Global warming in Memphis
From GeoClasses
How has (if at all) global warming affected Memphis? Report by Lydia Carpenter
Contents |
Abstract
Circumstantial evidence suggests that the Memphis area has seen unusual fluctuations in weather patterns relative to the past sixty years. The issue of global warming has become an explosive controversy in recent media reports, and has been blamed for all of the present unusual weather. The media often portrays an extreme assumption of global warming is solely caused by anthropogenic sources, however, there are changes in the Earth's climate that naturally occur, and these changes are not influenced by humans.
This research will further explore the climatic data for the Memphis region throughout the past sixty years and comparing these results to the predicted global changes stated by the International Panel of Climate Change (IPCC) summary report. Given the long-term predictions stated by the IPCC report, how has global warming affected the Memphis area?
Introduction
In this report, the analysis of climatic trends in Memphis for the last sixty years has been obtained by using the linear regression method. The need for this analysis is driven by circumstantial evidence that suggests that the Memphis area has seen unusual fluctuations within weather patterns relative to the past sixty years. Also the issue of global warming has become an explosive controversy in recent media reports, and has been blamed for most of the recent unusual weather.
Changes in the Earth’s climate have occurred since the formation of the Earth and have had a major impact on the rise and collapse of civilizations (Fagan, 2005). Unlike the other climatic changes, the present society contributes additional materials to the atmosphere, therefore being a catalyst in the atmospheric changes. Since researchers have linked the current warming trend to an abundance of certain materials, called greenhouse gasses, it is most certain that the rapidness of the warming trend in our Earth’s climate is greatly influenced by these sources (IPCC, 2007). There is the consensus of the scientific community that anthropogenic sources are a major factor in the current warming. Current research is now focused on providing alternatives for greenhouse gasses and educating the public about global warming without harming the economy.
Geography of Memphis
The city of Memphis is settled on the Chickasaw Bluff in the southwestern corner of Tennessee. It is located right next to the Mississippi River and also at the mouth of the Wolf River. The bluff contains many different layers of fine grained, loess soils that were deposited over a period of time since the last glacial maximum. These fine grained sediments were ground within the vast Laurentide Ice Sheet that covered most of North America during the last glacial maximum. When the ice sheet melted, these sediments were transported south by the Mississippi River and deposited on the flood plains. These sediments were then picked up by the prevailing westerly winds and deposited on the Chickasaw Bluff providing the area with fertile soils for agriculture and plant life.
The many different layers of sediment also work as a natural purification system in the recharge area of the Memphis Sand aquifer. This combined with the moist subtropical climate helps to provide the city with an abundance of some of the cleanest drinking water in the world. The Memphis area’s mild climate and fertile soil structure also allows for a wide variety of plant and tree species to flourish within the zone.
Climate
Memphis is located within North America’s humid subtropical climate zone (based on the Koppen-Geiger classification system; Oliver and Hidore, 2002). The summer months tend to be warm and dry while the winter months are typically cool and wet. During the spring and autumn seasons, Memphis will frequently experience severe weather associated with mid-latitude cyclones. This severe weather is typically caused by the occasional dips in the polar low front lines that displace the subtropical high climate zone that dominate the weather throughout the summer. During these severe weather occurrences, Memphis is vulnerable to high precipitation amounts and wind speeds that sometimes lead to flooding. This seasonal severe weather combined with the hot and dry temperatures of the summer months typically create these mixed broadleaf forest conditions that the Memphis area is adapted to (Oliver and Hidore, 2002).
IPCC 2007
Over the past 20 years, scientists from around the world have occasionally come together in what is known as the International Panel of Climate Change (IPCC) to discuss the issue of changes in the Earth’s climate. In February 2007, the IPCC released the most recent summary report for policymakers about the scientific consensus regarding the recent and predicted future climatic changes. The report also describes some of the potential effects of global climate change. Some of the changes that have been observed, according to the IPCC, are long-term warming trends of the Earth as a whole from the years of 1990 through 2005, along with a rise of precipitation over the eastern parts of North and South America, Northern Europe and Asia, and the drying of vegetation in the Sahel desert and the Mediterranean. The IPCC report also stated that the mid-latitude westerly winds, which affect the Memphis area, have increased in both hemispheres since the 1960’s, and as a result widespread changes in the climate will occur. Globally, there will be less frequent cold days and nights with more frequent warmer days and nights. The current media often portrays an extreme assumption that global warming is solely caused by anthropogenic sources, however, there are changes within the Earth’s climate that are naturally occurring, and outside of human influence.
Climatic trends in Memphis
In observing the past sixty years of climatic trends within Memphis it was found that, on average, the maximum temperature has slightly declined and the minimum temperature has slightly risen, while at the same time the precipitation amounts showed the greatest increase. This paper will further explore the climatic data for Memphis comparing the results to global changes.
