Guest Essay by Willis Eschenbach
Abstract
The Thermostat Hypothesis is that tropical clouds and thunderstorms, along with other emergent phenomena like dust devils, tornadoes, and the El Nino/La Nina alteration, actively regulate the temperature of the earth. This keeps the earth at an equilibrium temperature.
Several kinds of evidence are presented to establish and elucidate the Thermostat Hypothesis – historical temperature stability of the Earth, theoretical considerations, satellite photos, and a description of the equilibrium mechanism.
Historical Stability
The stability of the earth’s temperature over time has been a long-standing climatological puzzle. The globe has maintained a temperature of ± ~ 3% (including ice ages) for at least the last half a billion years during which we can estimate the temperature. During the Holocene, temperatures have not varied by ±1%. And during the glaciation periods, the temperature was generally similarly stable as well.
In contrast to Earth’s temperature stability, solar physics has long indicated (Gough, 1981; Bahcall et al., 2001) that 4 billion years ago the total solar irradiance was about three-quarters of the current value. In early geological times, however, the earth was not correspondingly cooler. Temperature proxies such as deuterium/hydrogen ratios and 16O/18O ratios show no sign of a corresponding warming of the earth over this time. Why didn’t the earth warm as the sun warmed?
This is called the “Faint Early Sun Paradox” (Sagan and Mullen, 1972), and is usually explained by positing an early atmosphere much richer in greenhouse gases than the current atmosphere.
However, this would imply a gradual decrease in GHG forcing which exactly matched the incremental billion-year increase in solar forcing to the present value. This seems highly unlikely.
A much more likely candidate is some natural mechanism that has regulated the earth’s temperature over geological time.
Theoretical Considerations
Bejan (Bejan 2005) has shown that the climate can be robustly modeled as a heat engine, with the ocean and the atmosphere being the working fluids. The tropics are the hot end of the heat engine. Some of that tropical heat is radiated back into space. Work is performed by the working fluids in the course of transporting the rest of that tropical heat to the Poles. There, at the cold end of the heat engine, the heat is radiated into space. Bejan showed that the existence and areal coverage of the Hadley cells is a derivable result of the Constructal Law. He also showed how the temperatures of the flow system are determined.
“We pursue this from the constructal point of view, which is that the [global] circulation itself represents a flow geometry that is the result of the maximization of global performance subject to global constraints.”
“The most power that the composite system could produce is associated with the reversible operation of the power plant. The power output in this limit is proportional to
where q is the total energy flow through the system (tropics to poles), and TH and TL are the high and low temperatures (tropical and polar temperatures in Kelvins).
The system works ceaselessly to maximize that power output. Here is a view of the entire system that transports heat from the tropics to the poles.
Figure 1. The Earth as a Heat Engine. The equatorial Hadley Cells provide the power for the system. Over the tropics, the sun (orange arrows) is strongest because it hits the earth most squarely. The length of the orange arrows shows relative sun strength. Warm dry air descends at about 30N and 30S, forming the great desert belts that circle the globe. Heat is transported by a combination of the ocean and the atmosphere to the poles. At the poles, the heat is radiated to space.
In other words, flow systems such as the Earth’s climate do not assume a stable temperature willy-nilly. They reshape their own flow in such a way as to maximize the energy produced and consumed. It is this dynamic process, and not a simple linear transformation of the details of the atmospheric gas composition, which sets the overall working temperature range of the planet.
Note that the Constructal Law says that any flow system will “quasi-stabilize” in orbit around (but never achieve) some ideal state. In the case of the climate, this is the state of maximum total power production and consumption. And this in turn implies that any watery planet will oscillate around some equilibrium temperature, which is actively maintained by the flow system. See the paper by Ou listed below for further information on the process.
Climate Governing Mechanism
Every heat engine has a throttle. The throttle is the part of the engine that controls how much energy enters the heat engine. A motorcycle has a hand throttle. In an automobile, the throttle is called the gas pedal. It controls incoming energy.
The stability of the earth’s temperature over time (including alternating bi-stable glacial/interglacial periods), as well as theoretical considerations, indicates that this heat engine we call climate must have some kind of governor controlling the throttle.
While all heat engines have a throttle, not all of them have a governor. In a car, a governor is called “Cruise Control”. Cruise control is a governor that controls the throttle (gas pedal). A governor adjusts the energy going to the car engine to maintain a constant speed regardless of changes in internal and external forcing (e.g. hills, winds, engine efficiency, and losses).
We can narrow the candidates for this climate governing mechanism by noting first that a governor controls the throttle (which in turn controls the energy supplied to a heat engine). Second, we note that a successful governor must be able to drive the system beyond the desired result (overshoot).
(Note that a governor, which contains a hysteresis loop capable of producing overshoot, is different from a simple negative feedback of the type generally described by the IPCC. A simple negative feedback can only reduce an increase. It cannot maintain a steady state despite differing forcings, variable loads, and changing losses. Only a governor can do that.)
The majority of the earth’s absorption of heat from the sun takes place in the tropics. The tropics, like the rest of the world, are mostly ocean; and the land that is there is wet. The steamy tropics, in a word. There is little ice there, so the clouds control how much energy enters the climate heat engine.
I propose that two interrelated but separate mechanisms act directly to regulate the earth’s temperature — tropical cumulus and cumulonimbus clouds. Cumulus clouds are the thermally-driven fluffy “cotton ball” clouds that abound near the surface on warm afternoons. Cumulonimbus clouds are thunderstorm clouds, which start life as simple cumulus clouds. Both types of clouds are part of the throttle control, reducing incoming energy. In addition, the cumulonimbus clouds are active refrigeration-cycle heat engines, which provide the necessary overshoot to act as a governor on the system.
A pleasant thought experiment shows how this cloud governor works. It’s called “A Day In the Tropics”.
