View of the crescent moon through the top of the earth’s atmosphere, as seen from the International Space Station. The photo was taken over the South China Sea, just south of Macau. The lower atmosphere is blue because blue wavelengths are scattered the most among the visible wavelengths by the atmosphere; redder wavelengths are not scattered as much and do not reach the eye from all directions except in greatly diminished intensities.
Wikimedia Commons / NASA Earth Observatory

Yesterday,  I read of a somewhat old study, born from a collaboration between MIT and  NASA, of which almost nobody in the general public has ever known. What it tells us emphasizes the tremendous complexity of Earth’s atmosphere, and how modest everyone should be in their claims of knowledge about how it works. Those who claim man is the primary cause of global warming because of his CO₂ emissions (Anthropogenic Global Warming, or AGW) should be especially modest, given the extreme simplicity of their model of the phenomenon of global warming. Those who support the AGW model like to claim with great certitude that “the science is settled.” Yet, because of the complexity of the planetary atmosphere, it is highly unlikely the science will ever be completely “settled” without many years of additional research.

The Atmosphere’s Energy Budget

The National Aeronautics and Space Administration (NASA) has an online publishing outlet and blog called NASA Earth Observatory, whose primary function is to be a source of satellite imagery for the general public. However it also publishes posts on scientific information concerning the atmosphere, climate, and the environment at a level understandable by non-scientists. The NASA Earth Observatory post from which I learned of the MIT-NASA study was entitled Does the Earth Have an Iris Analog? by David Herring. However, as the post does, I will begin with a description of the Earth’s energy budget.

Almost the entirety of energy available on Earth comes originally from the Sun. What comes from geological sources, nuclear power, and from the stars are an almost negligible fraction of what comes from the Sun. The energy we get from our food, from coal, oil, and natural gas has been captured by plants from the Sun, and sometimes stored for millions of years by fossilization.

Whether the planet warms or cools is determined by the way in which the Earth’s atmosphere interacts with incident solar radiation, and the mechanisms by which the planet eventually directs much of that energy back into space. When the Earth absorbs more than it reflects back into space, the planet warms. The degree to which Earth directs energy back into space and the mechanisms involved are matters of fierce scientific controversy.

The Sun on average irradiates the Earth with 340 watts of power per square meter. The atmosphere immediately reflects back into space 100 watts (the power of an ordinary light bulb) per square meter. The planet holds onto the remaining 240 watts per square meter, which is held as heat energy in the air, oceans, and land surfaces, or captured in photosynthesis by plants to produce the foods for all living things. Without the atmosphere and the greenhouse gases in it absorbing much of the solar input, this planet would be entirely too cold to support life.

So, what are the processes by which the planet either retains or ejects heat?

The AGW Model, and What It Does Not Explain

The AGW model of global warming is the very epitome of simplicity, which some might think makes it preferable under the operation of Occam’s Razor. However, a complicated system like the Earth’s atmosphere many times has convoluted contours that Occam’s Razor can not follow to shave the false postulates from the face of Reality. The only piece of AGW that most people hear about is that man is emitting large amounts of carbon dioxide, CO₂, into the atmosphere, and that CO₂ as a greenhouse gas absorbs infrared radiation. Thermal energy is the kinetic energy bound up in the random motion of particles composing a system, and temperature is a measure of the spread of that kinetic energy about zero.

Because man is emitting CO₂ into the atmosphere, which absorbs infrared photons, AGW supporters claim man is the cause of the observed global warming. The part of the story most people do not hear is that CO₂ is such a tiny, microscopic fraction of the atmosphere that it can not possibly by itself be the cause of global warming. For every one million molecules of all types in Earth’s atmosphere, there are approximately 400 CO₂ molecules. The fraction of the atmosphere that is CO₂ is then 0.0004, which works out to 0.04 per cent of the atmosphere. Since all plant life requires CO₂ to manufacture their food by photosynthesis, it is a great wonder that there is any life on Earth at all! CO₂ qualifies as a true atmospheric trace gas.

