Paleo in IPCC WG1 AR6

ar6 ipcc logoAnnouncement: Input to paleoclimate content of IPCC Working Group 1 Assessment Report (AR6).

Paleoclimatology is fundamental to understanding the climate system, and is an important part of the IPCC’s assessment of climate science. Likewise, the IPCC’s assessment provides an avenue for the paleo-science community to highlight its essential role in climate science. This announcement is to inform paleoclimate scientists about a developing summary of large-scale paleoclimate indicators, and to solicit input to this product for AR6.

Table of key paleoclimate indicators

Chapter 2 (CH2) of the Working Group I contribution to AR6 focuses on "The Changing State of the Climate System" including proxy-based inferences of major large-scale indicators. CH2 will include a table to report summary statistics that quantify key Earth system variables during multiple periods. This information will be used to determine the extent to which recent changes are outside (or not) of the envelope of the present inter-glacial period, an often-cited benchmark against which the magnitude of recent change will be gauged in CH 2.

The table lists key indicators of the climate system, including those that quantify change in the atmosphere, ocean, cryosphere and biosphere for each of multiple periods of the past. The periods include those under investigation by the Paleoclimate Model Intercomparison Project (PMIP): early Eocene (53-51 Ma), late Pliocene (3.3-3.0 Ma), Last Inter-glaciation (129-116 ka), Last Glacial Maximum (21-19 ka), last deglaciation, mid-Holocene (6 ka), Medieval Warm Period (950-1250 CE), and the Little Ice Age (1450-1850 CE), although other periods might be of interest as well.

The focus is on large-scale indicators, with highest priority placed on global averages that attest to the planetary state; lower priority is placed on hemispheric averages or smaller-scale indicators that characterize individual continents or ocean basins. Regional and site-level studies will not be included. Among the key indicators envisaged for which paleo records might provide sufficient evidence for a robust assessment are:

- Atmosphere: long-lived greenhouse gases, surface temperature, dust and other aerosols, troposphere circulation (e.g., Hadley, subtropical jets, storm tracks), monsoons, sea-level pressure, precipitation or effective precipitation

- Oceans: heat content, deep circulation, surface circulation, sea level, salinity, pH

- Cryosphere: ice sheets, glaciers, permafrost, sea ice, snow cover

- Biosphere: productivity, carbon stock, community turnover, range distribution

- Modes of variability: major inter-annual and multi-decadal

Other indicators are encouraged as well. For each indicator or climate-system component, the table will compile values that quantify its seasonal or annual mean state. Appropriate metrics include the mean, range, variance, rate of change, or other summary statistic. Ideally, each value will be accompanied by an estimate of the uncertainty and temporal resolution, and will be traceable to published and publically accessible primary data.

Avenue for input

Far too many relevant studies have been published since AR5 to cite individually in AR6. Instead, IPCC assessments typically emphasize up-to-date and compressive synthesis studies, including those that represent community-based efforts to summarize existing published information. Syntheses and new studies that quantify large-scale paleoclimate indicators for the stated periods of interest are especially encouraged.

To be considered for AR6-WG1, articles must be submitted for publication by 31 December 2019 and accepted for publication by 30 September 2020. In the meantime, the first-order draft of the WG1 report is now underway and will be finalized in March 2019. In preparing the first draft and the revised draft in early 2020, it would be helpful for WG1 authors to be informed about upcoming articles in various stages of planning or completion that contain results for the compilation described above. An online form is now available for this purpose here. If you cannot access the form, please send the following information to: This email address is being protected from spambots. You need JavaScript enabled to view it.

- Contact name (first and last)
- Contact email
- Large-scale climate indicator name (e.g. surface temperature)
- Scale of the paleoclimate indicator/component; choose one: global, hemisphere, continent/ocean
- Time period (e.g. Last Glacial Maximum)
- Citation if published or "in review;" otherwise, indicate "in preparation" for Dec 31 deadline
- Other pertinent information

Online form

Further information

Contact Darrell Kaufman: This email address is being protected from spambots. You need JavaScript enabled to view it.