JAMSTEC > Research Institute for Global Change (RIGC) > Reports > Publication of the IPCC Sixth Assessment Report (Working Group I)

Research Institute for Global Change (RIGC)

Publication of the IPCC Sixth Assessment Report (Working Group I) - Scientific Contributions of JAMSTEC Researchers and Their Messages

August 13, 2021

Introduction

On August 9, 2021, the 54th General Assembly of the Intergovernmental Panel on Climate Change (IPCC) held online and approved the Summary for Policymakers (SPM) of the Working Group I (WG1) Report (Natural Science Basis) of the IPCC Sixth Assessment Report (AR6), and released the main body of the report. The SPM was approved and the main body of the report was released (see press release from the four ministries). The preparation of the report was a lengthy process, starting with the approval of the outline at the 46th Plenary Meeting in September 2017 and the selection of authors in February 2018, followed by four author meetings and several rounds of drafting and expert review. It was also a rigorous effort to ensure proper evaluation of the latest scientific findings. This time, in particular, the COVID-19 pandemic greatly affected the progress of the report writing process and the meeting format, resulting in the publication of the report about four months later than originally planned.

WG1:Physical Science Basis (August 2021)

  Chapter Contents From JAMSTEC to Author team
  1 Framing, context, methods  
Large-scale climate change 2 Changing state of the climate system  
3 Human influence on the climate system  
4 Future global climate: scenario-based projections and a near-term information  
Processes 5 Global carbon and other biogeochemical cycles and feedbacks Patra (LA)
6 Short-lived climate forcers Kanaya(RE)
7 The Earth’s energy budget, climate feedbacks, and climate sensitivity  
8 Water cycle changes  
9 Ocean, cryosphere, and sea level change  
Regional climate change 10 Linking global to regional climate change  
11 Weather and climate extreme events in a changing climate  
12 Climate change information for regional impact and for risk assessment  

WG2: Impacts, Adaptation and Vulnerability (Feb 2022)

Chapter 10 Asia: Ishikawa (LA)

WG3:Mitigation of Climate Change (Mar 2022)

Outline Figure 1: Outline of the AR6 WG1 report and our contribution as LA and RE.

In this report, two researchers who have belonged to JAMSTEC for 20 years, starting as young researchers, joined the teams of lead authors*1 and review editors*2. Specifically, the main body of the report is divided into three sections (Outline Fig. 1): "Large-Scale Climate Change", "Processes", and "Regional Climate Change. "Within the "Processes" section, Deputy group leader Prabir Patra served as the lead author (Photo 1) for Chapter 5: Global Carbon and other Biogeochemical Cycles and Feedbacks, and Yugo Kanaya, Director of Earth Surface System research center, served as the review editor for Chapter 6: Short-Lived Climate Forcers. In addition, Dr. Michio Kawamiya, Director of research center for Environmental modeling and application (CEMA), participated in the general meeting from the outline decision to the adoption, and also served as a member of the data task group. Furthermore, Dr. Kaoru Tachiiri, Group leader, Dr. Ingo Richter, Deputy group leader, and Dr. Naveen Chandra, Researcher served as Contributing Authors, and there were extensive contributions from many researchers in expert review, research publications, Earth system model simulations, and observational data. In this topic series, we will gradually introduce these latest science and contributions.

Eight years have passed since the last AR5 was published in 2013, and global warming has gone from being a future concern to an imminent risk, and the debate on decarbonization has become a worldwide phenomenon. Against this backdrop, AR6 aims to provide a description that can be "communicated" to society, rather than a fragmented description from a scientist's point of view, with keywords such as "storyline" and "narrative". This is the reason why we have been working on this project. In light of this, we would like to introduce the whole storyline in this column as well.

Photo 1. group photo of the third lead author meeting in Toulouse (top) and group photo of the authors of Chapter 5 at the second meeting; Deputy group leader Patra is in the front row, left.

Photo 1. group photo of the third lead author meeting in Toulouse (top) and group photo of the authors of Chapter 5 at the second meeting; Deputy group leader Patra is in the front row, left.

In the afternoon of October 28, JAMSTEC will hold a series of lectures on the global environment for the general public, and on August 31, ”TOUGOU” program in which JAMSTEC participates will hold a series of lectures.

Introduction part edited by Yugo Kanaya (Earth Surface System Research Center, RIGC, JAMSTEC)

Introduction part edited by
Yugo Kanaya
(Earth Surface System Research Center, RIGC, JAMSTEC)

*1The LA (Lead Author) writes the chapters/parts of the assessment report and revises the draft several times in response to comments from reviewers (experts and governments), and plays a central role in the preparation of the assessment report.

