Pumphrey (2008) rightly observed that until fairly recently, no one would bought the idea that the world’s climate was changing, let alone that it was been influenced by human activities. The first insight into what is today known as global warming was first conceived by the Swedish scientist Arrhenius, who, late in the 19th century, suggested that the activities of the rapidly developing industries could cause the planet to warm up. Such ideas were often ignored, but over the course of the 20th century, opinions about climate change, “even rapid climate change” were becoming more apparent (Pumphrey, 2008, p.
1). As things stand now, there appears to be a growing pile of irrefutable evidences that point to the fact that human activities are affecting the heat/energy exchange between the earth, the atmosphere and space (Justus and Susan, 2006). The primary cause of global climate change has been attributed to the accumulation of carbon dioxide and other air pollutants in the earth’s atmosphere. These ‘green house gases’, as they are now known, form a blanket over the earth atmosphere, thus trapping the sun’s heat inside the planet and causing it to warm up (National Resources Defense Council, 2007).
A substantial population of the world’s scientist have agreed that human activities, especially the burning of fossil fuels, have increased atmospheric “concentrations of carbon dioxide (CO2) by 36% from pre-industrial levels of 280 parts per million (ppm) to 380 ppm over the past 150 years, leading to an increase in global average temperature of 0. 9oF over the past 100 years”. Consequently, there has been considerable increase in global average temperature and sea levels, decreases of sea ice in the Artic and melting of the planet’s continental ice sheets and mountain glaciers (Justus and Susan, 2006).
More frightening, however, is the assertion by scientists that if green house gases continue to accumulate at the present rates, more rapid and devastating consequences could result within a short period of time. While scientists largely agree on the evidences pointing to a warming planet, the severity and ramifications of its consequences is often a subject of controversy, doubts and heated debates. The drought in the Southwestern U. S presents one such example of the controversies and uncertainties surrounding the consequences of global warming. In the history of the Southwestern U.
S. , drought has been a relatively periodic occurrence, due to climate variability that characterizes this region. For example, after reviewing the history of climate changes in the region, Thompson and Anderson (2005) concluded that over the long term, the climate of the region is constantly changing and that in the “18,000 years since the last glacial maximum the southwestern United States has experienced conditions that ranged from much colder to somewhat warmer than today. Moisture conditions have also varied, both through time and across the region” (Thompson and Anderson, 2005).
However, despite these assertions, scientists through several studies have pointed out that the present multi-year drought in the region is not another result of climate variability but a consequence of climate change. They assert that the present climate situation might be the new climate of the region and that drier and more sever droughts lies ahead if urgent measures are not taken. The proposed study intends to support and add weight to the contention that climate changes is already impacting the region and that increasing global warming will increase the severity of drought in the Southwestern U.
S. Purpose Statement McNab and Karl (2003) observe that drought is a complex phenomenon that can be very difficult to define. They contend that the problem with defining drought derives partially from the fact that the term could be approached from different perspectives. That, notwithstanding, the central theme that underlie any definition of drought is the absent or deficiency of water. However, they point out that to completely define drought, the “component(s) of the hydrologic cycle affected by the water deficit and the time period associated with the deficit, must be specified”.
The Southwestern U. S is a region vulnerable to droughts due to its variable climatology that derives from its peculiar topography. The entire Southwestern states of the United States fall into a climatic region generally known as the ‘subtropics’. These regions are known to be dry and susceptible to drought because the atmosphere moves water ‘out of those regions into higher planes’ (Thompson, 2007). It is argued that the evaporation is higher in subtropics and the moist air from here is transported to temperate regions at higher latitudes.
This climatic condition sometimes causes excessive ‘dryness’ (drought) in these regions. The infamous dust bowl conditions of the 1930s and the severe droughts of the 1950s are typical examples. Pointing out the vulnerability of the region, Davis (2007) observe that “in some years, “exceptional drought” has engulfed the entire Plains from Canada to Mexico; in other years, crimson conflagrations on weather maps have crept down the Gulf Coast to Louisiana or crossed the Rockies to the interior Northwest” (Davies, 2007).
Based on this argument, it is convenient to describe the present drought in the region as a result of such climatic variability. Unfortunately, recent data on global warming indicate otherwise. Scientists have shown that this time, the drought in the region is not just a passing phase in climatic conditions, it is a reality that has come to stay. It is evident that this time, it is the base climate that is changing and dire consequences looms ahead.
