Hamburg Climate Futures Outlook 2021
Hamburg Climate Futures Outlook 2021
Photo: UHH/CLICCS
In the Hamburg Climate Futures Outlook, CLICCS researchers make the first systematic attempt to assess which climate futures are plausible, by synthesizing research from disciplines as varied as sociology, macroeconomics and earth system science. In this way, CLICCS helps to narrow down the multitude of future scenarios to inform policy and individual decisions.
Key FindingsClimate Protection: Deep Decarbonization by 2050 Currently not Plausible
CLICSS publishes a new, essential study on climate futures. The study represents the first systematic attempt to investigate whether a climate future with net-zero carbon emissions is not only possible but also plausible. The authors examine plausibility from a technical-economic perspective, but also with regard to the societal changes necessary for such a future. They conclude that deep decarbonization by 2050 is currently not plausible – the current efforts to bring about societal transformation need to be far more ambitious.
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Figures
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Plausibility of net global CO2 emissions by 2050. Download figure as jpeg file.
Figure 1: The speedometer shows the wide range of possible emissions in the year 2050 as described in existing emissions scenarios. Emissions could reach net-zero by 2050 (deep decarbonization) or could increase up to a doubling of current emissions (very high emissions). Approximate emissions in 2020 are indicated by the speedometer needle. Here we find a reduced range of plausible emissions scenarios, supported by a techno-economic plausibility assessment (Chapter 3) and a social plausibility assessment (Chapter 5), indicated by the shaded bands. Increasing emissions are not yet considered in the social plausibility assessment (gray band).
Components of the Social Plausibility Assessment Framework. Download figure as jpeg file.
Figure 2: The figure shows the chosen climate future scenario, deep decarbonization (right), and the selected key social drivers of deep decarbonization (left; see Chapters 5 and 8 for a description and analysis of the drivers). The assessment of the driver dynamic (center), their enabling and constraining conditions, and the potential global opportunity structure leads to a conjecture about the plausibility of the future scenario (Section 5.3).
The global opportunity structure. Download figure as jpeg file.
Figure 3: Social drivers (left) provide resources that become more material as they move from left to right in the figure. If the resources become visible to societal agents on a global level (center), these agents can use and combine them in material ways, which can influence driver-specific environments and therefore the enabling and constraining conditions of other drivers (right).
Projected 21st-century global surface warming. Download figure as jpeg file.
Figure 4: The 90% uncertainty ranges are indicated by shading around the central estimates (lines). Observed global surface warming is shown by the black line (Morice et al., 2021). The warming is simulated relative to the recent reference period 1995–2014 (left vertical axis). To convert to warming relative to the pre-industrial period, we note that the period 1995–2014 was observed to be warmer than the period 1850–1900 by 0.87°C (Morice et al., 2021; right vertical axis).
Detecting the effects of emissions reductions. Download figure as jpeg file.
Figure 5: Top figure shows atmospheric CO2 concentrations for two emissions scenarios, RCP2.6 and RCP4.5. Bottom figure shows an ensemble of 100 global surface warming responses to each concentration pathway (generated by the MPI-ESM Grand Ensemble; Maher et al., 2019). The ensemble mean warming is shown by the thick lines, individual simulations by thin lines. The bars describe the range of warming generated by each ensemble for the years 2040, 2060 and 2080.
Amplified regional internal variability. Download figure as jpeg file.
Figure 6: Simulations with the MPI Grand Ensemble are grouped according to when the global and decadal average surface temperature shows no warming (pre-industrial, pre-ind), or when it is warmer than the pre-industrial by either 1.5°C (blue) or 2°C (red). For each such decade, the figure shows how often the European annual summer temperature increase attains a certain value. The summer values are grouped in intervals of 0.075°C. Adapted from Suarez-Gutierrez et al. (2018).
Interviews
What Do We Mean by “Plausible”?
