Weather and Climate
A distinction must be made at the outset in the difference between climate and weather as it is a common fallacy to confuse the two.
Weather is the day to day atmospheric conditions at a location or region: temperature, precipitation, wind, humidity etc.
Climate is the atmospheric conditions of a location over a much longer period of time. Changes in weather can be dramatic, but changes in climate are usually more subtle. Climate is determined by long term weather patterns in a location or region by values of certain atmospheric elements. These are:
- Air temperature
- Humidity
- Type and amount of cloud
- Type and amount of precipitation
- Air pressure
- Wind speed and direction
A change to one weather element may provide the impetus for changes in other elements. A change in average temperatures in a climate region, for example, may increase cloud cover and precipitation. If these changes are prolonged over a period of time it will change the climate values for that element. Simplistically, Global Climate is the mean of long term local weather patterns around the world. So, while weather and climate are different, they are inter-related and changes in weather patterns over time can indicate a change in climate in that region.
Global Climate Change is a process brought about by prolonged changes to the values of atmospheric elements on a global scale. Increases or decreases in the mean temperature of the Earth will affect most weather elements and is a trigger for climate change.
Scotland and its Climate
Scotland is a small country with a population of around 5 million people; more than half the population live around the central belt. The country has a temperate climate due to the North Atlantic Oscillation which flows to the west and north from The Gulf of Mexico to Iceland. January and February are usually Scotland’s coldest months with average daytime temperatures of 5 to 7°C (Meteorological Office, 2005). It is the exception for temperatures to fall below -5 or -6°C, and then it is usually inland and away from the moderating coastal areas. In recent years winters have been less severe and shows a falling trend over the last six years in the twenty-year mean of the Hospital Degree Day calculations (18.5°C).
The Greenhouse Effect, Global Warming and Climate
Greenhouse Effect
In 1824, the Frenchman Jean-Baptiste (Joseph) Fourier predicted an atmospheric Effect which keeps the mean temperature of the planet higher than it would normally be. This Effect later became known as the greenhouse effect.
The greenhouse analogy is a simplified view of a complex process. However, the balance of gases in our atmosphere (Table 1) creates a state “similar” to that of a greenhouse; the glass (atmosphere) allows solar radiation through, mainly in the visible end of the spectrum, but it traps the redirected longwave infrared radiation allowing the greenhouse (Earth) to heat up; temperature, humidity are regulated and the environment created within is right for things to grow which is likely why the term “greenhouse effect” was used to describe it.
However, the term “greenhouse effect” used in this context is a misnomer. Although the commonly understood mechanism of trapping longwave radiation by the glass does occur, greenhouses heat up mainly due to the sunlight warming the earth inside the greenhouse, and the glass enclosure prevents heat loss by convection. However, because there is no convection from planet Earth to outer space, the major heating effect in a greenhouse cannot apply. So, while “Greenhouse Effect” is not a correct term, it is the most commonly used one and it will continue to be used here.
Changes to the balance of gases in the atmosphere are believed by many scientists to be responsible for the noted increase the global temperature, though this is still a contentious issue in some quarters. This has become known as an enhanced, or anthropogenic, greenhouse effect and the resultant increase in the mean global temperature is a driver for Climate Change. Various constituents of the Earth’s atmosphere, notably carbon dioxide, are responsible for absorbing longwave radiation. In 1750 the carbon dioxide level in the atmosphere was 278ppm and by 1998 this had risen to 365ppm (IPCC, 1998); in 2007 it stands at 381ppm (IPCC, 2007). Due the length of time between these reports, there are some scientists who believe the level is much higher than this now (they may be correct).
Greenhouse Gases (a little of the science)
The natural gases in the atmosphere affecting the Greenhouse balance are: Carbon Dioxide (CO2), Water Vapour and Ozone (O3). Other contributing gases are: Methane (CH4), Nitrous Oxide (N2O), Sulphur Hexafluoride (SF6) and Chlorofluorocarbons (CFxCLx). Greenhouse gases are not limited to this list, and it is significant to note in Table 1 that they are all trace elements in the atmosphere. The major constituents of our atmosphere, Nitrogen and Oxygen do not contribute to the greenhouse effect because homonuclear diatomic atoms such as N2 and O2 do not absorb infrared. The reason for this is that there is no net change to the dipole moment of these atoms.
