New paper finds significant decrease in cloudiness over the US past 30 years

A paper published today in the Journal of Climate finds a significant decrease in cloudiness over the contiguous United States during the past 30 years. According to the authors,

A loss of ~4.2% total cloudiness is observed between 1982 and 2012 over a North American domain centered over the contiguous United States.

The paper adds to others finding decreased cloudiness and "global brightening" due to fewer clouds and aerosols beginning in the 1980's [or perhaps earlier since satellite records only exist since 1979]. Most or all global warming over the past 30 years could be attributable to global brightening rather than increased CO2. A mere 1-2% change in cloudiness is sufficient to cause either global warming or cooling. 

Journal of Climate 2014 ; e-View

doi: http://dx.doi.org/10.1175/JCLI-D-14-00068.1

Entering the Era of 30+ Year Satellite Cloud Climatologies: A North American Case Study

Michael J. Foster*

Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison, Wisconsin, USA. Email: Mike.foster@ssec.wisc.edu

Andrew Heidinger

Center for Satellite Applications and Research, NESDIS, NOAA, Madison, Wisconsin, USA. Email:Andrew.Heidinger@noaa.gov

Abstract

The emergence of satellite-based cloud records of climate-length and quality hold tremendous potential for climate model development, climate monitoring, and studies on global water cycling and its subsequent energetics. This article examines the more than thirty-year PATMOS-x AVHRR cloudiness record over North America and assesses its suitability as a climate-quality data record. A loss of ~4.2% total cloudiness is observed between 1982 and 2012 over a North American domain centered over the contiguous United States. While ENSO can explain some of the observed change, a weather state clustering analysis identifies shifts in weather patterns that result in loss of water cloud over the Great Lakes and cirrus over southern portions of the United States. We characterize the radiative properties of the shifting weather states, and the results suggest that extended cloud satellite records may prove useful tools for increasing our knowledge of cloud feedbacks – a long-standing issue in the climate change community.

New paper finds the natural Pacific Decadal Oscillation controls North American temperatures via changes in cloud cover

A paper published today in Atmospheric Research describes a mechanism by which changes in the natural Pacific Decadal Oscillation [PDO] affect air temperatures and water vapor, which subsequently affects cloudiness over North America [planetary albedo], and therefore land surface temperatures. As noted by Dr. Roy Spencer in his book, 

"The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling."

According to the authors, "The TCM [thermodynamic model] generates a kind of atmospheric bridge by which the SST [sea surface temperature] produces a T7A [change in air temperature], the consequent condensation of water vapour anomaly and the corresponding εA [cloudiness] over the continent, affecting the planetary albedo and therefore the LST [land surface temperature]."

Fig. 1. PDO index for the summers (average of June, July and August) based on the CAF for SST over the North Pacific region during a period of 105 years, from 1900 to 2004 (ftp://ftp.atmos.washington.edu/mantua/pnw_impacts/INDICES/PDO). The global warming signal has been removed from the data. The upward bars indicate years with positive index, and the downward bars indicate years with negative index.

Simulation of the PDO effect on the North America summer climate with emphasis on Mexico

• Víctor M. Mendoza^a, , 
• Berta Oda^a, 
• René Garduño^a, 
• Elba E. Villanueva^a, 
• Julián Adem^a, b

• ^a Centro de Ciencias de la Atmósfera, UNAM, Ciudad Universitaria 04510, México DF, México
• ^b Member of El Colegio Nacional, México

Highlights

•

A thermodynamic model simulates the effect of the PDO phases on summer variables of Mexico.

•

Combined effect of cloudiness and evaporation according to the soil moisture during the y phases.

•

Cloudiness anomalies form an atmospheric bridge.

---

Abstract

Five composite anomaly fields (CAF) are built for the summer of each Pacific Decadal Oscillation (PDO) phase: skin temperature; air temperature (T₇), zonal (u₇) and meridional (v₇) wind at the 700 mb level; and precipitation (R).

