The scale, of course, was the biggest difference. Thousands of innocent lives lost, ruined or scarred compared with hundreds. There was the shock of 9/11, so unexpected and unprecedented in every sense compared with the inevitability and to a degree, in a post-IRA London, the familiarity of 7/7. There was the drama of 9/11; that drawn out dreadful spectacle on a beautiful early autumn day watched on TV around the world, or for some of us from our office windows. This compared to the underground horrors of 7/7, an event whose most powerful and lasting visual image was the No. 30 bus ripped open like a tin can.
In September of 2001, I'm prepared to admit that sitting in my 37th floor office I felt physically assaulted, and genuinely scared, a feeling that with the anthrax scares lasted several weeks. Two weeks ago I felt shocked, confused and sad, but not scared.
There were of course some immediate similarities-the wailing of sirens and the rivers of people flowing through the streets. The randomness of the attacks that affected so many people who wouldn't have been there if only... and might have been there if... . Four people from our office of 350 were on the Edgware Road train; one, Laura Webb, a lovely, bright, happy young woman, we now know to have died.
Both in New York and London there is a failure to understand: Who did this? Why? To what end? A series of questions that become more difficult to answer in London with the realization that the murderers were fellow citizens, living apparently normal lives in our midst.
The most important similarity, ultimately, will be our collective ability to cope and move on. The initial responses may have been different and perhaps true to national stereotype-New Yorkers reacted with public expressions of patriotism and their determination to overcome; Londoners were more stoical. But both in New York and already in London the human condition and the basic will to survive has prevailed. At least for those of us blessed not to be personally involved, things get back to "normal" with remarkable speed. Will things ever quite be the same again? No. Will it happen again? Probably. In the meantime, we have lives to live, jobs to do, families to love.
Finally, amidst all this self-awareness, perhaps we should not forget those around the world who deal with these kinds of atrocities on a constant basis; the citizens of Iraq, Israel, Palestine, Lebanon, India, Pakistan, Indonesia, the list is endless, who must look at the world's media attention directed at London during this week with some confusion.
Paul Hammersley is chairman-CEO of DDB London.