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’

Posted: January 19, 2021 by oldbrew in alarmism, Analysis, climate, Critique, Politics, Temperature

Image credit:

H/T Climate Depot

Nothing must stand in the way of the public being bombarded with supposed climate alarms, and told it’s their fault. Data jiggery-pokery serves a useful purpose in that aim – in this case, a kind of ‘climate reset’.
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Climates Multiple: Three Baselines, Two Tolerances, One Normal — 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.” …

“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).”

  1. dennisambler says:

    One of the emails from the Climate Research Unit at the University of East Anglia, released on 20 November 2009.

    From: Phil Jones

    To: “Parker, David (Met Office)” , Neil Plummer

    Subject: RE: Fwd: Monthly CLIMATbulletins

    Date: Thu Jan 6 08:54:58 2005

    Cc: “Thomas C Peterson”

    Neil, (Neil was Neil Plummer of Australia’s BOM, and a correspondent in the e-mail thread).

    Just to reiterate David’s points, I’m hoping that IPCC will stick with 1961-90.

    The issue of confusing users/media with new anomalies from a

    different base period is the key one in my mind. Arguments about

    the 1990s being better observed than the 1960s don’t hold too much

    water with me.

    There is some discussion of going to 1981-2000 to help the modelling

    chapters. If we do this it will be a bit of a bodge as it will be hard to do

    things properly for the surface temp and precip as we’d lose loads of

    stations with long records that would then have incomplete normals.

    If we do we will likely achieve it by rezeroing series and maps in

    an ad hoc way.

    There won’t be any move by IPCC to go for 1971-2000, as it won’t

    help with satellite series or the models. 1981-2000 helps with MSU

    series and the much better Reanalyses and also globally-complete


    20 years (1981-2000) isn’t 30 years, but the rationale for 30 years

    isn’t that compelling. The original argument was for 35 years around

    1900 because Bruckner found 35 cycles in some west Russian

    lakes (hence periods like 1881-1915). This went to 30 as it

    easier to compute.

    Personally I don’t want to change the base period till after I retire !



    At 09:22 05/01/2005, Parker, David (Met Office) wrote:


    There is a preference in the atmospheric observations chapter of IPCC

    AR4 to stay with the 1961-1990 normals. This is partly because a change

    of normals confuses users, e.g. anomalies will seem less positive than

    before if we change to newer normals, so the impression of global

    warming will be muted. Also we may wish to wait till there are 30 years

    of satellite data, i.e until we can compute 1981-2010 normals, which

    will then be globally complete for some parameters like sea surface




    I note they still intend to stay with 61-90 as the historical base, so they still have one of the coldest periods of the 20th Century to compare current temperatures with.

  2. tallbloke says:

    “anomalies will seem less positive than before if we change to newer normals, so the impression of global warming will be muted.”

    But we’re not activists rather than scientists – oh no.

  3. oldbrew says:

    To be clear: the period from 1961 to 1990 has been retained as a standard reference period for long-term climate change assessments.

    Source: WMO Guidelines on the Calculation of Climate Normals (2017 edition)
    – – –
    But: the definition of a climatological standard normal is the latest 30-year period up to a year ending with a 0, e.g. 1991-2020. So that will change every 10 years, as it has done this month, but 1961-1990 will still be the ‘standard reference’.

    It could in theory turn out that 1961-1990 warmed at a faster rate than some later (overlapping) 30-year periods — which would be awkward for CO2 obsessives to explain. Also, comparisons of successive 30-year periods can now be made every 10 years thanks to the overlaps.

    WMO says: Average. The mean of monthly values of climatological data over any specified period of
    time (not necessarily starting in a year ending with the digit 1).

    Not sure such averaging is a statistically sound practice 🤔

  4. stpaulchuck says:

    this climate scam is ALL on the media. If we had any intelligent news reporters this AGW nonsense would have never got out of the gate. Even it it had, by the time people like Nikolov and Zeller had published their remarkable papers along with a legion of others it would have been the end for all time of this crap.

    Instead we’ve got delusional SJW’s doing the news with their agendas driving it and the general public is getting a thorough screwing.

  5. pochas94 says:

    The lust for power. They don’t care how much misery they cause.

  6. hunterson7 says:

    In a way it is the public’s fault:
    The public tolerates the religious delusions dressed up as science that drives the climate consensus.

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