A World Trade Center (or World Trade Centre) has become a rather trite unit of measurement to represent around 3,000 human fatalities. Despite not being a precise figure (actually 2,752 died in the towers or on the planes that hit, but that wouldn't be a neatly rounded number), it is popularly used to describe the death toll of disasters, illnesses or other life threatening problems, especially those which attract far less coverage than the September 11 2001 attacks. As if to make a point.

For example, to describe the French heatwave disaster of August 2003...

The overall EU death toll is probably equivalent to five or more World Trade Centres - at least 20,000 victims.
http://www.socialistreview.org.uk/article.php?articlenumber=8604

or to describe deaths caused through energy production...

It considers over 15,000 fatalities related to oil, over 8000 related to coal and 5000 from hydro - in total, about seven World Trade Centres.
http://www.world-nuclear.org/info/inf68.htm

or people dying in a famine in Afghanistan...

we're talking the equivalent number of deaths to ten World Trade Centers, every day, for 150 days.
http://www.workingforchange.com/article.cfm?ItemID=12276

or Nagasaki...

That's the equivalent of 50 World Trade Centers of people vaporized.
http://www.globalresearch.ca/articles/MIL203A.html

or drink driving...

All of our threats on the outside pale when you consider that we have lost the equivalent of five World Trade Centers in the last year
http://edition.cnn.com/2002/US/12/18/drunken.driving/