Global warming could possibly be one of the most disastrous geohazards to affect Earth. Due to many factors, the average surface temperature on Earth is rising relatively rapidly. A rise in the average temperature could have profound consequences for living organisms now and in the future. Because a global rise in temperature could impact humans negatively in a variety of ways, global warming is a geohazard. Additionally, the effects of global warming have been accelerated by human activity. When systems theory is applied to the Earth, we find that changing even the smallest components of the atmosphere can create major changes.
There are many ways the Earth's temperature can rise. The Milankovitch cycle, plate tectonics, volcanic expulsions, meteors, the thermohaline cycle, sunlight, and pollution can all change the Earth's surface temperature.
The Milankovitch cycle is based on three factors that concern the Earth's position with respect to the sun (www.studyworksonline.com). The first factor is the shape of the Earth's orbit around the sun. This orbit "changes from more circular to more elliptical on a cycle of about 90,000 to 100,000 years" (www.studyworksonline.com). The Earth receives more solar radiation differential as the orbit becomes more elliptical, which leads to a larger yearly variation in weather. Currently we are in a more circular orbit, with a lesser degree of solar radiation differential.
The second Milankovitch factor is the "angle of the Earth's axis of rotation to the plane in which the planet orbits" (www.studyworksonline.com). This angle changes over a period of 41,000 years. Because the angle of the Earth's axis of rotation determines the four seasons, a smaller angle results in less defined seasons whereas a greater angle gives more intense seasons. We currently have an angle that is slightly greater than the middle. Thus, we must be somewhere near the middle of this 41,000 year cycle, and have slightly more pronounced seasons than average.
The third Milankovitch factor is the wobble of the Earth's axis. This wobble currently aims at the North Star, and will aim at the star Vega in about 12,000 years (www.studyworksonline.com). When the wobble points at Vega, the Earth will have much colder winters and much warmer summers. Eventually, in about 27,000 years the wobble will have returned to the North Star (www.studyworksonline.com).
Plate tectonics can alter surface temperature distribution, and do so by opening and closing areas that contain oceans (www.studyworksonline.com). "For example, during times when all the continents were joined into one supercontinent, continental climates dominated most of the land surface; that is, climate was more extreme, warmer in some places and cooler in others. But when the continents separated, as they have today, heat was much more evenly distributed on the earth's surface and climate around the globe was less extreme" (www.studyworksonline.com).
Volcanism has the potential to affect the atmosphere in a twofold manner. Volcanoes release sulfurous gases when they vent, which can add to greenhouse gases. However, when volcanoes erupt and release tons of volcanic ash, the ash can reflect solar radiation, leading to colder temperatures around the globe for up to several years. 74,000 years ago a supervolcano eruption at Toba, in northern Sumatra blasted immense amounts of volcanic ash and debris into the air. "Greenland ice cores show that the Toba blast was followed by at least six years of volcanic winter'" (Bryson, 2004). "The event, it is thought, may have carried humans right to the brink of extinction, reducing the global population to no more than a few thousand individuals. That means that all modern humans arose from a very small population base, which would explain our lack of genetic diversity" (Bryson, 2004). Yellowstone is considered to be the most likely candidate as a supervolcano to be overdue for eruption. It is considered active, and "the cycle of Yellowstone's eruptions averaged one massive blow every 600,000 years. The last one, interestingly enough, was 630,000 years ago" (Bryson, 2004).
When volcanoes don't erupt, temperatures can get warmer (www.studyworksonline.com). This may be bad news if plate tectonics and the resultant volcanic eruptions ever slow down in occurrence rate.
Meteor impacts can also result in a lot of particulate matter rising into the atmosphere. The effect is much the same as volcanic ash in the atmosphere. It is thought that the major extinction event of the dinosaurs may have followed from such an occurrence as well as the following decrease in light and heat on the surface of the Earth. People in many countries are trying to find methods to mitigate disasters originating from space, and there isn't much an average citizen can do in this regard.
