Academic journal article The Geographical Bulletin

Assessing Climate Change in Alabama Using Climate Normals

Academic journal article The Geographical Bulletin

Assessing Climate Change in Alabama Using Climate Normals

Article excerpt

INTRODUCTION

Climate change is a global and regional issue. Recent evidence suggests that human induced changes in greenhouse gas concentrations in the atmosphere have contributed to the recent rise in global average temperature, as well as other changes in the climate system. Global temperature increased by approximately 0.7°C (1.3°F) over the twentieth century. It is projected by climate models to continue to rise, between 1.1 and 6.4°C (2.0 and 9.7°F) by the end of this century, depending on the greenhouse gas scenario and climate model. Precipitation also changed over the twentieth century, increasing in some regions and decreasing in others. Climate models predict that precipitation will decrease in subtropical regions and increase in subpolar regions (Solomon et al. 2007).

Global temperatures are recorded at thousands of weather stations worldwide and also by ships at sea. Various global time series have been calculated, but all show similar trends. There have been temporal and spatial variations in the warming. Temperatures stayed relatively stable at the end of the nineteenth century, before warming from 1900 to 1940, cooling between 1940 and 1970, then warming again from 1970s to the end of the century. Land areas warmed more than oceans and the Northern Hemisphere more than the Southern (Trenberth et al. 2007).

In the United States climate has also changed. The country has warmed at a similar rate to the Earth as a whole, although the warming has varied in different parts of the country and in different seasons. In general, the warming has been greatest in the western half of the country and Northeast and during the winter half of the year. Changes in precipitation are much more complex than those in temperature. However, there is evidence that there have been increases in both intense precipitation and droughts, especially in the last few decades (Groisman et al. 2004, Groisman and Knight 2007, Lu, Lund, and Seymour 2005).

The Southeast did not see a statistically significant change in temperature over the twentieth century, although temperatures have increased in the region. Seasonally, winters have warmed the most. Again, precipitation did not show any statistically significant changes. Most seasons have become drier, with the exception of fall, which has become wetter. Temperatures are projected to rise in the Southeast anywhere between 2.5 and 5.0°C (4.5 and 9.0°F) by the end of this century. This may lead to an increase in the number of hot days and the heat index. Predictions of precipitation are less certain but are likely to lead to more droughts and water issues. There are also the possibilities of more coastal hazards such as more intense tropical cyclones in the future (Karl, Mellilo, and Peterson 2009).

It is important to study climate change regionally, at various spatial scales. Different patterns of climate change may exist at these different scales. Much past research, however, documents historic climate change and provides model projections of future changes at large regional scales, whether continental (Trenberth et al. 2007) or subnational (Karl, Mellilo, and Peterson 2009). Even reports which do focus specifically on state-level climate change (Twilley et al 2001, Wetzel and Twilley 2001) do not contain detailed historic temperature and precipitation data, or provide climate change information for different places within a state. This is partially related to climate model resolution, although those resolutions are improving all the time. This study provides a detailed study of historic climate change based on weather station data and analyzes historic trends at those locations.

DATA AND METHODS

Most climate changes analysis is carried out on global-scale gridded datasets, such as those used in the Intergovernmental Panel on Climate Change reports (Brohan et al. 2006, Hansen et al. 2001, Smith and Reynolds 2005). These data sets are based on station observations on land and at sea. …

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