Carbonomics no.2: How Does the Earth Stabilize the Climate?

This work outlines the geophysiological phenomena which have helped to stabilize the climate since life first appeared on Earth some two and a half aeons ago. The first chapter looks at the basic concepts needed to understand the climate. The first section provides some background about the climate and outlines what is meant by climatic stability/instability. The second section explores the four components of the climate - the Photosynthetic effect, the greenhouse effect, the albedo effect, and the heat effect. This fourfold structure will be used as the basis in the following two chapters for an evaluation of the various geophysiological factors involved in the stabilization/destabilization of the climate. The third section provides an historical sketch of the primary phenomena involved in stabilizing the Earth’s climate. The second chapter looks at the factors causing the climate to veer towards the extremes of global burning and global freezing. The third explores the way the Earth prevents the climate from veering off towards these extremes.

PART ONE: BACKGROUND

There are many factors which can disturb the Earth’s climate: increases in solar radiation, meteorite impacts, volcanic eruptions, geophysiological changes, etc. But there is only one way in which the climate could be changed so fundamentally that it would cause the demise of all life on Earth and that is a continual and unstoppable increase in global warming leading to global burning and the eventual burn up of the biosphere. The trend of increasing global freezing will never lead to such a calamity. Increases in global cooling leading to global freezing will eventually reach a point where the Earth cannot get any colder. Global freezing may lead to the emasculation of the terrestrial biosphere but it would not lead to the destruction of the Earth’s entire biosphere. Even if all land, even that in the tropics, was covered in ice sheets, life is likely to remain, and may even flourish, in the seas. If, therefore, life had a choice over this matter, it would choose to face the perils of global freezing rather than those of global burning, for at least some species would survive and there would be the prospect that one day the ice age would retreat. The Earth’s biosphere could recover from global freezing but it is unlikely to recover from global burning. It is only in the latter case that the Earth is likely to lose all of its life forms and become a dead planet like its neighbours in the solar system. Whilst the Earth’s climate might swing between global freezing and global warming, it would not be able to do so between global freezing and global burning.

Throughout the two and a half billion years that life has existed on Earth, the Earth has never experienced the climatic extremes of either global freezing nor global burning. As far as is known the Earth has neither frozen up nor burnt up causing the collapse of the biosphere, "There is no geological evidence that since the beginning of the Earth’s stable crust the entire Earth has ever frozen solid or that the oceans were volatilized .. The fossil records suggest that, from an astronomical point of view, conditions have been moderate enough for organisms to tolerate, and the biosphere has been in continuous existence for over 3000 million years ..." There has never been a runaway global burning disaster leading to an irreversible venus type climate nor a runaway freezing disaster leading to a martian type climate .. "the mean temperature at the surface of the Earth probably has stayed well within the range of 5-25C during the last three billion years." The Earth’s climate has swung between global warming and global cooling without veering off into either climatic extreme.

The idea that if global warming did not exist then the Earth would become as cold as outer space, a mere 80 miles above the surface of the Earth, is politically misleading. It is as if the consequence of a fall in global warming is that the sky would fall in and the cold of outer space would wrap itself around the surface of the Earth killing off all life on Earth. The public thus perceives a fall in global warming as a threat to their survival. Instead of seeing a decline in global temperatures as something to be welcomed it is now feared. But global warming is never going to disappear - the danger is not that global warming is going to disappear but that it will go on boosting global temperatures. Theoretically, if global warming didn’t exist then, as scientists estimate, global temperatures would be far lower but there is no chance of global warming suddenly disappearing. It could never happen in reality - even an asteroid smashing into the Earth would not eradicate global warming. Theoretically, if all life on Earth suddenly died, the planet would not plummet into the depths of an ice age. On the contrary, Carbon dioxide from volcanic eruptions would begin accumulating in the atmosphere and the planet would get warmer and warmer.

