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Clauser-ology: Cloudy with a chance of meatballs

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John Clauser’s theory of climate explained.

Some of you will have heard of John Clauser because he was an awardee of the 2022 Nobel Prize in Physics for his role in the experimental verification of quantum entanglement. Some of you will have heard of him because the first thing that he did after winning the Nobel was join a climate denial organization and make some rather odd claims about climate science. And some of you will never have heard of him (in which case, feel free to skip this post!).

At no point in his long and, by all accounts, successful, career has he ever published a paper on climate[1]. He has not penned an article, nor even a blog post or a tweet on the topic, and so any scientific basis for his opinions (if any) has been opaque… until recently. In the last few months he has given two interviews in which he goes into to detail about what he describes as a ‘missing element’ in climate science and what he imagines the consequences are for climate change. The first interview was for the Epoch Times (a far right-wing newspaper and media organization affiliated with Falun Gong). The second was a podcast with the somewhat troubled Chris Smith, an Australian journalist. (The material is somewhat similar in each). And more comprehensively, it was repeated in a recent video lecture as well.

And what is this supposed ‘missing element’? Clouds.

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The summary for policymakers of the Intergovernmental Panel on Climate Change sixth assessment reports synthesis

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The summary for policymakers of the Intergovernmental Panel on Climate Change (IPCC) sixth synthesis report was released on March 20th (available online as a PDF). There is a recording of the IPCC Press Conference – Climate Change 2023: Synthesis Report for those who are interested in watching an awkward release of the report.

It strikes me that the IPCC perhaps assumes that everyone is climate literate and are up to speed on climate change. While many journalists clearly got the message, expressed through news reports though e.g. the Guardian and Washington Post, I doubt that relevant leaders were swayed. One problem may be that journalists do not carry as much weight as scientists. 

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New misguided interpretations of the greenhouse effect from William Kininmonth

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I have a feeling that we are seeing the start of a new wave of climate change denial and misrepresentation of science. At the same time, CEOs of gas and oil companies express optimism for further exploitation of fossil energy in the wake of Russia’s invasion of Ukraine, at least here in Norway.

Another clue is William Kininmonth’s ‘rethink’ on the greenhouse effect for The Global Warming Policy Foundation. He made some rather strange claims, such as that the Intergovernmental Panel on Climate  Change (IPCC) allegedly should have forgotten that the earth is a sphere because “most absorption of solar radiation takes place over the tropics, while there is excess emission of longwave radiation to space over higher latitudes”. 

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Watching the detections

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The detection and the attribution of climate change are based on fundamentally different frameworks and shouldn’t be conflated.

We read about and use the phrase ‘detection and attribution’ of climate change so often that it seems like it’s just one word ‘detectionandattribution’ and that might lead some to think that it is just one concept. But it’s not.

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The CO2 problem in six easy steps (2022 Update)

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One of our most-read old posts is the step-by-step explanation for why increasing CO2 is a significant problem (The CO2 problem in 6 easy steps). However, that was written in 2007 – 15 years ago! While the basic steps and concepts have not changed, there’s 15 years of more data, updates in some of the details and concepts, and (it turns out) better graphics to accompany the text. And so, here is a mildly updated and referenced version that should be a little more useful.

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Another dot on the graphs (Part II)

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We have now updated the model-observations comparison page for the 2021 SAT and MSU TMT datasets. Mostly this is just ‘another dot on the graphs’ but we have made a couple of updates of note. First, we have updated the observational products to their latest versions (i.e. HadCRUT5, NOAA-STAR 4.1 etc.), though we are still using NOAA’s GlobalTemp v5 – the Interim version will be available later this year. Secondly, we have added a comparison of the observations to the new CMIP6 model ensemble.

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Making predictions with the CMIP6 ensemble

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The CMIP6 multi-model ensemble is a unique resource with input from scientists and modeling groups from around the world. [CMIP stands for the Coupled Model Intercomparison Project, and it is now in its 6th Phase]. But as we’ve discussed before (#NotAllModels) there are some specific issues that require users to be cautious in making predictions. Fortunately, there are useful ‘best practices’ that can help avoid the worst pitfalls.