If the natural greenhouse gases did not exist in our atmosphere then the temperature at the surface of the Earth would be much lower than it is now. The total quantity of solar radiation (Qs) the surface of the planet receives is given as:
[1] Qs = πR^2•S(1-A)
where R is the radius of the planet (6380 x 10^3m) S is the solar constant(1.37kW/m^2) and A is the albedo of the earth (reflection of solar energy from atmosphere, clouds, icefields, deserts etc.) which is around 29% of all solar energy reaching the Earth (Kushnir, 2000). The albedo effect referred to here is the "Bond" Albedo which is the total radiation reflected from an object compared to the total incident radiation from the Sun. This is different from the "Geometric" Albedo which is defined as the amount of radiation relative to that from a flat Lambertian surface which is an ideal reflector at all wavelengths (de Pater and Lissauer, 2001). The Bond Albedo is probably a truer representation of the Earth’s reflective properties.
Our atmosphere notwithstanding, the received solar radiation heats the surface of the earth to what is known as the Effective Temperature (Te). We may assume that the Earth acts as a black body emitting radiation in accordance with the Stefan-Boltzmann Law, which states that all radiation emits according to:
[2] Qr = σ • Te^4
where Qr is the total emitted radiation (W/m^2);
σ = Boltzmann Constant = 5.670 x 10^-8 J K^-4 m^-2 s^-1
This means that the total emission of infrared radiation (Qr) for the planet’s surface is given by:
[3] Qr = 4πR^2•σ•Te^4
The radiation emitted is a function of the surface temperature, and the temperature at the Earth’s surface is primarily in the infra-red region. However, in steady state there is a balance between incoming and emitted radiation, and by combining equations [1] and [2] we get:
[4] Te= [(S(1-A)/4 σ)] ^1/4
The result is, Te = 253K (-20°C). This would be the temperature of the Earth without a Greenhouse Effect – too cold for life as it has evolved on Earth. Fortunately, Earth has an atmosphere that provides the planet with an effect that absorbs some of the infrared radiation emitted from the surface, which raises the mean temperature of the planet to 288K (15°C) mainly due to the CO2 component.
Global Warming/Cooling
Throughout the 20th century an appreciable increase in global temperatures from the 288K (15°C ) has been detected by climatologists and other scientist. There are some disagreements as to the value of the increase, but the general consensus is that it is between 0.4-0.7°C (IPCC, 2004). There are two main periods during that time where the temperature increase was at its greatest: 1910-1945, and from 1976 till the present (Gore, 2006).
The first period appears to correspond to a dramatic increase in steel production mainly for armaments for two world wars, but there was also a massive increase in steel construction for ship building, bridge building, office, retail and domestic buildings and rail infrastructures. Coal mining was at its peak during this period. Indeed Sallie Baliunas (1998), in contradicting the consensus view of climate change, points out that some climate models show a greater increase in global temperatures before 1940 than after, when there was a greater increase in greenhouse gases. There have been major changes in the world economy since the 1960s. At the height of the Cold War, the birth of the petro-dollar saw a massive increase in manufacturing output (Elwood, 2001). Demand for cheap consumer goods in the affluent north helped drive new industries. The huge increase in car ownership and the decrease in quality of public transport may all have contributed to a huge rise in emissions of CO2, NOx and SOx from the combustion of fossil fuels. While Baliunas may be correct in highlighting the differences in temperature changes before and after 1940, it would be prudent to show caution when using short term models to identify long term changes in global temperatures.
Opposing Views on Climate Change
There are few who would challenge the current view that the mean global temperature is increasing (Mann et al., 1998, 1999), and the scientific consensus is that the change is due to anthropogenic interference (IPCC, 2004). Opposing views, however, which cite Nature as the main contributor to the variability of the present climate are many (Soon and Baliunas, 2003; Michaels, 2005; Singer, 1998; Lomborg, 1998). The aforementioned, among others, cite long term cycles of the sun as a radiative forcing which can increase solar output thereby increasing the solar budget of the Earth (Baliunas, 1998). For instance the Science and Environmental Policy Project when outlining the key environmental issues declares:
“Computer models forecast rapidly rising global temperatures, but data from weather satellites and balloon instruments show no warming whatsoever. Nevertheless, these same unreliable computer models underpin the Global Climate Treaty, negotiated at the 1992 Rio de Janeiro "Earth Summit," and are the driving force behind United Nations efforts to force restrictions on the use of oil, gas, and coal” (SEPP, 2006).