What is also at issue in scientists’ seemingly inconsequential fictitious comparison are differing views over what might be called the Earth’s natural state. The way that scientists are presenting global warming suggests the Earth is being kept artificially warm because it’s natural state resembles the cold of outer space. But, if there had been no life on Earth over the last three billion years the Earth’s climate would not be 33C colder - it would be far hotter than it is now - it would be far closer to the boiling temperatures of venus than the cold of mars - its nearest neighbours in the solar system. When the Earth was first formed there were vast quantities of Carbon in the atmosphere and much of this would still be there in the absence of life. Today, because of the spread of life around the planet, only a tiny fraction of the Earth’s original Carbon remains in the atmosphere. If, then, life suddenly disappeared from the Earth, Carbon dioxide would gradually be pushed back into the atmosphere and global temperatures would rise significantly to the level which could be expected for a planet in the Earth’s position in the solar system.

When scientists talk about what the Earth’s temperature would be if there was no global warming they are trying to persuade the public about the importance of global warming on Earth. Unfortunately, this artificial comparison is scientifically misleading because global warming will never disappear and the Earth’s natural tendency is not to freeze but to warm up. Even worse is that this portrayal of the climate has a dangerous political impact. It tends to make the public indifferent to, or even dismiss, the threat posed by rising global temperatures i.e. the exact opposite of what the scientists intended. The comparison scientists are using is fostering the belief that it is better to exacerbate global warming to keep the planet warm rather than allowing it to decline causing the Earth to freeze up like outer space. And yet, the threat to the Earth’s life support system is not from global freezing but from rising global temperatures which might eventually push the climate back to what it should be for the Earth’s position between mars and venus.

It has to be suggested the phrase, ‘global warming’, is itself highly misleading. It implies the Earth enjoys a delightful warmth in comparison to the freezing temperatures that would exist on a fictitious Earth without global warming. This artificial conceptualization of the climate is inaccurate because it runs counter to the Earth’s climate history whose primary feature is long term cooling. Scientists should be comparing the Earth’s current climate with the Earth’s history not with a fictitious Earth. For example, this suggests the climate that humans enjoyed when they first appeared on Earth was not global warming, a planet desperately trying to keep out the cold of outer space, but global cooling, the reduction in planetary temperatures brought about by life in order to prevent the sun from burning up the planet. In many ways it would be better if scientists used the temperature-free phrase ‘greenhouse effect’ rather than the value laden implications of the phrase ‘global warming’. Unfortunately, as will be explored later, the phrase ‘greenhouse effect’ also has its limitations.

In this work global burning is the climatic extreme beyond global warming whilst global freezing is the climatic extreme beyond global cooling. These climatic extremes pose a threat to life on Earth - in the case of global burning, to the survival of the biosphere itself. Unfortunately, these phrases can be used only as intuitively as global warming and global cooling. Roughly speaking, global freezing becomes a threat to terrestrial life when the Earth’s global average temperature starts dropping below 10C, whereas global burning becomes a threat to all life on Earth when global temperatures start rising above 18C. The phrase global burning is useful in denoting a climatic extreme but, to add to the confusion, it could also be used to indicate humans’ impact on the climate. In the ‘Carbonomics’ series, global burning is deemed to be anthropogenic increases in global temperatures - that is, when humans push global average temperatures towards 18C. It is unfortunate that global burning refers to both a natural, and an anthropogenic, phenomena - but this is just about par for the course where climate terminology is concerned.

In this work it is argued that ‘global warming’ consists of four different phenomena; the Photosynthetic effect, the greenhouse effect, the albedo effect and the heat effect. Each of these phenomena have varying impacts on the climate - some boosting, others reducing, global temperatures. This chapter looks at the influence of these factors on the Earth’s climate.

