Climate Change

The following is part of my research into climate change. I do not consider it complete; some sections need to be fleshed out a bit, but it's what I've got for now. Also, I had some formatting problems with the last half or so, hence the breaks instead of indents between paragraphs.

Climate Change

Climate change may be the most important scientific issue facing the global community (Maslin, 2009). In the past few decades several international organizations have formed to meet the need for scientific, political, and economic analysis.[1] Climatology and paleoclimatology are relatively new fields of research; the development of more sophisticated global-scale observations is needed to validate and refine existing atmospheric models (Crutzen, 2000). The large uncertainties surrounding climate change remain current areas of research (Raisanen, 2007).

Global climate change is thought to be primarily due to variations in the Earth’s orbit around the Sun and varying levels of greenhouse gases (Maslin, 2009; Stanley, 1999). These influence the Earth’s energy budget by affecting, respectively, the amount of energy received from the Sun or the amount of energy lost due to radiative cooling (Maslin, 2009).

Variations in the earth’s orbit thought to be responsible for climate change include changes in the earth’s precession, obliquity, and the eccentricity of its orbit. Planetary orbits are elliptical, and the eccentricity of a planet’s orbit is the ratio of the two foci to the major axis of the ellipse (Morrison, Wolf, & Fraknoi, 1995). In other words, eccentricity describes how stretched out the oval-shaped ellipse is; this determines the range of distances between the planet and the sun that is experienced during a revolution.

Obliquity describes the tilt of the earth on its axis (~23°) and precession is the approximately 26,000 year cycle in which the earth “wobbles” on its axis like a top (Morrison, Wolf, & Fraknoi, 1995). These variations affect the amount of incoming solar radiation (or insolation) received from the sun and therefore affect Earth’s climate (Maslin, 2009).

Orbital variations (sometimes called Milankovitch cycles after the scientist who popularized the theory) are an example of external forcing on earth’s climate. Greenhouse gases are an example of an internal forcing (Maslin, 2009). When the Sun’s radiation reaches the Earth, around 30% of it is reflected back out into space and the other ~70% is absorbed. Earth’s atmosphere absorbs around 20% of the energy and the earth’s surface absorbs the remaining 50% (Karl, 2003; Maslin, 2009). The energy absorbed by earth’s surface is then re-radiated in the form of infrared light (Karl, 2003). This infrared light (or heat energy) is mostly released into space; greenhouse gases, however, absorb some of this energy and re-radiate it within the earth’s atmosphere. This is the “greenhouse effect” from which greenhouse gases (hereafter GHG) receive their name, and the presence of GHG results in an increase in the earth’s average temperatures (Maslin, 2009). The greenhouse effect keeps earth habitable, as without any GHG the earth’s average temperatures would be around -18° C, over 30 ° C colder than current averages (Ward & Brownlee, 2000, p. 207).

Examples of GHG and their relative contributions to the global greenhouse effect include water vapor (60%), carbon dioxide (25%), ozone (8%), methane, and nitrous oxides (Karl, 2003). The atmospheric levels of these gases have varied throughout the earth’s history and contributed to past climate change (Maslin, 2009; Stanley, 1999).

Orbital variations and GHG are only two of a myriad of variables involved in earth’s climate system (Rind, 2002). Others include the ocean circulation system, variations in solar output, aerosols, vegetation, and various feedback mechanisms (Rind, 2002). Scientists are divided over the relative importance of each of these mechanisms, and the sheer number and dynamicity of these variables make accurate reconstructions and models difficult (Bony et al., 2006; Maslin, 2009; Raisanen, 2007).

What is clear is that the earth has experienced dramatic climate changes in the past; these changes include natural cycles between ice ages and warmer, interglacial periods as well as the corollary changes in sea level, temperatures, precipitation patterns, ocean circulation, atmospheric circulation, and ice cover. The exact mechanisms responsible for past climate change are a source of debate and uncertainty within the scientific community (Maslin, 2009; Paillard, 2006).

Past and Current Climate Change

The global average temperature of earth has increased by approximately .75 degrees Celsius over the past 150 years (Maslin, 2009; IPCC, 2007). According to the IPCC (2007) the consensus among scientists is that the primary cause of this global warming is anthropogenic (human-caused) carbon dioxide emissions. Since the industrial revolution humans have been burning fossil fuels (e.g. coal, oil, gasoline) for energy. The combustion of fossil fuels results in the formation of carbon dioxide, which is released into the atmosphere (Eubanks et al., 2006). Pre-industrial levels of carbon dioxide (CO₂) in the earth’s atmosphere were around 280 parts per million (ppm). Current levels are ~385 ppm, an increase of over 100 ppm (Maslin, 2009). Since CO₂ is a greenhouse gas, rising CO₂ levels result in an increase in the amount of outgoing infrared radiation absorbed within the earth’s atmosphere. This additional heat energy causes an overall warming of the earth (Eubanks et al., 2006).