I live in the deep, moist tropics, at 9°S, with a view of the South Pacific Ocean from my windows. Here’s what a typical day looks like. In fact, it’s a typical summer day everywhere in the Tropics. The weather report goes like this:
Clear and calm at dawn. Light morning winds, clouding up towards noon. In the afternoon, increasing clouds and wind with showers and thundershowers developing as the temperature rises. Thunderstorms continuing after dark, and clearing some time between sunset and early hours of the morning, with progressive clearing and calming until dawn.
That’s the most common daily cycle of tropical weather, common enough to be a cliché around the world.
It is driven by the day/night variations in the strength of the sun’s energy. Before dawn, the atmosphere is typically calm and clear. As the ocean (or moist land) heats up, air temperature and evaporation increase. Warm moist air starts to rise. Soon the rising moist air cools and condenses into clouds. The clouds reflect the sunlight. That’s the first step of climate regulation. Increased temperature leads to clouds. The clouds close the throttle slightly, reducing the energy entering the system. They start cooling things down. This is the negative feedback part of the cloud climate control.
The tropical sun is strong, and despite the negative feedback from the cumulus clouds, the day continues to heat up. The more the sun hits the ocean, the more warm, moist air is formed, and the more cumulus clouds form. This, of course, reflects more sun, and the throttle closes a bit more. But the day continues to warm.
The full development of the cumulus clouds sets the stage for the second part of temperature regulation. This is not simply negative feedback. It is the climate governing system. As the temperature continues to rise, as the evaporation climbs, some of the fluffy cumulus clouds suddenly transform themselves. They rapidly extend skywards, quickly thrusting up to form cloud pillars thousands of meters high. In this way, cumulus clouds are transformed into cumulonimbus or thunderstorm clouds.
The columnar body of the thunderstorm acts as a huge vertical heat pipe. The thunderstorm sucks up warm, moist air at the surface and shoots it skyward. At altitude the water condenses, transforming the latent heat into sensible heat. The air is rewarmed by this release of sensible heat and continues to rise within the thunderstorm tower.
At the top, the rising much dryer air is released from the cloud up high, way above most of the CO2, water vapor, and other greenhouse gases. In that rarified atmosphere, the air is much freer to radiate to space. By moving inside the thunderstorm heat pipe, the rising air bypasses any interaction with most greenhouse gases and comes out near the top of the troposphere. During the transport aloft, there is no radiative or turbulent interaction between the rising air inside the tower and the surrounding lower and middle troposphere. Inside the thunderstorm, the rising air is tunneled through most of the troposphere to emerge at the top.
In addition to reflecting sunlight from their top surface as cumulus clouds do, and transporting heat to the upper troposphere where it radiates easily to space, thunderstorms cool the surface in a variety of other ways, particularly over the ocean.
1. Wind driven evaporative cooling. Once the thunderstorm starts, it creates its own wind around the base. This self-generated wind increases evaporation in several ways, particularly over the ocean.
a) Evaporation rises linearly with wind speed. At a typical squall wind speed of 10 meters per second (“m/s”, about 20 knots or 17 miles per hour), evaporation is about ten times greater than at “calm” conditions (conventionally taken as 1 m/s).
b) The wind increases evaporation by creating spray and foam, and by blowing water off of trees and leaves. These greatly increase the evaporative surface area, because the total surface area of the millions of droplets is evaporating as well as the actual surface itself.
c) To a lesser extent, the surface area is also increased by wind-created waves (a wavy surface has a larger evaporative area than a flat surface).
d) Wind-created waves in turn greatly increase turbulence in the atmospheric boundary layer. This increases evaporation by mixing dry air down to the surface and moist air upwards.
e) As spray rapidly warms to air temperature, which in the tropics can be warmer than ocean temperature, evaporation also rises above the sea surface evaporation rate.
2. Wind and wave driven albedo increase. The white spray, foam, spindrift, changing angles of incidence, and white breaking wave tops greatly increase the albedo of the sea surface. This reduces the energy absorbed by the ocean.
3. Cold rain and cold wind. As the moist air rises inside the thunderstorm’s heat pipe, water condenses and falls. Since the water is originating from condensing or freezing temperatures aloft, it cools the lower atmosphere it falls through, and it cools the surface when it hits. Also, the droplets are being cooled as they fall by evaporation.
In addition, the falling rain entrains a cold wind. This cold wind blows radially outwards from the center of the falling rain, cooling the surrounding area. This is quite visible in the video below.
4. Increased reflective area. White fluffy cumulus clouds are not very tall, so basically they only reflect from the tops. On the other hand, the vertical pipe of the thunderstorm reflects sunlight along its entire length. This means that thunderstorms reflect sunlight from an area of the ocean out of proportion to their footprint, particularly in the late afternoon.
5. Modification of upper tropospheric ice crystal cloud amounts (Lindzen 2001, Spencer 2007). These clouds form from the tiny ice particles that come out of the smokestack of the thunderstorm heat engines. It appears that the regulation of these clouds has a large effect, as they are thought to warm (through IR absorption) more than they cool (through reflection).
6. Enhanced night-time radiation. Unlike long-lived stratus clouds, cumulus and cumulonimbus often die out and vanish in the early morning hours, leading to the typically clear skies at dawn. This allows greatly increased nighttime surface radiative cooling to space.
7. Delivery of dry air to the surface. The air being sucked from the surface and lifted to altitude is counterbalanced by a descending flow of replacement air emitted from the top of the thunderstorm. This descending air has had the majority of the water vapor stripped out of it inside the thunderstorm, so it is relatively dry. The dryer the air, the more moisture it can pick up for the next trip to the sky. This increases the evaporative cooling of the surface.
8. Increased radiation through descending dry air. The descending dry air mentioned above is far more transparent to surface radiation than normal moist tropical air. This increases overall radiation to space.
In part because they utilize such a wide range of cooling mechanisms, cumulus clouds and thunderstorms are extremely good at cooling the surface of the earth. Together, they form the governing mechanism for the tropical temperature.
