✨ climate: change baseline period in the MET temperature anomalies chart

[veronikasamborska1994]

hi @pabloarosado ! I am working on a short article with Hannah and we want to change the baseline period for this chart to "pre-industrial" times. I tried to explain the reasoning behind it in the metadata but let me know if anything is unclear. We also want to change the source name to "Adapted from.." to better reflect that this is what we've done. If you need to know more details you can see the last couple of comments in this github issue.

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chart-diff: ✅

• 1/1 reviewed charts
• Modified: 1/1
• New: 0/0
• Rejected: 0
• Data changes: 1
• Metadata changes: 1

data-diff: ❌ Found differences

= Dataset garden/met_office_hadley_centre/2025-01-21/near_surface_temperature
  = Table near_surface_temperature
    ~ Column lower_limit (changed metadata, changed data)
+       + description_from_producer: |-
+       +   The 1961-90 period is most often used as a baseline because it is the period recommended by the World Meteorological Organisation. In some cases other periods are used. For global average temperatures, an 1861-1890 period is sometimes used to show the warming since the "pre-industrial" period.
-       -   - Temperature anomalies are given in degrees Celsius relative to the average temperature over the period 1961-1990.
-       -   - Temperature anomalies are available for the Northern Hemisphere and the Southern Hemisphere.
-       -   - The global mean is calculated by averaging anomalies for northern and southern hemispheres.
+       +   - |-
+       +     Temperature anomalies show how many degrees Celsius temperatures have changed compared to the 1861-1890 period. This baseline period is commonly used to highlight the changes in temperature since pre-industrial times, prior to major human impacts.
+       +   - |-
+       +     The data includes separate measurements for the Northern and Southern Hemispheres, which helps researchers analyze regional differences.
+       +   - The global temperature anomaly is the average of both hemisphere measurements.
+       + display:
+       +   numDecimalPlaces: 1
+       + processing_level: major
+       + description_processing: |-
+       +   We switch from using 1961-1990 to using 1861-1890 as our baseline to better show how temperatures have changed since pre-industrial times. For each region, we calculate the mean temperature anomaly for 1961–1990 and for 1861–1890. The difference between these two means serves as the adjustment factor. This factor is applied uniformly to both the temperature anomalies and the confidence intervals to ensure that both the central values and the associated uncertainty bounds are correctly shifted relative to the new 1861–1890 baseline.

        ~ Changed values: 525 / 525 (100.00%)
                       region  year  lower_limit -  lower_limit +
                       Global  1865      -0.524457      -0.162159
          Northern hemisphere  1883      -0.586372      -0.205543
          Northern hemisphere  1904      -0.724007      -0.343178
          Northern hemisphere  1973      -0.005188       0.375642
          Southern hemisphere  1951       -0.33188       0.011886
    ~ Column temperature_anomaly (changed metadata, changed data)
-       - title: Global average temperature anomaly relative to 1961-1990
        ?                                                        ^    ^
+       + title: Global average temperature anomaly relative to 1861-1890
        ?                                                        ^    ^
+       + description_short: Global average land-sea temperature anomaly relative to the 1861-1890 average temperature baseline.
+       + description_from_producer: |-
+       +   The 1961-90 period is most often used as a baseline because it is the period recommended by the World Meteorological Organisation. In some cases other periods are used. For global average temperatures, an 1861-1890 period is sometimes used to show the warming since the "pre-industrial" period.
-       -   - Temperature anomalies are given in degrees Celsius relative to the average temperature over the period 1961-1990.
-       -   - Temperature anomalies are available for the Northern Hemisphere and the Southern Hemisphere.
-       -   - The global mean is calculated by averaging anomalies for northern and southern hemispheres.
+       +   - |-
+       +     Temperature anomalies show how many degrees Celsius temperatures have changed compared to the 1861-1890 period. This baseline period is commonly used to highlight the changes in temperature since pre-industrial times, prior to major human impacts.
+       +   - |-
+       +     The data includes separate measurements for the Northern and Southern Hemispheres, which helps researchers analyze regional differences.
+       +   - The global temperature anomaly is the average of both hemisphere measurements.
+       + display:
+       +   numDecimalPlaces: 1
+       + processing_level: major
+       + description_processing: |-
+       +   We switch from using 1961-1990 to using 1861-1890 as our baseline to better show how temperatures have changed since pre-industrial times. For each region, we calculate the mean temperature anomaly for 1961–1990 and for 1861–1890. The difference between these two means serves as the adjustment factor. This factor is applied uniformly to both the temperature anomalies and the confidence intervals to ensure that both the central values and the associated uncertainty bounds are correctly shifted relative to the new 1861–1890 baseline.

