UNDERSTANDING THE EARTH AS A PLANET

Chapter 4G

UNDERSTANDING THE EARTH AS A PLANET

A sketch of the view

Our global understanding of the Earth depends on what we think a planet like Earth is like. The mechanisms that regulate Earth's environment interact with each other in many loops and cycles. These loops and cycles are run by energy, and that energy comes either from the Earth itself or from extraterrestrial sources. The energy that comes from the Earth depends very much on the sort of planet the Earth is. And the useful energy that comes from the sun and the rest of the solar system depends on how the planet Earth relates to the rest of the system.

The Earth produces heat that rejuvenates its surface by creating, moving, and breaking up continents; by forming mountain ranges when the tectonic plates that carry the continents collide; by bringing new materials from the mantle into the crust, oceans, and atmosphere through volcanoes and mid-ocean ridges; and by recycling lands and gases through the spreading and subduction of the crust (the sinking of one plate under another when they collide). The rejuvenation of the Earth's surface creates a great variety in the environment, one of the crucial factors in the natural selection of living things. Moreover, the energy injected into the oceans and the atmosphere drives those systems and greatly influences how they interact with one another.

The Earth's gravitational energy keeps the atmosphere from dissipating into space, and thus it determines to a high degree the density of that atmosphere. That density in turn influences the chemistry of the environment and the climate of the planet. To see the point clearly it pays to compare our planet with others. For example, the density of Mars' atmosphere is so low (about one hundredth that of Earth's) that water cannot exist in liquid form: It goes directly from ice to vapor. One of the crucial differences between Mars and the Earth is precisely that the Earth's mass, and therefore its gravitational attraction, is much larger.

Internal heat and gravitation are both functions of the mass and structure of the Earth. Let us discuss heat. The main sources of internal heat are the release of energy from the decay of radioactive elements such as thorium, uranium, and potassium in the interior of the planet, and the energy left over from the gravitational collapse of the matter that formed the planet initially. Associated with this second source is the heat from differentiation, which occurs when denser materials move downwards and displace less dense materials towards the surface. And initially there was also, of course, the extraordinary heat that the bombardment of the Earth by asteroids generated, enough, in the bigger collisions, not only to vaporize oceans and atmosphere but to melt the entire surface.

Our ideas about these sources of heat are based partly on what we think is the structure of the Earth and partly on how we think the Earth was formed. We think that the Earth was formed by the accretion of planetesimals (chunks of the original materials of the solar system) over four and a half billion years ago. As the Earth grew, its gravitational attraction also grew and the Earth captured even more planetesimals. In a short time the Earth was colliding with many objects of diverse sizes. Many of these collisions would have generated a good deal of heat,^[1] as also did the compression of the accreting materials by the increasing gravitation. In the hot terrestrial interior, the heavier elements separated towards the center, eventually creating a metallic, radioactive core. Less heavy materials concentrated first in the mantle, and then in the lithosphere (the crust and the uppermost portion of the mantle upon which the crust rests). The heat from the core stirs up the mantle and leads to the convection currents that push tectonic plates apart at the ridges. Through those long trenches, a new surface is forged from the mantle that spills forth.^[2]

In trying to understand the mantle, the core, and so on, we do not observe them directly. We infer some of their properties from the measurements we make of the Earth, for example with seismic waves, using a technique called "seismic tomography,” which is based on the notion that seismic waves travel at different speeds through different materials (such as molten metal or solid rock). And then we use those measurements in the light of certain theories in order to discern other geophysical properties. Among those theories are our ideas of how a planetary body forms and how it distributes its energy. More specifically, they are theories of the evolution of a planetary body, adjusted to Earth's mass and position within the solar system (not just its distance from the sun but also its having a very large moon as well). To understand the Earth we must understand what kind of object it is. We know that Earth is a planet; thus we need to understand what a planet is, and more specifically what a planet like Earth is.

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[1]. Several theories would posit a cold accretion of the Earth. If the Earth had condensed from a gas nebula, a cold accretion would make sense. But on the prevailing view that the Earth accreted from planetesimals, I do not think it makes as much sense. Recent calculations do suppose a cold accretion -- the reasoning is that when planetesimals come together at low relative velocities they can easily stick together; this result allows for the expected quick planetary accretion. At low relative velocities, however, not much heat is produced. At high relative velocities, on the other hand, the colliding planetesimals would vaporize; and thus accretion would take a long time (see Alan P. Boss, "The Origin of the Moon," Science, January 24, 1986, vol. 231, pp.341-345). Nevertheless, it seems to me, that the quick initial accretion of bodies with low relative velocities leading up to the proto-Earth would be eventually followed by collisions at high relative velocities with bodies of varying sizes, long before the completion of the Earth's accretion. As long as the proto-Earth's mass was significantly higher than those of the other objects, some of the mass of those objects would be quickly accreted into the Earth by gravitational attraction, even if those objects vaporized upon impact. This "hot" phase in the formation of the Earth is quite reasonable in view of the presently favored hypothesis of the origin of the Moon, which would have the Earth colliding with a body the size of Mars (see below). Surely if this is plausible we should favor a scenario in which the proto-Earth is constantly bombarded by bodies too small to break it up but large enough to provide for a "hot" phase during its accretion.

[2]. 70% of the heat from the interior is dissipated in the motions of the plates. M. Carr, R.S. Saunders, R.G. Strom, D. E. Wihelms, The Geology of the Terrestrial Planets, NASA SP-469, 1984, p. 76.

