Clouds are liquid water droplets that reflect all wavelengths of light including infrared. They have very different properties than invisible water vapor.
Thick, low lying cumulus clouds block sunlight. High, thin stratus clouds tend to trap heat.
From NASA's Solar and Heliospheric Observatory's "Not So Frequently Asked Questions" section:
Many active regions produce giant outflows of material that are called Coronal Mass Ejections. These ejections drag with them some of the more intense magnetic fields that are found in the active regions. The magnetic fields act as a shield for high-energy particles coming from various sources in our galaxy (outside the solar system). These "cosmic rays" (CRs) cause ionization of molecules in the atmosphere, and thereby can cause clouds to form (because the ionized molecules or dust particle can act as "seeds" for drop formation).
If clouds are formed very high in the atmosphere, the net result is a heating of the Earth - it acts as a "blanket" that keeps warmth in.
If clouds are formed lower down in the atmosphere, they reflect sunlight better than they keep heat inside, so the net result is cooling. Which processes are dominant is still a matter of research.
THE ACQUITTAL OF CARBON DIOXIDE
by Jeffrey A. Glassman, PhD
"Carbon dioxide in the atmosphere [historically] is the product of oceanic respiration due to the well-known but under-appreciated solubility pump. Carbon dioxide rises out of warm ocean waters where it is added to the atmosphere. There it is mixed with residual and accidental CO2, and circulated, to be absorbed into the sink of the cold ocean waters. Next the thermohaline circulation carries the CO2-rich sea water deep into the ocean. A millennium later it appears at the surface in warm waters, saturated by lower pressure and higher temperature, to be exhausted back into the atmosphere. Throughout the past 420 millennia, comprising four interglacial periods, the Vostok record of atmospheric carbon dioxide concentration is imprinted with, and fully characterized by, the physics of the solubility of CO2 in water, along with the lag in the deep ocean circulation.
Notwithstanding that carbon dioxide is a greenhouse gas, atmospheric carbon dioxide has neither caused nor amplified global temperature increases. Increased carbon dioxide has been an effect of global warming, not a cause. Technically, carbon dioxide is a lagging proxy for ocean temperatures. When global temperature, and along with it, ocean temperature rises, the physics of solubility causes atmospheric CO2 to increase.
If increases in carbon dioxide, or any other greenhouse gas, could have in turn raised global temperatures, the positive feedback would have been catastrophic. While the conditions for such a catastrophe were present in the Vostok record from natural causes, the runaway event did not occur. Carbon dioxide does not accumulate in the atmosphere."
The graph above represents temperature and CO2 levels over the past 400,000 years. It is the same exact data Al Gore and the rest of the man-made global warmers refer to. The blue line is temps, the red, CO2 levels. The deep valleys represent 4 separate glaciation/ice-age periods. Look carefully at this historical relationship between temps and CO2 levels (the present is on the right hand side of the graph) and keep in mind that Gore claims this data is the 'proof' that CO2 has warmed the earth in the past. But does the data indeed show this? Nope. In fact, rising CO2 levels all throughout this 400,000-year period actually *followed* temperature increases -lagging behind by an average of 800 years! So it couldn't have been CO2 that got Earth out of these past glaciations. Yet Gore continually and dishonestly claims otherwise. Furthermore, the subsequent CO2 level increases due to dissolved CO2 being released from warming oceans, never did lead to additional warming, the so-called "run-away greenhouse effect" that Al Gore and his friends keep warning us about. In short, there is little if any evidence that CO2 had ever led to increased warming, at least not when the levels were within 10-15 times of what they are today. -etl
"The above chart shows the range of global temperature through the last 500 million years. There is no statistical correlation between the level of carbon dioxide in the atmosphere through the last 500 million years and the temperature record in this interval. In fact, one of the highest levels of carbon dioxide concentration occurred during a major ice age that occurred about 450 million years ago [Myr]. Carbon dioxide concentrations at that time were about 15 times higher than at present." [also see 180 million years ago, same thing happened]:
So, greenhouse [effect] is all about carbon dioxide, right?
Wrong. The most important players on the greenhouse stage are water vapor and clouds [clouds of course aren't gas, but high level ones do act to trap heat from escaping, while low-lying cumulus clouds tend to reflect sunlight and thereby help cool the planet -etl]. Carbon dioxide has been increased to about 0.038% of the atmosphere (possibly from about 0.028% pre-Industrial Revolution) while water in its various forms ranges from 0% to 4% of the atmosphere and its properties vary by what form it is in and even at what altitude it is found in the atmosphere.
In simple terms the bulk of Earth's greenhouse effect is due to water vapor by virtue of its abundance. Water accounts for about 90% of the Earth's greenhouse effect -- perhaps 70% is due to water vapor and about 20% due to clouds (mostly water droplets), some estimates put water as high as 95% of Earth's total tropospheric greenhouse effect (e.g., Freidenreich and Ramaswamy, 'Solar Radiation Absorption by Carbon Dioxide, Overlap with Water, and a Parameterization for General Circulation Models,' Journal of Geophysical Research 98 (1993):7255-7264).
The remaining portion comes from carbon dioxide, nitrous oxide, methane, ozone and miscellaneous other 'minor greenhouse gases.' As an example of the relative importance of water it should be noted that changes in the relative humidity on the order of 1.3-4% are equivalent to the effect of doubling CO2.
Water Vapor Rules the Greenhouse System
Water vapor constitutes Earth's most significant greenhouse gas, accounting for about 95% of Earth's greenhouse effect (4). Interestingly, many 'facts and figures' regarding global warming completely ignore the powerful effects of water vapor in the greenhouse system, carelessly (perhaps, deliberately) overstating human impacts as much as 20-fold.
Water vapor is 99.999% of natural origin. Other atmospheric greenhouse gases, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and miscellaneous other gases (CFC's, etc.), are also mostly of natural origin (except for the latter, which is mostly anthropogenic).
Human activities contribute slightly to greenhouse gas concentrations through farming, manufacturing, power generation, and transportation. However, these emissions are so dwarfed in comparison to emissions from natural sources we can do nothing about, that even the most costly efforts to limit human emissions would have a very small-- perhaps undetectable-- effect on global climate.
Water Vapor Confirmed As Major Player In Climate Change
ScienceDaily (Nov. 18, 2008) Water vapor is known to be Earth's most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, validating the role of the gas as a critical component of climate change.
So a clear winter’s night is just as warm as a cloudy one. Yeah right. The clouds hold in the heat. Like I said. They don’t block all wavelengths either. I’m not sure where you get your info from but a person can get sunburned on a cloudy day.