*2The REs (Review Editors) are responsible for checking that the review comments on the chapters they are in charge of have been properly considered and processed.
※LAs and REs are selected at the IPCC Bureau Meeting based on the list of candidates compiled by the IPCC Secretariat based on nominations from national experts and governments.

Emissions of greenhouse gases from human activity chiefly caused global climate change since 1850 and acceleration in the past 30 years

Prabir Patra, Chapter 5 Lead Author (Earth Surface System Research Center, RIGC, JAMSTEC)

Prabir Patra, Chapter 5 Lead Author
(Earth Surface System Research Center, RIGC, JAMSTEC)

Key points

◆ The likely range of net human-caused surface warming from 1850–1900 to 2010–2019 is 0.8°C–1.3°C, with a best estimate of 1.07 °C. It is likely that well-mixed greenhouse gases contributed a warming of 1.0°C–2.0°C, and other human drivers (principally aerosols) contributed a cooling of 0.0°C–0.8°C. (SPM A1.3)

◆ Current atmospheric CO2 concentrations are unprecedented in at least 2 million years and concentrations of CH4 and N2O are higher than at any time in at least 800,000 years. Since 1750, increases in CO2 (47%) and CH4 (156%) concentrations far exceed the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years, while N2O increased by 23% (very high confidence). (SPM A2.1, Chap 5, Chap 2)

◆The emissions of CO2 from fossil fuel continued increase till 2019 and that from land use change persists, and about 56% of these emissions are removed by the land and ocean during 1960-2019. These scientific findings are essential for considering the extent to which future cumulative emissions from human activities must be contained in order to limit global warming within the 1.5°C target. (Chap 5, Chap 6, Chap 7)

Quantification and Attribution of Global Warming

Global climate change due to the warming of the earth’s surface air temperature (SAT) is one of the imminent threats to the human civilization. The recently concluded 6th Assessment Report of the Working Group I (WG1) of the Intergovernmental Panel on Climate Change (IPCC) has reaffirmed human activity as the predominant cause of the observed global warming of 1.07 °C between 1850-1900 and 2010-2019 (Figure 1b). Rise in all major well-mixed greenhouse gases, e.g., carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and halogenated gases, have produced warming of 1.5±0.5°C in 2010-2019 compared to the 1850-1900 period. A part of this warming 0.4±0.4°C was offset by the sulphur dioxide producing reflective aerosols and other short-lived species (net total). Global SAT has increased at the fastest rate during 1970-2019 (latest 50 yr) compared to any other 50-yr period in the past 2000 years (Figure 1). The recent acceleration in global warming has manifested a variety of climate change related deteriorations, such as, 1) summer Arctic sea ice cover as measured in September has decreased by about 40% during 1979-1988 to 2010-2019, 2) global mean sea level has risen faster (at the rate of 1.7 mm yr-1) since 1901 than over any preceding century in the last 3000 yr, 3) hot extremes (including heatwaves) have become more frequent and more intense across most land regions since 1950, 4) frequency and intensity of heavy precipitation events have increased over most land areas since the 1950s, 5) global proportion of Category 3–5 tropical cyclone intensity has increased over the last four decades and the latitude where tropical cyclones in the western North Pacific reach their peak intensity has shifted northward.

Figure 1: Assessed contributions to observed warming in 2010–2019 relative to 1850–1900.

Figure 1: Assessed contributions to observed warming in 2010–2019 relative to 1850–1900.
Observed increase in global surface temperature (warming) and its very likely range (panel a) is shown in comparison with estimated temperature change attributed to total human influence, changes in well-mixed greenhouse gas concentrations, other human drivers (aerosols, ozone and land-use change), solar and volcanic drivers and internal climate variability (panel b). Panel c shows temperature changes from individual components of human influence, including emissions of greenhouse gases, aerosols and their precursors; land-use changes (land-use reflectance and irrigation); and aviation contrails. Estimates account for both direct emissions into the atmosphere and their effect, if any, on other climate drivers. Error bars in panels b and c show likely ranges. (SPM.2)

Long-term Changes in Greenhouse Gases Concentration – Natural vs Human Influences