Creative Solutions to the Problem of CO2?

Chapter 4F

Creative Solutions to the Problem of CO₂?

Those scientists who foresee a catastrophe vehemently disapprove of a wait-and-see attitude. By the time we have conclusive proof, they say, it may be too late. They want to curtail CO₂ emissions now. From a professional philosophical perspective, it appears at first sight that they are right: Under conditions of uncertainty it seems reasonable to move so as to avoid disaster.

First sight, however, might be as misleading in social policy as in love. Dissenters argue that the present conditions of uncertainty do not justify the drastic controls pessimist activists hunger for. They suggest two reasons why.

The first reason is that there may be alternative solutions even if the problem is truly serious. That is, we may be able to avert most, if not all, of the catastrophic scenarios without hindering the world’s industry in a massive scale. They do not have in mind the radical technological alternatives discussed in Chapter 2, e.g., solar power satellites and non-imaging optics, but rather ways of preventing the warming of the atmosphere even if fossil fuels continue to supply the lion’s share of our industrial energy.

Instead of our spending 250 billion dollars a year to reduce CO₂ emissions by 15%, as recommended by environmentalists (in the sort of rough financial estimate that can easily be off by a factor of two, most likely upward), a National Academy of Sciences panel (1992) suggested that we find means to compensate for any undue increase in greenhouse gases. The physicist Gregory Benford has cataloged several such means and has devised more of his own. One simple way to remove a large portion of the increase in CO₂ is to plant more trees. A campaign of reforestation in unused lands can be done for a few billion dollars, enhancing the quality of life, and giving us some breathing room in which to think of longer-term solutions.[1]

Plankton can provide another solution, since they can withdraw a considerable amount of fossil-fuel emissions as well. It is known that plankton are scarce in the polar oceans, in spite of the presence of large reserves of the nitrates and phosphates that plankton normally use. The reason seems to be the absence of iron in those oceans. But surely, John Martin suggests, we could ferry the needed iron dust for a relatively low price. According to Benford, for about ten billion dollars a year we could farm enough plankton to absorb as much as a third of a year’s fossil-fuel emissions.[2] This result is clearly superior to the 15% reduction that the draconian measures of the environmentalists would achieve for the sum of 250 billion!

Not surprisingly, such proposals would not be to the liking of environmentalists such as Bill McKibben, who believe that the only way to slow climate change is to use fewer fossil fuels.[3] The evidence seems to favor Martin’s idea, however. In a week-long experiment off the Galapagos Islands in 1996, 990 lbs. of iron made the waters bloom with plankton, Benford reports, which then covered 200 square miles, suddenly green.[4] This was just one of many successful experiments that have been carried out from 1993 to 2002. Some oceanographers worry that long-scale fertilization over a period of many decades may adversely affect the ocean;[5] but, as we will see below, this proposal has been offered only as a temporary measure.

Other possible solutions involve changing the albedo of the planet: If it reflects more sunlight, it will absorb less energy, and therefore the greenhouse effect will diminish, other things being equal. We might achieve this goal by increasing sulfur emissions in the South Pacific (which would increase cloud cover over the middle of the Pacific Ocean, the darkest and most solar-energy-absorbing area of the world). Or we might, alternatively, make jetliners burn a richer fuel mixture, which would leave a trace of fog high in the atmosphere. According to Benford, this process would offset a year’s worth of U.S. emissions for a mere $10 million!

Readers may worry about the possibility of hidden long-term environmental costs and dangers of such geo-engineering – ideological critics will be certain to do so. But all these suggestions are put forth as reversible experiments. In the case of the iron dumping, for example, if the iron dust is not continuously supplied, the polar ocean will return to its previous state in ten days or so.

The greenhouse problem is thus not a case of having to act in the face of uncertainty so as to avert disaster. For given the possibility of apparently reasonable, and significantly cheaper temporary solutions, the wise course of action is to reduce the uncertainty before imposing drastic permanent solutions. That is, we ought to increase our knowledge of the factors that may influence the warming of the atmosphere, and particularly of the ways they affect each other. We should, thus, attempt to gain a better global understanding of the Earth’s environment. Only then will our worries command the universal respect now demanded by the pessimists.

This result is strengthened by the realization that we know very little about how the global and regional environments interact. This is the second reason adduced by the dissenters. To see what they mean, think about how irrigation and other uses of land affect the local climate. Overgrazing in Northern Mexico makes for temperatures as much as four degrees Celsius hotter than you find in Arizona, just a few dozen meters away. On the other hand, irrigation in the plains of Colorado, where corn and other crops have replaced dry prairie, has reduced the mean temperature in July by two degrees Celsius. Transpiration by plants seems to cool the air and produce clouds over the plains. Further irrigation, then, may enhance the effect, for the plains’ winds will cool the nearby mountains, and that will increase rainfall there.[6] Some may wish to draw the conclusion that the global problem of climatic change will thus resolve itself into a collection of regional problems. It seems to me, however, that the wisest approach is to determine how regional climates interact with the global climate. Just to parade a trivial example: We would not want to increase irrigation in dry Southern California in a year when a strong El Niño is bound to dump near-disastrous amounts of rain on the region.

