In real estate appraisals the three most important factors to determine the value of a property are: Location, location, location.
Likewise, in climate modeling the three most important factors to estimate the future climate on earth are: Clouds, clouds, clouds.
CO2 is a strong greenhouse gas, second only to water vapor in affecting the climate on earth. If CO2 were to double from pre-industrial times, which it will have done in 50 years or so, global temperatures on earth will increase about 0.9 degree Celsius from pre-industrial times, if that was the only factor affecting the greenhouse effect. This corresponds to a radiative forcing of 4.9 W/m2. But water vapor is a stronger greenhouse gas than CO2, and, this is important, they are not orthogonal as defined by chemometrics, that means, the responses from water vapor and CO2 are not independent, and they are only partly additive. Check this figure: The bottom line is the absorption of water vapor, the green line is for CO2. The area of interest is between 8 and 20 microns, where CO2 absorbs more than H20 and is at the maximum of outgoing black body emission at 0F. The CO2 concentration is on the order of 400 ppm, the average global H2O concentration at surface level is around 12,500 ppm. Since both H2O and CO2 absorb in the same area, if water vapor concentration is more than 30 times higher, the CO2 con- centration doesn’t matter, it is all absorbed by H2O, and this is the reason there is no hotspot in the equatorial troposphere. All climate models predict there must be one, so there must be something seriously wrong with all climate models. Let us take a look at what factors IPCC consider in the consensus of climate models. See the following table:
This table is listing all the possible contributions to radiative forcings that IPCC chose to list. It does include the effect of aerosols on clouds, but it assumes that this is the sum total of the effect of clouds. Let us take a look at a picture of earth from space:The first impression of earth from space is: How beautiful! Green land, brown mountains, blue oceans and absolutely white clouds! The clouds seem to reflect all incoming sunlight, and indeed, clouds can have an albedo of about 0.9, versus ocean with an albedo of about 0,07. Taking a look at the energy flows, we can see that the clouds reflect about 79 W/m-2 back into space, or about 23% of the incoming sunlight.
But that is only half the story. Clouds are even more important than that for the energy balance of the earth. If you have a house with no air conditioning, and it is hot in the summer, you close the windows and close the shades during the day to keep the hot air and the sunshine out. Then during the night you open the windows and shades to let the cooler air in. In the winter you do the opposite, during the day you may or may not open the windows dependent on the temperature, but you always let in as much sunshine as possible. Then at night you draw the shades to retain as much warmth as possible. By manipulating the windows and shades you provided the negative feedback to keep the house somewhat temperature controlled. In fact, you acted as a governor, providing the negative feedback necessary to keep the house temperature controlled.
It is the same with clouds, they cool by day and warm by night, and they come and go, so it does matter a great deal when they do appear. At the risk of oversimplification let me take a stab at 3 cloud types, clouds, clouds, clouds.
Cumulus clouds, also called “Beautiful weather clouds.” The best example comes from Willis Eschenbach from his observations on a tropical island. The morning starts clear, and as the sun heats the moist air cumulus clouds appear around 9 a.m., and the temperature goes down!
Cumulus clouds have an albedo of about 0.9, so 90% of the incoming radiation of 341 W/m2, or up to 300 W/m2 less solar heat reaches ground at mid day.
The sun continues its path, and by mid afternoon Cumulonimbus clouds may appear. They are also called thunderstorms. In addition to have a very high albedo, they transfer a lot of heat to the upper atmosphere, rain out, keeping the ecosystem going, and cool the lower atmosphere.
The third very important type of clouds are frontal clouds. They carry energy in the form of water vapor from one area to another, in the northern temperate region typically from Southwest to Northeast, but they can also follow the jet stream, which exhibits a wave pattern.
The long and short of this oversimplification is that even a one percent change in the global average of cloud cover means more to the energy balance than all the factors listed by IPCC. In addition, cloud averages are misleading, day clouds cool, night clouds warm. So how are the climate models doing? Check this figure:
Not very encouraging. They all miss the mark. The only way to explain this discrepancy is that they all put too much emphasis on CO2 and way too little on clouds. But it helps to explain why they all miss the mark. See fig.
The clouds are the main temperature regulator in the ecosystem, providing a strong negative feedback once the temperature is favorable for cloud formation. Unless the oceans run dry we will never have to worry about a thermal runaway.
However, it can get cold, and we will get another ice age, which is the normal steady state for the earth. This will start by increasing cloud cover for whatever reason. Let me name a few:
Volcanoes: Volcanic eruptions like Pinatubo can decrease global temperatures by a degree or so for a few years. A super volcano like Yosemite erupting will trigger the next ice age.
Solar cycles: Solar cycle 24 is the most quiet in a century. A new solar minimum is to occur in the next few years and solar cycle 25 promises to be even quieter. When this happened last time it caused the little ice age, the winters were brutal indeed, and cloud covers increased, cooling the earth by at least half a degree.
The earth’s magnetic field is starting to act erratically. The magnetic north pole is speeding up and is now way up in the Arctic, near the North pole. The chart on the right shows the observed north dip poles during 1831 – 2007 as yellow squares. Modeled pole locations from 1590 to 2020 are circles progressing from blue to yellow. In addition the magnetic field is getting substantially weaker, maybe a breakup is possible having two North Poles and two South Poles. If this occurs, the protection from the cosmic radiation from the Sun will be weakened, causing more clouds and maybe trigger the next ice age.
Then there is the double star KIC 9832227. They are only 1,800 light-years away, an eclipsing binary pair, which means as they revolve around one another, each one briefly blots out the other from the perspective of a viewer on Earth. In 2021 or 2022 we will see them merge into one causing a red supernova. When this happens, because they are so close, we may even observe gravity waves. But from a climate standpoint there will be a burst of cosmic radiation, first the gamma rays coming at the speed of light, then with a slight delay the other cosmic radiation, coming at a time of the solar minimum and an unusually weak earth magnetic field. (Update: It will happen, but not any time soon, it is still maybe hundreds of years away)
This is new territory, and the best we can do is to increase CO2. It will not help much, but CO2 will help rather than hurt.
In any case, we are going to a cooler earth, and it is only a matter of time until we enter another ice age. The good news is, there is still time to develop and switch to Thorium based nuclear power generation when coal and oil are exhausted, and there is unlimited quantities of limestone to degass and make cement to keep the CO2 level up.
The good news is that thanks to increasing CO2 vegetation is increasing, reducing erosion, feeding another 2 billion people without starving, and also the fauna. The benefits flow from industrialized nations to developing nations that cannot afford fertilizers but benefit from the increased CO2. In addition, photo synthesis occur more efficiently, using less water with increasing CO2.