A new paper by McCrystall et al that has just appeared in Nature Communications illustrates these issues clearly by having some excellent analyses of the changes in Arctic precipitation regimes at different global warming levels, and examining the sensitivity of their metrics to both local and Arctic warming, but unfortunately relying on the CMIP6 multi-model mean for their headline statements and press release.

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References

  1. M.R. McCrystall, J. Stroeve, M. Serreze, B.C. Forbes, and J.A. Screen, "New climate models reveal faster and larger increases in Arctic precipitation than previously projected", Nature Communications, vol. 12, 2021. http://dx.doi.org/10.1038/s41467-021-27031-y

Net Zero/Not Zero

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At the COP26 gathering last week much of the discussion related to “Net-Zero” goals. This concept derives from important physical science results highlighted in the Special Report on 1.5ºC and more thoroughly in the last IPCC report that future warming is tied to future emissions, and that warming will effectively cease only once anthropogenic CO2 emissions are balanced by anthropogenic CO2 removals. But some activists have (rightly) pointed out that large-scale CO2 removals are as yet untested, and so reliance on them to any significant extent to balance out emissions is akin not really committing to net zero at all. Their point is that “net-zero” is not zero and hence will serve as a smokescreen for insufficient climate action. To help sort this out some background might be helpful.

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The definitive CO2/CH4 comparison post

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There is a new push to reduce CH4 emissions as a possible quick ‘win-win’ for climate and air quality. To be clear this is an eminently sensible idea – as it has been for decades (remember the ‘Methane-to-markets’ initiative from the early 2000s?), but it inevitably brings forth a mish-mash of half-remembered, inappropriate or out-of-date comparisons between the impacts of carbon dioxide and methane. So this is an attempt to put all of that in context and provide a hopefully comprehensive guide to how, when, and why to properly compare the two greenhouse gases.

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A deep dive into the IPCC’s updated carbon budget numbers

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Guest post by Joeri Rogelj (Twitter: @joerirogelj)

Since temperature targets became international climate goals, we have been trying to understand and quantify the implications for our global emissions. Carbon budgets play an important role in this translation.

Carbon budgets tell us how much CO2 we can emit while keeping warming below specific limits. We can estimate the total carbon budget consistent with staying below a given temperature limit. If we subtract the CO2 emissions that we emitted over the past two centuries, we get an estimate of the remaining carbon budget.

I have been involved in the estimation of carbon budgets since the IPCC Fifth Assessment Report in the early 2010s. And since the first IPCC estimates published in 2013, we have learned a lot and have gotten much better at estimating remaining carbon budgets. In the 2018 IPCC Special Report on Global Warming of 1.5°C (SR1.5), the latest insights were integrated in a simple framework that allowed to estimate, track, and understand updates to these carbon budgets.

The most recent Working Group 1 Report of the IPCC Sixth Assessment Cycle (WG1 AR6) provides an updated assessment of the remaining carbon budget. Here’s an insider’s view providing a deep dive into how they differ from previous reports.

The scientific basis underlying a carbon budget is our robust scientific understanding that global warming is near-linearly proportional to the total amount of CO2 we ever emit as a society. This is illustrated in Fig. SPM10 of the WG1 AR6 report, both for the past and for future projections.

Source: Figure SPM.10 from IPCC (2021)

The estimates of remaining carbon budgets also made it into the Summary for Policymakers – the most prominent place that can be given for any finding of the report. Table SPM.2 gives an overview of the latest estimates, for different temperature limits and different probability levels.

Source: Table SPM.2 from IPCC (2021)

How have these estimates changed since previous reports?

IPCC reported carbon budgets for the first time in 2013. And since, important advances have been made in how we estimate these. Five puzzle pieces combine to give carbon budget estimates, and allow us now to understand subsequent updates.

Source: Figure 5.31 in Canadell et al (2021)

Starting with the key message of the AR6 carbon budget update: carbon budget estimates in AR6 are very similar to those published in the SR1.5 in 2018, but they represent a significant update since AR5 in 2013.