In An Inconvenient Truth, the popular documentary[2] about global warming, Al Gore makes the claim that earth’s past ice ages and intervening warm periods are due to the rising and falling of carbon dioxide (CO₂) levels (Bender, 2006). Gore points to reconstructions of temperatures and CO₂ levels for the last 650,000 years drawn from ice cores in Antarctica. In this ice core record there is a clear correlation between high CO₂ levels and high temperatures and vice versa (Maslin, 2009, p. 7). Gore claims that these records offer evidence that CO₂ levels have driven past climate change; therefore, the dramatic anthropogenic increase in CO₂ levels seen over the last century will have a correspondingly large increase in global temperature. In the ice core records, however, a clear cause and effect relationship between CO₂ levels and temperatures does not exist (Caillon et al., 2003). In fact, the Vostok ice cores from Antarctica show that in the past temperatures have risen around 800 years before the CO₂ levels rise (Caillon et al., 2003; Maslin, 2009; Soon, 2007). The rising CO₂ levels are thought to amplify the warming that is already taking place, but are not the ultimate cause of the fluctuations between ice ages (Caillon et al., 2003; Maslin, 2009). Past ice ages and interglacial periods were caused by orbital and solar variations (Maslin, 2009).

In the Miocene period, 13.9 million years before present (BP), a global cooling episode was initiated by a change in earth’s obliquity (Holbour, Kuhnt, Schulz, & Erlenkeuser, 2005). This resulted in the extensive ice sheets that continue to cover Antarctica today (Holbour et al., 2005). Sea surface temperatures were high during this ice buildup; this is consistent with an orbital variation being the cause rather than a change in GHG levels (Holbour et al., 2005). CO₂ levels did decrease during this cooling episode, but this was due to orbital influences on the carbon cycle; this in turn led to further expansion of the Antarctic ice sheets (Holbourn et al., 2005).

In the past 2.5 million years orbital variation has been the dominant forcing involved in the transitions into and out of ice ages (Maslin, 2009). Over the past 423,600 years, during the late Pleistocene, Milankovitch cycles account for the majority of climate change (Meyers, Sageman, & Pagani, 2008). Both precession and obliquity cycles were involved in these changes (Huybers, 2006; Meyers et al., 2008).

During the last interglacial period, ~129,000 years BP, orbital variations caused a warming episode that resulted in extensive open water in the Arctic (Otto-Bliesner et al., 2006; Overpeck et al., 2006).

The current interglacial epoch, the Holocene, began around 10,000 years BP (Maslin, 2009). There is evidence for precessional forcing of climate change during this period, including changes in both ocean hydrology and atmospheric circulation and precipitation patterns (Partin, Cobb, Adkins, Clark, & Ferndandez, 2007; Shin, Sardeshmukh, Webb, Oglesby & Barsugli, 2006).

Milankovitch cycles correlate well with past climate change (Maslin, 2009; Meyers et al., 2008; Soon, 2007). The relationship between GHG levels and climate, on the other hand, is a source of controversy among scientists (Kerr, 2001). Historical records indicate a strong correlation between GHG and climate (Alley, Clark, Huybrechts, & Joughin, 2005). A reduction in GHG may have caused glaciation during the Carboniferous period 354-290 million years BP (Came et al., 2007). There is evidence that ~35 million years BP a reduction in CO₂ levels may have contributed to global cooling (Garzione, 2008; Stanley, 1999). Retallack (2007) found paleosol evidence indicating that CO₂ levels were a controlling factor throughout the Cenozoic (~65 million years ago - present). In contrast to these findings, reconstructions by Rothman (2002) show that CO₂ levels do not correlate well with warm or cool periods over the past 500 million years.

It is likely that both orbital variations and GHG levels have contributed to past climate change (Paillard, 2006). Other mechanisms such as varying solar output and shifts in ocean circulation also play an important role in regional and global climate change (Curry, Dickson, & Yashayaev, 2003; Rohling & Palike, 2005; Thornalley, Elderfield, & McCave, 2009). The earth is a dynamic interconnected system and further research is needed for any certain conclusions about the mechanisms that can explain past climate changes (Paillard, 2006; Rind, 2002). In particular, research into the interactions between orbital forcing and other mechanisms, such as ice-sheet or cloud feedbacks, is needed (Huyberys, 2006; Bony et al., 2006).

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[1] E.g., the International Panel on Climate Change (IPCC), Alliance of Small Island States (AOISIS), and the United Nations Framework Convention on Climate Change (UNFCCC).

