Case Study: Are There Regional Differences in Climate Change?

Models Describe Possible Future Climate

The average annual temperature in the United States increased by nearly 1 degree Fahrenheit (0.6 degrees Celsius) over the 20th century, and precipitation increased by 5-10% nationally, largely the result of heavier downpours.¹ Scientists use computer models to describe our current weather patterns and to visualize how our climate might change in the future. Two of the most widely used models each predict that the United States will become warmer over the next century, by roughly 5 to 9 degrees Fahrenheit (3 to 5 degrees Celsius).² These estimates exceed the projected global increase. However, these temperature changes are not uniform across the country. Some states will likely see dramatic increases in temperature, while other states will see only modest increases.

Similarly, precipitation forecasts vary from state to state. Some states may receive a significant increase in rainfall, while other states may experience little change in precipitation levels, or may even receive less precipitation than they do today. Heavier and more extreme precipitation events will likely occur more often, increasing the risk of flash flooding. Other regions of the country may experience more frequent droughts.

Climate changes can profoundly affect agricultural production within a state as well as other key sectors of the economy such as forestry and tourism. Agricultural productivity in some states may increase, for example, in response to higher carbon dioxide levels and a longer growing season. Warmer temperatures and higher precipitation levels could negatively affect human health, with impacts such as higher heat-related summer mortality, and a greater incidence of vector-borne diseases from increased insect populations (like mosquitoes).

In this chapter, you will access projected climatological data for California and Minnesota. You'll download minimum temperature, maximum temperature, precipitation, and solar radiation data for the years 2000 through 2100. You'll import the data into a spreadsheet application, then analyze it to interpret regional variability. Finally, you'll download data for your own state, or a third state of your choice, and compare it to these two states, and answer questions about regional differences in climate change.

A Cautionary Note About Model Projections

Scientists use computer models to describe mathematically the various factors that affect our climate and to characterize the interrelationships among these factors. These computer simulations can also be used to make projections as to how climate may change in the future. The data sets used in this chapter are derived from a model developed by the Canadian Climate Center. This model is widely used by scientists and researchers and is an integral component of the U.S. National Assessment.

Models are simplified representations of our physical environment. As such, there are limitations and uncertainties within all computer models. Some of these uncertainties are due to our incomplete understanding of the key processes that affect climate or the difficulty of incorporating these processes into the model. As our understanding of these processes improves and we are better able to describe these processes mathematically, these kinds of model uncertainties should diminish.

The limitations and uncertainties inherent in scientific models do not make these models useless or invalid. One test of the effectiveness of computer simulations is how well they predict historical climate shifts since we know how climate has changed in the past. Many models have successfully reproduced these historical climate changes. Models are also an essential tool for improving our understanding of Earth system science. We simply have no better means for predicting how climate may change in the future. Still, it's important to keep the inherent uncertainties and limitations of computer modeling in mind when using the model output data in this chapter. Projections of temperature and precipitation changes over the next century should be regarded as possible scenarios of what might happen and not an absolute assertion of what is to come.

For more information on climate models see: U.S. Global Change Research: Modeling 

References:

1 & 2 Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change - http://www.gcrio.org/NationalAssessment/foundation.html (link broken). Models are from the Hadley UK Centre for Climate Prediction and Research and the Canadian Centre for Climate Modelling and Analysis.