Statistical politics – Prof. Mike Hulme on ‘politically charged’ climate baseline changes from 1961-1990 to 1991-2020:

‘In an instant; today, the world’s climate has ‘suddenly’ become nearly 0.5°C warmer’

From Climate Depot

Hulme: “January  12021, a new World Meteorological Organisation (WMO) climatological standard normal came into effect. The ‘present-day’ climate will now formally be represented by the meteorological statistics of the period 1991-2020, replacing those from 1961-1990. National Meteorological Agencies in member states are instructed to issue new standard normals for observing stations and for associated climatological products. Climate will ‘change’, one might say, in an instant; today, the world’s climate has ‘suddenly’ become nearly 0.5°C warmer. It is somewhat equivalent to re-setting Universal Time or adjusting the exact definition of a metre.”

“So, what is the significance of the move to a new 1991-2020 WMO normal in January 2021? On the one hand, it is a pragmatic move to redefine ‘present-day’ climate for operational applications to that of the most recent 30-year period. On the other hand, it puts into play a third climatic baseline. Already existing is the ‘pre-industrial’ climate of the late nineteenth century and the ‘historic’ climate’ of 1961-1990, the latter about 0.3°C warmer than the former. And now there is the new ‘present-day’ climate of 1991-2020, in turn about 0.5°C warmer than the ‘historic climate’ of 1961-1990.”

“Combining a climatic tolerance of 2°C—or indeed 1.5°C—with a pre-industrial baseline yields a very different climate target than, say, using a 1986-2005 baseline, the period widely adopted by IPCC AR5 Working Group I as their analytical baseline. The choices of both baseline and tolerance are politically charged. They carry significant implications for historic liability for emissions (La Rovere et al., 2002), for policy design (Millar et al., 2017) and for possible reparations (Roberts & Huq, 2015).”

The paper:

https://www.academia.edu/44905791/Climates_Multiple_Three_Baselines_Two_Tolerances_One_Normal?email_work_card=view-paper

Excerpts:

Climates Multiple: Three Baselines, Two Tolerances, One Normal

By Mike Hulme

Excerpt:  Friday 1 January 2021, a new World Meteorological Organisation (WMO) climatological standard normal came into effect. The ‘present-day’ climate will now formally be represented by the meteorological statistics of the period 1991-2020, replacing those from 1961-1990. National Meteorological Agencies in member states are instructed to issue new standard normals for observing stations and for associated climatological products. Climate will ‘change’, one might say, in an instant; today, the world’s climate has ‘suddenly’ become nearly 0.5°C warmer. It is somewhat equivalent to re-setting Universal Time or adjusting the exact definition of a metre.

What started in the 1970s and 1980s as a pragmatic selection of the late nineteenth century as an analytical reference period (Nordhaus, 1977) had, by the twenty-first century, taken on great policy significance. Although the 2015 PACC formally adopted pre-industrial climate as its baseline, the precise temporal designation of ‘pre-industrial’ was left unspecified— whether for strategic political reasons (Geden, 2018), or simply because of a lack of awareness about the significance of the choice. Different ‘pre-industrial’ baselines have been adopted, either as discursive proxies for a general pre-industrial era or else used analytically to test the sensitivity of the ‘pre-industrial’ baseline to different definitions (Schurer et al., 2017). Equivalent diversity afflicts the designation of ‘present-day’ climate. Although often corresponding to a WMO 30-year normal, many other designations of ‘present-day climate’ have been adopted in different IPCC assessments—such as ‘1990’ (in IPCC AR1 and AR2) or the period 1986-2005 (in AR5)—and more generally by individual scientists. The WMO’s decision in 2015 suggests that for the purposes of climate change assessments, the 1961-1990 baseline should continue to be used.

Three Baseline Climates

So, what is the significance of the move to a new 1991-2020 WMO normal in January 2021? On the one hand, it is a pragmatic move to redefine ‘present-day’ climate for operational applications to that of the most recent 30-year period. On the other hand, it puts into play a third climatic baseline. Already existing is the ‘pre-industrial’ climate of the late nineteenth century and the ‘historic’ climate’ of 1961-1990, the latter about 0.3°C warmer than the former. And now there is the new ‘present-day’ climate of 1991-2020, in turn about 0.5°C warmer than the ‘historic climate’ of 1961-1990. And in addition to these three climatic baselines, there are the two climatic tolerances enshrined in the PACC of 1.5° and 2°C.

Climatic normals and baselines give precise numerical form to the rather intangible notion of climate: an idea that imposes a degree of imaginative order upon the human experience of atmospheric chaos (Hulme, 2016). While baselines can be either descriptive, predictive and/or normative, climatic tolerances are more explicitly normative. The adoption of particular baselines and tolerances is therefore an overtly political process with geopolitical, ethical and technological consequence. As with the adoption of other universal referential markers— for example the Greenwich Meridian as zero longitude, the metric system, or the formula for water as H2O —these processes entrain historical trajectories, cultural imaginaries, curious serendipities and power dynamics. I will investigate these contingencies at greater length in a subsequent article.

‘Dangerous climate change’ can be defined in either absolute or relative terms. But if defined in relative terms then it matters not just how much deviation from ‘normal’ is deemed tolerable, but crucially what is deemed ‘normal’ in the first place. Combining a climatic tolerance of 2°C—or indeed 1.5°C—with a pre-industrial baseline yields a very different climate target than, say, using a 1986-2005 baseline, the period widely adopted by IPCC AR5 Working Group I as their analytical baseline. The choices of both baseline and tolerance are politically charged. They carry significant implications for historic liability for emissions (La Rovere et al., 2002), for policy design (Millar et al., 2017) and for possible reparations (Roberts & Huq, 2015).


Some thoughts from Anthony:

The only temperature plot that isn’t a slave to baseline choices is absolute temperature. Anomaly based temperature is a statistical construct relying on the assumptions and choices of the statistician.

Here is an example of an absolute temperature plot from NASA GISS data.

Absolute temperature graph of NASA GISS data: 1880 to 2016

Of course, to be accurate for “absolute temperature”, we would plot the Kelvin scale. But, few understand the Kelvin scale; Fahrenheit and Celsius scales rule human perception.

Temperature trends in fact don’t change with changes in baseline, but any time there is a perceived step up, i.e ‘In an instant; today, the world’s climate has ‘suddenly’ become nearly 0.5°C warmer’ it could be used for political and propaganda purposes without ever acknowledging that it is a statistical up-tick, and not real.

But Hulme has it backwards, we won’t see a step up in above normal temperature reports.

Since the baseline is going up, the anomaly temperatures going forward, i.e., departure from normal, will be less since the “normal baseline” will now be higher.

In an email exchange with Dr. Roy Spencer, he notes:

No, the climate doesn’t suddenly become warmer. The new baseline is indeed warmer, but since the baseline is warmer, all temperatures relative to it become cooler. It doesn’t matter much to people if the global average temperature is (for example) 59 degrees F or 60 degrees.  But they DO pay attention to how much “above normal” temperatures are, and for at least the next 10 years, those numbers will be smaller.

Dr. Roy Spencer, via email 1/16/21

So it appears this will be a non-issue going forward. Lower “above normal” temperatures will cool some debate in the future.

via Watts Up With That?

https://ift.tt/3nQTCdp

January 16, 2021 at 08:03PM