the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence
Abstract. Intergovernmental Panel on Climate Change (IPCC) assessments are the trusted source of scientific evidence for climate negotiations taking place under the United Nations Framework Convention on Climate Change (UNFCCC). Evidence-based decision-making needs to be informed by up-to-date and timely information on key indicators of the state of the climate system and of the human influence on the global climate system. However, successive IPCC reports are published at intervals of 5–10 years, creating potential for an information gap between report cycles.
We follow methods as close as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. The purpose of this effort, grounded in an open data, open science approach, is to make annually updated reliable global climate indicators available in the public domain (https://doi.org/10.5281/zenodo.11064126, Smith et al., 2024a). As they are traceable to IPCC report methods, they can be trusted by all parties involved in UNFCCC negotiations and help convey wider understanding of the latest knowledge of the climate system and its direction of travel.
The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced. For the single year average, human-induced warming reached 1.31 [1.1 to 1.7] °C in 2023 relative to 1850–1900. This is below the 2023 observed record of 1.43 [1.32 to 1.53] °C, indicating a substantial contribution of internal variability in the 2023 record. Human-induced warming has been increasing at rate that is unprecedented in the instrumental record, reaching 0.26 [0.2–0.4] °C per decade over 2014–2023. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 54 ± 5.4 GtCO2e per year over the last decade, as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track a change of direction for some of the indicators presented here.
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CC1: 'Comment on essd-2024-149', Ken Mankoff, 08 May 2024
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Conflict of interest statement - I'm a Chief Editor (Ice domain) at ESSD. But I'm submitting this comment not in that capacity as this manuscript makes little mention of the cryosphere.
*** Title
I find the title overly broad (and uses the word "indicators" 2x). This manuscript ignores some key indicators of change (such as mass loss from ice sheets, sea level rise, and likely many others outside my research areas). In fact, L964/966 states, "This also has implications for the committed response of slow components in the climate system (glaciers, deep ocean, ice sheets) and committed long-term sea level rise, but this is not part of the update here." The abstract also suggests the focus of the manuscript is somewhat different from the title. L73-76 say "We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes."
From the abstract, forcings, emissions, GHG concentrations, budgets remaining, and attribution to humans are not "Indicators of Global Climate Change". They are "climate indicators" as per your Table 10. Surface temperature is an indicator of global climate change, as are temperature extremes. I suggest the title should better reflect the scope of the manuscript.
*** Land change
You highlight that land average maximum temperature change is "rising at a substantially faster rate compared to global mean surface temperature". If so, might it also be useful, relevant, and important to highlight what temperatures are rising (or dropping) slower than the global mean surface temperature?
L867: Is this a complete sentence?
*** Figures
Fig 1: Why and how does the remaining budget depend on future emissions? I can see the remaining budget depending on future "scenarios" (a broader term) where scenario includes drawdown technologies.
Fig 3B: I cannot see which legend goes with the large negative forcing. I assume this is tropospheric aerosols, but am not certain. I become more certain when I see aerosols as negative in 3A. Perhaps labels should be next to lines at the far right side? There is also a dotted line but no dotted legend.
Fig 4B: Are differences between AR6 and this study only due to different time periods, or also different methods? If different methods, can you do the same time periods as IPCC to show changes due only to methods and not time? Can the x-axis and display of this graphic be improved? For example, could the X axis span 1971 to 2023 and each of these could be box spanning the appropriate x-range, many of them overlapping?
Infographic: top right text I suggest removing words "being" and "the strength of".
Citation: https://doi.org/10.5194/essd-2024-149-CC1 -
CC2: 'Comment on essd-2024-149', Rasmus Benestad, 13 May 2024
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This is a timely paper that brings up the discrepancy between the slow IPCC cycles and the fast rate of change that the real world undergoes. It would be tempting to say that the IPCC also needs to adapt to climate change and adjust how it works to match the needs for up-to-date information about the changing climate. However, it neglects an important part of the climate system: the global hydrological cycle.