What it fails to address is that while data from satellites do show less warming than data from surface measurements, these satellites gather data from different slices of the atmosphere, including the stratosphere where ozone depletion creates a cooling effect. However, surface thermometers take temperature readings from the air close to the ground. Also, surface records exist from around 1860 while satellite records exist from only 1979. Over such a short period of time trends can be greatly affected by extreme conditions e.g. eruptions like Mount Saint Helens or Mount Pinatubo which can lower global temperatures for short periods (UCS, 2002).
Scientists such as those working with the IPCC agree that there is still much uncertainty, but urge a precautionary approach to the problem of global warming. Those who disagree or doubt that global warming is caused by increases in greenhouse gases appear to show more concern for the global economy. They believe that reducing emissions may cause more harm through economic depression. For this reason, many proclaim that there is little need for reducing CO2 and other greenhouse emissions (Baliunas, 1998). This researcher takes the precautionary view and supports the IPCC claims for the need to reduce emissions of such gases.
Reason for Caution
While temperature changes of 0.4°C and 0.7°C appear very small, it should be understood that the Little Ice Age experienced by Britain and parts of northern Europe between the 14th and 19th centuries occurred with less than 1°C reduction in mean global temperature. The mean global temperature during the last full ice age that saw thousands of metres of ice-cover across the northern hemisphere was less than 6°C lower than today. So it can take relatively small increases or reductions in mean temperatures to create significant climate change. Some scientists believe that a rise of 2°C could bring the planet to the climate “Tipping Point” (Hansen, 2006) resulting in accelerating temperature rises with catastrophic effects for humans and many other species.
Climate Change
Past, Present and Possible Futures
Arguments and disagreements over contemporary climate models notwithstanding, geologists have thrown up some dramatic theories on the historical instances of rapid climate change and its impact on life on the planet. Some geologists have ascertained that increases of this magnitude have occurred before with devastating effects.
Excessive increases in CO2 in the past have been shown to affect the Greenhouse balance hugely, as have excess emissions of Methane (CH4). CH4 is 21 times more potent as a greenhouse gas than CO2. Increased CO2 levels in pre-history are attributed to volcanism. However, the sharp and continuing rise since the beginning of the Industrial Revolution is seen as too much of a coincidence to be anything other than anthropogenic.
Changes in one aspect of the atmosphere can have impacts elsewhere. Increases in land and ocean temperatures can create positive feedback loops, which continue to amplify the initial effect, which could possibly result in the release of methane from tundra or ocean floors.
Methane is stored in tundra permafrost, and the ocean floor as methane hydrate. An organic hydrate is a fixed composition, or a stoichiometric compound, that has water molecules as an integral part of the crystalline structure. For such compounds a definite formula can be written. However, a definite formula cannot be written for an organic structure such as methane hydrate because there may be other “guest” gases contained within the structure. For that reason, natural gas hydrates are more suitably classed as non-stoichiometric compounds known as clathrates. A clathrate is, essentially, where the molecules of one substance are contained within the crystalline structure of another; usually consisting of gas molecules, normally methane, each surrounded by a cage of water molecules. The deposits of ice-like crystals trap natural gases under conditions of high pressure and low temperature and are found mainly in sea-floor sediments and permafrost.
It is interesting to note that in the Earth’s ancient atmosphere there was very little or no oxygen, and a lot of carbon dioxide. Under the influence of sunlight (UV and visible) reactions, similar to photosynthesis, among various organic molecules produced oxygen as a by-product – or in real terms, as a pollutant. O2 concentration increased as CO2 concentration dropped. As this change to the atmosphere came about, other reactions occurred using up the oxygen until eventually a balance was struck between O2 and CO2. This balance appears to be a delicate one. Life on Earth as we know it has evolved to survive within an arrangement of biomes all of which together create the greater ecosystem that gives the Earth the ability to support such a complex system of living organisms which includes homo-sapiens – us. It is a little odd then, that most life forms now depend on the pollutants created from the initial solar-radiation inspired chemical reactions within the “primordial soup”.