An energy balance model, named Thermodynamic Climate Model (TCM), is integrated on the NH to compute the summer anomalies (sub-index A) of the land surface temperature (LST),T₇, u₇, v₇, R  and cloudiness (ε). To study the effect of the PDO phases on Mexico’s climate, the CAF of the sea surface temperature (SST) is used in the TCM as an input. The output fields are objectively compared with their respective CAF (except SST_A) using an index of agreement, and the six variables are mainly discussed on the north Pacific and adjacent continents (NPAC), with emphasis on Mexico.

The TCM [thermodynamic model] generates a kind of atmospheric bridge by which the SST_A [sea surface temperature] produces a T_7A [change in air temperature], the consequent condensation of water vapour anomaly and the corresponding ε_A  [cloudiness] over the continent, affecting the planetary albedo and therefore the LST [land surface temperature].

The u_7A [zonal wind] forms a large meridional wave train over the NPAC [North Pacific and adjacent continents] centre, which is part of the Pacific/North American pattern in both PDO phases and is more intense in winter than in summer. In the PDO warm phase and over the eastern half of the NPAC [North Pacific and adjacent continents], the v_7A  [meridional wind] is positive, so that the moisture flux from the Pacific Ocean toward North America (NA) increases the precipitation during NA [North American] monsoon. These results have an acceptable agreement with the CAF.

We also analysed the combined effect of cloudiness and evaporation according to the soil moisture, over the eastern NA and the Gobi Desert for both PDO phases, showing its thermal moderator effect.

New paper finds climate sensitivity to CO2 is only 0.43C, about 7 times less than the IPCC claims

A new paper published in the Open Journal of Atmospheric and Climate Change by renowned professor of physics and expert on spectroscopy Dr. Hermann Harde finds that climate sensitivity to a doubling of CO2 levels is only about 0.43C, about 7 times less than the IPCC claims, but in line with many other published low estimates of climate sensitivity. 

The paper further establishes that climate sensitivity to tiny changes in solar activity is comparable to that of CO2 and by no means insignificant as the IPCC prefers to claim. 

The following is a Google translation from the German EIKE site with an overview of the main findings of the paper, followed by a link to the full paper [in English]. 

Assessment of global warming due to CO2 and solar influence

Currently climate sensitivity (discussed for example here ) is claimed by the IPCC mid-value to be 3.0 C (AR4) as the most probable value, but others have determined much lower values ​​of 1.73C or 1C or even 0.43C. Prof. Hermann Harde, renowned physicist and Spektral analytiker has determined from his new paper the climate sensitivity is 0.43 C

Only a few spectral lines from CO2 absorbed Image

Editor's note:

The "climate sensitivity" said quantity was invented to carry the presumption in meaningful ways into account that the global mean temperature of the atmosphere could possibly be driven in a certain way by increase in carbon dioxide concentration in the air. To this end, forces defined (postulated) called. "Forcings", whose influence, by means of certain physically based and mostly plausible assumptions, to accomplish this increase as migration out of balance. One of the factors is required for the climate sensitivity. It indicates how much K (° C) doubling the heating of the CO2 concentration rises.

Assessment of global warming by CO2 and Solar influence

Hermann Harde

Helmut-Schmidt-University Hamburg, Holstenhofweg 85, 22043 Hamburg

Our understanding of past and current changes in our climate is based partly on observations, but also on studies of feedback processes and modeling for climate.

In this work, an advanced two-layer climate model is presented, which is specifically geared to the influence of rising CO2 to calculate concentration in the atmosphere on global warming and the effects of a changing solar activity on our climate.

The model describes the atmosphere and the earth surface than two layers, which act simultaneously as absorber and Planck radiator. In equilibrium, thereby giving the earth as the atmosphere about the radiation and the heat exchange between the layers as much power again, as they absorb from the sun and the neighboring location.