We may not wish to postpone action until the pessimists’ computer models place the catastrophe beyond doubt. We may find a reasonable compromise by searching for a better global understanding of our planet (and of the problem of CO₂ in that context).[7] Even if the dissenters are right and global warming turns out to be a false alarm, sleeping free of worry will not be the only benefit to derive from that search. Our new views will improve our dealing with the Earth in a myriad of ways.

Eventually the story will likely be resolved by space technology used in combination with fields like oceanography and paleobiology. The idea behind the “Mission to Earth,” for example, was precisely to look at Earth from space the way we have looked at other planets. This most ambitious mission evolved into the somewhat more modest Earth Observing System, a multi-billion dollar, interdisciplinary effort to understand global climate by observing the Earth from space. The three main instrument platforms are called Terra, Aqua and Aura (to study, respectively, land, water, and atmosphere). It is clear to many scientists that even this effort must be surpassed. A recent meeting of the National Research Council attempted “to do for climate change what has been done for astronomy, planetary science, and solar physics: create consensus on a realistic, long-term blueprint for the field, including the most important questions to be answered and the tools needed to explore them.”[8]

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[1]. According to Benford, it would take a land the size of Australia covered with trees to soak up all the present increase in CO_2. “Climate Controls,” Reason, Vol. 29, No. 6, November 1997, pp. 24-31.

[2]. Ibid., p. 27.

[3]. William McKibben, The End of Nature,

[4]. op. cit.

[5] P.G. Falkowski, Scientific American, op. cit., p. 61.

[6]. Jennifer Couzin, “Landscape Changes Make Regional Climate Run Hot and Cold,” Science, Vol. 283, 15 January 1999, pp. 317-319.

[7]. This will, of course, make for improved climatic computer models.

[8] Andrew Lawler, “Stormy Forecast for Climate Science,” Science, Vol. 305, August 20, p. 1094. Unfortunately, I fear, the needed effort may be undermined by the political advocacy by scientists during the past several years. According to this article, “Whereas fiscal conservatives would attack any massive new research program as unaffordable, liberals are likely to see it as a ruse to delay action on the underlying problems that are causing global warming.” P. 1097.

Musings 2

Chapter 4D

Musings 2

Nevertheless it follows from Lovelock’s considerations that life influences to a large extent the climate of the planet. Life largely determines chemical composition, and chemical composition largely determines the range of many crucial physical factors such as freezing and boiling points, which in turn determine whether several substances will be in gaseous, liquid, or solid form. In the deep cold of Titan, the large moon of Saturn, there are large lakes, because the dense atmosphere, mostly nitrogen, contains 1% methane, and methane can exist as a liquid at those pressures and temperatures.[1] Those physical factors will also affect the patterns of heating (e.g., the greenhouse effect) and cooling (e.g., glaciation), and thus the transfer of energy throughout the system. It is not surprising, then, that by removing gases from the atmosphere, or by replenishing them, life on Earth exerts much influence upon the climate.

Stephen H. Schneider criticizes the notion of Gaia as a regulating mechanism, a sort of giant planetary thermostat, by drawing attention to the fact that on occasion life gives a positive feedback to the climatic changes taking place. He assumes too narrow an interpretation of Lovelock’s idea, however, for Gaia is a metaphor not merely for life on Earth, but for the whole interaction of life and the rest of the environment. Some parts of the total environment may thus temporarily accelerate climatic changes, as we have seen, but at some point other parts of the system bring about stability and often reversal. Had it not been that way so far, life would have disappeared from Earth long ago.

Still, the most Lovelock can conclude is that life on this planet is very resilient. But after this point is acknowledged, we still have much reason for concern. For example, he points out that the present industrial pollution of the planet cannot compare with the massive poisoning of the atmosphere by oxygen a billion years ago. When the free hydrogen in the atmosphere had been used up or escaped into space, bacteria began to withdraw it from H₂O in photosynthesis. The waste product, oxygen, was extremely toxic to most of the bacteria that dominated the Earth in those days.[2] Sure enough, life overcame this threat by developing organisms that used oxygen. But we should find no comfort in learning that those evolutionary solutions led to the replacement of one kind of life by another. If we foul up our own planet, life may survive – but we might not. Industrial waste fertilizes the water in our lakes and rivers and leads to the rapid growth of algae. This kills the fish, the frogs, and the water lilies. It is not much consolation to know that upon the ruins of the present order life will adapt and produce a new kingdom of scum.

The pessimists urge us to think about the Earth in the long run, and particularly about the drastic changes that we may bring about in the next few centuries because of our use of fossil fuels. But we may also wish to put their own concerns in the context of the truly long-run, not just centuries, but thousands of years, and then tens and hundreds of millions of years.

For the past 400,000 years, according to the temperature record found in deep ice in Antarctica, our planet has been going through glacial cycles of about 90,000 years, punctuated by short warm interglacial periods (about 11,000 years each). Indeed, our planet has been very cold for the last 2.5 million years and is likely to remain so for the next 2-10 million. As Peter D. Ward and Donald Brownlee point out in their book The Life and Death of Planet Earth, the present interglacial period has been unusually long already.[3] This prolonged period of warm may be accounted for by Milutin Milankovich’s theory of the influence of Earth’s orbit on its climate (to be discussed later in the chapter). But according to some calculations, the present warm period will give way to another glaciation in a few thousand years at most.[4] The temperature record shows, however, that the switch from warm to ice can take place almost suddenly, so we may be due for another “ice age” at any time. Of course, the descent of sheets of ice two miles high upon the Northern hemisphere would devastate our present civilization far more than the current warming of the atmosphere is likely to. Ironically, the much-maligned man-made global warming may stave off the ice for another 50,000 years![5]