Traditionally, data and climate indicators have emphasised temperature and warming but neglected the equally important aspect of disruption to the global hydrological cycle. While the global observation systems in the past were unable to provide reliable global status, modern satellite observations and reanalyses are becoming more mature. We have made the case for including global indicators for the hydrological part of Earth's climate system in https://doi.org/10.1007/s43832-024-00063-3 and https://doi.org/10.1371/journal.pclm.0000029 - there are indicators suggesting that the total amount of precipitation falling on Earth's surface each day has increased over the past and that the fractional surface area of the Earth receiving precipitation each day has shrunk. These are key to understanding changes in extreme rainfall and drought, and hence ought to be relevant in this paper (e.g. L97: "policymakers with annual updates of the latest scientific understanding on the state of selected critical indicators of the climate system and of human influence."). Preferably, resources such as https://pulse.climate.copernicus.eu/ should also display this kid of information too. Many of the headlines on natural disasters around the world refer to flooding and extreme rainfall (recently China, Brazil and Afghanistan), and Lussana et al. (https://doi.org/10.1002/joc.8375) reported that he hydrological cycle is undergoing changes in all regions, and a common features includes an increase in intense precipitation events and a decrease in the corresponding spatial extent.
Citation: https://doi.org/10.5194/essd-2024-149-CC2 -
CC3: 'Comment on essd-2024-149', Rasmus Benestad, 13 May 2024
reply
This is a timely paper that brings up the discrepancy between the slow IPCC cycles and the fast rate of change that the real world undergoes. It would be tempting to say that the IPCC also needs to adapt to climate change and adjust how it works to match the needs for up-to-date information about the changing climate. However, it neglects an important part of the climate system: the global hydrological cycle.
Traditionally, data and climate indicators have emphasised temperature and warming but neglected the equally important aspect of disruption to the global hydrological cycle. While the global observation systems in the past were unable to provide reliable global status, modern satellite observations and reanalyses are becoming more mature. We have made the case for including global indicators for the hydrological part of Earth's climate system in https://doi.org/10.1007/s43832-024-00063-3 and https://doi.org/10.1371/journal.pclm.0000029 - there are indicators suggesting that the total amount of precipitation falling on Earth's surface each day has increased over the past and that the fractional surface area of the Earth receiving precipitation each day has shrunk. These are key to understanding changes in extreme rainfall and drought, and hence ought to be relevant in this paper (e.g. L97: "policymakers with annual updates of the latest scientific understanding on the state of selected critical indicators of the climate system and of human influence."). Preferably, resources such as https://pulse.climate.copernicus.eu/ should also display this kid of information too. Many of the headlines on natural disasters around the world refer to flooding and extreme rainfall (recently China, Brazil and Afghanistan), and Lussana et al. (https://doi.org/10.1002/joc.8375) reported that he hydrological cycle is undergoing changes in all regions, and a common features includes an increase in intense precipitation events and a decrease in the corresponding spatial extent.
Citation: https://doi.org/10.5194/essd-2024-149-CC3 -
RC1: 'Comment on essd-2024-149', Matthew Jones, 19 May 2024
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Congratulations to the authors. This update on the inaugural report last year clearly represents a substantial effort, and the body evidence that it contains remains very valuable to a diverse sub-communities of Earth System Science.
My expertise connects more closely with some sections than others, and as such comments are concentrated on emissions estimates and fire fluxes. I trust that other reviewers will collectively have expertise across the board.
I think the authors have done an excellent job of explaining any new features / advances of the report, which is where I focussed my review.
Below, I identify some considerations and suggest minor revisions to the text to add clarity where required (All line numbers are from tracked2024.pdf.):
L499-L506: Might be relevant to cite Minx et al. (2021) here.
590-591: “The fossil fuel share of global greenhouse gas emissions was approximately 70% in 2022 (GWP100 weighted), based on the EDGAR v8 dataset (Crippa et al. 2023) and net land use CO2 emissions from the Global Carbon Budget.” I had understood from earlier data source descriptions that the GCB data for CO2-FFI and CO2-LU and PRIMAP-hist CR for other gases was being preferred to EDGAR in this update. For clarity I would perhaps avoid presenting results based on EDGAR except for validation/uncertainty characterisation. Or did I mis-understand?
842-844: “Such carbon cycle feedbacks are not considered here as they are not a direct emission from human activity, yet they will contribute to greenhouse gas concentration rise, forcing and energy budget changes discussed in the next sections. They will become more important to properly account for in future years.” Is it possible to put an indicative number on the potential magnitude of influence?
