For airports, in terms of passenger traffic,  the title-holder currently is Atlanta's Hartsfield-Jackson International Airport, according to data published by Airports Council International.  This has been true for the entire 2000-2010 period, the most recent data published on ACI's website.   ATL wrested the title from its previous holder, Chicago's O'Hare International, as of 1998, and by the year 2000, with an 8 million annual passengers lead over ORD, seemed to be in a position to 'never look back' again.  In the aftermath of September 11, 2001, traffic at both locations fell below the year 2000 levels, but Atlanta's lead had grown to 10 million annual passengers.

However, by 2010, O'Hare was no longer in second place, having been eclipsed by Beijing, China's Capital Airport.  To put this in perspective, as of 2000, Beijing was not in ACI's compilation of the world's top 30 airports, and didn't appear on that list for the first time until 2002, when its 27.2 million passengers placed it 26th in the world, just behind Tokyo-Narita (essentially an international-only facility), Singapore and Newark; and just ahead of Seattle, Orlando and Toronto. 

By the time of PEK's second-place finish in 2010, the passenger count was 73.9 million, almost triple the 2002 figure.  In contrast, Hartsfield-Jackson grew from 76.9 million passengers in 2002 to 89.3 million in 2010, an increase of 16 percent.  (During the same period, O'Hare increased from 66.6 million to 66.8 million.)  Beijing Capital's progress up through the ranks was relatively rapid: number 20 in 2004, 15th in 2005; 9th place in 2006; 3rd in 2009; and number two in 2010, as noted previously. 

Between 2009 and 2010, ATL grew 1.5 percent; PEK, 13.1 percent, according to the ACI statistics.  To put it in a different perspective, Atlanta's total growth in passengers between 2002 and 2010 was about 12.4 million; Beijing's increase in the single year between 2009 and 2010 was approximately 8.6 million.  While the figures for 2011 have not yet been published, it is very likely that there will be a new world champion in the not distant future.  If the 2009/2010 growth rates persist, this could occur as early as 2012. Even if ATL grew by 5 percent annually, and PEK "only" by 10 percent from the 2010 traffic levels, this would still be true.

Interestingly, former leader ORD's experience provides some perspective on Beijing's rapid growth.  Arriving essentially at the start of the jet age, and taking over from Chicago's Midway airport, the previous 'world's busiest', O'Hare had 10 million passengers in 1962.  In three years, by 1965, this had doubled, to 20 million, and grew to 30 million in 1968.  50 million passengers were achieved in 1986; 70 million was reached in 1997, immediately prior to the ascendency of Atlanta.  ORD's rapid growth in the early years benefitted greatly from the technological revolution provided by the switch from (largely) piston-powered aircraft to jets.

Beijing, in contrast, has achieved its recent growth rates via a rapidly-developing economy; by 2000, the global airline industry was relatively mature, from a technology standpoint.  While China's economy has grown by the proverbial 'leaps and bounds', the proportion of its population that regularly utilizes air transport is still considerably less than in the U.S. and Europe, for example.  Of course, as its overall economy grows, this augurs well for Beijing, and the rest of China's airports.  Truth in forecasting: not every growing time series proceeds sans perturbations; Beijing itself  fell from 27.2 million passengers in 2002 to 24.3 million in 2003 (and disappeared from the ACI's Top Airport rankings for that year).  For that matter, Tokyo Narita has now dropped out of the rankings, as Haneda Airport has gained additional international services.  However, barring something very unusual, ATL will probably be in the position of offering gracious congratulations to their colleagues in Beijing in the not distant future.

Some final food for thought:  while it might seem a little far-fetched, Dubai has been growing rapidly in recent years, and Emirates has lots and lots of very high-capacity aircraft on order...and DXB didn't appear in ACI's Top 30 until 2007 (at number 27); today, it's 13th.  Game on?