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.

Some big companies—including several European energy giants and U.S. utilities—have embraced the Paris talks as a path to greater predictability, including more certainty about the future price of carbon-based fuel.

But the biggest U.S. energy firms have withheld support, and coal giants are warning that efforts to curtail the use of affordable fossil fuels will hurt the poorest countries.

To succeed, leaders and their negotiators must bridge a decades-old rift between highly industrialized countries, whose growth was founded on the use of fossil fuels, and poorer countries demanding financial help for any deal that could impinge on their development.

Officials backing a climate accord in Paris have spent more than a year warning of rising sea levels, severe droughts and extreme weather that could come in future decades if countries don’t take steps now to curb emissions of carbon dioxide and other gases blamed for warming the atmosphere.

The main aim is to forge an agreement that would limit emissions enough to keep the average global temperature from rising more than 2 degrees Celsius above preindustrial levels—a threshold agreed upon by scientists over decades and codified by officials at earlier summits.

But all of the national offers to limit emissions expressed so far, if sealed in a Paris agreement and extended decades into the future, would likely still result in warming of 2.7 degrees, experts say. That is about 1 degree less warming than would likely occur without a deal. But it is also falls significantly short of the 2-degree goal, a frustrating outcome for island nations and other countries where small temperature changes can greatly affect weather and sea levels.

The U.S., Europe and other countries want the Paris accord to require countries to renew their emissions targets every five years or so, helping shift the world toward the 2-degree goal over time. “You need successive rounds of new targets that ratchet up ambitions, and we hope that will be on five-year cycles,” said Todd Stern, the U.S. special envoy to the talks.

More vulnerable developing countries want deeper cuts now from advanced economies to help them avoid adverse weather or even, in the case of some Pacific island nations, catastrophic inundation as ice caps melt and sea levels rise. Mr. Obama is set to meet leaders of island countries on Tuesday.

Other developing countries, including India, have resisted any commitments to revisit their targets in five years.

Emission-reduction plans offered by countries vary considerably, from steep cuts to carbon-dioxide emissions in the U.S. and Europe, to a Chinese goal to peak carbon emissions by 2030.

India’s national plan doesn’t involve any firm limits on greenhouse gases, although it does commit to bringing a massive amount of solar power online. Indian officials say they won’t commit to steps that could prevent hundreds of millions of its citizens from using cheap energy to emerge from poverty.

Perhaps the biggest fight between rich and poor countries centers on who will pay for green-energy transitions and climate adaptation in countries that haven’t emitted much carbon historically and don’t have easy access to capital.

Highly industrialized countries are working toward a 2020 goal of mobilizing $100 billion a year in public and private financing to help poorer countries reduce emissions or prepare for an adverse climate. Officials may pledge in Paris to renew or even increase that level of finding, observers say.

“The $100 billion by 2020—that’s the very first, critical step,” said Christiana Figueres, executive secretary of the United Nations climate-change body, in an interview in Washington. “It’s politically critical.”

Republicans in the U.S. hope to use various paths to weaken the accord. They are pushing to overturn the federal regulatory rules cutting carbon emissions from power plants, the main plank of the U.S. plan to cut overall emissions through 2025. They have warned foreign officials that the president’s efforts could be reversed after the next presidential election. And they have vowed to try to block Mr. Obama from following through on a pledge for the U.S. to contribute $3 billion to the new international fund to help developing countries.

Hanging over all this is the bigger question of whether the accord will be legally binding. Most developed countries want legally enforceable emissions targets to prevent countries from backsliding in their commitments. The U.S. and many developing countries, on the other hand, favor a looser, nonbinding approach for the targets. In the In the U.S., , Republican critics say any enforceable targets would require congressional consent.

U.S. officials say nonbinding targets—wrapped into a legally valid international agreement—would allow many countries divided on the talks to pledge deeper emissions without the threat of U.N. sanctions if they don’t meet their goals. “There aren’t compliance measures of that kind and there aren’t going to be, because people don’t support that,” Mr. Stern said in an interview.

Disputes over accountability have dogged climate discussions all the way back to the 1997 Kyoto Protocol, which bound developed countries—but not poorer nations—to emissions-reduction targets. The U.S. never ratified the Kyoto Protocol, whose commitments end in 2020.

In 2009, an accord partly brokered by Mr. Obama in Copenhagen failed to achieve a meaningful outcome as leading economies quarreled over key provisions.

The setback cast a cloud on international climate talks and discouraged governments form committing to another attempt during the recession years that followed.

But a big breakthrough on that front came last year, when the Obama administration helped persuade China to agree to peak its carbon emissions and build up massive renewable energy by 2030.