There is a considerable difference between the Earth’s temperature when measured from space (the average temperature of the troposphere and stratosphere) and that measured at the Earth’s surface .. "there are millions of infrared measurements by satellites, which see the Earth as a whole (including its atmosphere), and which monitor its infrared radiation to space - Earthlight, invisible to human eyes. In physics every radiant body has a spectrum of infrared radiation characteristic of its temperature. (When you switch on an electric toaster and the element heats up and reddens, the peak of its radiation spectrum shifts from the invisible infrared to visible light of shorter wavelength: the hotter an object is, the less red and more blue - hence white - its light is: eventually it becomes white hot). If the body in question is Earth, its temperature seen from space is measured to be minus 19C. But when measured from within the atmosphere its average temperature is plus 14C. The difference of 33C, which makes all the difference in the world to human beings, is the greenhouse effect." This has been explained in more theoretical terms, "The Earth gives off a total amount of radiant energy equivalent to that of a black body - a fictional structure invented by physicists that represents an ideal radiator - with a temperature of roughly -18C. The mean global surface air temperature is 14C .. some 32C warmer than the Earth’s black body temperature."

The greenhouse effect is the quantity of greenhouse gases in the atmosphere. The Photosynthetic effect helps to determine the concentration of water vapour, the most important greenhouse gas, and atmospheric Carbon, the second most important greenhouse gas. The concentration of Carbon greenhouse gases is determined not merely by global Carbon emissions (what is called here the supply side of the Carbon spiral) but by the Earth’s Photosynthesizers (both terrestrial and aquatic) extracting Carbon from the atmosphere (the demand side of the Carbon spiral). It is not possible to permanently reduce the concentration of atmospheric Carbon by relying solely on limiting Carbon emissions. Even if the main sources of Carbon emissions were curbed dramatically, the greenhouse effect could still get worse if there was a continuous reduction in the demand side of the Carbon spiral e.g. wholesale deforestation. The Photosynthetic effect cools the Earth by extracting Carbon from the atmosphere - but a fall in the Earth’s Photosynthetic capacity tends to warm the Earth.

As far as the scale of Photosynthesis is concerned, however, the situation is quite different. Since the start of the quartenary period, there have been a series of ice ages in which ice sheets have spread across the amero-euro-asian continents. However, the fall in global temperatures and the onset of ice ages didn’t produce a decline in Photosynthesis. On the contrary, there was an increase. This further boosted the amount of Carbon extracted from the atmosphere, causing a further fall in global temperatures reinforcing the ice age. Given that Photosynthesis declines when temperatures fall, it seems anomalous that Photosynthesis increases when the climate gets colder. The reason for this is that there is an overall gain in Forests around the world - the loss of Forests under ice sheets is smaller than the Reforestation of the land which emerges in the tropics as ocean levels fall. When global temperatures dip below 10C there is an increase in the spread of Photosynthesizers around the Earth but when global temperatures rise above 10C there is a decrease in the spread of Photosynthesizers.

The point of minimum global Photosynthesis is when the Earth’s tilt is at its maximum. At this point far more solar energy hits the ice covered areas of the poles and is reflected back into space, "As the energy available at the equator varies less than 10% during the year, the big changes over the higher latitudes mean that the gradient, or difference of heating, between low latitudes and places near the polar circle or beyond is greatest in mid winter. At that season the effective gradient is intensified by the spreading snow and ice, which means that by late january or early february in the northern hemisphere little radiation is absorbed north of about latitude 45N."; "Taking the broadest overall view, about 2.4 times as much radiant energy from the sun is available over a year at the equator as at the poles. The ratio varies during the year: near the summer solstice 1.4 times as much solar radiation falls on the pole during its twenty-four hour day as is available at the equator, so that it is only because of the high proportion reflected by the persistent snow and ice, and the clouds, that even in summer less radiation is absorbed at the pole than at the equator." The greater the Earth’s tilt, the more sunshine lands on polar ice, the lower the quantity of Photosynthesis.

The seasonality of solar energy on Earth is also determined by the shape of the Earth’s orbit around the sun. The Earth’s orbit varies over time between a circular, and an elliptical, course. When the orbit is circular the amount of solar energy reaching the Earth is virtually constant throughout the year whereas when the orbit is elliptical the amount of heat reaching the Earth varies during the year from one extreme, where the Earth is closest to the sun (perihelion), to the other extreme where the Earth is furthest from the sun (aphelion). The more elliptical the orbit the greater the seasonality; the more circular the orbit, the weaker the seasonality, "When the path is truly elliptical, with the Earth first relatively close to the sun and then further away, the solar energy received by the Earth may vary as much as 30% over the course of the year." The point of maximum Photosynthesis occurs when the Earth’s orbit is circular whilst the point of minimum Photosynthesis is when the Earth’s orbit is elliptical.

