NEW YORK—The risk of a major terrorism attack in the U.S. is lower for 2013 than it was for 2012 due to changes in the global terrorism landscape including the death of Osama bin Laden and one of his deputies, according to Risk Management Solutions.

Gordon Woo, RMS catastrophist, said at a conference held here last week that bin Laden's death and the removal of deputy Abu Yahya Libi—who RMS called a "conduit" between Pakistan's military commanders and Al-Qaeda operatives in Iraq, Yemen, and other countries located to its west—have interrupted the planning of large-scale operations. Woo added that the Arab Spring has also temporarily affected al Qaeda's ideological pull.

These factors have reduced the likelihood of the U.S. suffering a "macro attack," defined by RMS as premeditated events that cause losses in excess of $1 billion, more than 50 casualties, 250 injuries, and/or massive symbolic damage, said Woo.