Gas Hydrates and Greenhouse Effect

Gas Hydrate                   Non-flowing, ice-like, crystalline non-stoichiometric compound (a solid not having its component elements present in the exact proportions indicated by its formula) consisting of small gas molecules surrounded by and enclosed within a cage of water molecules that is similar to ice except that the crystalline structure is stabilized by the guest gas molecule within the water molecule cage. For that reason, these structures are also called clathrates, or cage compounds. They can exist only where high pressures and low temperatures squeeze water and methane into a solid form. Although many gases have molecular sizes suitable to form hydrate, marine gas hydrates are by far the most abundant. Gas hydrate can only form in the presence of sufficient amounts of gas and water and only under specific pressure and temperature conditions. In order to be stable, gas hydrate requires high pressures and comparatively low temperatures. Methane hydrate, which looks very much like ordinary ice, is stable in fairly shallow ocean floor sediments in polar regions and at water depths greater than 300 meters. At those depths it is known to cement otherwise unconsolidated sediments in a surface layer several hundred meters thick.

        Methane and other hydrocarbons trapped in marine sediments as hydrates represent an immense carbon sink. The worldwide deposits of carbon contained in gas hydrates are conservatively estimated to total twice the amount of carbon found in all known fossil fuels on Earth. Those resources have the potential of becoming dominant factors in the future analysis and development of unconventional and previously untapped energy resources. As analysis of those resources proceeds, the investigation of gas hydrate in terms of its interaction with climate as a so-called “greenhouse” gas will be a critical research issue. Other critical research topics include the role of gas hydrates in the carbon cycle and as a factor in the stability of sediments on continental slopes. Real World Examples: Recent mapping conducted by the USGS demonstrated large accumulations of methane hydrates off the coasts of North and South Carolina in an area called the Blake Ridge. Two large concentrations of gas hydrates were found, each about the size of Rhode Island. USGS scientists estimated that those areas contained more than 1,300 trillion cubic feet of methane, representing about 60 times the natural gas consumed in the entire U.S. in 2000. Gas hydrates are also found under the Arctic permafrost. In 2003 in the Canadian Northwest Territories, an international group of engineers drilled hundreds of yards below the permafrost in the Mackenzie River delta into hydrate deposits, pumped in hot water, and released the gas in a test to determine whether they could tap what may become a new energy source.

        Author’s Note: Originally discovered in 1810 in the laboratory of Sir Humphrey Davy, these compounds are found in nature and are stable under specific conditions of temperature and pressure. Very large amounts of natural gas can be stored in hydrate form and can be released to the atmosphere during hydrate decomposition in response to climate warming, undersea disturbances such as landslides or earthquakes, or changes in sea-level, particularly in coastal areas affected by contact with water of warmer temperature than the ground.

        Real World Problem: Sudden, large-scale releases of methane from hydrates can potentially cause rapid climate changes that may have catastrophic consequences for existing life, including animal, plant, and human especially through a drastic rise in global warming. Today, methane hydrates are stored naturally along continental margins where they are stabilized by water pressure and temperature. But the fear of scientists is that ocean warming or slope instability may result in methane hydrates becoming unstable and being released in large quantities to the atmosphere. The reason for that fear is that methane is 20 times more powerful as a so-called “greenhouse” gas than carbon dioxide. Gas hydrates also present hazards during exploration drilling, hydrocarbon production, and construction of oil and gas pipelines because they have the potential of becoming unstable during the drilling, production, or construction processes if the areas where hydrates are found become warmed and slope destabilization causes massive landslides that release huge amounts of methane, with potentially catastrophic global climatic consequences. Uncontrolled gas releases, blowouts, fires, and instability of sediments at well sites and along pipelines may occur without adequate safeguards.

        Today, gas hydrates constitute a largely unexploited means of energy recovery and in the future could play significant roles in climate change as well as energy consumption. The high risk of catastrophic release into the atmosphere makes hydrate exploitation one of the very realistic worries environmentalists have when energy companies talk about developing techniques to harvest methane hydrates on or below the sea-floor. For additional general information, see: http://woodshole.er.usgs.gov/project-pages/hydrates/ and for exploitation information see: http://emd.aapg.org/technical_areas/gas_hydrates/index.cfm

Greenhouse Effect             A terrible and fundamentally wrong physical analogy that no good geoscientist should use or accept uncritically. First of all, the atmosphere does not in any way act like a greenhouse, which works by trapping heat and suppressing convection. Think about it: if the atmosphere actually trapped energy and suppressed convection, the Earth’s surface temperature would continue to rise until all life would be cooked like lobsters in a pot. We know that’s not happening for many reasons but especially because the long-term average temperature of the atmosphere has been fairly constant (with exceptions that should be obvious) and, better yet, life still abounds on the Earth, which it would not if the so-called greenhouse effect actually existed.

