Explanation Global Warming & Cooling
A) 20 th Century Global Warming
1) 20th Century Solar Changes & Global Cloud Cover
As the thread on clouds notes, the sun is at its highest activity in 8 kyrs, the solar large scale magnetic field has doubled in the last 100 yrs, and in the last 20 years solar coronal holes have began to move towards the solar equator (The solar coronal hole creates a high speed solar wind when it passes in the Earth's direction).
"Electroscavenging"
The cloud thread in this forum describes a mechanism where rapid increases in the solar wind, causes an increase in the Global Electric Circuit which causes a potential difference between equator and Polar regions. The potential difference it is hypothesized (and data supports) removes atmospheric ions which causes low level clouds to dissipate. As the GCR created ions are removed, electroscavenging makes it appear that the Earth's temperature is no longer correlated with the solar cycle and GCR level.
A doubling of the sun's large scale magnetic field will shield the Earth from Galactic Cosmic Rays (GCR). Satellite data (See cloud thread, Palle's paper) indicates that there is a 99.5% correlation with changes in GCR and low level cloud level (over a 20 year period). An increase in GCR causes an increase in low level clouds and a decrease in GCR causes a decrease in low level clouds. The correlation between clouds and GCR holds up until 1993 at which time the satellite data indicates that low level clouds start to be reduced, which is consistent with the 'electroscavenging' process.
Palle estimates the warming due to the reduction in cloud cover 1993 to 2001 is 7.5 W/m2 or roughly three times the estimated forcing for CO2 (2.5 W/m2).
Some scientists questioned whether Palle's interpretation of the satellite cloud data was correct. Palle et al, then measured the Earth's albedo using telescopes that measured the Earth'shine reflected off of the moon. The Earth'shine data supported the satellite data.
2. CO2 and Global Warming
Is it possible that solar changes caused the majority of the 20th century warming? Yes, if Palle's data and analysis is correct. A separate thread should be started to discuss what is know concerning CO2 and its affects on the planet's temperature. Recent data indicates that there have been times in the planets history when CO2 levels have been high and the planet has been cold and visa versa. The relationship between CO2 and planetary temperature is not linear and it appears that there may be a strong negative feedback affect of clouds which regulates planetary temperature (stops the planet from warming when CO2 levels are high) rather than the assumed very strong positive feedback of water vapour with increasing planetary temperature that was assumed by the IPCC and is currently used in the climate models.
B) 21th Century Global Cooling
The 20th century warming (sun at its highest level in 8kyrs, doubling of solar large scale magnetic field, and the coronal holes moving towards the solar equator), seems to be a Henrich event which is named after the climatologist that discovered the semi-periodic event. A Henrich event is a warming of the planet which is then followed by an abrupt cooling (3C drop in temperature, 2C in five years, Younger Dryas, and then roughly 1C drop over a hundred years as the oceans cool.)
There is not consensus as to what causes the observed warming and abrupt cooling, however, there is evidence that the Younger Dryas cooling event could have been caused by a solar event. (i.e. There is a very large increase in cosmogenic nucleons, in the sea sediment data and ice core data which indicates a large increase in GCR flux during the Younger Dryas period.)
Attached is a link to the paper: "Reduced solar activity as a trigger for the start of the Younger Dryas?" that discusses the Younger Dryas Cooling event.
http://scholar.google.com/url?q=http://dept.kent.edu/geography/GEC/Reduced_solar_activity_as_a_trig.pdf&sa=X&oi=unauthorizedredirect&ct=targetlink&ust=1173034345556434&usg=__FlOTD7nJVxYUBokLsjE8z6DrfAk=
It should be noted that the Younger Dryas paper was written in 2000 before Palle's paper and findings. The Younger Dryas paper assumes the solar event is only a change in solar irradiance, rather than a change in planetary cloud cover which would be consistent with Palle's findings.
All of the public discussion associated with climate change has been concerning global warming and strongly focused on CO2. Attached is a link to lecture material by Strong that shows how the climate has changed over the last 100,000 years. Based on the climatic record interglacial periods are brief and end abruptly.
John Stone, Climate Record Over the Last 100,000 years
http://www.washington.edu/research/or/symposium/stone.pdf
When you look at the above climatic record, what do think, is causing the abrupt changes in planetary temperature and the glacial/interglacial cycle?