For the first time in history, all nonemergency civilian aircraft in the United States and several other countries including Canada were immediately grounded, stranding tens of thousands of passengers across the world.

Economic aftermath

The attacks had a significant economic impact on the United States and world markets. The Federal Reserve temporarily had reduced contact with banks because of outages of switching equipment in the lower NY financial district. Contact and control over the money supply, including immediate liquidity for banks, was restored within hours. The New York Stock Exchange (NYSE), the American Stock Exchange and NASDAQ did not open on September 11 and remained closed until September 17. NYSE facilities and remote data processing sites were not damaged by the attack, but member firms, customers and markets were unable to communicate due to major damage to the telephone exchange facility near the World Trade Center. When the stock markets reopened on September 17, 2001, after the longest closure since the Great Depression in 1929, the Dow Jones Industrial Average (“DJIA”) stock market index fell 684 points, or 7.1%, to 8920, its biggest-ever one-day point decline. By the end of the week, the DJIA had fallen 1369.7 points (14.3%), its largest one-week point drop in history. U.S. stocks lost $1.2 trillion in value for the week. As of 2005 Wall and Broad Streets near the New York Stock Exchange remained barricaded and guarded to prevent a physical attack upon the building.
September 11 from space: Manhattan spreads a large smoke plume
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September 11 from space: Manhattan spreads a large smoke plume

The economy of Lower Manhattan, which by itself is the third-largest business district in the United States (after Midtown Manhattan and the Chicago Loop) was devastated in the immediate aftermath. Thirty percent (28.7 million sq ft, 2.7 million m³) of Lower Manhattan office space was either damaged or destroyed. The 41-story Deutsche Bank Building, neighboring the World Trade Center, was subsequently closed because extensive damage made it unfit for habitation and beyond repair; it was scheduled for demolition. Power, telephone, and gas were cut off in much of Lower Manhattan. Citizens were not permitted to enter the SoHo and Lower Manhattan area without extensive inspection. Much of what was destroyed was valuable Class-A space. The pre-2001 trend of moving jobs out of Lower Manhattan to Midtown and New Jersey was accelerated. Many questioned whether these lost jobs would ever be restored, and whether the damaged tax base could ever recover.[84] The rebuilding has been inhibited by a lack of agreement on priorities. For example, Mayor Bloomberg had made New York's bid for the 2012 Summer Olympics the core of his capital development plan from 2002 until mid-2005, and Governor Pataki largely delegated his role to the Lower Manhattan Development Corporation which has been widely criticized for doing little with the enormous funding directed to the rebuilding efforts.[85][86] On the sites of the totally destroyed buildings, one, 7 World Trade Center, has a new office tower which was completed in 2006. The Freedom Tower is currently under construction at the site and at 1,776 ft (541 m) upon completion in 2010, will become the tallest building in North America and one of the tallest in the world. Three more towers are expected to be built between 2007 and 2012 on the site, and will be located one block east of where the original towers stood. North American air space was closed for several days after the attacks and air travel decreased significantly upon its reopening. The attacks led to nearly a 20% cutback in air travel capacity, and severely exacerbated financial problems in the struggling U.S. airline industry.[87]
Smoke plume coming from the WTC site, seen on Doppler radar
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Smoke plume coming from the WTC site, seen on Doppler radar
Smoke plume coming from the Pentagon site, seen on Doppler radar
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Smoke plume coming from the Pentagon site, seen on Doppler radar

Potential health effects

The thousands of tons of toxic debris resulting from the collapse of the Twin Towers consisted of: 50% nonfibrous material and construction debris; 40% glass and other fibers; 9.2% cellulose; and 0.8% asbestos,[88] lead, and mercury. There were also unprecedented levels of dioxin and PAHs from the fires which burned for three months.[89] This has led to debilitating illnesses among rescue and recovery workers, and the death of NYPD officer James Zadroga.[90] Health effects also extended to some residents, students, and office workers of Lower Manhattan and nearby Chinatown.[91]

There is scientific speculation that exposure to various toxic products and the pollutants in the air surrounding the Towers after the WTC collapse may have negative effects on fetal development. Due to this potential hazard, a notable children's environmental health center is currently analyzing the children whose mothers were pregnant during the WTC collapse, and were living or working near the World Trade Center towers. The staff of this study assesses the children using psychological testing every year and interviews the mothers every six months. The purpose of the study is to determine whether there is significant difference in development and health progression of children whose mothers were exposed, versus those who were not exposed after the WTC collapse.[92]

In the aftermath of the attacks, many U.S. citizens held the view that they had “changed the world forever.” The Bush administration declared a war on terrorism, with the stated goals of bringing Osama bin Laden and al-Qaeda to justice and preventing the emergence of other terrorist networks. These goals would be accomplished by means including economic and military sanctions against states perceived as harboring terrorists and increasing global surveillance and intelligence sharing. The second-biggest operation outside of the United States was the overthrow of Afghanistan's Taliban government, by a U.S.-led coalition. The U.S. was not the only nation to increase its military readiness, with other notable examples being the Philippines and Indonesia, countries that have their own internal conflicts with Islamic extremist terrorism.

Because the attacks on the United States were judged to be within the parameters of the North Atlantic Treaty Organization, NATO declared Article 5 of the military alliance to be met on September 12, 2001, making the US war on terror the first time since its inception that NATO would actually participate in a “hot” war.[75]