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Global Temperatures Rose As Cloud Cover Fell In the 1980s and 90s

October 31, 2018

By Paul Homewood

We’ve been discussing the sudden rise in UK and European temperatures in the 1990s, and I was reminded about a study undertaken by Clive Best and Euan Mearns looking at the role of cloud cover four years ago:


Clouds have a net average cooling effect on the earth’s climate. Climate models assume that changes in cloud cover are a feedback response to CO2 warming. Is this assumption valid? Following a study with Euan Mearns showing a strong correlation in UK temperatures with clouds, we  looked at the global effects of clouds by developing a combined cloud and CO2 forcing model to sudy how variations in both cloud cover [8] and CO2 [14] data affect global temperature anomalies between 1983 and 2008. The model as described below gives a good fit to HADCRUT4 data with a Transient Climate Response (TCR )= 1.6±0.3°C. The 17-year hiatus in warming can then be explained as resulting from a stabilization in global cloud cover since 1998.  An excel spreadsheet implementing the model as described below can be downloaded from

The full post containing all of the detailed statistical analysis is here.

But this is the key graph:


Figure 1a showing the ISCCP global averaged monthly cloud cover from July 1983 to Dec 2008 over-laid in blue with Hadcrut4 monthly anomaly data. The fall in cloud cover coincides with a rapid rise in temperatures from 1983-1999. Thereafter the temperature and cloud trends have both flattened. The CO2 forcing from 1998 to 2008 increases by a further ~0.3 W/m2 which is evidence that changes in clouds are not a direct feedback to CO2 forcing.


They conclude:

In conclusion, natural cyclic change in global cloud cover has a greater impact on global average temperatures than CO2. There is little evidence of a direct feedback relationship between clouds and CO2. Based on satellite measurements of cloud cover (ISCCP), net cloud forcing (CERES) and CO2 levels (KEELING) we developed a model for predicting global temperatures. This results in a best-fit value for TCR = 1.4 ± 0.3°C. Summer cloud forcing has a larger effect in the northern hemisphere resulting in a lower TCR = 1.0 ± 0.3°C. Natural phenomena must influence clouds although the details remain unclear, although the CLOUD experiment has given hints that increased fluxes of cosmic rays may increase cloud seeding [19].  In conclusion, the gradual reduction in net cloud cover explains over 50% of global warming observed during the 80s and 90s, and the hiatus in warming since 1998 coincides with a stabilization of cloud forcing.

Why there was a decrease in cloud cover is another question of course.

  1. Adrian permalink
    October 31, 2018 11:39 am

    Paul, so they’re saying it’s warmer when it’s sunnier?

    Clever buggers these scientists.

    • October 31, 2018 1:09 pm

      Some years ago the National Geographic Magazine devoted a whole issue to the sun. This was during a high sunspot period. They acknowledged the sun’s role, BUT then they ended the article by saying it had no effect of global temperature rise. HUH?

  2. Phoenix44 permalink
    October 31, 2018 11:44 am

    Willis Eschenbacj has done a lot on this as well, over at WUWT.

  3. October 31, 2018 11:57 am

    Strikes me that
    1. The unmeasured variable is the variation in solar insolation received at the surface. Cloud cover is inconstant. In particular it varies with the surface atmospheric pressure in the mid latitudes of the southern hemisphere where the high pressure cells are cloud free and the transparent/absorptive ocean is extensive.
    2. We know that the balance of surface pressure between the poles and the mid latitudes is important in determining whether the moving air comes from the pole or the equator. Its temperature varies accordingly.
    3. The biggest variation, by more than an order of magnitude occurs in the dead of winter, driven by variations in the strength of polar cyclones that originate at jet stream altitudes. The variation in mid- summer is inconsequential.
    4. At jet stream altitudes the heart of a polar cyclone is warmer than the surrounding air and has an elevated ozone content.
    5. Ozone absorbs infrared energy emanating from the surface of the planet and the atmosphere.
    6. Antarctic polar surface atmospheric pressure has been falling away for seventy years. The stratosphere at jet stream altitudes has been warming over the same interval of time. The warming is strongly episodic and it drives inter-annual change in near surface wind and temperature. The phenomenon is well recognised and is described as the “annular modes’.
    7. High latitude surface pressure depends on the formation and extent of polar cyclones. On the margins of Antarctica where polar cyclone activity is most intense there is a unique all year round low in planetary surface pressure. As pressure falls in high southern latitudes it rises across the rest of the globe, but nowhere more than in the mid latitudes of the southern hemisphere.
    8. As solar activity falls away more galactic cosmic rays enter the atmosphere, peak impact of ionising activity occurring at the Reneger- Pfotzer maximum in the lower stratosphere/upper troposphere where the partial pressure of ozone varies most markedly on inter-annual, decadal and longer time scales.

