Considerable research is being done on the effects that climate change may have on the U.S. and the world, including the transportation system like roads, rail, and waterways. We saw last year from Hurricanes Katrina and Rita in the Gulf coast how a new weather pattern impacted transportation, especially the Gulf oil refinery capacity.
What does the future hold, say in the next 50 or 100 years for climate change, such as consecutive days of extreme temperatures, sustained winds, hurricanes, high precipitation, melting of ice and rising of the sea levels, and how will these impact transportation as we know it?
The National Academy of Sciences held a conference Oct 12 in Washington, D.C. to discuss "Climate Change Impacts on U.S. Transportation." Several technical papers, which were not yet finalized, were discussed before an audience composed of mostly professionals in either climatology or transportation.
The first paper, "Climate Variability and Change with Implications for Transportation" (referred to as "Climate Change"), described the likely pattern of climate changes in the foreseeable future. It provided a foundation for the papers that followed it.
The final report will be published late summer 2007. At these high level discussions, if you can plow through the terminology and methodology, a lay person can glean some useful information about the future.
Weather vs. Climate
"U.S. temperatures have been rising over the last century, with more rapid increases since 1970 than earlier…," according to "Climate Change." Before 1970, natural causes were sufficient to explain climate changes, but in the period after 1970, man made factors, are required in the models for climate change.
In "Climate Change," there is related a story of an expert in climatology being asked on a day of near record temperature in California, whether the temperature was a result of global warming. He explained that it could not be determined whether the high temperature on any one day was due to man made factors in climate change. He added that a hot day like that, however, allows us to see into the future what our children will have to endure as part of the legacy of green house gas emissions.
This story illustrates the difference between weather and climate. "Weather" fluctuates a lot, especially day-to-day changes, and is hard to model. But "climate" is fairly stable and thus more predictable. Scientists can't model the "weather" with nice smooth curves; there are spikes and deep troughs in the graph, for example, of the daily maximum temperatures in Dallas, Texas.
Focus on Climate Extreme Changes, Not Averages
Transportation structures for surface transportation, waterways or airways are not impacted much by moderate changes in average temperatures. The global average temperature increase for the last century was 0.3º F. The U.S. was a little higher, at 0.4º F. However, this increase did not have any noticeable impact on the roads, rails, bridges, etc. that constitute the transportation infrastructure.
But changes in the climate extremes—e.g., the highest temperatures and the lowest temperatures—can have considerable impact on transportation. Extremes have been changing over the past decades and projections continue to change in the future. For engineers and planners, it's helpful to know what the future holds for climate changes when building a road or bridge, which are generally expected to last for 25 years or 100 years, respectively.
Nationally, the number of days exceeding 90º F and 100ºF has been increasing since 1970. But the change is not uniform across the country. Some cities like Dallas and Minneapolis are not showing a distinct pattern of increasing temperatures over the past couple of decades. On the other hand, the temperature increasing in the extremes is evident in Alaska and the West but not appreciably elsewhere in the U.S. In the Southeast, there was virtually no change in recent decades.
Washington, D.C. was one city where the daily temperatures were modeled. As expected, their model shows the number of colder days decreasing. The paper shows a graph of the probability of one day to twenty days attaining a maximum temperature reaching freezing (32º F). So, for example, the probability in 2007 that 6 days will attain a maximum of freezing temperature is about 48%. In 25 years, the probability drops to only about 40%. In 50 years, the probability of six days is only 19%. In one hundred years, the probability drops to only 3%. In general, the modeling is showing that climate changes are gradual in the first 50 years, but accelerate after that.
Transportation Impacts
"High temperatures limit the amount of time that road maintenance crews can work," states the paper, "Climate Change." It goes on to say, "restrictions typically begin at 85º F…Increased frequency of high temperatures will thus limit outdoor maintenance work."
According to the report, sustained high temperature can cause roadway buckling, and also increases the risk of tire blow-out on a hot pavement, especially in heavily loaded vehicles.
Air temperatures above 110º F can lead to rail buckling. "Lower speed and short trains, to shorten braking distance, and lighter loads to reduce track stress, are operational impacts," says the report.
"On hot summer days of high altitude airports, such as Denver International, may have to burn fuel, unloading weight, to have a safe take-off roll."
Fewer days with extreme lower temperatures have positive as well as negative impacts. On the positive side, milder winter conditions will likely improve the safety record of rail, air, and ships.
But milder winters will likely have very negative impacts as well. The colder regions like Alaska rely on frozen roads for access. Snow melt and thawing may prevent heavy truck hauling. "The Alaskan-Canadian Highway was built entirely on permafrost in World War II, and the Alaska rail follows this route. So fewer lower temperature days, resulting in permafrost thaw, has serious consequences for the transportation infrastructure," says "Climate Change."
While the number of days with precipitation has not increased, the number of extremely wet days is increasing. Heavy rain can result in road submersion, and flooded low-lying underpasses. Rain or snow can undermine the rail transportation by damages to the tracks and the railbed support structures.
Intense storms are projected to increase. Coastal transportation is especially vulnerable to the combined effects of storm surge and global sea-level rise.
Feeds