A warmer world could make current airport runways too short

A government report on climate-change impacts [PDF] in the United States, which was released earlier this year, began estimating the costs of warmer, more humid, less dense air:

Recent hot summers have seen flights cancelled due to heat, especially in high altitude locations. Economic losses are expected at affected airports. A recent illustrative analysis projects a 17 percent reduction in freight carrying capacity for a single Boeing 747 at the Denver airport by 2030 and a 9 percent reduction at the Phoenix airport due to increased temperature and water vapor.

Climate change will hit especially hard at high-altitude airports where the air is already thin, particularly in the Southwest, where temperatures have risen faster than elsewhere — by about 1.5 degrees F. compared to temperatures 40 years ago. (Alaska, where runways and highways are built on now-melting permafrost, is another story.)

But that doesn't mean adaptation isn't possible. In a phone conversation, Thomas Peterson, a climatologist at NOAA's National Climatic Data Center, and coauthor on the two later reports referenced above, ticks off a list of possible adaptations: Shift most flights to early morning or evening when the air is cool, for example. Or make runways longer.

But such retrofitting isn't always easy. For some airports, extending is difficult; there may be something in the way. In many coastal cities — New York, Boston, San Francisco — runways are at water's edge.

At first glance, that seems easy to solve: Truck dirt in, dump it, create dry ground, extend runway. But what about sea-level rise? Thermal expansion has already raised seas globally by about 8 inches in the past century, and it's predicted to raise seas by between 0.6 feet and 2 feet more this century.

That estimate doesn't include glacial melt, and the more scientists learn about how glaciers melt, the more uneasy they become about the prospect of Greenland and Antarctica melting. Both are melting faster than anticipated.

But let's say a few feet of sea-level rise is manageable. It's really storm surges that present the problem. In a warmer world, storms are predicted to become more intense. The storm that previously occurred every 100 years could arrive as frequently as every decade by century's end.

Still, no problem: Build a dike around the runway to keep it dry. Unfortunately, as mentioned in the second report referenced above, a wall at the end of your runway greatly limits its use:

Dikes can reduce the effective length of a runway. Assuming a typical descent angle of 3 degrees and that the runway stretches all the way to the dike, a one foot rise in sea level effectively shortens the runway by 20 feet.

In New York City, a Category 3 hurricane, such as the "Long Island Express" hurricane that roared through the area in 1938, could bring a 20-foot storm surge. (Here's a storm surge map for Long Island. And here's an article about New York City's efforts to prepare for more intense storms.)

According to the numbers above, a dike able to hold a 20-foot storm surge at bay would also render over 400 feet of runway useless. And that seems to negate the rationale for extending it in the first place.

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