But where is that mechanism?
The problem with my thought experiment of describing a typical tropical day is that it is always changing. The temperature goes up and down, the clouds rise and fall, day changes to night, the seasons come and go. Where in all of that unending change is the governing mechanism? If everything is always changing, what keeps it the same month to month and year to year? If conditions are always different, what keeps it from going off the rails?
In order to see the governor at work, we need a different point of view. We need a point of view without time. We need a timeless view without seasons, a point of view with no days and nights. And curiously, in this thought experiment called “A Day In the Tropics”, there is such a timeless point of view, where not only is there no day and night, but where it’s always summer.
The point of view without day or night, the point of view from which we can see the climate governor at work, is the point of view of the sun. Imagine that you are looking at the earth from the sun. From the sun’s point of view, there is no day and night. All parts of the visible face of the earth are always in sunlight—the sun never sees the nighttime. And it’s always summer under the sun.
If we accept the convenience that the north is up, then as we face the earth from the sun, the visible surface of the earth is moving from left to right as the planet rotates. So the left-hand edge of the visible face is always at sunrise, and the right-hand edge is always at sunset. Noon is a vertical line down the middle. From this timeless point of view, morning is always and forever on the left, and afternoon is always on the right. In short, by shifting our point of view, we have traded time coordinates for space coordinates. This shift makes it easy to see how the governor works.
The tropics stretch from left to right across the circular visible face. We see that near the left end of the tropics, after sunrise, there are very few clouds. Clouds increase as you look further to the right. Around the noon line, there are already cumulus. And as we look from left to right across the right side of the visible face of the earth, towards the afternoon, more and more cumulus clouds and increasing numbers of thunderstorms cover a large amount of the tropics.
It is as though there is a graduated mirror shade over the tropics, with the fewest cloud mirrors on the left, slowly increasing to extensive cloud mirrors and thunderstorm coverage on the right.
After coming up with this hypothesis that as seen from the sun, the right-hand side of the deep tropical Pacific Ocean would have more clouds than the left-hand side), I thought “Hey, that’s a testable proposition to support or demolish my hypothesis”. So in order to investigate whether this postulated increase in clouds on the right-hand side of the Pacific actually existed, I took an average of 24 pictures of the Pacific Ocean taken at local noon on the 1st and 15th of each month over an entire year. I then calculated the average change in albedo and thus the average change in forcing at each time. Here is the result:
Figure 2. Average of one year of GOES-West weather satellite images taken at satellite local noon. The Intertropical Convergence Zone is the bright band in the yellow rectangle. Local time on earth is shown by black lines on the image. Time values are shown at the bottom of the attached graph. The red line on the graph is the solar forcing anomaly (in watts per square meter) in the area outlined in yellow. The black line is the albedo value in the area outlined in yellow.
The graph below the image of the earth shows the albedo and solar forcing in the yellow rectangle which contains the Inter-Tropical Convergence Zone. Note the sharp increase in the albedo between 10:00 and 11:30. You are looking at the mechanism that keeps the earth from overheating. It causes a change in insolation of -60 W/m2 between ten and noon.
Now, consider what happens if for some reason the surface of the tropics is a bit cool. The sun takes longer to heat up the surface. Evaporation doesn’t rise until later in the day. Clouds are slow to appear. The first thunderstorms form later, fewer thunderstorms form, and if it’s not warm enough those giant surface-cooling heat engines don’t form at all.
And from the point of view of the sun, the entire mirrored shade shifts to the right, letting more sunshine through for longer. The 60 W/m2 reduction in solar forcing doesn’t take place until later in the day, increasing the local insolation.
When the tropical surface gets a bit warmer than usual, the mirrored shade gets pulled to the left, and clouds form earlier. Hot afternoons drive thunderstorm formation, which cools and air conditions the surface. In this fashion, a self-adjusting cooling shade of thunderstorms and clouds keeps the afternoon temperature within a narrow range.
Now, some scientists have claimed that clouds have a positive feedback. Because of this, the areas where there are more clouds will end up warmer than areas with fewer clouds. This positive feedback is seen as the reason that clouds and warmth are correlated.
I and others take the opposite view of that correlation. I hold that the clouds are caused by the warmth, not that the warmth is caused by the clouds.
Fortunately, we have way to determine whether changes in the reflective tropical umbrella of clouds and thunderstorms are caused by (and thus limiting) overall temperature rise, or whether an increase in clouds is causing the overall temperature rise. This is to look at the change in albedo with the change in temperature. Here are two views of the tropical albedo, taken six months apart. August is the warmest month in the Northern Hemisphere. As indicated, the sun is in the North. Note the high albedo (areas of light blue) in all of North Africa, China, and the northern part of South America and Central America. By contrast, there is low albedo in Brazil, Southern Africa, and Indonesia/Australia.
Figure 3. Monthly Average Albedo. Timing is half a year apart. August is the height of summer in the Northern Hemisphere. February is the height of summer in the Southern Hemisphere. Light blue areas are the most reflective (greatest albedo)
In February, on the other hand, the sun is in the South. The albedo situation is reversed. Brazil and Southern Africa and Australasia are warm under the sun. In response to the heat, clouds form, and those areas now have a high albedo. By contrast, the north now has a low albedo, with the exception of the reflective Sahara and Rub Al Khali Deserts.
Clearly, the cloud albedo (from cumulus and cumulonimbus) follows the sun north and south, keeping the earth from overheating. This shows quite definitively that rather than the warmth being caused by the clouds, the clouds are caused by the warmth.
Quite separately, these images show in a different way that warmth drives cloud formation. We know that during the summer, the land warms more than the ocean. If temperature is driving the cloud formation, we would expect to see a greater change in the albedo over land than over the ocean. And this is clearly the case. We see in the North Pacific and the Indian Ocean that the sun increases the albedo over the ocean, particularly where the ocean is shallow. But the changes in the land are in general much larger than the changes over the ocean. Again this shows that the clouds are forming in response to, and are therefore limiting, increasing warmth.