16 March 2021, by Ute Kreis
Which climate futures are possible and which are plausible? – in May, the “Hamburg Climate Futures Outlook,” a scientific report released by the Cluster, will address this question for the first time. We spoke with Prof. Anita Engels, a social scientist at Universität Hamburg, and Prof. Jochem Marotzke from the Max Planck Institute for Meteorology. Both are CLICCS Co-chairs.
What does the report focus on: what’s realistic or what’s politically feasible?
Anita Engels: “Realistic” may well come closest. We examine which options have a reasonable chance of becoming reality – and analyze political processes, corporate strategies, and consumer behavior, as well as social trends and discourses.
Jochem Marotzke: For those of us in the natural sciences, the various emissions pathways are initially on an equal footing. But if we look at the society around us, it’s a very different story.
Not everything that could happen will happen. What do you base this on?
Marotzke: In reality there are various factors that stand in the way of developments toward a climate-neutral society or delay them. Take coal-fired power plants, which have a planned lifetime of decades – with all the resulting emissions.
Engels: Nevertheless, how society will develop remains extremely difficult to predict. Certain trends can be identified, but history shows us that over and over again events happen that suddenly change everything. Like when the Berlin Wall came down. Maybe, looking back, the change was in the air. But it was simply impossible to predict that it would happen the way it did.
Nevertheless, you hazard a prognosis?
Engels: In the “Hamburg Climate Futures Outlook” we identify so-called social drivers, analyze pressures and sources of resistance, but also possibilities and promising opportunities for change – important evidence and arguments for which we have developed a systematic evaluation framework. In this regard, we draw on our own and recent international findings.
Who should read the report?
Engels: The report was written first and foremost for the scientific community. We want to assess where the field stands, and to some extent we explore uncharted scientific territory.
Marotzke: At the same time, the “Hamburg Climate Futures Outlook” offers guidance for decision-makers: Perhaps larger efforts are required than expected by some? On the other hand, are there “windows of opportunity” that we can capitalize on for change? Think about the coronavirus pandemic. It’s also discussed in the report.
What Matters Most Is Which Path We’re On
28 May 2021, by Ute Kreis
Strict climate protection measures, net zero emissions, or simply business as usual? When it comes to the future climate, there are a number of possibilities. But not all of them are plausible. For some developments, we lack the requisite know-how. For others, time is running out.
“We will have to actively remove greenhouse gases from the atmosphere if we want to achieve the Paris climate goals and limit global warming to two degrees,” says CLICCS Spokesperson Prof. Detlef Stammer. “Unfortunately, emissions aren’t declining quickly enough, which means that plants, forests and soils, our natural carbon sinks, aren’t enough. And the clock is ticking. As such, we also have to consider technological – large-scale technological – solutions.”
Solutions for which there are now concepts, but few established procedures. According to Stammer: “We’re calculating on the basis of technologies that we don’t even have yet, for instance, to remove relevant amounts of CO2 from the atmosphere. Therefore, it’s doubtful whether we’ll be able to use them in the next decade.” While it’s not completely impossible, he argues, it’s not plausible. However, the more investments are made, and the more corresponding laws are introduced, the more achievable the goal becomes: “What matters most is that the necessary framework conditions are met. They define which path we’re on.”
Further, the climate itself not only depends on the intensity of drivers like solar radiation and the amount of greenhouse gases in the atmosphere, but also fluctuates within certain limits, which are determined by the climate’s natural variability, and by fundamental laws of physics. Accordingly, some potential scenarios can be ruled out. For example, even if global warming accelerated rapidly, Greenland’s continental shelf couldn’t realistically suddenly melt. In reality, due to the enormous volume of ice involved, the process would still require a certain minimum time.
The real climate isn’t an average
As such, the future climate isn’t simply the average of all possibilities. Instead, it’s important to identify scenarios that are plausible – and to provide a basis for political decisions. “With our understanding of the climate system and the influence of human beings, but also natural variability, today we can better assess potential developments,” says Stammer. “At the same time, certain scenarios aren’t plausible, because the physical or social prerequisites can’t be met.”