Observed climate change in Arkansas

By | March 10, 2008

Arkansas Climate Change


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THERE IS no observational evidence of unusual long-term climate changes in Arkansas. No emissions reductions by Arkansas will have any detectable regional or global effect whatsoever on climate change.

Annual temperature: The historical time series of statewide annual temperatures in Arkansas begin in 1895. Over the entire record, there is no statistically significant trend. Instead, the record is dominated annual and decadal-scale variability. Temperatures during the past decade or so have been similar to those experienced in the 1920s and 1930s and follow a multi-decadal period extending from the late-1950s through the mid-1990s when statewide average temperatures were generally cooler than the long-term average.

Arkansas annual temperatures, 1895-2007

Seasonal temperatures: Likewise, there are no long-term seasonal trends. Instead, year-to-year and/or decade-to-decade variability is most evident. In no season do recent temperatures appear unusual compared with observed temperature history. There is no evidence of “climate change”:

Arkansas seasonal temperatures, 1895-2007

Precipitation: As with temperature, there is no statistically significant overall trend in total annual precipitation averaged across Arkansas. Instead the record is dominated by large interannual variations—ranging from over 71 inches of precipitation in 1957 to just under 33 inches in 1963. Recent years are not unusual when viewed against the long-term history.

Arkansas annual precipitation, 1895-2007

Drought: Since 1895, there has been no long-term trend in statewide incidence of drought in Arkansas.

Arkansas drought severity, 1895-2007

According to records compiled by the National Climatic Data Center since 1895, statewide monthly average Palmer Drought Severity Index values—a standard measure of moisture conditions that takes into account both inputs from precipitation and losses from evaporation—show no long-term trend during the past 112 years. The period of record is dominated by short-term variations, although some longer-term signals are present, such as the extended period of drought in the mid-1950s and period of extreme wetness in much of the mid-1970s. Compared with the middle part of the 20th century, when moisture conditions varied frequently between extreme moisture excess to extreme dryness, the conditions during more recent decades appear more well-behaved (fluctuate less).

Crop Yields: In Arkansas, the annual yields from leading cash crops such as cotton, rice, and soybeans have risen during the past 30 years. Factors other than climate are largely responsible for the yield rise.

Arkansas major crop yields, 1975-2007

Yields increase primarily as a result of technology—better fertilizer, widespread irrigation, more resistant crop varieties, improved tilling practices, modern equipment, and so on. The level of atmospheric carbon dioxide, a constituent that has proven benefits for plants, has increased as well. The relative influence of weather is minimal compared with those advances. The fluctuations of temperature and precipitation from one year to the next and are responsible for some of the year-to-year variation in crops yields but are responsible for little of the long-term upward trend. Through the use of technology, farmers are adapting to the climate conditions that traditionally dictate what they do and how they do it and producing more output than ever before. There is no reason to think that such adaptations and advances will not continue into the future.

Tornadoes: Lying partially within “tornado alley” Arkansas is one of the states most frequented by tornadoes. However, the apparent increase in the total number of tornadoes striking Arkansas is likely an artifact of the implementation of better technology, a larger organized tornado spotter network, and a growing population, rather than a real increase in the number of storms.

Some people suggest that the number of extreme storm events, such as tornadoes will increase in the future as a result of global warming and point to recent increases in the occurrence of tornadoes in the United States as proof. However, in the United States, as in Arkansas, the recent increase in tornado observations can be explained by non-climate factors such as the expanded use of Doppler radar by the National Weather Service, an increase in the number of observers (or “storm chasers”), and an increase in the population density. Consequently, small tornadoes that were once missed are now being detected by radar and the larger network or observers. The number of major tornadoes across Arkansas—those less likely to have ever been missed due to the amount of damage they leave behind—shows no such increase indicating that the apparent increase in the occurrence of all tornadoes is likely a reflection of our ability to detect them, rather than a true increase in the actual number of tornadoes to hit Arkansas.

Hurricanes: While one doesn’t often consider hurricanes to be an integral part of the climate history of Arkansas, these storms do play a significant role in Arkansas climate. The impact of hurricanes on Arkansas is largely beneficial as the remnants of tropical cyclones that pass near Arkansas have usually lost the ferocity of their winds and deliver copious moisture during a time of the year (late summer) when it is often most needed.

Rainfall from tropical cyclones

When a strong tropical cyclone makes a direct hit on the U.S. coastline, the result can be devastating. However, further inland, the remnants of tropical systems produce widespread copious rainfall which oftentimes proves beneficial to agriculture, forestry, and other water interests in the state. The late summer months is the time during the year when, climatologically, the precipitation deficit is the greatest and crops and other plants are the most moisture stressed. A passing tropical cyclone often brings much needed precipitation over large portions of the state during these late summer months. In fact, recent research shows that Arkansas, on average, receives about 10% percent of its normal September precipitation, and about 5% of its total June through November total precipitation from passing tropical systems.

