HONG KONG: Airports are a major global business, part of an industry that by one estimate transports the equivalent of nearly half the world’s population in a single year.

But the world’s airports were largely designed for an older era — a cooler one.

Many were built near seacoasts or river deltas to minimise disturbances to humans or avoid natural obstacles such as mountains. Others have short runways because of space restrictions, while planners in the past gave little thought to how extreme temperatures could affect aeroplanes and airports.

Climate change is making airport planners think again.

Low-lying airports could become increasingly vulnerable to storm surges. Hotter temperatures could cause the tarmac to melt, restrict take-off weights or require heavier aircraft to take off later in the day.

Now governments, companies and experts around the world are grappling with what could be a very expensive problem. Keeping the industry aloft requires colossal investment — $1.1 trillion in airport infrastructure projects are planned or underway, the CAPA Center for Aviation, a consulting firm in Australia, said in July.

“Airports understand well that climate change could have some far-reaching effects and that they are not immune to them,” said Angela Gittens, director-general at Airports Council International’s headquarters in Montreal.

Rising waters

Climate scientists predict that sea levels could rise as much as 6 or 7 feet this century, and aviation experts say that even a much smaller rise could lead to more flooding at runways or terminals.

Preliminary studies indicate that dozens of airports are at risk. A 2009 report by Eurocontrol, a Brussels-based agency that coordinates air traffic management across Europe, estimated that more than 30 major European airports sat on coastlines or within river floodplains.

Sea level rise and storm surges have a “somewhat-nearer-term flavour” for airports than other climate-related risks, such as rising temperatures, said Terence R. Thompson, a senior fellow at the Logistics Management Institute in Virginia who studies links between aviation and climate change.

“You’ve got this complex, multi-segment industrial site, and it’s not just, ‘Does the runway go underwater?’” he said. For example, the flooding of a taxiway could force pilots to take longer taxi routes from terminals to runways, causing delays at one airport that ripple across many others, he said.

Hot runways

Climate scientists predict a global increase this century in the annual number of hot days and heatwaves, and some airport planners worry that climate change could push airport infrastructure to the limits of its operating capacity.

Runways in northern Canada have been damaged by thawing permafrost, for example, leading officials to commission permafrost studies before a recent $240 million (Dh881.8 million) renovation of Iqaluit International Airport in the Canadian Arctic.

Concrete runway slabs at other airports could buckle from extreme heat, as similar slabs occasionally do on highways, and there is “serious concern” that asphalt on aprons and parking areas could melt, said Herbert Pumpel, a co-chairman of the World Meteorological Organisation’s Expert Team on Aviation, Science and Climate.

Then there are concerns about aircraft.

A plane’s maximum operating temperature depends on a variety of factors, including airport elevation. But as temperatures climb far higher than 100 degrees Fahrenheit, airlines can begin suspending operations for certain types of planes, as American Airlines did in June when daytime highs in Phoenix climbed to about 120 degrees.

Longer runways

Hot temperatures cause air density to decrease, reducing lift and forcing airlines to either reduce weight on flights or move departures to cooler hours of the day. Experts say that will most likely pose a long-term economic challenge for airports, especially those in humid climates, at high altitudes or with short runways.

The cost of having a short runway in a hot place became clear to planners at Brisbane Airport in Australia, who studied climate models and airlines’ financial data in 2009 while designing the airport’s second runway, said Karyn Rains, the project’s former environment manager.

They discovered that because of an expected spike in the number of annual 86-plus-degree days in Brisbane, airlines would be forced to spend more than $79 million per year by 2035 if the second runway were 8,202 feet, rather than 10,826 feet. Rains said that was mostly because larger planes would be unable to land at an 8,202-foot runway under certain hot weather conditions, and would need to burn extra fuel while waiting to land at the privately owned airport’s original, 11,811-foot runway.

In that sense, Rains said, spending $53.5 million for an extra 2,624 feet of tarmac, or 7.8 per cent of the second runway’s total estimated cost, made good business sense. “You ignore climate change impacts at your peril, really,” she said.

Lighter loads

A study this year in the journal ‘Climatic Change’, based on modelling for 19 major airports, found that 10 to 30 per cent of annual flights departing at the hottest time of the day could require weight restrictions by the middle or end of this century.

The reductions would be small, perhaps 4 per cent or less on average, the study said. But a reduction of even 0.5 per cent could mean, for example, that an airline had to trim 327.4kg, or about three passengers, from a 160-passenger flight on a Boeing 737-800, possibly imposing a substantial economic burden over time.