An external fault, which may have their origin in a change in solar activity or the concentration of greenhouse gases, changes the balance and thus leads to altered average temperatures of the earth and the atmosphere.

The model takes into account the short-wave and long-wave scattering of radiation in the atmosphere and clouds, in particular multiple-scattering and reflections between the surface and the clouds is included. It also takes into account the usual feedback processes such as changes in water vapor concentration, the temperature gradient with height (lapse rate), or albedo. In addition, but also the temperature-dependent heat fluxes by convection and evapotranspiration as well as induced by temperature and solar influence changes in cloud cover degree and whose repercussions are included on the balance with.     

While climate models radiation losses and their impact on the energy balance usually describe for the radiative forcing, in this work, changes in greenhouse gas concentrations are directly attributed to the short-term and long-wavelength absorption of these gases so that the key parameters in the representative model shown here. The absorptions by the major greenhouse gases water vapor, carbon dioxide, methane and ozone are determined from single-line calculations that rely on the HITRAN08 database and for the solar radiation the spectral range from 0.1 to 8 microns , for the infrared range the spectrum of 3-100 microns cover.

Due to the changing concentrations of greenhouse gases and atmospheric pressure with the ambient temperature and the height above the ground, the calculations for up to 228 sub-layers of the earth's surface into 86 km altitude, and additionally for three climate zones, the tropics, middle latitudes and the polar regions is performed. Then the absorbance change with increasing CO2 concentration to detect these bills for 14 different concentrations are 0 - 770 ppm repeated under otherwise identical conditions.

The changing propagation length of sunlight in a lower layer, which depends on the angle of incidence of the radiation to the atmosphere and thus on the latitude and longitude is taken into account by representing the earth as a truncated icosahedron (bucky ball) that the 32 surface elements with well-defined angles incident radiation is and then each of these areas is assigned to a climate zone.

The propagation of long-wave radiation, especially the radiation emitted by the atmosphere itself radiation in downward and upward direction which is substantially dependent on the temperature distribution in the vertical direction is calculated separately with an extended model for radiative transfer for each climate zone.

The short and long wavelength spectra show a pronounced saturation behavior with increasing water vapor and CO2concentration and a strong mutual overlap. Both effects lead to a significant weakening of the greenhouse effect with increasing concentration.

The method presented here relies on the climate model calculated in this work short-term and long-wavelength absorptions to Decrease the surface temperature and lower troposphere temperature as a function of CO2 to determine concentration. The temperature rise in a doubled CO2 concentration then provides directly the CO2equilibrium climate sensitivity.

Different scenarios for cloud-free and cloudy sky regularly be examined in detail, this. Taking into account all significant feedback effects and solar influences Corresponding simulations show the dominant influence of cloud cover change on global warming, this is triggered by a thermal and / or solar-induced cloud feedback. In particular, is clearly due to this strong influence of clouds that the measured warming in the last century can only be explained satisfactorily if a significant fraction is associated with an increased solar activity.

The simulations yield a CO2 -initiated warming of 0.2 ° C ( 100 ppm CO2 -Anstieg) and a solar fraction of 0.54 ° C over this period. This corresponds to a CO2 climate sensitivity of 00:56 ° C (doubling of CO2 ) and a solar sensitivity of12:54 ° C ( 0.1% increase in the solar constant). These results are in clear contradiction to the representations of the IPCC , the temperature rise over the last century exclusively anthropogenic emissions of greenhouse gases ( 95%assigns probability) and a climate sensitivity between 1.5 ° C and 4.4 ° C starts, during any influence is denied by the sun.

Peculiarities and differences with other studies

Spectral calculations

The spectral absorption of greenhouse gases as well as to the floor and looking to the all emitted long-wave radiation are the key parameters are for a climate model to hereby the CO2 to calculate climate sensitivity. Therefore, the essential foundations and results of these calculations are summarized in this paper first. These include in particular:

- New lines-lines-Spectra the absorption (not forcing): 
      short-wave absorption of 0.1 - 8 microns for water vapor, CO2, CH4 , 
      long-wavelength absorption of 3-100 microns for water vapor, CO2, CH4 and O3 , 
      all essential calculations with high spectral resolution (better than 1 GHz), 
      with high local resolution for 228 atmospheric layers above 86 km altitude 
      and for three climate zones.