In order for those scientists who believe in AGW to build a case, they must have some positive feedback mechanism from CO₂ heating to multiply its effects. In fact the most potent greenhouse gas of them all, partially because it is the largest component of the greenhouse gases, and partially because of the wide thermal spectrum it absorbs, is water vapor. The AGW feedback model then is that the very tiny additions of thermal energy added through CO₂ heating causes more water from the oceans to evaporate, which contributes far more to atmospheric heating. Man then adds more carbon dioxide to the atmosphere, causing even more heating, causing additional water evaporation, causing . . . etc., etc. All in all, a very weak argument, both quantitatively and for other reasons I will now discuss.

A Much Better Model, and Why It Is Not the Final Word

I first became doubtful  about the AGW explanation for global warming when I read a book by Dr. S. Fred Singer, an atmospheric physicist and emeritus professor of environmental science at the University of Virginia, and collaborator Dennis T. Avery, director of the Center for Global Food Issues at the Hudson Institute and a food policy analyst for more than 30 years. Entitled Unstoppable Global Warming: Every 1,500 Years, the book was a severe criticism of the AGW model, arguing that a roughly 1,500 year cycle of warming and cooling has caused most of the observed global warming. The previous warming cycle was the Medieval Warm Period, which lasted from roughly 900 AD to 1300 AD, with a following cooling cycle called the Little Ice Age (which was not at all an actual ice age) from 1300 AD to 1850 AD. Singer and Avery list the most recent long-term periods of warming and cooling as follows:

• 600 to 200 BC: An unnamed cold period of 400 years before the Roman Warming.
• 200 BC to about 600 AD: The Roman Warming of 400 years.
• 600 to 900 AD: The Dark Ages cold period of 300 years.
• 900 to 1300 AD: The Medieval Warm Period of 400 years.
• 1300 to 1850: The Little Ice Age of 550 years.

If this all represents a single periodic process, logically one period of cooling plus one period of warming would represent one full cycle of the process. If you do the arithmetic, this record gives an average that is closer to 1000 years (precisely 980 years) than it is to 1500 years. Apparently the 1500 years comes from a much longer record of cooling and warming periods taken from sources such as glacier ice cores. Concerning the physical record of these periods, Singer and Avery write at the end of a prologue titled Earth’s Climate Timeline,

Through at least the last one million years, and the recent ice ages, a 1,500 year warm-cold cycle has been superimposed over the longer, stronger ice ages and interglacial phases. In the North Atlantic, the temperature changes, from peak to trough, of these “Dansgaard-Oeschger cycles” has been about 4°C. The shift into cold phases has often been very abrupt.

Finding actual periods of complex periodic physical phenomena is a very imprecise business, since the total phenomenon is almost certainly the sum of many processes, some non periodic, with varying periods, each one modifying the observable effects of all the others.

Taking 500 years as the length of a half-cycle of warming and cooling, and the year 1850 as the end of the last cooling cycle, we can then predict that until sometime around 2350 AD we will be in a period of overall warming with a maximum temperature increase of approximately 4°C.

However, what kicked off the current hysteria about global warming is an additional, much shorter cycle of warming-cooling, where each period of warming or cooling lasts around 30-35 years. Below is the record of temperature “anomalies” from some average temperature in the 1950s produced by averaging temperatures over the entire surface of the globe from land and sea stations. This plot was constructed by the National Climatic Data Center (NCDC) of the National Oceanic and Atmospheric Administration (NOAA).

Given the sparseness of measuring stations prior to the 1950s, especially at sea, it is no wonder the error bars prior to 1950 are huge compared to the measurements. From this data you can discern a period of warming from roughly 1910 to 1940, a period of warming pause or very slight cooling from 1940 to 1975, followed by a warming period from 1975 to sometime in the late 1990s. Since then we have been in a warming pause, which, if the past is prologue, will last until sometime in the late 2020s. Whatever the process that creates these shorter periods, remember they modulate the longer term warming period of around 500 years. Therefore, when the short term cycle is warming it accentuates the long-term warming, and when it is cooling it merely ameliorates the long-term warming.