When adjusting for the emissions since AR5 and SR1.5, AR6 remaining carbon budget for limiting warming to 1.5C with 50% chance is about 300 GtCO2 larger than in AR5, but virtually the same as in SR1.5.

Source: Data from IPCC (2014), Rogelj et al (2018), and IPCC (2021)

For 66% probability, the AR6 budget is about 60 GtCO2 larger than in SR1.5.

Source: Data from IPCC (2014), Rogelj et al (2018), and IPCC (2021)

The budget is so much larger than in AR5, because since 2013 more accurate methods have been published that ensure that model uncertainties over the historical period are not accumulated into the future. This is best illustrated by this technical figure from SR1.5.

Source: Figure 2.3 from Rogelj et al (2018) – note how the red dot marked 2010 moves to the purple dot marked 2010, once historical modelling uncertainties are corrected for.

Between SR1.5 and AR6 every piece of the carbon budget was reassessed:

  • warming to date
  • how much warming we expect to get per tonne of CO2
  • how much warming would still occur once we reach net zero CO2
  • how much non-CO2 warming we can expect
  • Earth system feedback otherwise not covered

Let’s dive into each piece of this puzzle to understand what has changed between SR1.5 and AR6.

Warming to date – SR1.5 used a 0.97°C warming estimate between 1850-1900 and 2006-2015. This estimate already included corrections for the incomplete global coverage of observations and the different ways in which global surface temperature can be estimated. The AR6, based on a full reassessment of all available data, assesses 0.94°C of global surface temperature increase for the same period.

In isolation, this update results in central estimates being about 65 GtCO2 larger in AR6 than in SR15. For the 33% and 67% estimates that’s about 110 and 50 GtCO2 higher, respectively.

Warming per tonne of CO2 – The next piece of the puzzle is the warming we project per tonne of CO2. SR1.5 used an estimate of 0.8-2.5°C per 1000 GtC (=3664 GtCO2). AR6 assessed this quantity, also known as the Transient Climate Response to Cumulative Emissions of CO2 (or TCRE), to fall in the 1.0-2.3°C range.

Having the same central estimate, the update in TCRE causes no shift in 50% estimates, but the higher and lower percentiles are narrowed. For a 67% chance, AR6 estimates are about 50 and 100 GtCO2 larger compared to SR1.5 for 1.5°C and 2°C of global warming, respectively.

Warming after net zero CO2 – The third piece of the puzzle is the how much warming is expected to still occur once global CO2 emissions reach (and remain at) net zero. This is known as the Zero Emissions Commitment to emissions of CO2 (or ZEC).

The AR6 estimate confirms the SR1.5 estimate of no further CO2-induced warming or cooling once global CO2 emissions reach and stay at next zero. The uncertainty surrounding this value are reported separately. ZEC therefore causes no changes between SR1.5 and AR6.

Non-CO2 warming contribution – The fourth puzzle piece is the projected warming from non-CO2 emissions. As SR1.5, AR6 uses deep mitigation pathways assessed by SR1.5 (Rogelj et al, 2018; Huppmann et al, 2018), but with climate projections updated entirely with dedicated climate emulators that integrate the scientific information across chapter.

By coincidence (and it is really coincidence), the updates in radiative forcing from tens of different gases, climate sensitivity, and carbon-cycle uncertainties result in no net shift in the estimate of non-CO2 warming for the remaining carbon budget.

Pure luck, given the many updated pieces of scientific knowledge that were integrated in AR6, but convenient for explaining differences in carbon budget estimates.

Updated non-CO2 warming estimates lead to no change in remaining carbon budget estimates compares to SR1.5.

Other Earth system feedbacks – The last piece is to account for Earth system feedbacks that would otherwise not be covered. SR1.5 assumed an additional blanket reduction of 100 GtCO2 for this century for these feedbacks. This was a crude estimate and therefore not included as a central part of the remaining carbon budget numbers in SR1.5 AR6 updates this assessment entirely and includes this contribution in its main estimates.

Taking into account not only permafrost thaw, but also a host of other biogeochemical and atmospheric feedbacks, the AR6 estimates to appropriately include the effect of all these feedbacks, remaining carbon budgets have to be reduced by 26 ± 97 GtCO2 per degree Celsius of additional warming.

