An Adelie penguin stands atop a block of melting ice near the French station at Dumont d’Urville in East Antarctica.

World leaders will launch an ambitious attempt to hold back the earth’s rising temperatures, urging each other to find common cause in two weeks of bargaining meant to steer the global economy away from dependence on fossil fuels.

They arrive at United Nations climate change talks in Paris on Monday armed with promises and accompanied by high expectations. After decades of struggling negotiations marked by the failure of a previous summit in Copenhagen six years ago, some form of landmark agreement appears all but assured by mid-December.

Warnings from climate scientists, demands from activists and exhortations from religious leaders like Pope Francis, coupled with major advances in cleaner energy sources like solar power, have all added to pressure to cut the carbon emissions held responsible for warming the planet.

Most scientists say failure to agree on strong measures in Paris would doom the world to ever-hotter average temperatures, bringing with them deadlier storms, more frequent droughts and rising sea levels as polar ice caps melt.

Facing such alarming projections, the leaders of more than 150 countries responsible for about 90 percent of the world’s greenhouse gas emissions have come bearing pledges to reduce their national carbon output, though by different degrees.

Achieving an international agreement committing both rich and developing nations to the fight against global warming would mean “we can have confidence that we’re doing right by future generations,” U.S. President Barack Obama said earlier this month.

On the eve of the summit, hundreds of thousands of people from Australia to Paraguay joined the biggest day of climate change activism in history, telling world leaders there was “No Planet B” in the fight against global warming.

French police detained scores of protesters after violent clashes in the center of Paris. The police fired tear gas to disperse about 200 protesters, some of them masked, who responded by hurling rocks and candles at them.

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