- Detailed radiative transfer calculations for the downward and upward infrared radiation, based on a novel and generalized radiative transfer model.  

Climate model

The model calculates the impact of a growing CO2 concentration as well as increased solar activity on global warming:

- It determines the energy balance and heat transfer by radiation between Earth's surface and atmosphere under equilibrium conditions.

- It uses the calculated short-term and long-wavelength absorption and the upward and downward radiative fluxes in the atmosphere as a key parameter for the climate model.

- It takes into account clouds influences and multiple scattering of short and long wave radiation by clouds and the atmosphere.

- The radiation and heat fluxes are calibrated to the corresponding satellite data.

- The model reacts to changes Bewölkungs with a bottom temperature change applied to the ISCCP -Observations over the period 1983 - 2010 are adjusted.

- It takes into account the well-known feedback processes by water vapor, changes in the vertical temperature distribution of the atmosphere as well as by changes in reflectance at the surface.

- In addition, a temperature-dependent heat transfer by convection and evapotranspiration is incorporated, processes, which are not considered in other climate models.

- The model also takes into account a thermally induced cloudiness change as a feedback process that is driven determined by both the greenhouse gases such as by a change in radiation intensity of the sun and the instrumental climate as well as the solar sensitivity.

- Alternatively, a non-thermally induced, purely solar stimulated cloudiness change is considered, which acts exclusively on the solar sensitivity and the climate sensitivity unchanged.

Results

The essential results of this work are to perform:

- The spectra show very strong saturated absorption for water vapor and CO2 and a significant overlap and mutual influence of these gases the amount of CO2 significantly limit the greenhouse effect.

- For the radiative transfer calculations for the three climate zones, the ratio of the votes of the atmosphere heat radiation to the ground and all can be determined.

- There are first presented calculations on the influence of clouds on the global temperature at the ISCCP based -Observations.

- The presented simulations allow a clear distinction between results that are valid for cloud-free and cloudy sky and the dominant influence of cloudiness on global temperature as reflect on the climate sensitivity.

- Climate sensitivity over medium cloud cover ( 66% ) is only half as large as under cloud-free conditions.

-   feedback :

o  water vapor feedback: It is determined from the Spektralberechnungen for the three climate zones and provides a significantly lower contribution than in the  IPCC Reports with listed. It consists of a stronger positive part, caused by the long-wave absorption increases with the temperature, and a smaller damping share by short-wave radiation. 
The linear increase in absorbance with temperature arises from the exponential increase in water vapor concentration according to the Clausius-Clapeyron -law other hand, a logarithmic increase in the absorption of the vapor concentration due to the spectral saturation effects.

o  Vertical temperature change : Due to the changing radiation fluxes in upward or downward direction in modified vertical temperature distribution in the atmosphere (lapse rate) results in a resultant positive feedback contribution in contrast to those in the literature, where ia is assumed to be slightly negative feedback.

o  surface albedo : From the IPCC accepted.

o  Convection: With increasing CO2 concentration, the temperature of the lower troposphere increases less rapidly than the ground temperature. As a result of heat flow increases due to convection and conduction of heat from soil to the atmosphere, and further contributes to a negative feedback on.

o  Evapotranspiration : Also increases with increasing soil temperature of the latent heat flux and thus contributes to a significant negative feedback contribution.

o  Thermally induced cloudiness change : A thermally driven change of cloudiness can be caused by greenhouse gases, in this case CO2 , and also by variations in the solar radiation power. Changes in cloudiness cause a strong positive feedback, which in this case affects both the climate like in the solar sensitivity.

o  Non-thermal solar induced cloudiness change : The cloud cover can also be affected by cosmic radiation and / or increased UV radiation, both of which are caused by changes in solar activity. This feedback acts only on the solar sensitivity and lets the climate sensitivity unaffected.