Supporting the argument that the aridity in the Southwestern U. S is different this time, Davis (2007), point out that “Lake Powell had fallen by nearly eighty feet in three years, and crucial reservoirs along the Rio Grande were barely more than mud puddles. The Southwestern winter of 2005-06, meanwhile, was one of the driest on record, and Phoenix went 143 days without a single drop of rain”.
Noting that some scientists have regarded the present situations as the worst drought in 500 years and with the several scientific evidences showing the link between global warming and severe drought, Davis concluded that the present climate condition is not “simply episodic drought but the region’s new ‘normal weather'” (Davies, 2007). Statement of the Problem Both global warming and droughts portend grave dangers for both the region and the world at large. Despite the sometimes dissenting voices in the science world, there is unanimous certainty that the planet is warming up.
The Intergovernmental Panel on Climate Change (IPCC) in its 2007 report stated that it is ‘unequivocal’ that the planet is heating up and that, with utmost certainty, the warming is caused by human activities. It is clearly understood that increased global temperatures will facilitate the propagation of certain deadly bacteria and the spread of diseases. For example, Kolivras and Andrew (2004) carried out a study that revealed that the presence and spread of four diseases; hantavirus, plague, dengue and coccidioidomycosis in the Southwestern U. S could be attributed to the increased in temperature in this region.
Again, it is clear that higher global temperatures will lead to increase in the incidence and severity of droughts which will affect agricultural production, causing global food crisis. Also, the melting of continental and Artic ice, due to global warming, will cause flooding and other devastating problems that will affect millions of people globally. Persistent drought, on the other hand, also severely impacts a society. Besides the shortage of food and water that characterizes drought conditions, Davis (2007) also point out that drought rapidly destabilizes the natural ecosystem.
Buttressing this fact, he observed that, without sufficient moisture to produce protective sap, “millions of acres of pinyon and ponderosa pine have been ravaged by plagues of bark beetles; these dead forests, in turn, have helped to kindle the firestorms that have burst into the suburbs of Los Angeles, San Diego, Phoenix and Denver, as well as destroyed part of Los Alamos” (Davies, 2007). However, despite the frightening consequences of droughts and/or global warming, the real issue here is the misunderstanding of the problem at hand.
A clear understanding of the real cause and nature of the drought in the Southwestern United States will greatly help in containing the problem before it get out of hand. In a study for the Lamont Doherty Earth Observatory, Columbia University, Richard Seager and other scientists point out that all the models used for the third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) indicated a general decrease in rainfall in the subtropics during the 21st century and gradual drying up of the region with increasing concentrations of atmospheric carbon dioxide (Seager et al, 2007).
The present drought in the region is therefore, evidently a consequence of a much bigger problem, the realization of this fact is important in shaping public attitudes and opinions required for finding a lasting solution to the problem. Theoretical Framework The states of the Southwestern United States fall in a climatic region known as the subtropics. The climate in these regions is characteristically dry because the atmosphere moves water out of these regions. Moist air from these regions is often transported to temperate regions at higher latitudes.
This phenomenon is referred to as the “Hadley cell” (Thompson, 2007). This flow of moist air away from subtropics induces rising air over the equator and descending air over the subtropics. The descending air over the subtropics suppresses precipitation, which further increase dryness of the regions. With global warming, the blanket of greenhouse gas in the atmosphere heat up the air over the subtropics enabling it to carry and transport more moisture away from the region.
Furthermore, with increasing global temperatures, ‘Hadley cell’ (the flow of air out of the subtropics) expands pole ward, bringing the United States Southwestern region under the increasing influence of descending air, further compromising precipitation and further worsening drought. The link between reduced precipitation and drought was established by McNab and Karl (2003) who asserted that “precipitation can be considered to be the carrier of the drought signal and stream flow and ground-water levels can be considered to be the last indicators of the occurrence of a drought” (McNab and Karl, 2003).
It has been argued that whilst past droughts in the region was because La Nina brought ‘cooler ocean temperatures to the equatorial Pacific, which resulted in drier conditions over North America’, the present drought is caused by changing climatic conditions characterized by increasing global temperatures that enable more moisture to be transported out of the region and suppressed precipitation.
Courtney from Study Moose
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