Thunderous New “Atmosphere” Publication: “Warming Of Last 20 Years Mainly Caused By Cloud Changes”

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Science never quits. New findings by German researchers challenge IPCC claim that greenhouse gases have driven recent warming. Data point to low cloud cover changes. 

Warming of the last 20 years mainly caused by cloud cover changes

By Fritz Vahrenholt and Hans-Rolf Dübal
(Translated, edited and subheadings by P. Gosselin)

Hans-Rolf Dübal and Fritz Vahrenholt have investigated the Earth’s radiation balance over the past 20 years in a peer-reviewed publication appearing in ” Atmosphere”.

The net radiative flux, i.e. the difference between solar irradiance and longwave and shortwave radiation, determines the change in the energy content of the climate system. If it is positive, the Earth is warming; if it is negative, it means cooling. The NASA-operated satellite-based CERES project has now been providing such radiation data, as well as data on the evolution of cloud cover in temporal and spatial resolution for two decades. These data are determined both in relation to an altitude of approx. 20 km (TOA = “Top of Atmosphere”), and also in relation to the Earth’s surface.

This publication: “Radiative Energy flux variation from 2001 – 2020“, Dübal, H.-R.; Vahrenholt, F., appearing this week in Atmosphere 2021, 12, 1297 has brought to light a surprising result for climate science: the warming of the Earth in the last 20 years is mainly due to a higher permeability of clouds for shortwave solar radiation. During the period, shortwave radiation has strongly decreased (see figure) and this equally for the northern and southern hemisphere (NH and SH). With solar irradiance remaining nearly constant, this means that more shortwave radiation reached the Earth’s surface, contributing to warming.

The long-wave back radiation (the so-called greenhouse effect) contributed only to a lesser extent to the warming. It was even compensated to a large extent by the also increasing permeability of the clouds for long-wave radiation emanating from the earth. The authors came to this clear conclusion after evaluating the CERES radiation data.

Net positive energy influx due to less low clouds

NASA researchers led by Norman Loeb, along with Finnish researcher Antero Ollila, had already recently pointed out that shortwave solar radiation increased from 2005 to 2019 due to the decrease in low clouds. Dübal and Vahrenholt now have examined TOA and ground-level radiation fluxes for the entire period and related them to changes in cloud cover. The net energy influx was positive throughout the period, increasing from 0.6 W/m² to 0.75 W/m² from 2001 to 2020.

The 20-year average was 0.8 W/m². The next chart shows the drivers behind this change and these are clearly in the area of shortwave radiation in the cloudy areas, which account for about 2/3 of the Earth’s surface (SW Cloudy Area, +1.27 W/m²). This is in contrast to the assumption presented by the IPCC in its latest report that the warming due to the increase of longwave back radiation was solely due to the anthropogenic greenhouse effect.

Radiation flux differences modulated by cloud cover changes

The IPCC attributes 100% of the warming to this effect and justifies it with model calculations. However, the analysis of the measured data by Dübal and Vahrenholt show that the warming due to the decreased shortwave radiation (1.4 W/m²) and the increased longwave radiation (1.1 W/m²) is mainly due to the cloud effect.

Climate system enthalpy

The authors also considered the effect of this radiative excess on the heat content of the climate system for a longer period since 1750, where “enthalpy” means the sum of heat, work, and the latent heat, i.e., heat of evaporation of water, heat of melting of ice, energetic change of the biosphere (plant growth), and so on. Since about 90% of this enthalpy remains as heat in the oceans, conclusions about enthalpy evolution can also be drawn by looking at long-term ocean heat content (OHC).

Good agreement was found between these two independent datasets for the period 2001-2020. Moreover, existing OHC data were evaluated for earlier, longer periods to provide an overall picture. This shows that warming since 1750 has not been continuous, but has occurred in heating spurts, designated A, B, and C, during each of which a high net radiative flux (0.7 to 0.8 W/m²) acted for 20-30 years, interspersed with milder periods.

The onset of these heating episodes coincided with the change in sign of another known natural climate factor, the AMO (Atlantic Multidecadal Oscillation). The crucial question, whether the present heating phase C will soon come to an end as in cases A and B, or whether it will continue, can only be decided on the basis of longer observations and must therefore remain open.