Altogether these updates mean AR6 remaining carbon budget estimates are very similar compared to SR1.5, while they additionally include the effect of Earth system feedbacks that would otherwise not be covered.

Selecting a remaining carbon budget requires two normative choices as a minimum: the global warming level that is to be avoided, and the likelihood or chance with which this is achieved. Further choices involve how deeply non-CO2 emissions can be reduced.

In addition to updates to science underlying carbon budget estimates, the AR6 also provides a larger set of likelihood levels for its remaining carbon budget estimates (see Table SPM.2 above). As in previous reports, AR6 provides remaining carbon budget estimates for a 33%, 50%, and 67% chance of keeping warming to a given temperature limit. In addition, however, the AR6 also provides the bracketing percentiles for the central 66% range (the range covered between 17% and 83%), so that the uncertainty of the central estimate can be adequately understood.

These values can be used in a variety of ways. For example, the central estimate for the remaining carbon budget for keeping warming to 1.5°C is now 500 GtCO2 starting from the beginning of 2020, with a 66% uncertainty range of 300–900 GtCO2.

Designing a policy for limiting warming to 1.5°C with this global 500 GtCO2 number in mind means that in 1-out-of-2 cases warming will end up below and in 1-out-of-2 cases it will end up above 1.5°C. Alternatively, it can also be understood to mean that in 1-out-of-2 cases policy measures will have to be sharpened beyond the policies consistent with a 500 GtCO2 budget over the coming decades if warming is effectively to be kept to 1.5°C. Similar examples can be given for 1.7°C or other levels (see Table 5.8 in the underlying chapter; Canadell et al (2021)).

A last item affecting the selection of remaining carbon budgets is the expectation of how deeply non-CO2 emissions can be reduced. All remaining carbon budget estimates in AR6 assume that non-CO2 emissions such as methane are reduced consistent with a deep decarbonisation pathway that reaches net zero CO2 emissions. Depending on how effectively these non-CO2 emissions can be reduced, the remaining carbon budgets can vary by 220 GtCO2 or more.

Bottom line of this technical explanation remains, however, that these budgets are small, our current annual global CO2 emissions of about 40 GtCO2/yr are reducing them rapidly, and all budgets require CO2 to decline to net zero while global emissions have not yet shown to decline.

It’s nice to have remaining carbon budgets, but now we need to get on with it and make sure that global CO2 emissions start to decline.

If you would like to know all the ins and outs of AR6 remaining carbon budgets have a look at Section 5.5 in Canadell et al (2021). The entire section describes the assessment of TCRE and remaining carbon budgets, while Box 5.2 presents a more technical comparison with carbon budget estimates from previous reports.

Joeri Rogelj is Director of Research, Grantham Institute Climate Change & Environment, Imperial College London, UK, and Senior Research Scholar, International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria

Parts of this post have been published earlier as a twitter thread.

References

Huppmann, D., Rogelj, J., Kriegler, E., Krey, V., et al. (2018) A new scenario resource for integrated 1.5 °C research. Nature Climate Change. [Online] 8 (12), 1027–1030. Available from: doi:10.1038/s41558-018-0317-4.

Josep G. Canadell, J. G., P. M.S. Monteiro, M. H. Costa, L. Cotrim da Cunha, P. M. Cox, A. V. Eliseev, S. Henson, M. Ishii, S. Jaccard, C. Koven, A. Lohila, P. K. Patra, S. Piao, J. Rogelj, S. Syampungani, S. Zaehle, K. Zickfeld, 2021, Global Carbon and other Biogeochemical Cycles and Feedbacks. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.

IPCC (2014) Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [MassonDelmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press

Rogelj, J., Shindell, D., Jiang, K., Fifita, S., et al. (2018) Mitigation pathways compatible with 1.5°C in the context of sustainable development. In: Greg Flato, Jan Fuglestvedt, Rachid Mrabet, & Roberto Schaeffer (eds.). Global Warming of 1.5 °C: an IPCC special report on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. [Online]. Geneva, Switzerland, IPCC/WMO. pp. 93–174. Available from: http://www.ipcc.ch/report/sr15/.