[2] An Inconvenient Truth won multiple Oscars and is currently the 4^th highest grossing documentary

(see Box OfficeMojo.com)

The Miller-Urey Experiment

The Origin of Life

Though Darwin’s theory of evolution applies to the diversification of biological life, not the origin of biological life, scientists have nonetheless attempted to find a naturalistic explanation of life’s origin through recourse to Darwinian type events. Competition between the first self-replicating molecules is thought to have led to increasingly efficient and complicated bio-molecules until the first primitive cell emerged. The question then is: where did these first self-replicated molecules come from? Every living thing known to science utilizes the same set of bio-molecules to reproduce: DNA, RNA, and proteins. These are enormously complicated molecules that, respectively, contain genetic information, the ability to translate and transport genetic information, and the ability to construct molecular machines (including other proteins) based on that information. Without all three components in place and functioning, there is no self-replication. The difficult task facing origin of life scientists is to discover which bio-molecule came first, and how, and then to show how the other bio-molecules developed to form the first reproducing organism.

Darwin himself thought that life may have arisen from a “warm little pond,” and in the early 20th century the scientists J.B.S. Haldane and A.I. Oparin independently speculated that a pre-biotic organic soup must have arisen early in the Earth’s history. Haldane and Oparin postulated a reducing atmosphere for the early Earth, an atmosphere containing abundant hydrogen, methane, ammonia, and water vapor. It was a logical assumption, as hydrogen is the most abundant element in the universe, and methane and ammonia are both hydrogen containing compounds. In this environment organic molecules were thought to naturally accumulate into the organic soup, and eventually, into life itself.

Miller’s Experiment

In 1953 a graduate student name Stanley Miller decided to test what may be called the “Oparin-Haldane Hypothesis.” Working under his advisor, Harold Urey, Miller created an experimental set-up to explore whether synthesis of organic molecules was possible in the hypothetical atmosphere of the early Earth.

Miller’s device (see Figure 1) contained three main compartments filled with water, methane, ammonia, and hydrogen. The water was boiled and electrical charges were sent through the vapors, which then passed into the next compartment and cooled and condensed. He ran the device for a week and then analyzed the resulting compounds. Miller discovered that among the compounds were some amino acids, the building blocks of proteins. This result sent a ripple through the scientific community. Miller had uncovered experimental evidence demonstrating the first steps of how life could have arisen purely through natural means. The experiment has become a staple in science textbooks, often accompanied by words like "the Miller-Urey experiment has shown that biological molecules can accumulate through natural means, and events like these led to the formation of life on Earth.1" But just how significant were Miller’s results?





Figure 1


First, it had been known for a century that organic compounds could be synthesized from inorganic ones, so the fact that organic materials can result from reactions with non-biological materials had already been discovered (Schopf 2002).

Second, it turns out that Miller’s experiment has several problems. One major problem with the Miller experiment is the assumption of a reducing atmosphere. Electrical sparks in an oxidizing atmosphere (like our current atmosphere) do not lead to any organic compounds. As mentioned above, the atmosphere was originally thought to be reducing (composed of hydrogen, methane, and ammonia) because of the abundance of hydrogen in the universe. The problem is that hydrogen is too light for earth's gravity to hold it, and it escapes out of our atmosphere (Brinkman 1969)(Catling et al. 2001). Geochemists and atmospheric scientists currently believe the Earth’s original atmosphere was neutral, not reducing (Miyakawa et al. 2002)(Shapiro 1986)(Schopf 2002)(Stanley 1999). The atmosphere came from the interior of the earth through volcanic outgassing. Small amounts of oxygen also had to be present due to photodissociation2, though the exact levels at which oxygen was present remain unclear (Brinkman 1969)(Stanley 1999). What is clear is that oxygen is present as far back as the rock record goes (Rosing and Frei 2003). In any case, it is now recognized that the early atmosphere was neutral and consisted of nitrogen, carbon dioxide, and water vapor with trace amounts of hydrogen, oxygen, and other gases (Schopf 2002)(Shapiro 1986)3.

In addition to hydrogen not being present except in trace amounts, the existence of methane and ammonia on the early Earth are also problematic. Since there was little oxygen on the early Earth, there was no ozone (O3) layer to absorb ultra-violet light. In addition, the younger sun would have produced ultra-violet light levels 30 times stronger than current levels (Schopf 2002)4. Methane and ammonia are both rapidly decomposed by UV rays and plausible suppliers of large amounts of these gases on the early earth do not exist. Neither could have been present on the early earth except in trace amounts (Schopf 2002)(Shapiro 1986). So, hydrogen, methane, and ammonia could at best be trace gases in the early atmosphere, but Miller's experiment postulated an atmosphere containing only them and water vapor. Clearly this is a fundamental flaw. Neutral atmospheres when sparked create only the simplest biological molecules, and this only with considerable hydrogen sources (Schopf 2002.) Since there are no plausible significant hydrogen sources for the early Earth's atmosphere, Miller’s experiment is something of a non-starter. However, there are other problems still.