- Due to the different effects of the two cloud effects on global warming, the simulations allow a distinction between thermal and solar-induced cloud changes as well as an indication of the weighting of these contributions.

-   Calculated climate and solar sensitivities:

o Without any thermal or solar-induced cloudiness change, but taking into account all other relevant feedback processes (water vapor, vertical distribution of temperature, albedo, convection and evapotranspiration), the climate sensitivity to calculate CS = 00:43 ° C . 

This very low value is due to the highly saturated steam - and CO2 absorption, low water vapor feedback and the negative feedback by convection and evapotranspiration.

o CO2 induced thermal Bewölkungs feedback (in accordance with the ISCCP -Observations for cloudiness change), but not including the solar thermal component results in a maximum climate sensitivity of CS = 1.73 ° C . 
A rise to 100 ppm CO2 over the last century would under these assumptions, then to a global warming of 0.6 ° Ccontribute.

o With thermally induced Bewölkungs feedback, caused by CO2 and increased solar activity of 0.2% over the last century, an unrealistically high global warming would 1:32 ° C ( 0.6 + 0.72 ° C ) result.

o Without thermal but solar induced Bewölkungs feedback (in accordance with the ISCCP -Observations for cloud modification) a climate sensitivity of is CS = 12:43 ° C and a solar sensitivity of SS = 12:32 ° C calculated. 

With an increased solar activity of 0.2% over the last century then controls the solar heating of 0.64 ° C and CO2only 0.1 ° C when measured in accordance with the global warming of 0.74 ° C .

o For a lower solar activity of only 0.1% and also a smaller underlying negative convection and Evapotransipirations feedback results in a climate sensitivity of CS = 0.56 ° C, the solar sensitivity to SS = 0.54 ° C . 
then controls CO2 0.2 ° C and the Sun 0.54 ° C warming effect. 

To all boundary conditions of increased solar activity and CO2 concentration over the last century to meet, and this is in agreement with the observed warming and the change of cloud cover during the period 1983-2010 , is a combination of both cloudiness influencing mechanisms used with a thermal share of 9% and a dominant solar contribution of 91%.

o A value for the equilibrium climate sensitivity of ~ 0.6 ° C makes it more likely represents an upper limit for this. If a solar anomaly of 0.2% based on, this value is reduced to only ~ 0.4 ° ​​C.

Full paper available here:

 http: //www.scipublish .com / journals / ACC / recent   

Abstract:

We present an advanced two-layer climate model, especially appropriate to calculate the
influence of an increasing CO2-concentration and a varying solar activity on global warming.
The model describes the atmosphere and the ground as two layers acting simultaneously as
absorbers and Planck radiators, and it includes additional heat transfer between these layers due
to convection and evaporation. The model considers all relevant feedback processes caused by
changes of water vapour, lapse-rate, surface albedo or convection and evaporation. In particular,
the influence of clouds with a thermally or solar induced feedback is investigated in some detail.
The short- and long-wave absorptivities of the most important greenhouse gases water vapour,
carbon dioxide, methane and ozone are derived from line-by-line calculations based on the
HITRAN08-databasis and are integrated in the model. Simulations including an increased solar
activity over the last century give a CO2 initiated warming of 0.2 ˚ C and a solar influence of
0.54 ˚ C over this period, corresponding to a CO2 climate sensitivity of 0.6 ˚ C (doubling of CO2)
and a solar sensitivity of 0.5 ˚ C (0.1 % increase of the solar constant).

Other related articles & comments: article  answer  this  this 

New satellite dataset finds global temperatures decreased from 1982-2006

A new peer-reviewed paper published in Energy & Environment analyzes 24 years of data from the European Meteosat weather satellite and finds global temperatures decreased over the period 1982-2006. According to the authors, 

"Our observations point to a decrease in planetary temperature over almost the entire hemisphere, most likely due to an increase of cloudiness." 