The thermohaline cycle is a process within the oceans by which heat is redistributed throughout the globe. Deep water currents bring warmth from the equator toward the poles, and colder water is brought from polar regions, sinking and traveling deeply back toward the equator. This system helps keep Britain and Ireland from having winters as cold as Russia. The system also moves nutrients around, allowing more space for ocean life to thrive in. The thermohaline cycle "may also be very sensitive to change. According to computer simulations, even a modest dilution of the ocean's salt content, from increased melting of the Greenland ice sheet, for instance, could disrupt the cycle disastrously" (Bryson, 2004). In other words, as global temperature increases and glaciers continue to melt, we can expect changes in the thermohaline cycle, different weather that results from the cycle, and changes in life in the ocean.
Another thing that should have raised the Earth's average temperature is sunlight. "One of the oddities of our solar system is that the Sun burns about 25 percent more brightly now than when the solar system was young. This should have resulted in a much warmer Earth" (Bryson, 2004). It seems, however, that the Earth may have a negative feedback loop where temperature is concerned.
Life itself, in order to stay alive, helps to regulate the temperature on the Earth's surface. Between trees and some "tiny marine organisms that most of us have never heard of" (Bryson, 2004), a large amount of carbon is continuously removed from the atmosphere. Bryson, in reference to the marine organisms, states that "by locking the carbon up in their shells, they keep it from being reevaporated into the atmosphere, where it would build up dangerously as a greenhouse gas" (Bryson, 2004). When these creatures die, their shells build up into limestone deposits under the ocean. "A six-inch cube of Dover chalk will contain well over a thousand liters of compressed carbon dioxide that would otherwise be doing us no good at all" (Bryson, 2004).
The predominant anthropogenic cause of global warming is pollution of the atmosphere and the hydrosphere. Gases such as methane, carbon dioxide, CFCs, and nitrogen and sulfuric wastes are being sent into the atmosphere. In the oceans, unregulated human waste dumping as well as massive oil and petroleum product spills also pollute. This can endanger one of the planets main carbon sinks, the tiny marine organisms that fix carbon. Less of these organisms would mean less carbon being absorbed from the atmosphere, which would mean warmer temperatures.
Carbon dioxide and methane in the atmosphere are considered greenhouse gases. In other words, solar radiation is allowed in through the atmosphere, is converted to heat at the surface, and is trapped in by these gases. "Study of the atmospheric carbon cycle shows that only about half of the anthropogenic emissions show up as increased carbon dioxide levels. This puzzle is not fully explained, but it seems that some terrestrial sinks are functioning as a negative feedback, that is to say they have increased their uptake as the atmospheric concentration has increased" (www.vic.com.au/nip24).
By cutting down forests we are damaging our other primary carbon sink, and exacerbating global warming. Such methods as slash and burn agriculture are therefore doubly dangerous. Slash and burn agriculture kills carbon sinks and releases the carbon into the atmosphere.
The problem with assessing global warming is that nobody is sure just how much of a temperature rise life on Earth can withstand before we reach a breaking point. There must be some threshold at which temperature rises will be too great for the negative feedback loop of carbon sinks to handle. Will anthropogenic releases of carbon dioxide and other greenhouse gases take us to this breaking point, even though what we release is so little compared to the average output of the planet itself?
The temperature rise that began accelerating around the time of the Industrial Revolution indicate that our increasing emissions are having indisputable effects on global warming. "Since the end of the last glacial period global temperature has risen about 4 degrees Celsius, with about 1 degree of that coming since the beginning of the Industrial Revolution (that is, one-quarter of the temperature change came in just 150 years whereas 3/4 of it came in the previous 10,000 years)" (www.studyworksonline.com). In other words, humanity's penchant for burning fossil fuels and releasing carbon into the atmosphere has dangerously accelerated the rise in temperature.
The effects of global warming will be numerous, as well as probably disastrous. Humans have become accustomed to living with things the way they are. Global warming will change weather patterns, water resources, food resources, and habitats of nearly all living organisms. Anthropogenic pollution worsens these effects, and is creating a situation where the global warming could conceivably exceed natural negative feedback loops, in essence transforming into a positive feedback loop with dire consequences. In other words, a runaway greenhouse effect much akin to that on Venus, which "has so much carbon dioxide that it is the hottest place in the solar system, an intense 900 degrees F" (www.studyworksonline.com).