Chapter 5 focused on the human influences that have caused the increase in 3 of the most significant well-mixed greenhouse gases. Figure 2 also shows that the concentrations of the 3 species have increased in the past 2000 years as measured in the air bubbles trapped in Law Dome ice core and directly in ambient air. As seen for the acceleration in global SAT in the past 50 years, concentrations of CO2, CH4 and N2O have also increased at faster rates during 1970-2020. The Antarctic ice core record covering the past 800 kyr provides an important archive to explore the carbon-climate feedbacks prior to anthropogenic perturbations (Figure 2). Major GHGs, CH4, N2O and CO2 generally co-vary on orbital timescales, with consistently higher atmospheric concentrations during warm intervals of the past, allowing us to separate the sensitivity of concentration changes to natural climate and that of human influences. Since AR5, the number of ice core records and the temporal resolution of their data for the last 800 kyr have improved, in particular for the last 60 kyr. Additionally, the advent of isotopic measurements on GHGs extracted from air trapped in ice, allows for more robust source apportionments and inventory assessments. Major pre-industrial sources of CH4 comprise wetlands (including subglacial environments) and biomass burning. Pre-industrial atmospheric N2O concentrations were regulated by microbial production in marine and terrestrial environments and by photochemical removal in the stratosphere. Pre-industrial atmospheric CO2 concentrations were largely regulated by exchange with exogenic terrestrial and ocean carbon reservoirs. The 1900-2019 increase of rate of CO2 is 0.95 ppm yr-1, which is more than 300 times faster than that during 800-0 kyr. For CH4, the 1900-2019 growth rate of 7.9 ppb yr-1 is more than 500 times faster compared to 800-0 kyr period.

Figure 2: Atmospheric concentrations of CO2, CH4 and N2O in air bubbles and clathrate crystals in ice cores (800,000 BCE to 1990 CE).

Figure 2: Atmospheric concentrations of CO2, CH4 and N2O in air bubbles and clathrate crystals in ice cores (800,000 BCE to 1990 CE). Note the variable x-axis range and tick mark intervals for the 3 columns. Ice core data is over-plotted by atmospheric observations from 1958 to present for CO2, from 1984 for CH4 and from 1994 for N2O. The time-integrated, millennial-scale linear growth rates for different time periods (800,000–0 BCE, 0–1900 CE and 1900–2017 CE) are given in each panel. For the BCE period, mean rise and fall rates are calculated for the individual slopes between the peaks (inter-glacials) and troughs (ice ages), which are given in the panels in left column. The data for BCE period are used from the Vostok, EPICA, Dome C and WAIS ice cores. The data after 0–yr CE are taken mainly from Law Dome ice core analysis. The atmospheric observations are taken from NOAA cooperative research network. BCE = before current era, CE = current era. (Figure 5.4)

Recent Acceleration in CO2 in Atmosphere due to Enhanced Human Activities

Here, for the sake of brevity detailed discussions around the CH4 and N2O cycling will be covered in the future articles. Direct measurements of atmospheric CO2 began in 1957 at the South Pole Observatory (SPO) and in 1958 at Mauna Loa Observatory (MLO), Hawaii, USA (Figure 3). Recently, high density total column CO2 (XCO2) data products are made available since 2009 by dedicated greenhouse gases observing satellites, such as GOSAT. Annual mean CO2 growth rates are observed to be 1.56 ± 0.18 ppm yr-1 (average and range from 1 standard deviation of annual values) over the 61 years of atmospheric measurements (1959–2019), with the rate of CO2 accumulation almost tripling from an average of 0.82 ± 0.29 ppm yr-1 during the decade of 1960–1969 to 2.39 ± 0.37 ppm yr-1 during the decade of 2010–2019. The latter agrees well with that XCO2 from GOSAT (Figure 3b). Multiple lines of evidence unequivocally establish the dominant role of human activities in the growth of atmospheric CO2. First, the systematic increase in the difference between the Mauna Loa and South Pole records (Figure 3a) is caused primarily by the increase in emissions from fossil fuel combustion in industrialised regions that are situated predominantly in the northern hemisphere. Second, measurements of the stable carbon isotope in the atmosphere (δ13C–CO2) are more negative over time because CO2 from fossil fuels extracted from geological storage is depleted in 13C (Figure 3c). Third, measurements of the δ(O2/N2) ratio show a declining trend because for every molecule of carbon burned, 1.4 molecule of oxygen (O2) is consumed (Figure 3d). These three lines of evidence confirm unambiguously that the atmospheric increase of CO2 is due to an oxidative process (i.e. combustion). Fourth, measurements of radiocarbon (14C–CO2) at sites around the world show a continued long-term decrease in the 14C/12C ratio. Fossil fuels are devoid of 14C and therefore fossil-fuel-derived CO2 additions decrease the atmospheric 14C/12C ratio.