        It is also not true to say that radiation is trapped by atmospheric gases and then is subsequently re-radiated or that so-called greenhouse gases act as a global blanket. That’s pseudo-scientific nonsense. So, if those claims are nonsense, which they are, what’s really going on? The answer is simple and straightforward. The Earth’s surface is warmer than it would be in the absence of an atmosphere because it receives energy from two sources, the Sun and the atmosphere, which receives energy from the Sun but mainly from the Earth via radiation, latent heat, and convection. In the end, NO greenhouse effect can be determined, only an atmospheric effect that warms the Earth’s surface. The energy emitted by the atmosphere is derived partly from energy received in the form of solar and terrestrial radiation but the energy emitted is not the same radiation nor is it even the same spectrum as that energy that might have been received previously. In other words, the Earth is heated because atmospheric gases absorb outgoing radiative energy and re-emit a portion of that energy back towards Earth.

        Author’s Note: Of course, the real problem is that the term is so enshrined in public consciousness by being repeated ad nauseam by the news media and in uncritical scientific publications that eradicating it is impossible. For more detailed discussions on this fascinating topic, all readers should consult a wonderful web site that was created by Alistair B. Fraser, Emeritus Professor of Meteorology, Pennsylvania State University. It is chock full of very useful information on greenhouses gases as well as numerous other topics: “Bad Meteorology” at: http://www.ems.psu.edu/~fraser/BadMeteorology.html.

        The “greenhouse effect” was discovered by Jean-Baptiste-Joseph Fourier in 1824, first reliably experimented on by John Tyndall in 1858, and first reported quantitatively by Svante Arrhenius in 1896.

        Early in his remarkable career, Fourier revolutionized the world of mathematics with equations that are now known as the Fourier series, which he created in a successful effort to elucidate heat diffusion and movement (On the Propagation of Heat in Solid Bodies and The Analytical Theory of Heat). But it was during his several travels to Egypt in the late 1790s and early 1820s that he began thinking about why the Earth’s heat remained close to the surface and was not re-radiated into space. After reflection, Fourier came up with a novel idea, that much of the energy failed to escape because the atmosphere, including its water vapor and clouds, worked like an invisible dome, or bell-jar, absorbing part of the heat and re-radiating it back to the Earth’s surface. His view of the atmosphere was that it functioned like a gigantic thermal envelope that prevented heat from escaping.

        Despite his wide-spread influence in mathematics, Fourier’s work on the atmosphere received scant attention from the scientific community and was soon regulated to the proverbial back burner. In the 1860s, Irish physicist John Tyndall began analyzing properties of the atmosphere, especially those of heat, light, and acoustics. Part of his lab work included construction of the first ratio spectrophotometer, an instrument he used to measure the absorptive powers of such gases as carbon dioxide, various hydrocarbons, ozone, and water vapor. Among his most important discoveries were the vast differences in gases and vapors in absorbing and transmitting radiant heat. He discovered that hydrogen, nitrogen, and oxygen are almost transparent to radiant heat, while other gases are very opaque. Tyndall’s experiments also showed that molecules of water vapor, carbon dioxide, and ozone were the best absorbers of heat radiation and that even in small quantities those gases absorbed heat much more efficiently than the atmosphere itself, a phenomenon that had great meteorological significance. He concluded that water vapor was the most important gas in controlling the Earth’s surface air temperature and later speculated that changes in water vapor and carbon dioxide could be related to climate change.

        About 30 years later that topic was revisited by the Swedish chemist, Svante August Arrhenius (1859-1927), whose earlier contributions on the conductivities of electrolytes had won him considerable standing among a select group of northern European scientists, several of whom became the first recipients of the Nobel Prize in chemistry. Arrhenius was captivated by the idea that ground temperatures might be influenced by heat-absorbing gasses in the atmosphere. His interest had been sparked by one of the then current scientific rages sweeping Europe: the cause of the prehistoric ice ages. He was well aware of earlier scientific work in the field, especially Tyndall’s, and wrote that Fourier had maintained that the atmosphere acted much like the glass in a hothouse, which was probably the first use of that inappropriate and unfortunate analogy, later referred to as the “so-called greenhouse effect” by the climatologist Glen Trewartha. Arrhenius was also familiar with research by the American physicist, Samuel Langley, that had demonstrated that if Earth’s atmosphere did not possess selective energy absorptive qualities then the surface temperature would fall to around -200° C. Locked in the grip of fierce determination to solve that puzzle, Arrhenius spent a full year (1895-1896) doing mathematical analysis so arduous and tedious that it would have numbed a stone, only to finally emerge with the first theoretical energy budget model that could be used to calculate the influence of the effects of carbon dioxide on the Earth’s surface temperatures.

        Arrhenius’s work in 1896 quantified the atmospheric CO₂ effects found by the geologist, Arvid Gustaf Högbom, one of the first serious investigators of the carbon cycle, but also demonstrated that variations in the CO₂ content of the atmosphere may have accounted for glacial and interglacial periods. His Heraclean mathematical effort had resulted in the construction of a series of tables that demonstrated how water vapor and carbon dioxide were responsible for warming the Earth. In particular, his now well-known Table VII demonstrated with mathematical rigor exactly how increases or decreases in CO₂ would affect surface temperatures (Arrhenius’s Table VII actually consisted of five tables arranged side by side, with each representing a different concentration of what he called “carbonic acid”).