    Global cloud cover rises to a maximum in January when the Earth as a whole is coolest even though the Earth is closest to the sun at this time and radiation 6% more intense. Global cloud falls to a minimum in July due to the heating of the atmosphere by the vast land masses of the northern hemisphere. It is at this time that global average surface temperature peaks. In northern hemisphere summer the CO2 content of the atmosphere falls to its annual minimum due to the increased photosynthetic activity of vegetation because summer temperatures favour growth.

    A warmer globe with more CO2 in the atmosphere would enhance productivity and life would be easier for man and beast. We are living in a golden age and the prospect of a warmer planet should be welcomed.

    • October 31, 2018 1:20 pm

      Re galactic cosmic rays: they rise and fall with the ~11 year solar cycle i.e. with solar wind strength. However as Piers Corbyn points out no corresponding temperature signal seems to exist.

      • Gerry, England permalink
        October 31, 2018 1:57 pm

        Svensmark et al have shown that cosmic particles can seed clouds. There is a relationship in their somewhere but given that all the research cash goes to trying to prove human global warming, very little is being spent to sort out what will be a very inconvenient relationship for many.

  4. October 31, 2018 12:29 pm

    Reblogged this on Climatism and commented:
    Good find. Makes sense.

  5. October 31, 2018 12:51 pm

    Reblogged this on Science is distorted by progressive philosophy.

  6. October 31, 2018 1:46 pm

    Euan Mearns said:
    Our analysis using sunshine as a cloud proxy is applicable to day time cloud only. It is well established that cloud cover at night time is significantly different to cloud cover during the day.

    Something to be aware of.

  7. October 31, 2018 3:36 pm

    “Why there was a decrease in cloud cover is another question of course.”

    I suspect oceans are the dominant influence on climate change over periods of decades to centuries and perhaps even out to a few millennia. The oceans store so much energy in comparison to the atmosphere and it is variation in cloud cover that modulates the amount of energy stored in the oceans, primarily in the tropics and middle latitudes. CO2 is a minor bit player and might possibly have a small effect in reducing OLR with clear sky conditions in deserts, including the polar deserts. CO2 has very little if any effect in the tropics and middle latitudes where most of the solar energy is absorbed by oceans and cloud cover and water vapor are the dominant players. Changing albedo of land surfaces and from snow and ice are probably greater influences on climate than CO2 on scales of months, years, and decades. Sea ice is probably affected mainly by ocean temperature and currents. The tinkered gloom and doom climate models have little if any skill in properly handling water in its various forms, which is by far the dominant player in regional and global climate change over years, decades, and centuries.

  8. October 31, 2018 10:13 pm

    erl happ, agree that solar insolation at the surface is the key variable, and in fact it has been measured since early last century. The leading research on global brightening/dimming is done at the Institute for Atmospheric and Climate Science of ETH Zurich, led by Martin Wild, senior scientist specializing in the subject.

    Here is a key graph from Wild:

    “Figure 2. Changes in surface solar radiation observed in regions with good station coverage during three periods.(left column) The 1950s–1980s show predominant declines (“dimming”), (middle column) the 1980s–2000 indicate partial recoveries (“brightening”) at many locations, except India, and (right column) recent developments after 2000 show mixed tendencies. Numbers denote typical literature estimates for the specified region and period in W m–2 per decade. Based on various sources as referenced in Wild (2009).

    The latest updates on solar radiation changes observed since the new millennium show no globally coherent trends anymore (see above and Fig. 2). While brightening persists to some extent in Europe and the United States, there are indications for a renewed dimming in China associated with the tremendous emission increases there after 2000, as well as unabated dimming in India (Streets et al. 2009; Wild et al. 2009).”

    My synopsis with links is

  9. November 1, 2018 4:44 am

    Reblogged this on Climate Collections.

  10. Brian Jones permalink
    November 1, 2018 10:55 pm

    I thought most of any observed warming occurred at night. Which is interesting in that my experience is that clear nights are colder.

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