In fact an explanation for this short-term warming-cooling process has probably been found. I will not go through a detailed justification for this model, which you can find in my post Solar Wind, Cosmic Rays and Clouds: The Determinants of Global Warming, but I will give a short description. There are two basic, interacting phenomena. The first is the solar wind, which intensifies when the Sun increases its power output. The second is the effect of cosmic rays, mostly highly energetic protons originating from outside our solar system, on penetrating deep into our atmosphere. Each high energy charged particle in the incident

cosmic ray flux ionizes multiple atmospheric particulates to create nucleation centers. The nucleation centers attract water molecules by electrostatic attraction to form clouds. These tropospheric clouds, reflecting solar radiation back into space, act as a sunshade for Earth, decreasing the heating of the planet. The interaction between the two phenomena results from the collision of the solar wind with the cosmic rays. Although the cosmic ray particles are more energetic than those in the solar wind, the solar wind is much more dense. After multiple collisions with solar wind particles, the cosmic ray particles can be swept away from the inner solar system. In this way a stronger solar wind can limit the cloud cover on Earth by reducing Earth’s exposure to the cosmic rays that seed the clouds. When that happens, the planet warms. When the sun becomes less active, the entire mechanism goes into reverse. Increased cosmic ray exposure causes additional cloud cover and the planet cools slightly or experiences a pause in global warming.

The mechanism just described is not the major cause of global warming or cooling: the long-term roughly 500 year long period of warming is. However, the solar wind-cosmic ray-cloud cover mechanism does explain the roughly 30 year periods of warming and cooling observed in the 20th century, in particular the warming period between roughly 1970 and 2000 that gave rise to all of the AGW hysteria. The good news is that while overall warming caused by the 500 year period process will last until sometime between 2300 and 2400, the overall warming will be of the order of 4°C. This warming in addition to the atmospheric increase of the plant food CO₂ will be exceedingly good news for plants in general.

There is one more important piece of evidence that all this warming is a natural process not caused by man. The AGW hypothesis depends completely on the idea that man is the major producer of the increase in atmospheric CO₂. (I will ignore for the moment the fact CO₂ is such a minuscule trace gas that it can hardly cause enough temperature increase to cause huge increases in water vapor.) The concentrations of CO₂ are certainly increasing approximately linearly with time, as evidenced by the plot below.

Although the fact the two curves in the plot are roughly parallel is highly suggestive, it does not show in fact man is the main cause for the rise in CO₂ concentrations. There is yet one more piece of evidence available found by comparing correlations of atmospheric CO₂ concentrations with air temperature and separately with oceanic water temperature. In the post Most Of The Rise In CO2 Likely Comes From Natural Sources, it is shown that increasing CO₂ concentrations have a much greater correlation with sea temperatures than with the HadCRUT4 air temperatures. This is indicated by what is called the coefficient of determination, r², which for a linear least squares fit is related to the root-mean-square (RMS) deviation of the temperatures to the linear fit. When  r²=1, the linear regression perfectly fits the data and when it is zero the line does not fit the data at all. The r² for the the correlation of CO₂ concentrations with HadCRUT4 air temperatures is 0.05386, while the r² for the the correlation of CO₂ concentrations with sea temperatures, the HadSST2 series, is 0.5528, ten times as large as the correlation with air temperatures.

How can this be? The only plausible explanation is that it is sea temperatures driving most of the increase in observed CO₂ concentrations, not CO₂ concentrations driving an increase in air temperatures. The solubility of CO₂ in sea water decreases as sea temperatures increase. When the sea warms, CO₂ is driven from solution into the atmosphere. We can interpret this only to mean that the predominate increase in CO₂ is from the seas warming, not from human emissions. We have now had approximately 170 years of the oceans heating since the end of the Little Ice Age, meaning we should be expecting such concentration increases as CO₂ is driven from the seas into the atmosphere.