Weather patterns will become more severe as more moisture is evaporated into the atmosphere from the oceans, which will grow in size as the ice caps, particularly in the northern hemisphere, melt. The oceans will also grow in size due to temperature rise and the resultant volumetric expansion. More surface area of the oceans means more evaporation, which leads to more water vapor in the air and will also add to the greenhouse effect while contributing more precipitation. This increase in precipitation will most likely fall in certain areas, like India (attributed to Lester Brown, Plan B) with devastating consequences. The severe storms would result in more floods, more hurricanes, more tornadoes, and more topsoil erosion.
Topsoil erosion would have two causes. The first would be due to increased flooding and rainfall. The second cause would be the increasing desertification of other areas of the world. Rising temperatures will exacerbate the already growing problem of desertification in areas where overgrazing, over-plowing, and recreational activities have previously made an environmental impact. Drought will also cause more farmlands to be abandoned as water resources are diverted to thirsty cities (attributed to Lester Brown, Plan B). Water resources, already on the brink of exhaustion in many areas of the globe, will be taxed beyond recovery. Deep fossil aquifers that replenish very slowly will be drained much more quickly under warmer conditions. As coastal freshwater is increasingly harvested by cities, saltwater incursion will destroy wetlands and render many coastal wells worthless.
Many niche species will have trouble finding bridges to new areas that they can survive in, and will likely succumb to the effects of global warming. This damage to the food chain could have disastrous consequences, essentially endangering every creature that is too selective in its feeding practices. Decreasing salinity in the oceans due to ice cap melting may also endanger life in the seas. It could also disrupt the thermohaline cycle and worsen the severe weather. In the long term, it is suspected that this could lead us into the next Ice Age, which would have further disastrous consequences for the northern hemisphere. If pollution of the oceans continues, there may come a point where the tiny marine organisms that fix carbon are endangered, which would lead to further global warming. Basically, it's a pretty cataclysmic state of affairs that humanity has set course to achieve.
But are things really going to get this bad? It is possible that life would never have survived on Earth without a negative feedback loop regulating temperature changes, so it is possible that we are overreacting. It is equally possible that we have overwhelmed the natural negative feedback loop already, and are heading toward disaster. The facts are that we know that we've had an impact on global temperature since the Industrial Age, and that to a large degree, this correlates directly with carbon dioxide emissions. So, temperature is rising faster than it would naturally, but it is still possibly within the acceptable bounds of the Earth's temperature regulating capacity.
It is possible, even likely, that the problem is overstated by the media, who only react to, and publish, sensationalistic material. Many environmentalists, in order to get the message out into the open, have gone with this sensationalism in order to bring a change in values toward being more harmonious with the Earth. Apocalyptic movements and disaffected individuals will also gravitate toward such end of the world' views because they desire the cataclysmic change in society that would result, due to their views that society is corrupt, will not change in a reasonable amount of time, and that they don't have a sense of belonging. Other greedy individuals who make their money or acquire power from fear may also enjoy the benefits that an apocalyptic environmental view can give them. Regressive people, who view technology and science as evil, also would love to see an abandonment of the industrial and post-industrial worldviews.
Considering all of these factors, one must ask oneself whether or not the threat of global warming is real, and if so, what to do about it. Having accelerated global warming, it is humanity's responsibility to mitigate our own causes. There is little if anything that can be done about natural causes. We need to plant forests, stop slash and burn agriculture, find alternatives to CFCs (especially in foreign developing nations), and reduce ocean pollution. We could regulate ships' waste dumping and smokestack emissions. We could eat less cattle and harvest their methane to use as a clean-burning fuel. We could harvest landfill methane as well. We could put scrubbers on smokestacks and stricter emissions laws on vehicles. We need to strengthen the Clean Air Act and stop sales of Clean Air credits. We need to find alternative energy that is renewable, sustainable, and has little in the way of emissions impact.
Global warming is a geohazard that could have profound consequences. The main cause of the accelerating increase in global temperature is anthropogenic. Humanity needs to reduce the anthropogenic causes in order to facilitate the Earth's return to a more natural temperature regulation by way of the long-term carbon cycle. Although we may not have yet exceeded the Earth's capacity to regulate the temperature through negative feedback, we may be getting close. It is our responsibility to do whatever we can to avoid this disaster, since mitigating only deals with symptoms.
2.) Bryson, Bill. 2004. A Short History of Nearly Everything. Broadway Books, N.Y.
3.) Appenzeller, Tim and Dimick, Dennis R.. 2004. National Geographic Magazine. Volume206 Issue 3. Washington.