How the Governor Works
Tropical cumulus production and thunderstorm production are driven by air density. Air density is a function of temperature (affecting density directly) and evaporation (water vapor is lighter than air).
A thunderstorm is both a self-generating and self-sustaining heat engine. The working fluids are moisture-laden warm air and liquid water. Self-generating means that whenever it gets hot enough over the tropical ocean, which is almost every day, at a certain level of temperature and humidity, some of the fluffy cumulus clouds suddenly start changing. The tops of the clouds streak upwards, showing the rising progress of the warm surface air. At altitude, the rising air exits the cloud, replace by more air from below. Suddenly, in place of a placid cloud, there is an active thunderstorm.
“Self-generating” means that thunderstorms arise spontaneously as a function of temperature and evaporation. They are what is called an “emergent” phenomenon, meaning that they emerge from th background when certain conditions are met. In the case of thunderstorms, this generally comes down to the passing of a temperature threshold.
Above the temperature threshold necessary to create the first thunderstorm, the number of thunderstorms rises rapidly. This rapid increase in thunderstorms limits the amount of temperature rise possible.
“Self-sustaining” means that once a thunderstorm gets going, it no longer requires the full initiation temperature necessary to get it started. This is because the self-generated wind at the base, plus dry air falling from above, combine to drive the evaporation rate way up. The thunderstorm is driven by air density. It requires a source of light air. The density of the air is determined by both temperature and moisture content (because curiously, water vapor at molecular weight 16 is only a bit more than half as heavy as air, which has a weight of about 29). So moist air is light air.
Evaporation is not a function of temperature alone. It is governed a complex mix of wind speed, water temperature, and vapor pressure. Evaporation is calculated by what is called a “bulk formula”, which means a formula based on experience rather than theory. One commonly used formula is:
E = VK(es – ea)
where
E = evaporation
V= wind speed (function of temperature difference [∆T])
K = coefficient constant
es = vapor pressure at evaporating surface (function of water temperature in degrees K to the fourth power)
ea = vapor pressure of overlying air (function of relative humidity and air temperature in degrees K to the fourth power)
The critical thing to notice in the formula is that evaporation varies linearly with wind speed. This means that evaporation near a thunderstorm can be an order of magnitude greater than evaporation a short distance away.
In addition to the changes in evaporation, there at least one other mechanism increasing cloud formation as wind increases. This is the wind-driven production of airborne salt crystals. The breaking of wind-driven waves produces these microscopic crystals of salt. The connection to the clouds is that these crystals are the main condensation nuclei for clouds that form over the ocean. The production of additional condensation nuclei, coupled with increased evaporation, leads to larger and faster changes in cloud production with increasing temperature.
Increased wind-driven evaporation means that to get the same air density, the surface temperature can be lower than the temperature required to initiate the thunderstorm. This means that the thunderstorm will still survive and continue cooling the surface to well below the starting temperature.
This ability to drive the temperature lower than the starting point is what distinguishes a governor from a negative feedback. A thunderstorm can do more than just reduce the amount of surface warming. It can actually mechanically cool the surface to below the required initiation temperature. This allows it to actively maintain a fixed temperature in the region surrounding the thunderstorm.
A key feature of this method of control (changing incoming power levels, performing work, and increasing thermal losses to quelch rising temperatures) is that the equilibrium temperature is not governed by changes in the amount of losses or changes in the forcings in the system. The equilibrium temperature is set by the response of wind and water and cloud to increasing temperature, not by the inherent efficiency of or the inputs to the system.
In addition, the equilibrium temperature is not affected much by changes in the strength of the solar irradiation. If the sun gets weaker, evaporation decreases, which decreases clouds, which increases the available sun. This is the likely answer the long-standing question of how the earth’s temperature has stayed stable over geological times, during which time the strength of the sun has increased markedly.
Gradual Equilibrium Variation and Drift
If the Thermostat Hypothesis is correct and the earth does have an actively maintained equilibrium temperature, what causes the slow drifts and other changes in the equilibrium temperature seen in both historical and geological times?
As shown by Bejan, one determinant of running temperature is how efficient the whole global heat engine is in moving the terawatts of energy from the tropics to the poles. On a geological time scale, the location, orientation, and elevation of the continental land masses is obviously a huge determinant in this regard. That’s what makes Antarctica different from the Arctic today. The lack of a land mass in the Arctic means warm water circulates under the ice. In Antarctica, the cold goes to the bone …
In addition, the oceanic geography which shapes the currents carrying warm tropical water to the poles and returning cold water (eventually) to the tropics is also a very large determinant of the running temperature of the global climate heat engine.
In the shorter term, there could be slow changes in the albedo. The albedo is a function of wind speed, evaporation, cloud dynamics, and (to a lesser degree) snow and ice. Evaporation rates are fixed by thermodynamic laws, which leave only wind speed, cloud dynamics, and snow and ice able to affect the equilibrium.
The variation in the equilibrium temperature may, for example, be the result of a change in the worldwide average wind speed. Wind speed is coupled to the ocean through the action of waves, and long-term variations in the coupled ocean-atmospheric momentum occur. These changes in wind speed may vary the equilibrium temperature in a cyclical fashion.
Or it may be related to a general change in color, type, or extent of either the clouds or the snow and ice. The albedo is dependent on the color of the reflecting substance. If reflections are changed for any reason, the equilibrium temperature could be affected. For snow and ice, this could be e.g. increased melting due to black carbon deposition on the surface. For clouds, this could be a color change due to aerosols or dust.
Finally, the equilibrium variations may relate to the sun. The variation in magnetic and charged particle numbers may be large enough to make a difference. There are strong suggestions that cloud cover is influenced by the 22-year solar Hale magnetic cycle, and this 14-year record only covers part of a single Hale cycle. However, I have yet to find any significant evidence of this effect on any surface weather variables, including clouds.