Methods
Linear Regression
Linear regression is used to describe the relationship between variables by calculating the trend line that best fits the data set. This method gives information about the magnitude and reliability of the trends. When a set of data with one independent variable and one dependent variable exists, the points may be plotted on a graph and a line may be drawn to achieve the best-fit straight line through the data. In this context, the equation of the line y=mx+b helps to determine the slope of the plotted data set. The value m signifies the slope of the equation with y representing the dependant and x the independent variable. The value b symbolizes the initial starting point of the data set; in this report the value b will signify the year 1948 which is the starting year of the data set.
Slope and R-Squared Values
The slope of the line will help to show what direction the line is moving, this is also called a trend. If the slope of a line shows a positive number than the trend is increasing, if it is negative the trend is decreasing. The slope of a line is displayed at the top corner as the equation y=mx+b, having m equal the slope. The linear regression method also calculates an R-squared value that is labeled in many textbooks as a correlation coefficient. The R-squared value is applied to help determine how reliable the trend line measures the plotted points. A maximum R-squared value of 1 symbolizes a perfect linear relationship between the given points. Values less than 1 indicate less confidence in the linear relationship; the minimum R-squared value of 0 indicates no linear relationship in the data. The R-squared value of the linear regression method will determine the confidence in the slope of the trend. If the r-squared value is 1, the confidence of the trend is very like to the results. The r-squared value will never drop below 0 though the closer the r-squared value is to 0, the less the confidence of the trend line given.
Results
The graphing of points for the maximum and minimum temperatures as well as precipitation amounts were observed on a monthly and yearly scale from the years of 1948 through 2004. When observing the data, it was difficult to obtain an overall trend due to fluctuations in data. The confidence in these trends proved to not be very high due to this variability. The next step was to reduce this variability by taking the overall yearly averages in five year increments.
The five year averages were then plotted on a graph to possibly determine any overall warming or cooling patterns in a cyclical type pattern. According to final observations, these trends also did not prove to be highly confident though giving a broad perspective that Memphis does follow some type of 10 to 20 year cycle of both temperature and precipitation. Regardless of the fluctuations within the monthly averages, the graph showing five year increments in maximum and minimum temperature does indeed show a slight cycle in warming and cooling trends for many of the months out of the year. The precipitation amounts show a sustainable rise and fall in trend with about a 10 to 20 year cycle. Closer investigation of this cyclical pattern shows that currently Memphis is on the current rise of this cycle though it is still quite unknown if the cycle will continue with an upslope in trend.
 5 year average of maximum January temperatures from 1948 to 2004. |
 5 year average of maximum July temperatures from 1948 to 2004. |
 5 year average of maximum May temperatures from 1948 to 2004. |
 5 year average of maximum September temperatures from 1948 to 2004. |
 5 year average of minimum January temperatures from 1948 to 2004. |
 5 year average of minimum July temperatures from 1948 to 2004. |
 5 year average of minimum May temperatures from 1948 to 2004. |
 5 year average of minimum September temperatures from 1948 to 2004. |
When examining the data set for average global changes, the results show a “hockey-stick” pattern where undoubtedly there has been a remarkable spike in the global temperatures for the past fifty years. This shows that on a global scale, a rising trend does exist and it has not yet shown any signs of stability. When observing the Memphis local climatic patterns, the two do not correlate with each other on a noticeable level, but it is probable that minimal effects do exist.
Discussion
The cause of fluctuation in local temperature and precipitation averages may be a result of a larger scale pattern such as the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) is a series of changes throughout sea level pressure.For example, if there is any rise in the NAO, countries such as the United States may experience a warmer winter season. Identifying this pattern would require future research. The idea that the effects of global warming have not significantly affected the Memphis region does not mean that these effects will continue to go unnoticed. Memphis’ region, being a large agricultural and industrial hub depends greatly on the everyday weather for survival. Being a large city in North America also provides the conditions to greatly contribute to the global changes. However given the results of this analysis Memphis may not directly observe the consequences.
Data and Resources
- Monthly data: Media:328493604527dat.txt
- Station information: Media:328493604527stn.txt
- Inventory information: Media:328493604527inv.txt
- Documentation: Media:3220doc.txt
- Images: United States Historical Climatology Network dataset (www.co2science.org)
- Excel file for importing data: Image:Sort monthly data.xls
Raw results
- Global warming raw results
- Image:MaxTempMonthNew.xls - This is the mean maximum monthly and yearly temperature averages for the years 1948 through 2004.
- Image:MinMonthTempNew.xls-This is the mean minimum monthly and yearly temperature averages for the years 1948 through 2004.
- Image:PrecipNew.xls-This is the mean monthly and yearly precipitation amounts for the years 1948 through 2004.
- Image:MaxTempMonthNew 5 yr.xls-This is the average maximum temperature in five year increments from the years 1948 through 2004.
