He suggests that some unknown mechanism has
caused global cloud cover to decrease over the past century.
Not exact matches
My father is somewhat of a climate «sceptic» and insists that the prediction of 0.3 C cooling is based only on solar irradiance and does not take into account increased
cloud cover caused by low sun activity (he beleives that we are going to be facing extreme
global cooling over the next few decades).
For
cause and effect: You never know, but I don't think that
cloud cover regulates the sun cycle... Globally, the variation of
cloud cover during a sun cycle is around 2 %, which can have a substantial influence on
global temperatures.
For example, episodic deviations in
cloud and snow
cover, dust and smoke, etc, will have some radiative effect that could
cause some
global average temperature change.
Roy Spencer is the driving force behind the «internal variability» hypothesis, which posits that some unknown and undefined mechanism is
causing cloud cover to change, which, by changing the overall reflectivity of the Earth, is the driving force behind the current
global warming.
And because
cloud cover gates the Sun on and off, it is the most powerful feedback in all of Earth's climate to amplify solar variations and to mitigate
global warming from any
cause.
This empirical finding contradicts Spencer's hypothesis that
cloud cover changes are driving
global warming, but is consistent with our current understanding of the climate: ocean heat is exchanged with the atmosphere, which
causes surface warming, which alters atmospheric circulation, which alters
cloud cover, which impacts surface temperature.
Clouds are one of the big unknowns about
global warming as they can have a range of effects, warmer temperatures
caused by
global warming will result in higher rates of evaporation and therefore will result in higher
cloud cover.
Something
caused decreased
cloud cover, less reflected SW and
global warming in the late 20th century.
«The overall slow decrease of upwelling SW flux from the mid-1980's until the end of the 1990's and subsequent increase from 2000 onwards appear to
caused, primarily, by changes in
global cloud cover (although there is a small increase of
cloud optical thickness after 2000) and is confirmed by the ERBS measurements.»
A slight change of ocean temperature (after a delay
caused by the high specific heat of water, the annual mixing of thermocline waters with deeper waters in storms) ensures that rising CO2 reduces infrared absorbing H2O vapour while slightly increasing
cloud cover (thus Earth's albedo), as evidenced by the fact that the NOAA data from 1948 - 2008 shows a fall in
global humidity (not the positive feedback rise presumed by NASA's models!)
New paper finds changes in
cloud cover caused global brightening & dimming, not man - made aerosols
«The overall slow decrease of upwelling SW flux from the mid-1980's until the end of the 1990's and subsequent increase from 2000 onwards appear to
caused, primarily, by changes in
global cloud cover (although there is a small increase of
cloud optical thickness after 2000) and is confirmed by the ERBS measurements... The overall slight rise (relative heating) of
global total net flux at TOA between the 1980's and 1990's is confirmed in the tropics by the ERBS measurements and exceeds the estimated climate forcing changes (greenhouse gases and aerosols) for this period.
Spencer has postulated elsewhere that natural factors, such as PDO swings, might be the underlying
cause for changes in
cloud cover, which result in changes in
global temperature, IOW that
clouds act as part of a natural forcing, rather than simply a feedback to anthropogenic (or other) forcing.
In that post, I looked into the ocean at 10 - 100m depth, and found enough extra energy absorption
caused by a 1983 - 2009
cloud cover decline to match the
global warming claimed for CO2.