Even some AGW proponents have been forced to admit by circumstances that much of the source of the observed CO₂ concentration increase is the oceans. Due to the many troubles of the world economy, especially those of China, which is the world’s biggest CO₂ emitter, the world human-produced CO2 emissions were held roughly constant in the years 2013 through 2015. I do not have data for 2016. With human emissions having become constant in the presence

of enormous CO₂ sinks in the biosphere, many thought that CO2 atmospheric levels should themselves have stabilized, or at least slowed with the slope of the linear increase in concentrations decreasing. It has not. Some, such as Scripps Institution of Oceanography CO₂ Group Director Ralph Keeling, say this merely shows that current CO₂ emissions must be decreased 50% more to achieve stability. Yet if it is the warming oceans that is producing almost all the increase, of what use is cutting human emissions more?

The planetary atmosphere is an exceedingly complicated system, involving solar physics and solar wind, coupling with the oceans and the land, the electrodynamics of charged particles, chemistry, fluid mechanics, thermodynamics, and even the quantum mechanics of how photons are absorbed and emitted by individual molecules. Everything written above is not even close to being the entire picture about global warming. This fact was driven forcibly home to everyone on all sides of the controversy last year when there was a singular, large spike of almost 0.5°C, which is now dropping fast back to the temperatures of the current warming pause. This temperature spike cries out for explanation by the skeptics of AGW, teaching us to be humble about our level of understanding. The AGW enthusiasts on the other hand seized on the evidence of renewed warming at the beginning of the spike, but are now learning humility as the global temperature average rapidly falls.

What caused the spike? Nobody really knows, but one thing is absolutely sure. There was no spike in CO₂ concentrations so human CO₂ emissions is not an explanation. There is some speculation the spike was caused by a redistribution of thermal energy from equatorial regions of the Pacific Ocean to the atmosphere. This is during the El Niño phase of the El Niño-Southern Oscillation (ENSO), sometimes called the warm phase of ENSO. The opposite, cold phase of ENSO is often called La Niña. La Niña is a condition of unusually cold ocean surface temperatures compared with El Niño. Just as El Niño couples to and warms the atmosphere, La Niña couples to and cools the atmosphere. El Niño has just ended and La Niña, if history is to be believed, is about to begin.

Lindzen’s Atmospheric Iris Hypothesis

This brings us to the MIT-NASA study  I mentioned at the beginning of this essay. After giving a short exposition on the planet’s energy budget, the NASA Earth Observatory post Does the Earth Have an Iris Analog? by David Herring begins to relate the project of Dr. Richard Lindzen, a professor of meteorology at the Massachusetts Institute of Technology to investigate the effects of “forcings” and “feedbacks” on the atmosphere. Begun in the early 1980s before the hysteria of anthropogenic global warming took hold, Lindzen was specifically interested in the effects of atmospheric water vapor and clouds on climate. Herring quotes Lindzen as saying

When the hullabaloo began over global warming, it became clear the answer depended a lot on the feedback from water vapor and clouds. We (scientists) didn’t know how to deal with them.

Intensely aware the AGW theory could work only if heating from CO₂ would lead to additional water vapor in the air, Lindzen studied the physics of how water vapor got into the atmosphere, how it left the atmosphere, and how that affected temperature. The effects of CO₂ over most of the infrared spectrum are negligible compared to water vapor, which captures most of the energy over infrared frequencies. Apparently what makes CO₂ interesting at all is that it captures thermal energy over some small segments of the infrared spectrum that water vapor can not. The AGW theory holds the small extra warming provided by carbon dioxide increases the capacity of the air to hold more water vapor, but the water vapor really does most of the heat capture. It has been estimated that a 13% increase in water vapor concentrations is equivalent in heating to a 200% increase in CO₂.

Because of the greater temperature of the air in the tropics, the tropical air has a greater capacity for holding water vapor, and the bulk of greenhouse heating could be expected there. What influenced Lindzen to concentrate on water vapor in the tropics was an image, reproduced below, constructed from data from the Special Sensor Microwave Water Vapor Sounder (SSM/T-2), flying aboard a U.S. military satellite.

What caught Lindzen’s attention were the the dry white areas in the image. What could possibly be causing them? Since clouds moisturize the air in and around themselves, Lindzen’s team concentrated on the effects of clouds in the tropics.