Heatwaves: The population of Arkansas has likely become less sensitive to the impacts of excessive heat events over the course of the past 30-40 years. This is true in most major cities across the United States—a result of the increased availability and use of air-conditioning and the implementation of social programs aimed at caring for high-risk individuals—despite rising urban temperatures.

Heat-related mortality trends across the U.S.

A number of studies have shown that during the several decades, the population in major U.S. cities has grown better adapted, and thus less sensitive, to the effects of excessive heat events (Davis et al., 2003a,b). Each of the bars of the illustration above represents the annual number of heat-related deaths in 28 major cities across the United States. There should be three bars for each city, representing, from left to right, the decades of the 1970s, 1980s and 1990. For nearly all cities, the number of heat-related deaths is declining (the bars are get smaller). And although there are no cities from Arkansas that were included in the Davis et al. studies, in most cities in states nearby to Arkansas that were part of the investigation, there is not a bar present at all in the 1990s. This indicates that there are no statistically distinguishable heat-related deaths during that decade (the most recent one studied)—meaning that the population of those cities has become nearly completely adapted to heat waves. This is likely to be the case in Arkansas cities as well, as these cities share characteristics of the climate of those of neighboring cities. This adaptation is most likely a result of improvements in medical technology, access to air-conditioned homes, cars, and offices, increased public awareness of potentially dangerous weather situations, and proactive responses of municipalities during extreme weather events.

The pattern of the distribution of heat-related mortality shows that in locations where extremely high temperatures are more commonplace, such as along the southern tier states, the prevalence of heat-related mortality is much lower than in the regions of the country where extremely high temperatures are somewhat rarer (e.g. the northeastern U.S.). This provides another demonstration that populations adapt to their prevailing climate conditions. If temperatures warm in the future and excessive heat events become more common, there is every reason to expect that adaptations will take place to lessen their impact on the general population.

Vector-borne diseases: Diseases such as malaria and dengue fever, which have been erroneously predicted to spread due to global warming, are related less to climate than to living conditions. These diseases are best controlled by direct application of sound, known public health policies.

The two tropical diseases most commonly cited as spreading as a result of global warming, malaria and dengue fever, are not in fact “tropical” at all and thus are not as closely linked to climate as many people suggest. For example, malaria epidemics occurred as far north as Archangel, Russia, in the 1920s, and in the Netherlands. Malaria was common in most of the United States prior to the 1950s (Reiter, 1996). In fact, in the late 1800s, a period when it was demonstrably colder in the United States than it is today, malaria was endemic in most of the United States east of the Rocky Mountains—a region stretching from the Gulf Coast all the way up into Northern Minnesota and which encompasses Arkansas. In 1878, about 100,000 Americans were infected with malaria; about one-quarter of them died. Malaria was eradicated from the United States in the 1950s not because of climate change (it was warmer in the 1950s than the 1880s), but because of technological advances. Air-conditioning, the use of screen doors and windows, and the elimination of urban overpopulation brought about by the development of suburbs and automobile commuting were largely responsible for the decline in malaria (Reiter, 1996).

The effect of technology is also clear from statistics on dengue fever outbreaks, another mosquito-borne disease. In 1995, a dengue pandemic hit the Caribbean and Mexico. More than 2,000 cases were reported in the Mexican border town of Reynosa. But in the town of Hidalgo, Texas, located just across the river, there were only seven reported cases of the disease (Reiter, 1996). This is just not an isolated example, for data collected over the past decade has shown a similarly large disparity between the high number of cases of the disease in northern Mexico and the rare occurrences in the southwestern United States. There is virtually no difference in climate between these two locations, but a world of difference in infrastructure, wealth, and technology.

Impacts of climate-mitigation measures in Arkansas

lobally, in 2003, humankind emitted 25,780 million metric tons of carbon dioxide (mmtCO2: EIA, 2007a), of which Arkansas accounted for 62.4 mmtCO2, or only 0.24% (EIA, 2007b). The proportion of manmade CO2 emissions from Arkansas will decrease over the 21st century as the rapid demand for power in developing countries such as China and India outpaces the growth of Arkansas’ CO2 emissions (EIA, 2007b).

During the past 5 years, global emissions of CO2 from human activity have increased at an average rate of 3.5%/yr (EIA, 2007a), meaning that the annual increase of anthropogenic global CO2 emissions is more than 10 times greater than Arkansas’ total emissions. Even a complete cessation of all CO2 emissions in Arkansas will be undetectable globally. A fortiori, regulations prescribing a reduction, rather than a complete cessation, of Arkansas’s CO2 emissions will have no effect on global climate.