"The cloud filtered temperature change patterns, in figure 2c, indicate that the largest decrease occurs in the more cloudy regions of the hemisphere: the tropics and the temperate zones, while in the desert belt the temperature decrease is much smaller. This suggests that cloudiness changes could be the mechanism behind the observed global cooling since 1982: an increase in cloudiness would decrease global radiation and increase rainfall and evapotranspiration. Both effects tend to decrease the surface temperature."

Full paper available here

Meteosat Derived Planetary Temperature Trend 1982-2006 

Andries Rosema¹, Steven Foppes¹, Joost van der Woerd¹

¹EARS Earth Environment Monitoring Ltd., Delft, the Netherlands Kanaalweg 1, 2628 EB Delft, the Netherlands

Abstract

24 year of Meteosat hourly thermal infrared data have been used to study planetary surface temperature change. Thermal infrared radiation in the 10.5-12.5mm spectral window is not affected by CO2 and only slightly by atmospheric water vapor. Satellite thermal infrared data have been converted to brightness temperatures as prescribed by Eumetsat. Hourly brightness temperature images were then composed to corresponding noon and midnight temperature data fields. The resulting data fields were cloud filtered using 10, 20 and 30 day maximum temperature substitution. Filtered data were subsequently averaged for two 10 yearly periods: 1986-1995 and 1996-2005. Finally the change in brightness temperature was determined by subtraction. In addition nine locations were selected and data series were extracted and studied for the period 1982-2006. Our observations point to a decrease in planetary temperature over almost the entire hemisphere, most likely due to an increase of cloudiness. Two small areas are found where a considerable temperature increase has occurred. They are explained in terms of major human interventions in the hydrological balance at the earth surface.

Related posts on clouds

New paper shows negative feedback from clouds 'may damp global warming'

A paper published today in The Journal of Climate uses a combination of two modelling techniques to find that negative feedback from clouds could result in "a 2.3-4.5% increase in [model projected] cloudiness" over the next century, and that "subtropical stratocumulus [clouds] may damp global warming in a way not captured by the [Global Climate Models] studied." This strong negative feedback from clouds could alone negate the 3C alleged anthropogenic warming projected by the IPCC.

As Dr. Roy Spencer points out in his book, 

"The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling."

According to the authors of this new paper, current global climate models "predict a robust increase of 0.5-1 K in EIS over the next century, resulting in a 2.3-4.5% increase in [mixed layer model] cloudiness." 

EIS or estimated inversion strength has been shown by observations to be correlated with cloudiness, as demonstrated by the 2nd graph below from the University of Washington, indicating a 1 K increase in EIS results in an approximate 4-5% increase in low cloud cover [CF or cloud fraction]. Thus, a combination of observational data and modelling indicate clouds have a strong net negative feedback upon global warming that is "not captured" by current climate models. 

Related posts

Journal of Climate 2012 ; e-View

doi: http://dx.doi.org/10.1175/JCLI-D-12-00188.1

CMIP3 Subtropical Stratocumulus Cloud Feedback Interpreted Through a Mixed-Layer Model

PETER M. CALDWELL,* YUNYAN ZHANG, and STEPHEN A. KLEIN

Lawrence Livermore National Lab, Livermore CA

Abstract

Large-scale conditions over subtropical marine stratocumulus areas are extracted from global climate models (GCMs) participating in Phase 3 of the Coupled Model Intercomparison Project (CMIP3) and used to drive an atmospheric mixed layer model (MLM) for current and future climate scenarios. Cloud fraction is computed as the fraction of days where GCM forcings produce a cloudy equilibrium MLM state. This model is a good predictor of cloud fraction and its temporal variations on timescales longer than 1 week but overpredicts liquid water path and entrainment.