The relationship between the shape of the Earth’s orbit and the Earth’s tilt is constantly changing which means the points of maximum and minimum Photosynthesis on Earth also constantly change. It has been suggested that, "We know the Earth’s orbital changes don’t alter the total amount of sunlight received by the Earth by more than a couple of tenths of a percent, but the orbital effect could change the latitudinal and seasonal distribution by as much as 10% ..."The shortest seasons occur when a hemisphere’s summer coincides with the Earth being at its closest to the sun, "If winter in a given hemisphere occurs when the Earth is farthest from the sun, then summer will occur when the two are closest, and this hemisphere will experience strong seasonal variations in temperature. The orientation of the Earth’s pole changes in a 21,000 year cycle, tracing out a circle on the sky, so the degree of seasonality, or the difference between seasons, of both hemispheres varies over this orbital cycle."

The second greenhouse effect is brought about by the Earth’s stratospheric ozone layer trapping ultra-violet light from the sun. Whilst most of the solar energy reaching the Earth is visible light, a small proportion is invisible, short-wave, ultra-violet radiation. Stratospheric ozone absorbs incoming ultra-violet radiation which warms the stratosphere, "About 7% of the sun’s energy is radiated at shorter wavelengths, below 0.4 micrometers, in the ultraviolet. This radiation is absorbed by molecules of oxygen and ozone in the stratosphere and warms the layer directly." The weakest of this is ultraviolet-a whilst ultraviolet-c is the most powerful radiation. Uv-a streams through the atmosphere, uv-b is blocked by ozone whilst uv-c is blocked by oxygen. Ultra-violet-b and uv-c are converted to less energetic forms of radiation, "Radiation with a wavelength between 0.2 and 0.4um is called ultraviolet (uv); at wavelengths below 0.29um, most uv is absorbed by stratospheric oxygen and ozone." As a greenhouse gas stratospheric ozone also absorbs outgoing, long wave, infra-red radiation from the Earth’s surface/atmosphere and this also warms the stratosphere. As far as stratospheric ozone is concerned, whilst its tropospheric greenhouse effect absorbs infra-red radiation from the Earth’s surface, its stratospheric greenhouse effect absorbs ultra-violet radiation from the sun.

The warmest part of the Earth’s atmosphere is the surface. This is because firstly, the surface of the Earth absorbs more solar energy than any other part of the Earth. Secondly, the solar energy absorbed by the Earth’s surface is radiated back into the atmosphere and this infra-red radiation has the most tropospheric greenhouse gases to pass through before escaping into outer space. Thirdly, most tropospheric gases, like the Earth’s atmosphere, are closest to the Earth’s surface, "Even though the atmosphere extends upwards beyond 80km, 50% of the total mass of air is found below 5km, at which altitude (16,000 feet) its average density has dropped by nearly half compared to its density at sea level." As a consequence, the temperature of the atmosphere falls with altitude. The higher the altitude, the cooler the temperatures - which is why mountains, despite being closer to the sun, are capped with snow. However, temperatures start to increase again in the stratosphere because of the double greenhouse effects of stratospheric ozone. Beyond the stratosphere, temperatures fall again with increasing altitude. Over the last few decades there has been an increase in tropospheric temperatures but a fall in stratospheric temperatures. Temperatures have been falling dramatically in the mesosphere and the thermosphere.