Though it may seem trivial, the spark itself in Miller’s experiment is problematic, as there is no natural counterpart to the type of spark Miller used. He actually has tried simulating a lightning-type spark and, in his own words "very few organic compounds were produced and this discharge was not investigated further” (Shapiro 1986).

Miller's apparatus also contained a crucial piece: a trap which separated some of the resulting compounds, saving them from further exposure to energy. In nature, there is no such convenient trap, and the same energy that caused any molecules to bond would just as quickly (and in fact more commonly) break down those molecules. Energy is far more likely to break things down than to build them up. Effectively harnessing energy requires delicate, complicated, specific processes carried out by appropriate molecules. These processes do not occur in organic soup, and the soup would have moved toward equilibrium (the breakdown of all biological molecules is energetically favored in water) (Shapiro 1986)(Schopf 2002).
Interestingly, the specific arrangement of the device itself is in part responsible for the result of biological molecules. Miller had previously done the same experiment, with the same chemicals and spark, but with the pieces of the apparatus in a different arrangement and no biological molecules formed. The design of the apparatus favored the production of certain types of organic molecules, but in nature the process would not be so ordered (Shapiro 1986).

Ignoring all these problems, let us consider Miller's results anyway. The majority (85%) of the result can be referred to as tar, or organic goo, bearing no relevance to biological life (Shapiro 1986)(Schopf 2002). Of the approximately 50 major small organic compounds relevant to life, two were produced in Miller's experiments in a meaningful amount. These were the two simplest amino acids, glycine and alanine. There are twenty amino acids relevant to life, and though six were produced in Miller's experiment, only the aforementioned two were present in more than a miniscule amount. In addition, around half of the already small amounts of amino acids that were present are irrelevant to life due to the chirality problem (Shapiro 1986)(Schopf 2002). The chirality problem is that amino acids come in two forms, mirror images of the other. Only one type (the left-handed ones) are relevant to biology, and amino acids which spontaneously form will end being about half one type and half the other.

Miller’s results consisted of small amounts of a few of the molecules needed for life.5 The majority of a simple organism like a bacterium is composed of proteins (microscopic molecular machines), nucleic acids (DNA and RNA), polysaccharides (sugars), and lipids (fatty membranes). "None have been detected, in any amount, in a Miller-Urey experiment" (Shapiro 1986).

Conclusion

In short, even if the Miller experiment had turned out to simulate realistic conditions on the early Earth, its results are truly a most insignificant step toward figuring out how life arose. It is clear that the significance of this experiment has been grossly exaggerated. Miller himself has said as much. The severe problems with the experiment have led to interest in a variety of other ideas to explain the origin of life, including hydrothermal vents, meteorite seeding, and even panspermia (the idea that extraterrestrials planted the first life forms here).
So then, students should be taught that the Miller experiment is what it appears to be: a historically important but outdated and flawed experiment.

A further note: even if Miller’s experiment had generated every last biological molecule known to man, present in exactly the right proportions, we still would not have solved the origin of life. One could have all the right pieces together, in any conditions, and still “life” would not emerge. Scientists are unable to re-create any kind of cell even with all the right materials and controlled conditions. How then did it happen by accident on the early Earth?








1. Some modern textbooks do acknowledge the deficiencies in Miller’s experiments, but the Miller experiment remains an icon of pre-biotic evolution.
2. Photodissociation is the breakdown of H2O into hydrogen and oxygen by sunlight.
3. Scientists estimate that oxygen levels just 1% of current levels would prevent organic molecules from forming at all on the early earth.
4. The strong UV rays would have also instantly destroyed any biological molecules that had formed.
5. Subsequent Miller-type experiments have resulted in the production of almost all of the 20 amino acids found in proteins. While interesting, see the rest of this essay.



Works Cited

Brinkman, R.T., 1969, The photodissociation of water vapor, evolution of oxygen and escape of hydrogen in the earth’s atmosphere. PhD. Diss., California Institute of Technology, http://resolver.caltech.edu/CaltechETD:etd-10062004-120013

Catling et al., 2001, Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of the Early Earth. Science, 839-843

Miyakawa et al. 2002. Prebiotic synthesis from CO atmospheres: implications for the origin of life. PNAS, 14628-14631

Rosing, M.T. and Frei, R., 2003. U-rich Archaean sea-floor sediments from Greenland – indications of > 3700 Ma oxygenic photosynthesis. Earth and Planetary Science Letters, 237-244.

Schopf, W., ed. 2002. Life’s Origin: the beginnings of biological evolution, California, UCAL Press

Shapiro, R. 1986. Origins: a skeptic’s guide to the creation of life on earth, New York, Simon & Schuster Inc.

Stanley, S. 1999. Earth System History, New York, W.H. Freedman and Company