctic conditions, the loss of West Antarctic glaciers and a multi-metre sea-level rise.
Risks increase with temperature. More climate system elements are heading towards tipping points or experiencing qualitative change. These include the slowing of the Atlantic conveyor ocean current, accelerating ice-mass loss from Greenland, and declining efficiency of the Amazon forests and other land-based stores of carbon.
Is 1.5°C safe?
Since 1°C is not safe, warming of 1.5°C would be more dangerous. It would set in train sea-level rises of many metres, sufficient to drown significant components of human civilisation. In past climates, atmospheric CO2 similar to today’s level have been associated with sea levels around 25 metres above the present. Statements such as “Only limiting warming to below 1.5ºC will keep projected sea level rise under one metre in the long run” (Climate Analytics) have no basis in fact and run contrary to clear evidence that West Antarctica is already primed for a multi-metre sea-level rise.
A 1.5ºC global rise in temperature is likely to cause the loss of permafrost area estimated to be four million square kilometres. And 1.5°C would destroy the world’s coral ecosystems including the Great Barrier Reef, reducing them to remnant structures. And it’s the world’s poorest people who will suffer the biggest disruptions to their local climate as temperatures rise. Some tropical regions have already experienced climate warming of 1.5°C.
What would be safe?
What is safe are the climate conditions and the sea level which prevailed during the stable climate of the last 9000 years in which human civilisation developed, known as the Holocene. During that period, the global average temperature was no more than 0.5°C hotter than a late-19th-century baseline. By comparison we are now more than 1°C hotter than that baseline. Prof. James Hansen says 1.5°C “is not an appropriate goal” and “an appropriate goal is to return global temperature to the Holocene range within a century”.
If BECCS is not the answer, how can we drawdown carbon?
There are many ways to reduce the amount of carbon in the air, including better farming techniques, regenerative agriculture, soil carbon and biochar, and technologies that can directly capture CO2 from the air. The most cost-effective, large-scale drawdown action is the restoration of carbon-dense and biologically rich natural forests.
Isn’t this academic if in reality we are heading for 3°C or more of warming?
Absolutely not! Sustained political failure means we are heading towards a disaster, but we have the economic and technological capacity to get out of this huge mess. We need to be clear about exactly what would be safe and how we can get there.
What needs to be done?
The big questions are what is necessary to avoid a climate catastrophe and return to a safe climate, and how to achieve emergency-speed national and sub-national actions to make it happen. A campaign in the USA, “Well under 2°C: Fast action policies to protect people and the planet from extreme climate change”, led by respected scientists, advocates the “three levers” approach:
- The carbon neutral lever to achieve zero net emissions of CO2 with renewables and energy efficiency;
- The super pollutant lever to cut short-lived climate pollutants such as methane, black carbon, tropospheric ozone and HFCs to maximum extent possible; and
- Atmospheric carbon extraction lever to thin the atmospheric CO2 blanket.
Is that enough?
Zero emissions and carbon drawdown cannot be completed fast enough to prevent or reverse the significant tipping points currently crossed, and others close at hand. The other policy option is to use solar radiation management (blocking some incoming energy from the sun by using particles such a sulfates) to reduce the amount of warming until the “three levers” have time to get the climate system heading in the right direction. Solar radiation management only makes sense with very rapid actions towards zero emissions plus drawdown; and if there is a demonstrable, clear, net environmental benefit from it. Much work is needed to see if that is the case, and it should only used if that is so. But we need to be honest about what will be lost and what tipping points will be crossed if it is not considered.
How can we succeed?
We know human society is capable of amazing acts, whether it is building the pyramids, wiping out diseases, or facing down big natural emergencies. We can succeed by transcending the political failure and bring the fossil-fuel era to a close. We can build an ethos of common purpose: an emergency, whole-of-society response which draws on our collective community power and skills. We can mobilise to create change at the speed we need to protect ourselves and future generations.