Conclusions and Musings
1. The sun puts out more than enough energy to totally roast the earth. It is kept from doing so by the clouds reflecting about a third of the sun’s energy back to space. As near as we can tell, over billions of years, this system of increasing cloud formation to limit temperature rises has never failed.
2. This reflective shield of clouds forms in the tropics in response to increasing temperature.
3. As tropical temperatures continue to rise, the reflective shield is assisted by the formation of independent heat engines called thunderstorms. These cool the surface in a host of ways, move heat aloft, and convert heat to work.
4. Like cumulus clouds, thunderstorms also form in response to increasing temperature.
5. Because they are temperature driven, as tropical temperatures rise, tropical thunderstorms and cumulus production increase. These combine to regulate and limit the temperature rise. When tropical temperatures are cool, tropical skies clear and the earth rapidly warms. But when the tropics heat up, cumulus and cumulonimbus put a limit on the warming. This system keeps the earth within a fairly narrow band of temperatures (e.g., a change of only 0.7°C over the entire 20th Century).
6. The earth’s temperature regulation system is based on the unchanging physics of wind, water, and cloud.
7. This is a reasonable explanation for how the temperature of the earth has stayed so stable (or more recently, bi-stable as glacial and interglacial) for hundreds of millions of years.
Further Reading
Bejan, A, and Reis, A. H., 2005, Thermodynamic optimization of global circulation and climate, Int. J. Energy Res.; 29:303–316. Available online here.
Richard S. Lindzen, Ming-Dah Chou, and A. Y. Hou, 2001, Does the Earth Have an Adaptive Infrared Iris?, doi: 10.1175/1520-0477(2001)082<0417:DTEHAA>2.3.CO;2, Bulletin of the American Meteorological Society: Vol. 82, No. 3, pp. 417–432. Available online here.
Ou, Hsien-Wang, Possible Bounds on the Earth’s Surface Temperature: From the Perspective of a Conceptual Global-Mean Model, Journal of Climate, Vol. 14, 1 July 2001. Available online here (pdf).
the article is a great one – am i wrong but is the concept[s] supporting this article similar to Dr. Lindgren’s “Iris” hypothesis??
quick question – in the formation of cumulonimbus systems isn’t the existance of a significant temperature difference between the upper and lower troposhere also a critical factor?
in AGW theory – the upper troposhere is supposed to warm more than the lower Trop. – if this were to happen then shouldn’t there have been by now some noticeable decline in cumulonimbus systems over time? – so my question to you Willis is – have you noticed any such declines? thanks again
So the AGW fear mongers are screaming over estimated changes of 1.6 to 4 W/m^2, and the thermostat is presently causing changes of -60 W/m^2 due to only albedo changes. And the umpteen AGW scientists hadn’t found, reported, and incorporated -60 W in their models? Shameful.
Oh, I’m sure the climate models have some interesting albedo parameters, but surely they haven’t included this behavior despite many people staring at satellite images or else we’d have heard of it from the modeling magicians.
DJ (03:18:27) :
Just when might this thermostat kick in? It’s been an extraordinary hot May at the planets surface and that is post La Nina (http://data.giss.nasa.gov/gistemp/). We will almost certainly see the largest positive monthly temperature anomaly every observed by man at the earth’s surface in the coming months.
It’s not going to be a pretty sight next year as we go post El Nino and have a warming sun. Watch for a big step up in sea level, a sharp decline in sea ice, and the hottest year on record.
Yep, just wait ’til next year. Or the year after that. You sound like a Cubs fan. Are you a Cubs fan?
It really doesn’t matter whether it’s hot or cold. It’s the cause that’s the question. By now, you should know the Hansen/Gore/IPCC man-made climate change through greenhouse gas emissions hypothesis is full of holes you could float an iceberg through. It’s been completely invalidated by the observed real climate.
BTW: Did you miss the NASA announcement about the low 2007 summer Arctic ice melt being caused not be heat but by winds blowing the ice flows out into warmer waters?
This “governor” works whether the Sun has gone up the H-R diagram, or down.
Takes care of the tropics, but what about the rest of the planet?
If the tropical temperature is regulated, that would mean there isn’t much heat excess to be diverted poleward to prevent ice ages.
So, if there is a limit to the governor’s ability to handle more than X% incoming/outgoing, then whatever is left over or defecit is available/not available to moderate the rest of the planet.
In that case, a limited governor has a range of 100% effectiveness.
It can be overrun/starved.
What would be it’s range?
So assuming that the CLOUD experiments come back validating the GCR theory (And Svensmark’s theory is very strong in my opinion) would that make GCR’s the governor of the governor?
I loved this piece it was clear enough for a “Block-head” layman like me to understand
O/T
If you think AGW is questionable try this for stretching the credulity.
http://www.telegraph.co.uk/news/newstopics/howaboutthat/5540634/Phoenix-crop-circle-may-predict-end-of-the-world.html
The fact that the earth is colder now than it was during the age of the dinosaurs, despite the sun warming up in between, emphasises my point that what happens to temperature on the earth is far more influenced by what is happening with the earth than what is happening with the sun.
Graphs showing CO2 and temperature changes also indicate a clear link between the levels of CO2 and temperature, no matter what nitpickers may say.
http://www.ccs.neu.edu/home/gene/peakoil/co2-400k-years.gif
The same day this terrific piece appears on WUWT, this drivel, by a Left Coast crackpot named Jamias Cascio, appears in the Wall Street Journal:
“It’s Time to Cool the Planet”
“Cutting greenhouse gases is no longer enough to deal with global warming, says Jamais Cascio. He argues that we also have to do something more direct—and risky.”
http://online.wsj.com/article/SB10001424052970204771304574181522575503150.html
rcrejects: Your link didn’t work. This one should:
http://rcrejects.wordpress.com/2009/06/15/gavin-schmidt-and-michael-mann-caught-being-economical-with-the-truth/
Nice to see them get caught exaggerating.