In the truly long run, but long before the sun becomes a red giant, the Earth’s thermostat is likely to malfunction. It was Lovelock himself who realized that Gaia would eventually fail as the planet’s self-regulatory mechanism. In a 1982 article with M. Whitfield, he argued that life was steadily removing CO₂ from the atmosphere – it actually has been doing so for the last 400 million years, when plants conquered the land – and in about 100 million years the level of CO₂ will go below 150 parts per million (ppm)of air.[6] This level is important because most plants require at least that much atmospheric CO₂ to survive. Newer forms of plants – grass, palm trees – use slightly different mechanisms for photosynthesis and can go well below the 150 ppm. The flora of the future, then, will have a very different view: gone will be the apple orchards and the rose gardens, replaced by new and exotic varieties of plants. But, eventually, the level of atmospheric CO₂ will go below 10 ppm and photosynthesis will come to an end altogether. More recent studies following on Lovelock and Whitfield’s footsteps have revised their estimate to between 500 million and a billion years.[7]

The loss of plants will be a catastrophe for animals, obviously, but also for marine life, since it depends so much on the run-off of the soil nutrients that result from the presence of plants. Those few animals that can manage to survive will be obliterated in a few million years by the rising temperatures, for eventually significant levels of atmospheric CO₂ will rise in the atmosphere by geological processes but will no longer be kept in check by photosynthetic organisms. Several scenarios have been proposed to explain what will happen after that point. To me it seems simple to imagine that a highly increased level of solar energy coupled with high levels of atmospheric CO₂ will quickly lead to the sort of runaway greenhouse effect that vaporized Venus’ oceans.

It is possible, nonetheless, that Lovelock and those who refined his prediction of doom have not given Gaia enough credit. After all, just as cyanobacteria were able to survive in small, protected pockets the flooding of the planet by oxygen, a few plants may just barely survive near vents that outgas CO₂, lie low until the CO₂ rises again, and then explode once more through ocean and land. Other photosynthetic life on land and in the ocean will thrive also, as their ancestors now do, and together with the plants will begin to regulate the climate and, literally, give the Earth a new lease on life.

Of course, this new, though not improved, version of the planetary thermostat gives even less reassurance than the previous one. Indeed, it turns out that the thermostat has allowed the entire planet to become a ball of ice once or twice in the eons before the Cambrian explosion.[8] We cannot escape the need to reach a better understanding of our global environment.

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[1]. Methane on Titan would thus be the counterpart of water on Earth. Other possible counterparts, in other planets, would be ammonia, which freezes at -78 degrees Celsius and boils at -33 degrees Celsius, and methyl alcohol, whose range is from -94 to +65 degrees Celsius.

[2]. Adapted from L. Margulis and D. Sagan, Microcosmos, Summit Books, New York, 1986, p. 237.

[3] Ward and Brownlee, op. cit., pp. 71-86.

[4] R. Chris Wilson, Stephen Drury, and Jenny L. Chapman, The Great Ice Age, 2000. Cited by Ward and Brownlee, p. 82.

[5] Ward and Brownlee, op. cit., p. 83. On the other hand, global warming, according to some speculations, might trigger the ice age by shutting off the water circulation patterns in the Atlantic (warm water going north closer to the surface and cold water going south closer to the bottom of the ocean).

[6] J.E. Lovelock and M. Whitfield. 1982. “Life Span of the Biosphere.” Nature 296. Pp. 561-563.

[7] This account is borrowed from Ward and Brownlee, op. cit., pp. 101-116.

[8] Ward and Brownlee, op. cit., p. 75.

Zubrin

Last week I attended a convention of the International Mars Society and had an opportunity to exchange some ideas with Robert Zubrin. A few weeks ago I had expressed the thought that, given the startling space budget proposed by the Obama administration, and particularly the ending of the Constellation Program that would have returned us to the Moon, it would take imaginative thinkers like Zubrin to come up with strategies that would permit us to make a silk purse out of a sow's ear. I suggested then that perhaps going with a modular construction of space ships would permit us to get around the lack of the heavy-lift booster canceled by the administration. But Zubrin himself would have none of it, as he made quite clear to me. He thinks that a heavy-lift booster is essential. Once we have a booster in the class of the Saturn V again, we will be in a position to put an outpost on Mars. He insisted that modular technology has not been successful so far, and that there is no point in trying to reinvent the wheel when we already have the know-how to get the job of manned exploration done, the exploration of Mars included. His solution is to put political pressure on the House of Representatives to approve the space budget already approved by the Senate, which restores the heavy-lift booster and other capabilities we need to go to Mars. He would rather skip the Moon and go straight to Mars, but is willing to put up with the Moon delay as long as we are back to the technology level of the Apollo era. We could have been on Mars by 1985 or even earlier if we had kept up Kennedy's example of setting up ambitious missions and going all out to meet those goals. Indeed, for all the money, time and energy we have wasted on the Shuttle and the International Space Station, we could have thriving outposts on both the Moon and Mars by now. More on all this in a few weeks.