Decreasing cloudiness since 2000

To investigate the beginning of Phase C around the year 2000, further datasets were used, especially the cloudiness measurements of EUMETSAT, a European satellite project. Here it can be seen that the beginning of phase C is accompanied by a decrease in cloudiness, coinciding with the above-mentioned change in sign of the AMO. From the radiation measurements it can be deduced that 2% less cloud cover means about 0.5 W/m² more net radiation flux.

This could explain most of the 0.8 W/m² mentioned above.

Cloud changes stronger than greenhouse effect

This is also corroborated by the analysis of the near-surface radiation balance. Here an increase of the greenhouse effect is found, which correlates well with the increase of the greenhouse gases water vapor and CO2, but only for the “clear sky” areas. This correlation does not apply to the cloud-covered areas, which make up about 2/3 of the earth. Interesting is the statement on the greenhouse effect.

“We could prove the increased greenhouse effect of the sum of all greenhouse gases (water vapor, CO2 etc.) under ‘clear sky’ conditions with 1.2 W/m² increase in the last 20 years,” says Hans-Rolf Dübal. “However, on an area-weighted basis, this increase is overcompensated by the increasing radiation of longwave radiation in the cloudy area’s amounting to -1.48 W/m².”

The time span of 20 years is still too short to decide conclusively whether the current heating phase is a temporary or permanent development. In the former case, climate projections need to be fundamentally revised. The physical mechanism that led to the cloud thinning is discussed differently in the literature.

“The cloud changes can be triggered by a decrease in aerosols, by atmospheric warming due to natural causes (e.g., the AMO or the PDO), by anthropogenic warming due to CO2, or by a combination of these individual factors,” says Fritz Vahrenholt. “However, one thing can already be stated: the warming of the last 20 years has been caused more by change in clouds than by the classical greenhouse effect.”

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18 responses to “Thunderous New “Atmosphere” Publication: “Warming Of Last 20 Years Mainly Caused By Cloud Changes””

  1. Tom Anderson

    It is a pity we still have to pay tribute to “CO2 warming,” when evidence continues to accumulate that the gas’s predominant (>99%) spectral radiation band is in the 15-micron wavelength at minus 80° (-80°) Celsius, while its warmer, far more active if smaller band, 9.6 microns at (+29°C), is centered within the 8-12-micron radiant energy that passes direct to space through the atmospheric window. The pity is that this information seems confined to physicists. Where are the rest of us?

  2. John F Hultquist

    Two snips from the text:

    1: higher permeability of clouds for shortwave

    2: the decreased shortwave radiation (1.4 W/m²) and the increased longwave radiation

    _ _ _ _ _ _ _

    I found this hard to follow, but I think the summary is that processes in the oceans cause more or fewer clouds that increase or decrease Earth’s whiteness (reflectivity; albedo).
    When there are fewer clouds, measurements at the Top Of the Atmosphere (TOA) show less energy is reflected ( “the decreased shortwave radiation” ), more short waves reach the surface where absorption happens and, with that, in turn, producing more longwave radiation (outgoing) that is measured at the TOA.

    We just need to know how the World Ocean works.

    1. Wi

      In reply to “We just need to know how the oceans work ….” It is not the ocean which we need to ‘know’… about. We need to understand what caused the earth to warm. And what caused the change in planetary cloudiness.

      Global warming the theory said the recent warming was caused by CO2, not changes to the earth’s cloudiness.

      Solar wind bursts remove ions clouds and inhibit cloud formation in specific regions of the earth causing a reduction in cloud cover. Ions help clouds form and change cloud properties.

      GCR (Galactic cosmic rays…. which are primarily very high speed cosmic protons) are the primary source of ions in the atmosphere. GCR is modulated by changes in the solar cycle.

      High speed solar wind bursts are caused by solar coronal holes. A large number of solar coronal holes suddenly appeared during the solar 22/23 minimum and continued to appear on the sun in large numbers and a low latitudes for maximum effect on the earth. Previously solar coronal holes occurrence and number correlated with the sun spot cycle.

      The changes to the earth’s cloudiness were found to be regional, not global. And the changes were found to be caused solar wind changes to the ionosphere which remove cloud forming ions from clouds.

      The mechanism where a solar wind burst causes changes to the earth’s ionosphere which in turn removes cloud forming ions and inhibits the formation of clouds, is called electroscavening.