I particularly like Fig 2
You are looking at the mechanism that keeps the earth from overheating. It causes a change in insolation of -60 W/m2 between ten and noon.
I think that it illustrates well that the way climatologists have been looking at climate is analogous to as if car engine designers took the average temperature of the whole car and calculated anomalies for the total. The conclusion would be that there would be little energy coming out.
In a similar way, by homogenizing the whole earth as far as all inputs and outputs go, it is inevitable that the heat engine analogy has been lost in the GCMs.
What is important is that there is not only a change in insolation of 60 W/m2 between ten and noon, there is an anomaly of 1200W/m2 between day and night in that swath. Now, going to insolation, a 0.1% change in insolation from minimum to maximum of the solar cycle is 12W/m2, and the question of how much more/less evaporation etc results from this difference may not be trivial, particularly if most of the ocean heating comes from the ultraviole, which varies much more than that.
Another analogy: we boil water in a pan and take the anomaly ( before/after) of the average temperature of everything in the kitchen. Would you predict from that anomaly that the water would boil?
Thanks Willis!
I note that some comments view this post as a new idea, but there is nothing in it that hasn’t been understood for a long time. That is why so many operational meteorologists and traditional climatologists have been skeptics of an AGW crisis for decades.
Bill talks about the warming influence of nighttime clouds. Others have mentioned this as well. Nighttime clouds are rare in the tropics and that is were the majority of the solar heating takes place. Slight changes in the amount of nighttime clouds at higher latitudes is a small factor compared to slight changes in daytime cumulus development in the tropics. It may make a big difference in England, but not in the global temperature scheme.
Willis also pointed out that evaporation has a linear relationship with the wind. Global wind is driven primarily by the temperature difference between the equator and the poles. The AGW theory predicts that the poles will warm more than the tropics. The net result would be an overall reduction in the global wind and, consequently, a reduction in evaporation, particularly in the mid latitudes where the wind is primarily the result of the global temperature difference. Water vapor, by far the most important greenhouse gas, would be reduced, resulting in cooling at these latitudes, offsetting the warming produced by CO2.
Everywhere we look, the potential warming effect of increasing CO2 is thwarted by the Earth’s natural systems.
So what has caused the recent, minor fluctuations in global climate. Stephen Wilde hits the nail on the head several posts up. It’s the ocean and solar cycles, obviously! Now what is missing from every single GCM? The ocean and solar cycles.
Thanks Stephen!
This is what Roy Spencer has been talking about from the point of view of the cloud only explained from the point of view of the sun. The sun has a better vantage point, before it was hard to see the heat pump/shield regulator system for the clouds.
Thank you Mr. Willis Eschenbach.
A very clear explanation of the convective system with a focus on the tropics.
However, there is much more to it.
The convective system (causing cooling) also works without forming clouds.
When a desert heats up for example, huge airmasses are heated up and transported into high altitudes where they cool down.
Because there are no clouds this process continues all day around.
I read a story of some soaring pilots who flew their gliders in the Gobi Desert.
They needed oxygen to maintain their flight as their gliders were carried up to altitudes above 6.000 meters in thermals that allowed climbing speeds of 20 meteres per second.
At high altitude they needed electric foot warmers to prevent their feet from freezing as their faces were burned by the sun coming through the perspex canopy measuring anoutside temperature of minus 40 degree Celsius.
This convective process works continuous and constantly as long as the sun shines.
At night, with clear skies the heat absorbed by the sand and rock is radiated into space causing temperatures to drop far below 0 degree Celcius.
This cooling proces is very rapid and causes the rocks to crack.
It is one of the major forces responsible for corrosion.
At night in the desert you can hear the rocks crack with big bangs, like gun shots.
The convective process in the deserts are the major source of fine dust, the nuclea that make condensation into clouds possible.
At the tropics approx. 30% of the condensation nuclea are small particles from bio material, from spider eggs to flower pollen.
In Europe where fine dust is measured for many years now it is found that 60% of the finedust captured in the big cities comes from the Sahara desert.
Only a relativ small part is caused by the tire wear, brakes and exhaust emissions from cars and industry.
Because of the spin of the earth wind and ocean patterns are formed (coreolis forces) Pressure differences cause air masses flowing from area’s with high pressure to area’s with low pressure. This is the cause why air masses from homogenic source area’s are transported and collide with eachother.
Look at the weather maps and see the Low pressure area’s move and fronts collide. When a warm air mass collides with a colder airmass, the entire boudary is lifted causing convection and cooldown.
A cold front comes with intense vertical cloud building along the entire front often followed by clear skies and large fields of cumulus clouds.
A warm front comes with, (cirro stratus, alto stratus) low and medium altitude clouds causing rain over a huge area.
Just to make my point, there is much more to the earth’s heat engine than meets the eye.
Our sun sends in the equivelent of all the enery we use world wide in less than 30 minutes of time. Our contribution has ample effect on the earth’s heat engine and so does CO2.
To proof any warming effect caused by CO2 is as futile as proofing how much solar energy is transformed into sound from cracking rocks in the desert to wind blowing through the trees.
Thanks.
Nicely done!
A very well stated description of the effect of thunderstorms and other convective clouds on the earths temperature. I have lived in a strong thunderstorm environment here on the high plains of Colorado all my life, and in the last couple decades done severe storm spotting.
It is intuitively obvious to anyone who experiences these thunderstorms on a regular basis how much heat they can transport, and how effective they are as thermostats. It is not unusual for temperatures to drop by 30+ degrees F in a matter of 30-90 minutes. You go from sweltering in direct sun to shivering in cold rain in a matter of minutes. The cooling is strong enough to effect the entire eastern half of the state of Colorado for the rest of the day. As mentioned in the article, the skies invariably clear near sunset and you have brilliant clear sky and cool temps in the evening.