Conceptual Musings on CO2

CHAPTER 4C

Conceptual Musings on CO₂

At first sight it seems that increases in CO₂ lead to increases in temperature by trapping infrared radiation. And the higher temperature will lead to more water vapor, which will lead to higher temperatures and so on. If this were the whole story, any increase in CO₂ would inevitably lead to a runaway greenhouse effect. If that were to happen the temperature of the Earth would be measured in the hundreds of degrees Celsius (as in Venus) and life would have long disappeared from the planet. But surely there have been fluctuations in the level of CO₂. Indeed, it seems that in the past the level of CO₂ has been much higher than it is now: 10 to 30 times higher in some eras, and also a bit lower than it is now (two thirds of today’s level during the last ice age).[1] Thus we should expect the Earth to be lifeless by now. But of course it is not.

We know, therefore, that the Earth itself must have mechanisms that regulate the level of CO₂ and its effect on temperature. It is clear, then, that to understand the significance of the increase of CO₂ we first need to understand those mechanisms.

Three mechanisms are particularly influential in the regulation of carbon and thus of temperature: plate tectonics, stone weathering, and terrestrial life.

Let us begin with life. As CO₂ increases, plants and bacteria that thrive on it will displace others that do not. But as these life forms become very successful and proliferate, there will be more of them to remove CO₂ from the atmosphere, and thus the temperature will begin to go down.[2]

It used to be thought that plants were by far the main biological sink of CO₂ in the planet, even though as Lynn Margulis and James Lovelock argued many years ago, bacteria have a much greater influence on the composition of the atmosphere than plants do.[3] This particular controversy has been pretty much settled by the launching in 1997 of a satellite capable of keeping a close watch on the world’s populations of phytoplankton (Sea Wide Field Sensor). Whereas plankton remove as much as 45 billion to 50 billion metric tons of inorganic carbon, plants handled about 52 billion metric tons.[4] We should see this pattern repeated time and again: Firm knowledge about problems of the global climate seems more likely when we can investigate them with space science and technology.

Plants, however, contribute to the removal of CO₂ not merely by photosynthesis, but also as part of the so-called “silicate-carbonate geochemical cycle,” which works by taking the calcium living beings produce and combining it with carbonic acid to make limestone. As astrobiologists Peter D. Ward and Donald Brownlee explain

Here we have a wonderful partnership. Animals such as coral are harnessing calcium. The roots of plants exude an acid that helps to break down rocks, accelerating weathering by the wind and rain generated by the atmosphere and oceans, creating the [carbonic] acid necessary to convert the calcium to limestone. All combined are working together to take excess carbon dioxide out of the atmosphere and bury it in “reservoirs” of rock within the Earth, and thus balance temperature.[5]

To understand the regulation of CO₂ we also need to determine the ways in which CO₂ is put back into the atmosphere. The oxygen produced by the organisms that remove CO₂ is itself taken up by other organisms, which end up producing more CO₂ as waste. Plankton stores carbon in the ocean, but much of that carbon is returned to the surface via upwelling and ocean currents in a few hundred years at the most.[6] Most of those carbonates that fall to the bottom of the ocean become part of the crust, and because of the spreading of the ocean floors, through plate tectonics, they are eventually pressed onto continental shells as plates collide (in subduction zones) and finally find their way into volcanic eruptions as CO₂ again. Of course there is a long lag in this geologic cycle, perhaps in the millions of years.

Let us continue, then, with the scenario in which the planet begins to cool. As more water freezes in the polar caps, the level of the oceans drops, and more land is exposed to the wind and the rain. Phosphates and calcium in great abundance come to the oceans. The phosphates feed the plankton, which will then make more carbonates from atmospheric CO₂. As a result, the temperature will decline even more (a case of positive feedback). Will the Earth finally become like Europa, the Jovian satellite, a beautiful ball of ice?

No (but see below). As the ocean surface is reduced, the ability of the planet to support plankton is also reduced. A saturation point is eventually reached, and the temperature becomes stable. After a long time the combination of plate tectonics and volcanism will begin to increase the level of CO₂ and the temperature will begin to rise again (although big volcanic eruptions put up large amounts of dust that initially may cool the planet more instead).

It would be a terrible mistake to conclude from these speculations that the planet's mechanisms are bound to take care of any and all environmental consequences of burning fossil fuels. As a first approximation we might say that all such mechanisms working together have served as if the Earth had a thermostat. But all the mechanisms guided by thermostats operate successfully only within limits. On a very hot summer day, the air conditioner may be stretched beyond its specifications and be unable to bring the temperature down anywhere near the thermostat setting. Likewise, if the energy that we receive from the sun were to increase continuously, as it presumably will – up to the apocalyptic end in a few billion years when the sun will become a red giant – the feedback mechanisms of the planet will moderate the temperature somewhat, but the heat from the sun will eventually overwhelm, and finally scorch into oblivion all: life, oceans, and air.

Short of that calamity, many changes in the environment can be disastrous enough. At first sight, however, we find reason for optimism in the work of some observers. In presenting his famous Gaia hypothesis, J. Lovelock has compared the totality of Earth's life, the biota, to a super-organism with a fierce instinct for self-preservation. As his “Gaia” metaphor is pressed to explain the natural history of our planet, it does become clear that life has always managed to adapt to profound changes in the environment. It also becomes clear that the biota is a very effective mechanism in the regulation of that environment.

