The goal for next week’s Paris summit was lofty all along: to hatch a climate accord strong enough to keep global warming at bay, built on promises from nearly 200 countries to limit their greenhouse-gas emissions. President Barack Obama and other leaders will face immediate distractions when they huddle just outside the French capital on Monday to kick off a final two-week effort to reach a global accord. Since the Nov. 13 terror attacks, Paris is under a huge police clampdown, with downtown rallies banned under a national state of emergency. Mr. Obama plans already to spend part of his brief time there on antiterrorism talks with French President François Hollande. Diplomats say the attacks have galvanized world leaders to demonstrate solidarity, increasing the chances of success on the climate front. Still, the recent violence won’t soften unease over the climate accord in many countries, including the U.S., where Mr. Obama faces stiff opposition from Republicans in Congress and other critics.