Another analogy to the thunderstorm as a heat control mechanism, would be a pan of water slowly heated. As it nears the boiling point, the steam bubbles “turn on” a very powerful heat transport system when you reach the boiling point. In spite of increased heat input they vigorously cool the water due to the boiling.
The thunderstorm is like that rising column of steam in the boiling water is just another convective process that “turns on” suddenly when conditions are right, and once started is a very powerful heat transport system carrying heat energy to very high altitudes.
From the storm spotters point of view, you watch the development of thunderstorms with a more microclimate point of view.
In the mid day near noon the sun will be intense, sky is clear and humidity rises along with temperatures as the suns radiant energy warms the soil and drives water vapor into the air. This is like charging a battery, you are storing solar energy in the latent heat of evaporation of the water.
In the early afternoon, when conditions are favorable for convection, you will begin to see small pop corn cumulus clouds start to form. To the average person they seem to be more or less constant, but as a storm spotter you are watching the clouds more closely than most, and notice that many of them are “bubbling” they grow briefly then they deflate, grow briefly then deflate. On some days it never goes beyond this situation. I attribute that effect to the increased shading and increased reflection of solar energy being sufficient to hold the atmosphere below the temperature necessary to “break the cap” and start active convection.
In an atmosphere that favors large thunderstorm development, you have a very specific temperature/density profile where a lower layer of warm moist air, once it reaches a critical density (temperature and humidity) suddenly bursts through the upper air layers which are cooler and dryer. If the profile is correct this results in sudden dynamic (and almost explosive) growth of the convection column.
At that point, it is as if you have flipped a switch. A small parcel of warm most air that is for what ever reason lifted above some critical altitude, ( see lfc Level of free convection, and lcl lifting condensation level), and starts to condense moisture. As the humidity condenses to water droplets, it releases that stored latent heat of evaporation/condensation warming the parcel of air up. Due to the warming the parcel is even lower density than it was before, and even more buoyant so it rises faster and condenses more humidity. This is the “heat engine” part of the process. Stored solar energy in the form of latent heat of the water vapor, is now actively pushing warm moist air to rise due to buoyancy.
This can form updraft columns of air thousands of feet across, rising at well over 100 mph. Updraft speeds can get high enough to hold a 2.5 inch diameter ball of ice aloft forming very large hail.
It is a humbling experience to watch one of these explosive thunder cells grow. Some of them rise so rapidly that you literally have to slowly lean your head back to watch the top of the thunderstorm convection column rise at rates of 100-200 mph.
Typical updraft speeds are high enough (peak velocities estimated as up to 100 meters/second) that over shooting tops of severe thunderstorms can punch up above the tropopause into the stratosphere by as much as 1-3 kilometers and occasionally to 5 km into the stratosphere.
(Source for peak updraft velocities – Thunderstorm Morphology and Dynamics Edwin Kessler pp 136)
This means that your water vapor has now been lifted to elevations of as high as 85,000 ft in the tropics and 55,000- 65,000 ft in temperate regions. This completely bypasses the radiant heat transfer process in the lower dense atmosphere by physically moving millions to tons of water and warm air to very high altitudes, where it quickly losses heat to space and freezes out to ice crystals, giving up even more heat as the latent heat of fusion is released.
It is hard for people to comprehend the vast amounts of energy transported by this process, but the energy content of the moisture lifted by a thunderstorm is stunning.
Water load carried to high altitude varies strongly with the updraft speed. For low updraft speeds of about 2.5 m/s about 80% of the moisture condensed falls as precipitation. This amounts to about 30% of the total moisture in the air.
With updrafts of about 10 m/s only about 53% of the moisture condensed reaches the ground as precipitation. As a result you have a dynamic process that moves more or less heat to high altitude depending on the heat surplus in the lower atmosphere. To use the analogy of a throttle, the hotter and wetter the lower atmosphere (higher instability conditions) the more water the storm can carry to high altitude due to its higher updraft speeds. In the higher updraft case, more heat is carried to high altitude, but also more water is carried outside the updraft column to evaporate and cool the surrounding air. This causes significant mass cooling of the local air even though much of the condensed water never makes it back to the ground as precipitation. This cooling generates strong cold outflow winds which in many cases serve as triggers for lifting and development of additional thunderstorms.
Here in the high plains you can watch these cold out flow boundaries run for hundreds of miles on Doppler radar and kick off hundreds of other thunderstorms. Sometime you can even see the out flow boundary bounce off the mountains near Denver and then sweep back out across the plains triggering a second wave of storm development later in the evening.
Thunderstorm development is a case of tipping points! Once you reach critical conditions of instability, a very small nudge can “turn on” the convective process, and set off massive heat transport to high altitudes. At lower instability levels the atmosphere will hover close to the turn on point but never release that stored energy in the form of convection and lifting to high altitudes.
(Thunderstorm Morphology and Dynamics Edwin Kessler pp 307)
In short you have a dynamic system that the more heat induced instability is generated by heating and high humidity, the stronger the storms become and the more efficient they become and carrying large amounts of heat to very high altitudes.
In this case the one true “tipping Point” of the global heat system is the one that the AGW folks consistently ignore or dismiss as trivial, only to fabricate a hypothetical tipping point that they cannot prove exists to support their hypothesis.
Larry
Thank you Willis for this clear and concise view of homeostasis and Earth’s climate. As IW (05:33:13) notes, the mathematics are found universally in all manner of systems, from the microbiological to the cosmic.
That an elegant balancing system may be the real mechanism of climate and not man’s insignificant contribution to a trace gas, tells us much about the competing, heavily funded AGW theory. In light of nature’s magnificent governance, AGW must begin with the premise that man is… bad. And that he, unlike other natural systems, is incapable of self-governance. Therefore his behavior must be controlled by external forces – forces rejecting man’s deserved place in the natural world – forces steeped in misanthropy and a fundamental need for control.