Figure 3: Time series of CO2 concentrations and related measurements in ambient air.

Figure 3: Time series of CO2 concentrations and related measurements in ambient air. (a) concentration time series and MLO-SPO difference, (b) growth rates, (c) 14C and 13C isotopes, and (d) O2/N2 ratio. The data for Mauna Loa Observatory (MLO) and South Pole Observatory (SPO) are taken from the Scripps Institution of Oceanography (SIO)/University of California, San Diego. The global mean CO2 are taken from NOAA cooperative network (as in Chapter 2), and GOSAT monthly-mean XCO2 time series are taken from National Institute for Environmental Studies. CO2 growth rates are calculated as the time derivative of deseasonalised time series. The Δ(O2/N2) are expressed in per meg units. The 14CO2 time series at Barring Head, Wellington, New Zealand (BHD) is taken from GNS Science and NIWA. The multivariate ENSO index (MEI) is shown as the shaded background in panel (b; warmer shade indicates El Niño). (Figure 5.6)

Nature Continues to Absorb Human Emission Burden, but How Long

The CO2 emitted from human activities during the decade of 2010–2019 (decadal average 10.9 ± 0.9 PgC yr-1) was distributed between three Earth system components: 46% accumulated in the atmosphere (5.1 ± 0.02 PgC yr-1), 23% was taken up by the ocean (2.5 ± 0.6 PgC yr-1) and 31% was stored by vegetation in terrestrial ecosystems (3.4 ± 0.9 PgC yr-1) (high confidence). Of the total anthropogenic CO2 emissions, the combustion of fossil fuels was responsible for 81–91%, with the remainder arising from land-use change, forestry, and other land uses (e.g., deforestation, degradation, or peat drainage). Over the past six decades, the fraction of anthropogenic CO2 emissions that has accumulated in the atmosphere (referred to as airborne fraction) has remained near constant at approximately 44% (Figure 4). The ocean and land sinks of CO2 have continued to grow over the past six decades in response to increasing anthropogenic CO2 emissions (high confidence). Interannual and decadal variability of the regional and global ocean and land sinks indicate that these sinks are sensitive to climate conditions, e.g., ENSO and volcanic eruptions, and therefore to climate change (high confidence). Uncertain land use change fluxes influence the robustness of the trends. Although no statistically significant trend is observed in the past airborne fraction, coupled climate-carbon cycle projection models suggest, 1) implied emissions taken-up by the land and ocean sinks declines through the 21st century in higher emission scenario, and 2) land and ocean sinks take-up an increasing fraction of the implied emissions in scenarios that assume CO2 stabilisation in the 21st century.

Figure 4: Airborne fraction and anthropogenic (fossil fuel, land use change, and cement production) CO2 emissions.

Figure 4: Airborne fraction and anthropogenic (fossil fuel, land use change, and cement production) CO2 emissions. Airborne fraction is calculated as the ratio of annual CO22 growth rate in atmosphere and anthropogenic emissions. The multivariate ENSO index (shaded) and the major volcanic eruptions are marked along the x-axis. (Figure 5.7)

Natural and Anthropogenic Components of Global CO2 Budget

The global CO2 budget encompasses all natural and anthropogenic CO2 sources and sinks (Table 1). Since AR5, a number of improvements have led to a more constrained carbon budget presented here. Some new additions include: (i) the use of independent estimates for the residual carbon sink on natural terrestrial ecosystems, (ii) improved and new emission estimates from agriculture, forestry and other land use, (iii) the expansion of constraints from atmospheric inversions, both based on surface networks and the use of satellite retrievals. While we contributed only CO2inversion and a synthesis of regional carbon fluxes in AR5, inversion results of all 3 species are contributed to the AR6. Our inversion uses an improved chemistry-transport model for better representing atmospheric circulation in troposphere and stratosphere. Over the past decade (2010–2019), 10.9 ± 0.9 PgC yr-1 were emitted from human activities which were distributed between three Earth system components: 46% accumulated in the atmosphere (5.1 ± 0.02 PgC yr-1), 23% was taken up by the ocean (2.5 ± 0.6 PgC yr-1) and 31% was stored by vegetation in terrestrial ecosystems (3.4 ± 0.9 PgC yr-1) (Table 1). There is a budget imbalance of 0.1 PgCyr--1 which is within the uncertainties of the other terms. Over the industrial era (1750–2019), the total cumulative CO2 fossil fuel and industry emissions were 445 ± 20 PgC, and net emissions from land FOLU (=land use change) were 240 ± 70 PgC (medium confidence). The equivalent total emissions (685 ± 75 PgC) was distributed between the atmosphere (285 ± 5 PgC), oceans (170 ± 20 PgC) and land (230 ± 60 PgC), with a budget imbalance of 20 PgC or less, leading to an atmospheric burden increase of 279 ± 5 PgC.