GCM cloud fraction compares poorly with observations of mean state, variability, and correlation with estimated inversion strength (EIS). MLM cloud fraction driven by these same GCMs, however, agrees well with observations, suggesting that poor GCM low cloud fraction is due to deficiencies in cloud parameterizations rather than large-scale conditions. However, replacing the various GCM cloud parameterizations with a single physics package (the MLM) does not reduce inter-model spread in low-cloud feedback because the MLM is more sensitive than the GCMs to existent inter-model variations in large-scale forcing. This suggests that improving GCM low cloud physics will not by itself reduce inter-model spread in predicted stratocumulus cloud feedback.

Differences in EIS and EIS change between GCMs are found to be a good predictor of current-climate MLM cloud amount and future cloud change. CMIP3 GCMs predict a robust increase of 0.5-1 K in EIS over the next century, resulting in a 2.3-4.5% increase in MLM cloudiness. If EIS increases are real, subtropical stratocumulus may damp global warming in a way not captured by the GCMs studied.

From the University of Washington Dept. of Atmospheric Sciences:

A new scaling for low cloud cover

Contact | Publications | Research | UW Atmospheric Sciences | UW

Observations show that on daily to interannual timescales, stratiform low cloud fraction CF is strongly correlated with the lower tropospheric stability LTS, defined as the difference between the potential temperature q of the free troposphere (700 hPa) and the surface, LTS = q₇₀₀-q₀ (Klein and Hartmann 1993).

Relationships between LTS and CF from observations in the tropics (Slingo 1980) and subtropics (Klein and Hartmann 1993) have been used in the parameterization of low cloud cover in general circulation models (e.g. Slingo 1987; Rasch and Kristjansson 1998) used to predict climate changes. They are also a key assumption in the thermostat hypothesis of Miller (1997) and in the climate sensitivity study of Larson et al. (1999). Both of these studies result in a strong negative low cloud feedback on climate changes due to a marked increase in low cloud cover as the sea surface temperature SST increases. However, it has yet to be demonstrated whether the observationally-derived LTS-CF relationships will hold in a changed climate.

We have derived a new formulation, called the estimated inversion strength (EIS) to estimate the strength of the PBL inversion given the temperatures at 700 hPa and at the surface (Wood and Bretherton 2006). The EIS, which like LTS depends only upon the 700 hPa and surface temperatures, accounts for the general observation that the free-tropospheric temperature profile is often close to a moist adiabat and its lapse rate is strongly temperature dependent. Therefore, for a given LTS, the EIS is greater at colder temperatures. We demonstrate that while the seasonal cycles of LTS and low cloud cover CF are strongly correlated in many regions, no single relationship between LTS and CF can be found that encompasses the wide range of temperatures occurring in the tropics, subtropics, and midltatitudes. However, a single linear relationship between CF and EIS explains 83% of the regional/seasonal variance in stratus cloud amount (see Figure below), suggesting that EIS is a more regime-independent predictor of stratus cloud amount than is LTS under a wide range of climatological conditions.

The result has some potentially important implications for how low clouds might behave in a changed climate. In contrast to Miller's (1997) thermostat hypothesis that a reduction in the lapse rate (Clausius-Clapeyron) will lead to increased LTS and increased tropical low cloud cover in a warmer climate, our result suggests that low clouds may be much less sensitive to changes in the temperature profile if the vertical profile of tropospheric warming follows a moist adiabat. There is some evidence that recent syntheses of state-of-the-art climate models are demonstrating a weaker cloud feedback than previously thought (Soden et al. 2006). Our results give some physical basis for why this might be expected. They also provide strong constraints for evaluating these models.

LEFT: Low cloud cover CF, vs LTS (top) and vs EIS (bottom). Solid circles show long term seasonal means from the tropics and subtropics, while open circles are for the colder midlatitude regions. Notice that EIS is a much more appropriate measure across a broader range of temperatures, which suggests it may have skill in predicting how low clouds may change in a future climate. 