Could human intervention destroy the natural elegance? Absolutely. Tinkering with fission-based weapons and territorial conflict can do this in an instant. Does human nature need guidance in achieving natural balance within its species? Yes. Should that guidance come in the guise of cataclysmic climate change and forced political manipulation? No, because it is false and proof thereof destroys the credibility of its proponents and their entire agenda.
Most likely a better approach to evolutionary guidance would be to do what Willis has done in this post. That is, suggest to people the beautiful, tempered complexity of a great natural system. And remind them that they too, are naturally capable of this same elegant balance. What better schoolyard than a life-affirming planetary system – to teach life-affirming, enlightened behavior?
“Lindsay H (05:01:54) :
Mike Lorrey (02:51:36) :
One thing this post leaves out is the important part that life has played in sequestering most of the early terran atmosphere in limestone deposits. Earth’s atmosphere was, at one point, 52 times more dense than today, with a large CO2 component.
interesting
can you give a reference for the 52 times more dense quote ??”
Martyn J Fogg, “Terraforming: Engineering Terrestrial Environments”
Yes Dennis, those graphs clearly show hundreds of years time-lag between changes in temperatures and changes in CO2 levels. Except the temperature increases come first.
How can the future effect the past? First it warms, then CO2 goes up. How can increased CO2 cause the increase in temps? Is this some type of quantum-temporal paradox?
And what about the times when temps and CO2 show no correlation? Are you saying that sometimes future CO2 levels causes past warming, but sometimes it doesn’t?
That reminds me of the last episode of Star Trek, the Next Generation where Picard caused some anomaly that gets bigger in the past until it prevents life on Earth from ever evolving. Wow!
The morning begins at some initial temperature that is mainly controlled by the ocean surface temperature.
The daily cycle loads the air with energy. This energy is then transported away by the Hadley cell and by Thunderstorm formation.
What about a simple model based upon a number of Hadley cells as isentropic heat engines that are linked? This should be simple to do.
Good article but you lost me at this point.
“Now, some scientists have claimed that clouds have a positive feedback. Because of this, the areas where there are more clouds will end up warmer than areas with less clouds.”
I don’t know where you’re getting this, I thought it was widely accepted that low to mid altitude clouds cool.
Leif Svalgaard (06:22:30) :
DocWat (03:55:01) :
moving the earth away from the sun and partially compensating for the increase in solar output… any astronomers out there got comments?
The collision happened so early in the Earth’s history that what happened before does not matter. At the time the Earth and Moon finally reassembled from the debris after the impact, the Sun was 30% less luminous and has slowly increased since.
It’s supposed the collision happened 35-110 Ma after the solar system started. This means that the Sun has had about 4.69 x 10^9 billion years to reach the current luminosity. The Sun is about halfway of its lifespan, which is about 10 billion years {τ = [0.1 (0.007) (M c2)] / L = 3.3 x 10^17 s = 10.6 billion years} (the small upper dot is for “solar”).
By the way, I was taught since kindergarten by professor Melly that the oceans act like giant thermostats. Of course, she didn’t use the word “thermostat” for teaching very basic climatology to her young students. It’s not a hypothesis, but an observation of a natural phenomenon. Congratulations for this descriptive essay, Willis!
Correction: the Sun has had about 4.69 x 10^9 billion years; erase that shaming figure!!! Sorry… 🙂
dennis ward (08:54:04) :
Graphs showing CO2 and temperature changes also indicate a clear link between the levels of CO2 and temperature, no matter what nitpickers may say.
I suggest you dig a little deeper, dennis ward. If you do, you’ll notice what the nitpickers actually say: in your little graph, temperature precedes CO2, by 800 years on average. Now, using your obvious infinite wisdom, you need to march over to some website that provides a good definition of causality (cause and effect) and understand what the implications are. Note, too, that such a relationship alone cannot provide any direct evidence of the true cause, i.e., this does not rule out the sun as the causative agent (even if other evidence does).
Mark
DJ (03:18:27) :
“Just when might this thermostat kick in? It’s been an extraordinary hot May at the planets surface and that is post La Nina (http://data.giss.nasa.gov/gistemp/). ”
Hey, I actually followed the link. Wow, I would be worried too if the only input I had on climate issues was this GISS page!
2005 and 2007 are the warmest years on record? amazing…
Depends on which part of the planet you’re on. Here in the US Pacific Northwest it’s still unseasonably cool. We’re barely getting into the mid 70s on sunny days, more often only the mid 60s (because the clouds are sticking around).
We had three hot days in June, that’s it.
Global Warming ain’t global.
The Earth’s Radiation Energy Balance
http://cimss.ssec.wisc.edu/wxwise/homerbe.html
Some excellent animations and information
“The solar and terrestrial properties of clouds have offsetting effects in terms of the energy balance of the planet. In the longwave, clouds generally reduce the radiation emission to space and thus result in a heating of the planet. While in the solar (or shortwave), clouds reduce the absorbed solar radiation, due to a generally higher albedo than the underlying surface, and thus result in a cooling of the planet. View the maps of cloud forcing given above. Does the presence of low level clouds over oceans heat or cool the planet? What about the convective clouds over the oceans?
The latest results from ERBE indicate that in the global mean, clouds reduce the radiative heating of the planet. This cooling is a function of season and ranges from approximately -13 to -21 Wm-2. While these values may seem small, they should be compared with the 4 Wm-2 heating predicted by a doubling of carbon dioxide concentration.
In terms of hemispheric averages, the longwave and shortwave cloud forcing tend to balance each other in the winter hemisphere. In the summer hemisphere, the negative shortwave cloud forcing dominates the positive longwave cloud forcing, and the clouds result in a cooling. For deep convection the solar and longwave effects also cancel.”
Another document suggesting observed tropics cancellation of cloud forcing
http://ams.allenpress.com/archive/1520-0442/7/4/pdf/i1520-0442-7-4-559.pdf