Indeed, if a spaceship were exploring our solar system, it might be able to determine from a long distance that life was plentiful on Earth. The reason is that our atmosphere is not chemically stable. For example, oxygen forms 21% of the volume of the atmosphere. From a purely chemical point of view this high percentage is very surprising, for oxygen is a very reactive element (it combines easily to form compounds); thus it should be swept up in a rather short time. Life, however, replenishes the free molecular oxygen that is lost to chemical reactions. And given the large amount of oxygen, the percentage of other gases would be impossible except for the action of life. Methane, for instance, is 10²⁹ times more abundant than it ought to be. According to Lovelock and Margulis, nitrogen is one billion times and nitrous oxide ten trillion times more abundant than they would be, given chemistry alone.[7]

Since nitrogen makes up nearly 75% of the atmosphere, the impact of life on the composition of the atmosphere cannot be underestimated. Although nitrogen would not be detectable in the Earth’s spectrum, the exploring spaceship might still be able to determine the existence of life on Earth, long before arriving, from the extremely high concentrations of trace gases such as methane and nitrous oxide.[viii]

The converse is also true. By spectral analysis, Lovelock determined in the early sixties that life on Mars would be very unlikely. His determination was confirmed when the two Viking spacecraft landed in 1975 and found that the chemistry in the Martian soil could not support life. Lovelock had played the role of the visiting spaceship scientist and drew the appropriate conclusions from the fact that Mars' atmosphere is in chemical equilibrium.[ix] As we will see later, however, our enthusiasm for this approach should be tempered by the realization that the atmosphere of Venus is not quite in equilibrium, even though Venus is lifeless.[x]

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[1]. For an account see H.D. Holland, B. Lazar, and M. McCaffrey, "Evolution of the Atmosphere and Oceans," in Nature. Vol. 320, March 6, 1986. p. 33. For variations in CO2 levels throughout the history of the planet see E.T. Sundquist and W.S. Broecker, The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present. American Geophysical Union, Washington, D.C. 1985.

[2]. The importance of life to the climate has been particularly emphasized by J. Lovelock and L. Margulis. See their "Atmospheres and Evolution," in J. Billingham, (ed.), Life in the Universe, MIT Press, 1981, pp 79-100. See also their "Atmospheric Homoestasis by and for the Biosphere: The Gaia Hypothesis," Tellus 26:2, 1973. Most of the scenarios described in the pages below are offered merely to illustrate the many factors that may play a role in the behavior of the climate. They should not be ascribed to any one particular investigator.

[3]. Lovelock and Margulis. Op.cit.

[4] P.G. Falkowski, “The Ocean’s invisible forest,” Scientific American, Vol. 287, No. 2, August 2002, pp. 56-57.

[5] Peter D. Ward and Donald Brownlee, The Life and Death of Planet Earth, Times Books, 2002, p. 61.

[6] Ibid., p. 57.

[7]. Lovelock and Margulis, "Atmospheres and Evolution." Op.cit. p.81.

[viii]. This is a recurring theme in Lovelock's work. See his article in Nature, London, No. 207, p.568.

[ix]. See Lovelock's analysis of J. and P. Connes (J. Opt. Soc. Am., 1966, No.9, p. 896) in Lovelock and A.J. Watson, "The Regulation of Carbon Dioxide and Climate: Gaia or Geochemistry," Planetary and Space Science, vol. 30, no. 8, p 795.

[x] Although the Viking controversy is not entirely settled, as we will see in Ch. 6.

Global Problems: CO2 and the Climate

Chapter 4B

Global Problems: CO₂ and the Climate

Carbon dioxide (CO₂), water (H₂O) and sunlight are the main ingredients used by plants and many bacteria to make the organic compounds they need to survive and prosper (in the process called photosynthesis). Carbon dioxide (CO₂) is thus essential to life on Earth. But in excessive amounts it may lead to the undue warming of the atmosphere, the infamous “global warming.”

CO₂ has been increasing at a rate that seems alarming: 25% since the industrial revolution and 10% since 1957. Many scientists attribute most of this increase to human action.[1]

According to several climate models, at this rate the CO₂ will double sometime in this century, raising the average global temperature anywhere from 1 to 5 degrees Celsius.[2] That higher temperature may transform the Earth in undesirable ways. For example, the polar caps might melt, slowly raising ocean levels and flooding out of existence New York, Hong Kong, Rio de Janeiro and many of the other great coastal cities of the world. The loss of land would destroy the livelihood of a billion people, while the new climate may turn the great agricultural areas of the American and Canadian Midwest into deserts.[3]

Some react to this problem of “global warming” by advocating an end to the practices that increase the CO₂ in the atmosphere. But that solution is far from easy, for we create CO₂ every time we burn fossil fuels – that is, every time we operate a factory, fly a plane, drive an automobile, or run a tractor. Modern society runs largely on the burning of fossil fuels and changing this habit will require much sacrifice and thus encounter great resistance. Not surprisingly, dissenters demand to know just how bad the problem really is and what alternative solutions exist.

The problem does seem to be catastrophic if one listens to the judgment of the majority of professional climatologists. Until recently they based their pessimistic conclusions on three main factors: the theory of the green-house effect, the fact that the temperature has risen by one degree Celsius in the last hundred years, and the projections they derive from computer models of the climate. Let us take a brief look at each in turn, and then let us look again at the ensuing controversy in the context of the long-term future.