        ~ Changed values: 525 / 525 (100.00%)
                       region  year  temperature_anomaly -  temperature_anomaly +
                       Global  1865              -0.332481               0.029816
          Northern hemisphere  1883              -0.427063              -0.046234
          Northern hemisphere  1904              -0.578273              -0.197443
          Northern hemisphere  1973               0.021601               0.402431
          Southern hemisphere  1951              -0.176157               0.167609
    ~ Column upper_limit (changed metadata, changed data)
+       + description_from_producer: |-
+       +   The 1961-90 period is most often used as a baseline because it is the period recommended by the World Meteorological Organisation. In some cases other periods are used. For global average temperatures, an 1861-1890 period is sometimes used to show the warming since the "pre-industrial" period.
-       -   - Temperature anomalies are given in degrees Celsius relative to the average temperature over the period 1961-1990.
-       -   - Temperature anomalies are available for the Northern Hemisphere and the Southern Hemisphere.
-       -   - The global mean is calculated by averaging anomalies for northern and southern hemispheres.
+       +   - |-
+       +     Temperature anomalies show how many degrees Celsius temperatures have changed compared to the 1861-1890 period. This baseline period is commonly used to highlight the changes in temperature since pre-industrial times, prior to major human impacts.
+       +   - |-
+       +     The data includes separate measurements for the Northern and Southern Hemispheres, which helps researchers analyze regional differences.
+       +   - The global temperature anomaly is the average of both hemisphere measurements.
+       + display:
+       +   numDecimalPlaces: 1
+       + processing_level: major
+       + description_processing: |-
+       +   We switch from using 1961-1990 to using 1861-1890 as our baseline to better show how temperatures have changed since pre-industrial times. For each region, we calculate the mean temperature anomaly for 1961–1990 and for 1861–1890. The difference between these two means serves as the adjustment factor. This factor is applied uniformly to both the temperature anomalies and the confidence intervals to ensure that both the central values and the associated uncertainty bounds are correctly shifted relative to the new 1861–1890 baseline.

        ~ Changed values: 525 / 525 (100.00%)
                       region  year  upper_limit -  upper_limit +
                       Global  1865      -0.140506       0.221792
          Northern hemisphere  1883      -0.267755       0.113074
          Northern hemisphere  1904      -0.432538      -0.051708
          Northern hemisphere  1973        0.04839        0.42922
          Southern hemisphere  1951      -0.020434       0.323332


Legend: +New  ~Modified  -Removed  =Identical  Details
Hint: Run this locally with etl diff REMOTE data/ --include yourdataset --verbose --snippet

Automatically updated datasets matching weekly_wildfires|excess_mortality|covid|fluid|flunet|country_profile|garden/ihme_gbd/2019/gbd_risk are not included

Edited: 2025-02-26 10:49:25 UTC
Execution time: 19.90 seconds

[pabloarosado]

Thanks Veronika, I agree with the changes in the processing. Actually, we could consider adopting a pre-industrial baseline in other places too.
I have suggested avoiding the "Adapted from". This is similar to "Our World in Data based on...", which we have discussed multiple times, and reached the conclusion that it's unnecessary, because it takes space from our charts and doesn't necessarily convey the message we want to the user. Having a footnote mentioning an important modification, plus a more detailed explanation in the description_processing (as you already did) should be enough.
However, if Hannah or you disagree, I'd suggest:
(1) Adding the "Adapted from..." in the grapher chart admin, rather than the snapshot metadata (given that the snapshot itself is not adapted).
(2) Mentioning that we need to redefine our guidelines with this regard, so we can figure out a better way to express adaptations that do not affect consistency across charts or our internal analytics.

Please let me know if you want to discuss any of this, thanks!

[pabloarosado]

The producer of the data product should still be "Met Office Hadley Centre". The data product we are importing is still the same, and what has changed is the way we process the data.

[pabloarosado]

Please revert the changes in the snapshots, and we can figure out an alternative way to surface the adaptation. Modifying "producer" in our metadata will cause us headaches in the future (e.g. when doing analytics at the producer level).

[veronikasamborska1994]

I'll let Hannah know! This is something she thought was important to do.

[veronikasamborska1994]

thanks @pabloarosado! I'll talk to Hannah about this and let you know. For now, I've changed it to the original name of the producer. Let me know if you want me to add this code to other datasets and recalculate the baseline. Happy to do this or if you are planning regular updates of these soon happy to leave it to you.