Table 1. Global anthropogenic CO2 budget accumulated since the Industrial Revolution (onset in 1750) and averaged over the 1980s, 1990s, 2000s, and 2010s. The table does not include natural exchanges (e.g., rivers, weathering) between reservoirs. Uncertainties represent the 68% confidence interval. (Table 5.1)

  1750-2019
Cumulative
(PgC)
1850-2019
Cumulative
(PgC)
1980–1989
Mean Annual Growth Rate (PgC yr-1)
1990–1999
Mean Annual Growth Rate(PgC yr-1)
2000–2009
Mean Annual Growth Rate(PgC yr-1)
2010–2019
Mean Annual Growth Rate(PgC yr-1)
Emissions
Fossil fuel combustion and
cement production
445 ± 20 445 ± 20 5.4 ± 0.3 6.3 ± 0.3 7.7 ± 0.4 9.4 ± 0.5
Net land use change 240 ± 70 210 ± 60 1.3 ± 0.7 1.4 ± 0.7 1.4 ± 0.7 1.6 ± 0.7
Total Emissions 685 ± 75 655 ± 65 6.7 ± 0.8 7.7 ± 0.8 9.1 ± 0.8 10.9 ± 0.9
Partition
Atmospheric increase 285 ± 5 265± 5 3.4 ± 0.02 3.2 ± 0.02 4.1 ± 0.02 5.1 ± 0.02
Ocean sink 170 ± 20 160 ± 20 1.7 ± 0.4 2.0 ± 0.5 2.1 ± 0.5 2.5 ± 0.6
Terrestrial sink 230 ± 60 210 ± 55 2.0 ± 0.7 2.6 ± 0.7 2.9 ± 0.8 3.4 ± 0.6
Budget imbalance 0 20 -0.4 -0.1 0 -0.1

Concept of Remaining Carbon Budget (to be explained further in next article)

Mitigation requirements over this century for limiting maximum warming to specific levels can be quantified using a carbon budget that relates cumulative CO2 emissions to global mean temperature increase (high confidence). For the period 1850–2019, a total of 650 ± 65 PgC (2380 ± 240 GtCO2) of anthropogenic CO2 has been emitted. Remaining carbon budgets (starting from 1 January 2020) for limiting warming to 1.5°C, 1.7°C, and 2.0°C are 140 PgC (500 GtCO2), 230 PgC (850 GtCO2) and 370 PgC (1350 GtCO2), respectively, based on the 50th percentile of TCRE. For the 67th percentile, the respective values are 110 PgC (400 GtCO2), 190 PgC (700 GtCO2) and 310 PgC (1150 GtCO2). These remaining carbon budgets may vary by an estimated ± 60 PgC (220 GtCO2) depending on how successfully future non-CO2 emissions can be reduced.

Further reading:

1)
モデル解析を基にした温室効果気体の全球規模循環に関する研究 -2016年度堀内賞受賞記念講演- (Study of the global cycle of greenhouse gases using atmospheric chemistry-transport model) (Japanese text only)
https://www.metsoc.jp/tenki/english/TENKI_e-index17.html
2)
China's Carbon Dioxide (CO2) Emissions Have Been Overestimated - Advancement in verification of fossil fuel CO2 and CH4 sources from China -
http://www.jamstec.go.jp/e/about/press_release/20170516_2/
3)
Anthropogenic and natural contributions to CO2 flux change in Southeast Asia
http://www.chiba-u.ac.jp/general/publicity/press/files/2018/20180518co2.pdf
4)
大気観測が捉えた新型ウイルスによる中国の二酸化炭素放出量の減少 ~波照間島で観測されたCO2とCH4の変動比の解析~ (Japanese text only)
http://www.jamstec.go.jp/j/about/press_release/20201105/
5)
世界のCO2収支 2020年版を公開 ~国際共同研究(グローバルカーボンプロジェクト)による評価~ (Japanese text only)
http://www.jamstec.go.jp/j/about/press_release/20201211/

◆IPCC AR6 WGI citation

Full report
IPCC, 2021: 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.
AR6 Climate Change 2021: The Physical Science Basis

Summary for Policymakers
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 [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.

Chapter 5
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.