The theory of the greenhouse effect seems about as solid as we could wish. Sunlight is absorbed by the Earth’s surface and re-radiated in the infrared. CO₂ does trap infrared radiation, as do other “greenhouse” gases, such as methane (CH₄), nitrous oxide (N₂O), and ordinary water vapor.[4] And when you trap energy in the atmosphere you make it warmer. Indeed, there is little question that the Earth does experience a very large greenhouse effect. The average air temperature on the surface of the Earth is 14°C (57°F), which is about 32°C higher than the radiant temperature of the Earth (what the Earth radiates). This means 32°C more than can be accounted by the combination of sunlight and internal heat. So we can see not only that the greenhouse effect exists on a large scale, but also that it is a good thing, otherwise the mean temperature of the Earth would be well below freezing.

CO₂ is an important factor in this greenhouse effect, even though its percentage in the atmosphere is just 0.035 – its increase coincides with the rise of temperature in the last century. Until recently, however, dissenters have questioned this worry on two fronts. The first is whether there is a connection between the increase in CO₂ and the rise in temperature, for most of the increase in temperature took place up to the 1940s, even though in the last twenty years CO₂ has increased almost half as much as in the previous 200. Moreover, dissenters dispute even the modest increase in world temperature in the last twenty years on the basis of satellite readings of lower atmospheric temperature (up to a height of seven kilometers). These readings actually show a slight decrease. According to the dissenters, satellite data of the lower atmosphere should be considered far more reliable than inferences drawn from a collection of readings from highly localized weather stations around the world, especially those from cities, where concrete and pollution create “islands of heat.”[5]

In their second front, dissenters argue that changes in temperature result from natural fluctuations in the climate. Ninety million years ago a cold-blooded crocodile, Champosaur, lived only 600 miles from the North Pole. The climate in the Arctic then was like Florida’s today. It is also well known that many hundred years ago England used to enjoy wine from its own vineyards, for the whole of Europe was much warmer then. About the same time the Americas were suffering from devastating droughts. That warm climate gave way to the Little Ice Age, about 400 years ago. But now the Earth seems to be returning to the balmy days of English wine, a time long before the industrial revolution and its massive use of fossil fuels.[6]

In the last few years, the pessimists have challenged the interpretation of the satellite data, largely to their own satisfaction, although the dissenters remain unconvinced. “A stubborn argument against global warming may be discredited by a reanalysis of the data central to its claims,” announces a Science commentary on a crucial report. But the authors of the report themselves point out that the relevant models cannot be used “to determine which of the two satellite data sets is closer to reality.”[7] The pessimists then announce that their “newest global-warming forecast is backed by data from myriad satellites, weather balloons, ships at sea, and weather stations…”[8] as well as by ice-core, animal and plant studies. But, according to S.F. Singer, former director of the U.S. Weather Satellite Service, a report from the National Research Council “confirms that the atmosphere has not warmed appreciably for the past 20-odd years.”[9] (See Figure 4.1) Singer does acknowledge that we are in a period of warming, but he claims this is just part of a natural cycle induced by changes in solar radiation. We can see this rough 1470-year cycle, he adds, superimposed on both glaciation and inter-glacial periods of the last 400,000 years, and perhaps of the last million years.[10]

The third basis for the pessimistic conclusions is the use of computer models of the climate. The computer models attempt to simulate the behavior of the climate some years from now by considering how a relatively few factors affect it. Dissenters point out that these models are gross simplifications of the real climate and the myriad of factors that do affect it (which in many cases are themselves not well understood, as we will see below). Pessimists cannot point to significant forecasts of climate change, which is the acid test required by dissenters.

In fairness, though, we must keep in mind that the climatologists are warning us about the probable effects of the accumulation of greenhouse gases over a period of several decades. They also worry that by the time those disastrous effects are large enough to convince the skeptics, it will be too late to reverse the trend and prevent a catastrophe.

Furthermore, their computer models have been tested somewhat successfully by the retrodiction of significant climatic changes in our distant history (a retrodiction is a prediction concerning what we will find out about the past). That is, in some instances when scientists have applied their climate models to determine what should have happened at, say, the time of the dinosaurs, they have gotten some rough agreement with what we believe really happened (given our knowledge of the geological record). But as climatologist Stephen Schneider puts it, this is valuable circumstantial evidence, but it cannot confirm or deny the model’s detailed regional projections.[11]

As of this writing, a bitter controversy rages on between the two sides, complete with name-calling, accusations of biased reporting,[12] and charges of fraud.[13] This controversy, to make matters worse, has been drawn along political lines, with the Left generally taking the side of strict regulation and the Right that of industry. The left tends to say that there are no two sides, but that would be rather unusual in the history of science.

It is not my purpose to settle this political controversy. My intent is rather to examine the matter philosophically and to argue that we face a condition of uncertainty in which we have a duty to act wisely, and that we will not be able to do so unless we make liberal used of space technology in the context of investigating the Earth as a planet. And to do the latter well, as I have already suggested, requires a vigorous exploration of the solar system.

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[1]. Schneider, S. H., Laboratory Earth, Basic Books, 1997, p. 66.

[2]. Ibid, p. 50.

[3]. These are, of course, only educated guesses. Melting of icebergs floating in water would not raise the water levels, but melting of glaciers over land, as in Antarctica, would.

[4] They have that name because they work in the manner of a greenhouse: they let the sunlight through but trap the heat in.

[5]. The two sides agree that there was a substantial increase in global surface temperatures in 1998 (0.58EC above the baseline of the 1961-1990 period). But skeptics blame El Niño and point out that later in the year the atmospheric temperatures decreased to the baseline average. Science News, Vol. 155, January 2, 1999, p. 6. I expect that this debate will continue for years.

