It's called “Article 99.” With an intensifying Israeli offensive and escalating civilian casualties, U.N. Secretary-General Antonio Guterres invoked a rarely exercised power this week to warn the Security Council of an impending “humanitarian catastrophe” in Gaza. Guterres invoked Article 99 of the U.N. Charter — last used over half a century ago — which says the secretary-general may inform the council of matters he believes threaten international peace and security.