Possible Temperature Rises in the Next Century
There is a scientific view that a “methane burp” from the oceans in the late Palaeocene epoch, around 55 million years ago, caused a mass extinction of life on earth (Lynas, 2004). The Palaeocene extinction was not as great as the one 251 million years ago which brought the Permian epoch to an end – geological evidence from the earliest Triassic period, which immediately followed the Permian, shows a series of massive volcanic eruptions in what we now know as Siberia (Benton, 2003). Massive releases of CO and CO2 led to a rapid warming of the planet which appears to have destabilised the superconcentrated clathrates leading to the release of methane into the atmosphere. The black mudstone which forms the Permo-Triassic border is evidence of anoxia, or the lack of oxygen (Benton, 2003) which may have been responsible for the largest extinction in the history of the planet. This may have been the result of normal negative feedback systems* being overwhelmed or reaching a tipping point which allowed the release of methane on a massive scale due to heating of the oceans through global warming. The rise in global temperature at that period, which lead to a positive feedback loop, is estimated to have been 6°C (Benton, 2003) – the IPCC predicted in its early Assessment Reports an increase in global temperatures of between 2-6°C in the 21st century (IPCC, 1990,1995). These first reports concluded that “the balance of evidence suggests that there is a discernable human influence on global climate.”
- * In nature, Negative Feedback maintains stability within a system – one operator within a system tends to negate another e.g. natural pest control: predator feeds on pest keeps pest numbers down; eating too many pests reduces food-stock; reduces predator numbers maintaining homoeostasis. Positive feedback creates imbalances in a system and can create serious problems, this works similar to a microphone and speakers system where the feedback of sound creates a sound loop (known onomatopoetically as wow) which rises until either the microphone or amplifier is removed from the system. Positive and negative in this sense are the antithesis of how the words are used in everyday English.
The IPCC’s Third Assessment Report (IPPC, 2001) predicted an increase of around 10°C by 2100 and stated: “There is new and stronger evidence that most of the Earth's warming observed in the last 50 years is attributable to human activities.” The report is one of the more comprehensive studies of global warming to date and was approved unanimously. Scientists at the International Annual Conference and General Assembly of the Climate Alliance in Berlin in June 2003 appeared to agree with the IPCC’s model and concluded that temperatures could rise by between 7-10°C in the same period. If this is so then a release of a huge amount of methane could be possible. There are a number of estimates as to the amount of gas hydrates there are. The Benfield Hazard Research Centre (BHRC) point to the “consensus value” of several independent estimations of 10,000 gigatonnes (Gt). However, others estimate the value that best reflects current knowledge of submarine gas hydrate to be in the range of 500-2500Gt (Milkov and Sassen, 2002; Milkov, 2004).
Possible Implications for Human Societies
As previously mentioned, clathrates form under conditions of high pressure and low temperature and are usually stable in deep ocean floor sediments. These hydrates can cement and support loose sediments on the ocean floor in a surface layer hundreds of meters thick. If the hydrates are released these layers may collapse or slip causing tsunamis not unlike the one in the Indian Ocean on 26 December 2004. Geologist point to the Storegga Slide, a similar occurrence around 7,000 years ago, on the ocean floor between Iceland and Norway. An area of continental shelf, around the size of Wales with a total volume of 5,600km3 slipped causing a 20m tsunami which wiped out Neolithic communities on the north-east coast of Scotland (Maslin, 2004), and most likely the west coasts of Scandinavian countries as well. If such a slide happened today the damage to life and the environment would be colossal.
Temperature may have an effect on gas hydrates, but a more efficient way of destabilising gas hydrates on the sea floor is to remove pressure from it (Maslin, 2003). For instance, when a land-based icesheet melts and is removed, the underlying crust begins to move upwards as the weight is removed. This would be the same for a huge icesheet in shallow waters sitting and exerting its weight on the sea floor, but not for icesheets where the weight is supported by deep water. This upward movement is known as isostatic rebound and this can be seen in Britain where the north of Scotland is rising at a rate of around 3mm a year while the south of England is sinking at around 2mm per year. In short, the British mainland is tilting from the NW to the SE. This rebound will affect the continental shelf, and as offshore isostatic rebound occurs the sea level above the continental shelf becomes lower. This means that there will be less weight and pressure on the marine sediment, therefore the possibility exists of huge amounts of methane being quickly released. We are, at present, witnessing huge areas of icesheet melting on Greenland and Antarctica, and if these assumptions are correct on historical environmental occurrences, then it may be time to look seriously at how to reverse the effects of wasteful societies.
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