Wigley (1998) examined the climate impact of adherence to the emissions controls agreed under the Kyoto Protocol by participating nations, and found that, if all developed countries meet their commitments in 2010 and maintain them through 2100, with a mid-range sensitivity of surface temperature to changes in CO2, the amount of warming “saved” by the Kyoto Protocol would be 0.07°C by 2050 and 0.15°C by 2100. The global sea level rise “saved” would be 2.6 cm, or one inch. A complete cessation of CO2 emissions in Arkansas is only a tiny fraction of the worldwide reductions assumed in Dr. Wigley’s global analysis, so its impact on future trends in global temperature and sea level will be only a minuscule fraction of the negligible effects calculated by Dr. Wigley.

We now apply Dr. Wigley’s results to CO2 emissions in Arkansas, assuming that the ratio of U.S. CO2 emissions to those of the developed countries which have agreed to limits under the Kyoto Protocol remains constant at 39% (25% of global emissions) throughout the 21st century. We also assume that developing countries such as China and India continue to emit at an increasing rate. Consequently, the annual proportion of global CO2 emissions from human activity that is contributed by human activity in the United States will decline. Finally, we assume that the proportion of total U.S. CO2 emissions in Arkansas – now 1.1% – remains constant throughout the 21st century. With these assumptions, we generate the following table derived from Wigley’s (1998) mid-range emissions scenario (which itself is based upon the IPCC’s scenario “IS92a”):

Table 1
Projected annual CO2 emissions (mmtCO2)

In Table 2, we compare the total CO2 emissions saving that would result if Arkansas’ CO2 emissions were completely halted by 2025 with the emissions savings assumed by Wigley (1998) if all nations met their Kyoto commitments by 2010, and then held their emissions constant throughout the rest of the century. This scenario is “Kyoto Const.”

Table 2
Projected annual CO2 emissions savings (mmtCO2)

Table 3 shows the proportion of the total emissions reductions in Wigley’s (1998) case that would be contributed by a complete halt of all Arkansas’ CO2 emissions (calculated as column 2 in Table 2 divided by column 3 in Table 2).

Table 3
Arkansas’ percentage of emissions savings

Using the percentages in Table 3, and assuming that temperature change scales in proportion to CO2 emissions, we calculate the global temperature savings that will result from the complete cessation of anthropogenic CO2 emissions in Arkansas:

Table 4
Projected global temperature savings (ºC)

Accordingly, a cessation of all of Arkansas’ CO2 emissions would result in a climatically-irrelevant global temperature reduction by the year 2100 of no more than two thousandths of a degree Celsius. Results for sea-level rise are also negligible:

Table 5
Projected global sea-level rise savings (cm)

A complete cessation of all anthropogenic emissions from Arkansas will result in a global sea-level rise savings by the year 2100 of an estimated 0.03 cm, or one hundredths of an inch. Again, this value is climatically irrelevant.

Even if the entire Western world were to close down its economies completely and revert to the Stone Age, without even the ability to light fires, the growth in emissions from China and India would replace our entire emissions in little more than a decade. In this context, any cuts in emissions from Arkansas would be extravagantly pointless.


Davis, R.E., et al., 2003a. Decadal changes in summer mortality in the U. S. cities. International Journal of Biometeorology, 47, 166-175.

Davis, R.E., et al., 2003b. Changing heat-related mortality in the United States. Environmental Health Perspectives, 111, 1712-1718.

Energy Information Administration, 2007a. International Energy Annual, 2005. U.S. Department of Energy, Washington, D.C., http://www.eia.doe.gov/iea/contents.html

Energy Information Administration, 2007b. Emissions of Greenhouse Gases in the United States, 2006. U.S. Department of Energy, Washington, D.C., http://www.eia.doe.gov/oiaf/1605/ggrpt/pdf/0573(2006).pdf

Intergovernmental Panel on Climate Change, 2007. Summary for Policymakers, (http://www.ipcc.ch/SPM2feb07.pdf)

Knight, D.E, and R.E. Davis, 2007. Climatology of tropical cyclone rainfall in the Southeastern United States, Physical Geography, 28, 126-147.

National Climatic Data Center, U.S. National/State/Divisional Data, (www.ncdc.noaa.gov/oa/climate/climatedata.html)

Reiter, P., 1996. Global warming and mosquito-borne disease in the USA. The Lancet, 348, 662.

Wigley, T.M.L., 1998. The Kyoto Protocol: CO2, CH4 and climate implications. Geophysical Research Letters, 25, 2285-2288.