Global warming defies humans’ common sense. This tells us that the closer we get to the sun the warmer we should feel. Although the sun bathes the Earth in sunlight, the greenhouse effect does more to keep the Earth warm than direct sunlight, "The surface of the Earth receives about 18% of its heat directly from the sun and a little less from solar radiation scattered on the way through the atmosphere by clouds: some 65% of the radiation reaching the ground is in the form of infra-red energy radiated back down to the surface by the atmosphere - the natural greenhouse effect." To put this colloquially, "The atmosphere is primarily heated from below by the warm surface of the Earth." This is why the story of Icarus who flew high in the sky and allegedly burnt his wings is a myth. The closer he flew to the sun, the colder he would get - as all jet pilots now know.

The most important of the natural greenhouse ‘gases’ is water vapour. Estimates for the amount of water vapour in the atmosphere vary between 1-4%, "Air contains 350 parts per million (ppm) of CO2 but this pales into insignificance compared to water vapour which ranges between 1 and 4 per cent (i.e. 10,000 to 40,000 ppm) depending on temperature and humidity. According to keith beyer, water accounts for 99% of the greenhouse effect." Another commentator gives a different estimate, "Water vapour accounts for 65% of .. the greenhouse effect." Other natural greenhouse gases include Carbon dioxide (CO2), methane (CH3), and nitrous oxide. There are about 40 minor contributors. The biggest anthropogenic contributor to the greenhouse effect is Carbon whether in the form of Carbon dioxide CO2, methane CH3, Carbon monoxide (CO), or chlorofluorocarbons (cfcs).

The albedo effect is different from the heat effect. The sunlight impinging on the Earth’s surface is either absorbed, and thus counted as a part of the heat effect, or it is reflected back into the atmosphere and thus constituting the albedo effect. Sunlight is either reflected back into the atmosphere without a change in the nature of the visible radiation or it is absorbed and later re-radiated back into the atmosphere as invisible, long-wave, infra-red, radiation. Since solar energy is either absorbed or reflected, the heat effect varies inversely with the albedo effect. The lower the albedo effect, the greater the absorption of solar energy, the greater the release of infra-red energy, the greater the heat effect - the absorption of solar energy is explored in the following section. The higher the albedo effect, the less sunlight is absorbed, the smaller the heat effect.

The albedo effect is also different from the greenhouse effect - although there are overlaps between the two. The difference between them can be illustrated by assuming a constant level of greenhouse gases: if the Earth’s surface was a perfect mirror reflecting sunlight straight back into the atmosphere, the Earth would freeze because most of the sunlight would pass through the greenhouse gases into space. Although there are greenhouse gases in the atmosphere, the greenhouse effect would ineffectual. If, on the other hand, the Earth’s surface was covered in tar it would absorb huge amounts of solar energy. This energy would be released into the atmosphere in the form of infra-red radiation, a considerable part of which would be absorbed by greenhouse gases causing a huge rise in global temperatures. In these two extremes, although the concentration of greenhouse gases remains the same, the greenhouse effect is entirely different and the affect on global warming is correspondingly different. Even if the concentration of greenhouse gases is the same, the greenhouse effect is different - dependent on the albedo/heat effects. In other words, the greenhouse effect depends upon the concentration of greenhouse gases and the heat effect, the amount of infra-red radiation released into the atmosphere by the surface of the Earth.

Given the important influence of the albedo effect on the climate it is surprising that, "Until recently, global reflectivity has been largely ignored by environmentalists because it seemed impossible to influence the planet’s colour or gloss, one way or the other." There are still commentators who seem to believe it has little significance, "There have been no systematic climatic variations of the albedo effect in Earth history, nor systematic climate changes attributable to a variable albedo effect." Logically, the Earth’s albedo effect must have changed over the aeons as continents appeared on Earth, grew, migrated around the Earth, and as ice sheets, deserts, Forests, etc have appeared and disappeared, "Once formed, clouds significantly influence the magnitude of incoming (solar) and outgoing (terrestrial) radiation. Water, in its various phases, dominates the planetary response to temperature forcing. For example, the reflection of shortwave energy and the emission of longwave energy by clouds accounts for about one-half of the total radiation leaving the atmosphere, and in terms of shortwave radiation alone, clouds account for roughly two-thirds of the planetary albedo."