I cannot see where the acronym “ODS” is defined. Likewise, I can’t see where the acronym “IMO” is defined. As a general point, please could you check that all acronyms are defined.
I suggest using “GFED4s” throughout the manuscript. Also, is it definitely GFED4s and not GFED4.1s ? The update (GFED5) is upcoming and will have significantly greater area burned and emissions, and so flagging the GFED version used in different publications has never been more important.
170-173: “Whether human-caused burning, a feedback due to the extreme heat or naturally occurring, we choose to include them in our tracking, as historical biomass burning emissions inventories have previously been consistently treated as a forcing (for example in CMIP6), though this assumption may need to be revisited in the future”. Do you mean “consistently treated as an anthropogenic forcing”? (If so and as an aside, that is quite an assumption! But I appreciate it’s not really up to the authors to deal with that issue here).
169-170: You could mention the World Weather Attribution results showing impact of climate change on fire weather in Canada this year. This may be relevant too: https://essopenarchive.org/doi/full/10.22541/essoar.170914412.27504349
Also, a couple of further points while on the ‘fire’ theme:
-- Is it relevant to your analyses that biomass burning emissions were extremely high in the northern extratropics but low in the African and South American savannahs? (i.e. Two of the regions with greatest contribution to mean annual). Basically, is the strange spatial distribution of short-lived forcers relevant on top of the global anomaly?
-- Should the relevance of fire be discussed in other sections beyond "Non-methane short-lived climate forcers” (I.e. for other gases)? My reading is that fire emissions are not included in the emissions data for CO2 / LLGHGs, except for those associated with LULUC. Presumably, the assumption is that any C lost is be recuperated as vegetation recovers, giving Net Zero on century-scale time horizons. If that is the case then it could be helpful to state it explicitly, given the enormous quantity of C emitted by Canadian fires (on the order of 0.5 GtC; https://atmosphere.copernicus.eu/copernicus-canada-produced-23-global-wildfire-carbon-emissions-2023) - equivalent to about 5 years of UK CO2 emissions. Recovery on the century horizon might be optimistic, especially when loss of old growth forest and peat / organic soils is considered (i.e. C dynamics are totally different to tropical grassland fires).
1676-1677: “We determinefromprovisionaldatathataviationactivityin2023hadnotyetreturnedtopre-COVIDlevels” What is the provisional data?
2031-2036: Perhaps add a statement to clarify that human-induced warming is the dominant contributor to total warming here?
Section 7: I am curious how these results compare with our dataset "National contributions to climate change due to historical emissions of carbon dioxide, methane, and nitrous oxide since 1850” (paper: https://www.nature.com/articles/s41597-023-02041-1; latest data: https://zenodo.org/records/10839859). In that dataset, we apply IPCC-recommended TCRE and GWP(*) constants to estimate national contributions to climate change (as well as the global total). Our input emissions data sources are similar to those used here (but NB our work included CO2, CH4, and N2O only). Can a comparison be made or is this challenging, e.g. due to incomplete overage of the forcers in our paper? Please don’t feel obliged to do exhaustive work on this unless you think the comparison of your numbers with estimates based on “Emissions*GWP*TCRE” is useful in some way. (I am happy to remain curious.)
Figure 9: Is Berkeley Earth diverging from ERA5 after ~2015? If so, an explanation of possible reasons might be worthwhile.
2832-2835: The special note on HadEX seems a little out of place given the huge number of datasets that are adopted into this paper. Perhaps this should go in the acknowledgements or some other appropriate section? Or perhaps the data usage / licensing statements of lots of other datasets should also be given.
Table 10: Cell in row “Greenhouse gas emissions”, column “Methodological since AR6”. My reading of the methods section was that GCB-FFI values had also replaced EDGAR values. Flagging this in case a clarification is needed.
Table 10 is a really great summary of everything new in this report, with nice level of accessible detail, complementing a very comprehensive report.
Citation: https://doi.org/10.5194/essd-2024-149-RC1
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Indicators of Global Climate Change 2023 (v2024.04.25) Chris Smith et al. https://doi.org/10.5281/ZENODO.11064126
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