Climate indicators

The recent IPCC AR6 WGI report summarises the state of knowledge of physical climate science, but the final version of the Summary for Policymakers (SPM) did not include a figure showing a range of indicators of our warming planet.

An earlier draft of the SPM included a figure like that below which aimed to put recent changes into a longer context of changes over the past 2000 years, and to show how other climate metrics have changed in recent decades. Many of these time series were shown in disparate places of the report, and have been brought together in this updated graphic which also indicates key milestones and discoveries in climate science.

Indicators (from top to bottom): atmospheric carbon dioxide concentration, ocean heat content, global sea level, global mean surface temperature, global lower tropospheric temperatures, Arctic sea ice amount, Kyoto cherry blossom date, specific humidity over land. Key moments in the history of climate science are indicated: the invention of the efficient steam engine by James Watt in 1790, the identification of the primary greenhouse gases by John Tyndall in 1861, the first estimate of climate sensitivity by Svante Arrhenius in 1896, and the discovery that the world was warming by Guy Callendar in 1938.

Data sources:
Atmospheric CO₂: Law Dome ice core, Mauna Loa
Ocean Heat Content: 0-2000m from IPCC AR6 updated with NCEI
Global sea level: Kopp et al., IPCC AR6 updated with AVISO
Global temperature: PAGES2k, HadCRUT5
Lower tropospheric temperature: RSS
Arctic sea ice: Kinnard et al., NSIDC
Cherry blossom date: Aono et al.
Humidity: HadISDH

3 thoughts on “Climate indicators

  1. Hello Ed,

    Thank you for this overview plot. Can we clarify if the sea-ice indicator is sea-ice AREA (as opposed to extent)? The plot says Area, but extent is very often used.

    Also, the curve seems to start in late 1970s, so I am not sure why you refer to Kinnard et al (mostly pre-satellite data, I presume).

    And to confirm: this is not the same sea-ice area indicator as used in IPCC AR6 WG I ?

    All the best,

    1. Sorry, my bad ! I now see the Kinnard et al. curve all the way to the left 😐 . Now I understand why the two citations Kinnard and NSIDC.

    2. Thanks Thomas – the AR6 chose to focus on sea-ice area in many of its assessments, so that is a change from AR5. The Kinnard et al. proxy data was calibrated on extent observations, so is not directly comparable to the area from satellite observations. And, I have used the NSIDC sea ice area data from the Climate Explorer for the Arctic index as it is easily updatable.

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