      Enric Palle found the cloud change by analyzing top of atmosphere changes in reflected sunlight/cloud cover using satellite measurement and the measurement of the changes to the amount of earthlight that is reflected off of the Moon.

      This is a technical summary of the mechanism… Changes to the ionosphere caused by solar wind bursts create a space charge differential removes ions from clouds.

      Ions in the atmosphere increases the effectiveness the formation of clouds. So a change in the amount of ions in the atmosphere in the region where clouds form is the major ‘variable’ in cloud formation.

      The following is an excerpt from a summary paper explains the concepts.

      “The role of the global electric circuit in solar and internal forcing of clouds and climate

      The solar wind affects the galactic cosmic ray flux, the precipitation of relativistic electrons, and the ionospheric potential distribution in the polar cap, and each of these modulates the ionosphere-earth current density.

      On the basis of the current density-cloud hypothesis the variations in the current density change the charge status of aerosols that affect the ice production rate and hence the cloud microphysics and climate [e.g., Tinsley and Dean, 1991; Tinsley, 2000].

      The underlying mechanism is that charged aerosols are more effective than neutral aerosols as ice nuclei (i.e., electrofreezing) and that the enhanced collections of charged evaporation nuclei by supercooled droplets enhance the production of ice by contact ice nucleation (i.e., electroscavenging). Both electrofreezing and electroscavenging involve an increase in ice production with increasing current density [e.g, Tinsley and Dean, 1991; Tinsley, 2000].

      The current density-cloud hypothesis appears to explain solar cycle effects on winter storm dynamics as well as the day to-day changes of Wilcox and Roberts Effects [e.g., Tinsley, 2000].

      Kniveton and Todd [2001] found evidence of a statistically strong relationship between cosmic ray flux, precipitation and precipitation efficiency over ocean surfaces at midlatitudes to high latitudes, and they pointed out that their results are broadly consistent with the current density-cloud hypothesis.

      1. Ulric Lyons

        “Previously solar coronal holes occurrence and number correlated with the sun spot cycle.”

        There were major lows in the solar wind strength at sunspot maximum in 1969 and 1979-80, but the major lows then shifted to around a year after sunspot minimum in 1997 and 2009.
        And low cloud cover has declined since the solar wind weakened from 1995, because of the warmer AMO, warmer SST’s reduce low cloud cover apart from in the central topics and over the Arctic Ocean.

  3. Tom Anderson

    It is a pity we still have to pay tribute to “CO2 warming,” when evidence continues to accumulate that the gas’s predominant (> 99%) spectral radiation band is in the 15-micron wavelength at minus 80° (-80°) Celsius, while its warmer, far more active next smaller band, 9.6 microns at (+29°C), is centered within the 8-12-micron range of energy passing direct to space through the atmospheric window.

    This information seems confined to physicists. Everyone else talks sagely of radiant energy transfer while omitting this threshold qualification. Freeman Dyson’s continued insistence that CO2 was a cooling gas, for example, was politely ignored. To our detriment, I would say.

    See, e.g., Chapter 8, Salby, Murry L., “Physics of the atmosphere and climate (Cambridge U. Pr., 2012);” Lightfoot, H.D., Orval A. Mamer, “Calculation of Atmospheric Radiative Forcing (Warming Effect) of Carbon Dioxide at Any Concentration,” Sage Journals, research article, Dec. 1, 2014; Witteman, W.J., “The absorption of thermal emitted radiation by CO2”(Principia Scientific, February 2020).

  4. John F Hultquist

    Unrelated to the post:
    I’m having a computer problem with respect to about 20% of sites not responding to my connection requests.
    My above post shows this with the odd upper left section. I now see a gray square with a tiny image therein and the word John. Underneath is an F and the following line has my last name.

    If this isn’t what you see – ignore me and deleted this message.
    There should be an image where the box is, but if I try to load it I get a message: took too long to respond
    In fact, no gravatars appear on any site I can get to.

    As mentioned, this is an issue for numerous sites that I regularly visit. This is happening with my bank, WUWT, my email account, and the local road reports.

    1. stewartpid

      John have u done an update lately?
      My microsoft 10 seemed to get badly out of date despite the auto updates and I had to do a manual update and it fixed a whole mess of issues … mostly slowness but other stuff too!