References:

Klein, S. A. and D. L. Hartmann: 1993, The seasonal cycle of low stratiform clouds. J. Climate, 6, 1588-1606.

Miller, R. L.: 1997, Tropical thermostats and low cloud cover. J. Clim., 10, 409-440.

Rasch, P. J. and J. E. Kristjansson: 1998, A comparison of the CCM3 model climate using diagnosed and predicted condensate parameterizations. J. Clim., 11, 1587-1614.

Slingo, J. M.: 1980, A cloud parameterization scheme derived from GATE data for use with a numerical model. Quart. J. Roy. Meteorol. Soc., 106, 774-770.

Slingo, J. M.. 1987, The development and verifcation of a cloud prediction scheme for the ECMWF model. Quart. J. Roy. Meteorol. Soc., 113, 899-927.

Soden, B. J. and I. M. Held, 2006: An assessment of climate feedbacks in coupled ocean-atmosphere models. J. Clim., 19, 3354-3360.

Wood, R. and D. L. Hartmann: 2006, Spatial variability of liquid water path in marine boundary layer clouds: The importance of mesoscale cellular convection. J. Clim., 19, 1748-1764.

Wood, R. and C. S. Bretherton, 2006: On the relationship between stratiform low cloud cover and lower tropospheric stability. J. Clim., in press.

New paper finds cloudiness in Spain has significantly decreased since 1960

A paper published today in Climate of the Past finds that Total Cloud Cover (TCC) has significantly decreased over Spain by about 4% since 1960, the same period during which the IPCC claims there is no explanation other than man-made greenhouse gases to account for global warming. Poorly-understood natural fluctuations in cloud cover could alone account for global warming or global cooling, as discussed by Dr. Roy Spencer in his book, 

"The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling."

Until cloud effects are much better understood (as well as a host of other factors such as ocean oscillations), computer climate models will remain computer fantasy games. 

Estimated Total Cloud Cover (TCC) over Spain declined from 1961-2010

Full paper is available here


Clim. Past, 8, 1199-1212, 2012
www.clim-past.net/8/1199/2012/
doi:10.5194/cp-8-1199-2012
Increasing cloud cover in the 20th century: review and new findings in Spain

A. Sanchez-Lorenzo¹, J. Calbó², and M. Wild^1
1Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
²Group of Environmental Physics, University of Girona, Girona, Spain
 Abstract. Visual observations of clouds have been performed since the establishment of meteorological observatories during the early instrumental period, and have become more systematic and reliable after the mid-19th century due to the establishment of the first national weather services. During the last decades a large number of studies have documented the trends of the total cloud cover (TCC) and cloudy types; most of these studies focus on the trends since the second half of the 20th century. Due to the lower reliability of former observations, and the fact that most of this data is not accessible in digital format, there is a lack of studies focusing on the trends of cloudiness since the mid-19th century. In the first part, this work attempts to review previous studies analyzing TCC changes with information covering at least the first half of the 20th century. Then, the study analyses a database of cloudiness observations in Southern Europe (Spain) since the second half of the 19th century. Specifically, monthly TCC series were reconstructed since 1866 by means of a so-called parameter of cloudiness, calculated from the number of cloudless and overcast days. These estimated TCC series show a high interannual and decadal correlation with the observed TCC series originally measured in oktas. After assessing the temporal homogeneity of the estimated TCC series, the mean annual and seasonal series for the whole of Spain and several subregions were calculated. The mean annual TCC shows a general tendency to increase from the beginning of the series until the 1960s; at this point, the trend becomes negative. The linear trend for the annual mean series, estimated over the 1866–2010 period, is a highly remarkable (and statistically significant) increase of +0.44% per decade, which implies an overall increase of more than +6% during the analyzed period. These results are in line with the majority of the trends observed in many areas of the world in previous studies, especially for the records before the 1950s when a widespread increase of TCC can been considered as a common feature.

 Final Revised Paper (PDF, 1578 KB)   Discussion Paper (CPD)   


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