[6]. Recently some researches have argued that on the basis of such evidence we cannot prove that the global temperature was higher then.

[7] J.R. Christy and R.W. Spencer, Science, Vol. 301, 22 August 2003, pp. 1046-1047.

[8] “The Weather Turns Wild,” U.S. News and World Report, February 5, 2001, p. 47. This article was based on a report from the United Nations’ Intergovernmental Panel on Climate Change. See also Harries, J.E., et al, “Increases in Greenhouse Forcing Inferred from the Outgoing Longwave Radiation Spectra of the Earth in 1970 and 1997,” Nature, Vol. 405, March 15, 2001.

[9] See his letter to Science, Vol. 301, 1 August 2003, p. 595. The report in question is Reconciling Observations of Global Temperature Change, National Academy Press, 2000. See also Donald Kennedy’s response, Ibid. I must confess that I am very puzzled by those who claim that the last twenty years were the hottest in the last thousand, while at the same time all sides agree that the rise in temperature since 1900 to now is 0.6C and that the rise in temperature from 1900 up to 1979 was also 0.6C.

[10] S.F. Singer and D.T. Avery (2007). Unstoppable Global Warming: Every 1500 years. Rowman and Littlefield.

[11]. Op. cit., p. 51.

[12] The battle is often fought through the most prestigious organs of the press, which tend to favor the doomsday scenarios. For example, on March 5, 1999, the Washington Post ran the headline “Shrinkage Detected in Greenland’s Ice.” According to the World Climate Report, the “real” story is that even though Greenland’s southern glaciers are receding, that recession is more than compensated for by a thickening of the ice sheet in West Greenland, the largest ice mass in the Northern Hemisphere (March 15, 1999). Indeed, satellite data indicate that there had been a cooling trend around Greenland for the previous twenty years.

[13] According to Singer, the claim that scientists had found a “human fingerprint” in the current warming was inserted into the executive summary of the United Nations’ Intergovernmental Panel on Climate Change (IPCC) “for political, not scientific reasons. Then the ‘science volume’ was edited to take out five different statements – all of which had been approved by the panel’s scientific consultants – specifically saying no such ‘human fingerprint’ had been found.” The editor, a U.S. government employee, later admitted his “indefensible action,” claiming he had been under pressure from higher U.S. government officials. Singer and Avery, op. cit., p. 10. Singer’s source is Frederick Seitz, former president of the National Academy of Sciences, in “A Major Deception on Global Warming,” Wall Street Journal, 12 June 1996, editorial page. Also, S.F. Singer, Climate Policy from Rio to Kyoto: A Political Issue for 2000 and Beyond (Palo Alto, CA: Hoover Institution, Stanford University, 2000), p. 19.

The Immediate Future of Exploration

The NASA Budget

For those of you who are interested in supporting exploration, I thought I would pass on this urgent message I received from the Planetary Society:

The NASA budget is coming to a critical vote tomorrow -- July 15 -- by the U.S. Senate Committee on Commerce Science and Transportation. This is the Committee that authorizes the NASA program. The planned authorization bill has some good features -- fully funding the President’s request for an increased budget for NASA, strong space and Earth science programs, and redirecting human space flight towards exploration into the solar system. It also increases support for the deep-space rocket and spacecraft necessary to take astronauts there.

But it has two big drawbacks:

It stops the rapid development of commercial rockets for Earth orbit crew transportation, while authorizing no new government program to replace the shuttle.
It cuts out most of the technology development (90%!) and robotic precursor missions related to the future of exploration, two of the brightest lights in the new exploration strategy.

Two amendments are being introduced tomorrow to correct these problems: one by Senator Mark Warner of Virginia and the other by Senator Barbara Boxer of California. Together they will restore much of the technology program (increasing it by $356 million) and permit commercial launch vehicles to be developed to allow astronaut flights to the International Space Station sooner.

We urge you to call your Senators today and ask them to support the Warner and Boxer NASA Authorization Amendments -- especially if one of them is on the Senate Committee. A phone call is necessary -- there's no time for a written letter (these amendments just were announced late yesterday). These are the Committee members:

Democrats
Jay Rockefeller, West Virginia, Chairman
Daniel Inouye, Hawaii
John Kerry, Massachusetts
Byron Dorgan, North Dakota
Barbara Boxer, California
Bill Nelson, Florida
Maria Cantwell, Washington
Frank Lautenberg, New Jersey
Mark Pryor, Arkansas
Claire McCaskill, Missouri
Amy Klobuchar, Minnesota
Tom Udall, New Mexico
Mark Warner, Virginia
Mark Begich, Alaska

Republicans
Kay Bailey Hutchison, Texas, Ranking Member
Olympia Snowe, Maine
John Ensign, Nevada
Jim DeMint, South Carolina
John Thune, South Dakota
Roger Wicker, Mississippi
Johnny Isakson, Georgia
David Vitter, Louisiana
Sam Brownback, Kansas
Mike Johanns, Nebraska
George LeMieux, Florida

You may call your Senator directly in Washington by calling the U.S. Capitol main number 202-224-3121 or find their office numbers through The Planetary Society Legislative Action site. Please call today; the vote is tomorrow morning.

Thank you for your consideration and prompt action -- no one is more devoted to the future of human and robotic space exploration than Members of The Planetary Society.

Sincerely,

Louis Friedman
Executive Director