      1. John F Hultquist

        I haven’t. I’ve been relying on auto-update. Thanks for the idea.

        _ _ _
        Pierre, I apologize for my intrusion with this O/T stuff. -John

    2. Richard Greene

      My very old 2009 MacBook Pro computer has ancient software that has had no updates available for many years, yet loads this website perfectly.
      A few websites don’t load with a normal format, and a few have JPEGS that don’t show up at all. But not here. Did your problem start on October 1, 2021 ? If it did, you may find a fix at the website

  5. Fritz Vahrenholt

    Dear John,
    your summary an your interpretation is absolutely correct

  6. Fritz Vahrenholt

    and instead of an

  7. pochas94

    The radiation clear window is the part of the spectrum that is transparent to outgoing infrared radiation from the surface. When the window is open window IR escapes directly to space. With a cloud overhead, the window is closed, window radiation is thermalized and reflected downward, resulting in surface warming.


    il est surprenant que l’on ne cite que l’AMO comme maerqueur des épisodes de pointes de chaleur de ces dernières décennies
    en réalité on peut établir un enchainement assez systématique :
    episodes ENSO El Nino, suivis, à 2 ou 3 mois d’un AMO et de l’échauffement de Troposphère
    J’ai constaté que le déclanchement ENSO est liè à des épisodes durables de anticyclone sur l’Ouest Pacifique avec très faibles nébulosités pendants de longs mois s’étendant vers le Centre puis l’Est Pacifique selon le scénario ENSO typique.

  9. CO2isLife

    I’ve been saying this for years. The oceans are warming. 13 to 18 Micron LWIR won’t warm water. Visible radiation warms the oceans. If the oceans are warming, more visible radiation much be reaching them. Sure enough, if you go to Climate4You and look up the cloud cover, you will see that fewer clouds corresponds to warmer temperatures. CO2 has nothing to do with the warming.

  10. William Astley

    These are links to papers that support my comment above, that the reduction in cloud cover which was observed… Is physically caused by observed solar wind changes, which occurred when the warming occurred, in the same time period.

    The changes in solar wind speeds are known to be due to solar coronal holes which anomalously appeared in the solar minimum and later in large numbers in the solar cycle.

    This is a copy to a link to a review paper that explains how changes in atmospheric ionization caused by solar changes affect cloud cover.

    Atmospheric Ionization and Clouds as Links Between Solar Activity and Climate

    “Electroscavenging depends on the buildup of space charge at the tops and bottoms of clouds as the vertical current density (Jz) in the global electric circuit encounters the increased electrical resistivity of the clouds.

    Space charge is electrostatic charge density due to a difference between the concentrations of positive and negative ions. Calculations indicate that this electrostatic charge on aerosol particles can enhance the rate at which they are scavenged by cloud droplets.

    The aerosol particles for which scavenging is important are those that act as insitu ice forming nuclei (IFN) and CCN. Both IMN and electroscavenging depend on the presence of atmospheric ions that are generated, in regions of the atmosphere relevant for effects on clouds, by galactic cosmic rays (GCR)”

    This is link to a paper that found planetary temperature is correlated to changes in an index that is effected by both sunspots and solar coronal holes.

    Once again about global warming and solar activity
    “It could therefore be concluded that both the decreasing correlation between sunspot number and geomagnetic activity, and the deviation of the global temperature long-term trend from solar activity as expressed by sunspot index are due to the increased number of high-speed streams of solar wind on the declining phase and in the minimum of sunspot cycle in the last decades.”

    According to Echer et al. (2004), the probable cause seems to be related to the double peak structure of geomagnetic activity. The second peak, related to high speed solar wind from coronal holes, seems to have increased relative to the first one, related to sunspots (CMEs) but, as already mentioned, this type of solar activity is not accounted for by the sunspot number. In Figure 6 the long-term variations in global temperature are compared to the long-term variations in geomagnetic activity as expressed by the ak-index (Nevanlinna and Kataja 2003). The correlation between the two quantities is 0.85 with p

  11. Ulric Lyons

    Weaker solar wind states driving a warm AMO phase since 1995 have reduced low cloud cover, apart from in the central tropics and over the Arctic Ocean. It’s a self amplified negative feedback.


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