Opinion: Emissions targets still lacking, but world leaders taking heed of climate science

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Opinion: Emissions targets still lacking, but world leaders taking heed of climate science

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It’s never been clearer that “drastic and rapid” emissions cuts are needed to curb catastrophic climate change. While targets put forward at COP26 might have fallen a little short, at least world leaders and policy-makers appear to be taking heed of climate science.

Much was made of the perceived successes and failures of the 26th Conference of the Parties (COP26). Hailed as successes were the international commitment to protect forests and an agreement to “phase down” coal use. But these were also failures, because this commitment lacked details on implementation and legal “teeth”, and the phase-down might open the door to some countries burning coal for many years to come. Underpinning negotiations were the simulations of our future climate, set out in the 6th Assessment Report of the Intergovernmental Panel on Climate Change, released just months prior. In the face of the most weighty and consequential decisions policy makers face today, science must, and arguably did, play a pivotal role.

The first volume of the IPCC report – dealing with physical climate change – appeared in August. Its Summary for Policymakers said it is “unequivocal that human influence has warmed” the climate system, and that strong and rapid reductions of CO2 emissions, reaching net zero, are required for the climate to eventually stabilise. Failure to achieve this would result in continuing warming and increasing frequency and intensity of most types of weather extremes. Incidentally, several countries participating in COP26 had recently experienced such catastrophic weather extremes, all made much more likely (or even at all possible) by climate change.  

However, the influence of science was not restricted to this momentous time. Many media outlets have reported that Nationally Determined Commitments (NDCs) would result in 2.4 degrees of warming by the end of the century (optimistically assuming that the NDCs will actually be met…). But these claims are not directly based on the 6th Assessment Report. The report discusses the future in terms of predefined Shared Socioeconomic Pathways (SSPs). At their core, these are stories of plausible future human behaviour, including conflicts, competition, technological progress and uptake, regional rivalry, and international collaboration to combat climate change. After translating these stories into future CO2 abundances and other physical “climate drivers”, the SSPs are like islands of knowledge, gained by running climate models driven with these scenarios, in the sea of possible climate futures. By interpolating smartly between these islands, we can however fill in the voids between them; this is how the projection of 2.4 degrees of warming under the present NDCs was arrived at.

As a climate scientist, I am pleased to see that my discipline is playing such an important and growing role, when really our common future is at stake… this is a reason for hope and a counterexample to the many falsehoods that often poison our discourse in this and other contexts. 

Olaf Morgenstern

A complication here is that several well-established present-generation climate models simulate more warming than observed during recent decades. They also produce more future warming in response to CO2 increases than the previous generation of models. The 6th Assessment Report confronts this problem head-on and — despite these models “running hot” — confirms the “climate sensitivity” to CO2 increases that has been established in previous reports. It explicitly accounts for and removes the influence of this modelling problem on the projected future global-mean surface temperature and on sea-level rise in these reference scenarios. These thus corrected projections are used in the interpolation step mentioned above, which then, in real time during the course of a climate conference, provide answers to politically charged questions, such as how new emissions’ reductions commitments would impact on global warming.

The role of science in the COP26 process is exemplified in that now over 90% of the world is covered by zero-carbon targets, up from 30% just two years ago. The parties to the Glasgow Climate Pact express “alarm and utmost concern that human activities have caused around 1.1°C of global warming to date and that impacts are already being felt in every region”. This is an unusually strong language for 197 countries to agree on. While COP26 clearly left more progress to be desired, to me it is a sign that increasingly the voice of science is being heard. As a climate scientist, I am pleased to see that my discipline is playing such an important and growing role, when really our common future is at stake. Given the dire prospects implied in high-emissions scenarios, such as the disappearance of whole nations whose territories would be swallowed by the sea, to me this is a reason for hope and a counterexample to the many falsehoods that often poison our discourse in this and other contexts. 

The IPCC working group II report, Impacts, Adaptation and Vulnerability, will be released in February. This will be followed by the IPCC Working Group III report on mitigation in March. Keep an eye out on our blog for more information, and contributions from our scientists.

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