Specifically, what Linden wanted to find out was what the effects of moist tropospheric cumulus clouds above very warm seas did to much higher level cirrus clouds above them. Cumulus clouds live in the lowest level of the atmosphere,

the troposphere, which extends from the Earth’s surface to roughly 12 km above the Earth. It’s height contracts to about 9 km at the poles and expands to around 17 km at the equator, and it is the layer in which virtually all of the weather lives. Nearly all atmospheric water vapor is found in the troposphere. The water molecules in cumulus clouds tend to have already absorbed most of the infrared molecules they can, so they tend to be reflective of infrared radiation without absorbing much. By reflecting back into space almost all the incident solar radiation, these clouds are net coolers of the planet. These are the clouds that are predominantly seeded by cosmic rays.

Much higher in the sky are the cirrus clouds, which exist at altitudes between 16.5 km and 45 km above the Earth. They typically form in thin, wispy filaments that are too thin to be much of a barrier to either incoming solar radiation or to radiation reflected by the Earth back into space. Because they are composed

mostly of small ice crystals, the water molecules within them are relatively cold, meaning very few of them have fully populated the infrared transitions to higher energy excited states. They will gobble up most infrared photons that come their way, and they therefore, unlike their cumulus cousins, warm the atmosphere. One speculation is that as global warming proceeds, increased water vapor reaching the high altitudes of cirrus clouds form more cirrus that covers a wider area, thereby increasing both temperatures and humidity below it. On the other hand, anything that decreased the area of cirrus clouds would allow more outgoing infrared radiation from the Earth, also called Outgoing Longwave Radiation (OLR) in the literature, to escape to space,

Lindzen’s crew used measurements from the Japanese Geostationary Meteorological Satellite-5 to make their measurements of both cumulus and cirrus cloud cover as a function of sea surface temperature. They made these measurements over the largest and warmest body of water in the world, called the Indo-Pacific Warm Pool. Lindzen told the NASA Earth Observatory,

We wanted to see if the amount of cirrus associated with a given unit of cumulus varied systematically with changes in sea surface temperature. The answer we found was, yes, the amount of cirrus associated with a given unit of cumulus goes down significantly with increases in sea surface temperature in a cloudy region.

This turned out, not surprisingly, to be a very controversial conclusion. It said that somehow the Earth had an adaptive infrared iris that expanded wide when ocean waters underneath reached high enough surface temperatures. If it actually exists, it would be a natural mechanism for limiting global warming, no matter what the cause of the warming. Lindzen did not initially propose a mechanism for this infrared iris, and the reaction against his idea was swift, with some claiming the data available to them did not support the conclusion. One paper by Bing Lin et. al. concluded that Lindzen’s Iris effect did indeed cause a decrease in cirrus clouds, but because those clouds had higher albedos than assumed by Linden — presumably reflecting a significant amount of incident solar radiation back into space — reducing them actually “would cause a significant but weak positive feedback to the climate system, instead of providing a strong negative feedback.”

Most recently in the controversy, an April 2015 paper in Nature Geoscience, “Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models” by Thorsten Mauritsen and Bjorn Stevens supported the adaptive infrared iris idea by providing a mechanism in terms of a vertically convective cell that is illustrated below.

In their model the radiative cooling caused by strong OLR in the “dry and clear” part of the cell is balanced by the latent heat released by precipitation in the moist and cloudy part of the cell. The processes they propose would favor the increase of the “dry and clear” areas to increase the outbound infrared flux (OLR).

Conclusions

Is Lindzen correct? Does the planet possess an adaptive infrared iris that grows in size to increase the infrared energy loss to space as the planetary temperatures rise? This is a complicated controversy, which I suspect will not be settled anytime soon. Such a mechanism would help explain why the temperature variations in the “1500 year” Dansgaard-Oeschger cycles are limited to only about 4°C. As for the Dansgaard-Oeschger cycles themselves, which are the major cause of the current global warming, their cause is a great mystery.

How many other natural phenomena in our complicated planetary atmosphere that bear on global warming have we not yet found? Do you still feel we should spend 7% of GDP per year until 2050 to reduce human CO₂ emissions?

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