* the absorption of solar energy and its release back into the atmosphere either through

long wave, infra-red radiation,

evapotranspiration (the release of water vapour containing latent heat by Plants), or,

metabolic thermal pollution (the heat emitted during a body’s metabolism);

condensation, (it has been argued that, "The largest single heat source for the atmosphere is the release of latent heat of condensation during cloud formation; this energy is partly responsible for the circulation of the upper troposphere (Salati, 1987; Paegle, 1987)."

* anthropogenic thermal pollution; and,

* temperature inversions. Although the atmosphere normally conducts heat from the Earth’s surface into outer space, there are occasions when it traps heat around the Earth. Perhaps the most common example of a heat inversion is the trapping of warm air over valleys containing major cities. The warm air in a valley cannot rise into the atmosphere, as it normally does, because it is trapped by a layer of cold air above. This is what is called a temperature, or heat, inversion. The reason this is important is because one of the latest environmental nightmares, which helps to explain the extraordinary rise in global temperatures over the last two decades, is the discovery that the stratosphere is cooling rapid and trapping heat in the troposphere.

1.2.5.2: The Absorption of Solar Energy.

Solar energy on Earth is either absorbed or reflected by a surface and, as a consequence, the heat effect varies inversely with the albedo effect. The lower the albedo effect, the more sunlight is absorbed, the greater the heat effect. The higher the albedo effect, the less sunlight is absorbed, the lower the heat effect. Most of the solar energy reaching the Earth is in the visible part of the electromagnetic spectrum but if it is absorbed by a surface it is re-radiated back into the atmosphere in the form of invisible, long wave, infra-red radiation .. "nearly all of the heat energy of sunlight is in the visible part of the spectrum. (Objects) .. lose heat by radiation: not by radiating light, because they are not hot enough, but by radiating at long wavelengths of what is called the infrared - wavelengths longer than those emitted by a red-hot object."

Whilst the sunlight reflected back into the atmosphere by the albedo effect of a surface, passes through the greenhouse effect (but is often reflected back to Earth by the albedo effect of clouds), the infra-red radiation released into the atmosphere by the heat effect is absorbed by greenhouse gases (rather than clouds). On the one hand, the albedo effect of the Earth’s surface reflects sunlight back into the atmosphere which is not affected by greenhouse gases but, on the other hand, the heat effect releases infra-red radiation which is affected by greenhouse gases.

1.2.5.3: Heat Inversions.

One of the latest manifestations of the heat effect is the global temperature inversion caused by the growing temperature differential between the troposphere and the stratosphere. The greater the difference between the warmth of the troposphere and the cold of the stratosphere, the greater the temperature inversion trapping heat around the Earth. It is turning out that the main damage caused by cfcs’ destruction of the stratospheric ozone layer is not the increase in ultra-violet radiation reaching the surface of the Earth as the cooling of the stratosphere which is reinforcing the troposphere-stratosphere temperature inversion. This may be responsible for the sudden burst in global burning over the last two decades, "When warm air rises through the troposphere - in the huge clouds of the tropics, for instance - it is forced to a halt at the tropopause, where the troposphere ends and the stratosphere begins. This happens because the ozone in the lower stratosphere is very efficient at absorbing solar heat directly, making the air there warmer than in the upper troposphere. The result is a temperature inversion that blocks the air below in much the same way that a layer of warm air will seal in a city’s smog. (However) .. despite the temperature inversion lid that the stratosphere puts on the troposphere, the two zones are not entirely cut off from one another. The cold base of the arctic stratosphere is periodically heated up when slugs of warm, buoyant air from the troposphere break through the barrier. The fear is now that these breakouts have become less frequent."

The oceans absorb most of the solar radiation reaching the Earth’s surface. However .. "it takes over 40 times as much energy to warm the top 100 m of the ocean as to warm the entire atmosphere by the same amount."

In conclusion, the contribution of each of the four factors highlighted in this chapter will be explored when analyzing the stabilization/destabilization of the Earth’s climate.

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HOW DOES THE EARTH STABILIZE THE CLIMATE?

PART ONE: BACKGROUND