World leaders kicked off two weeks of climate change talks outside Paris on Monday, saying that by striking an ambitious deal to cut emissions that are warming the planet they can show terrorists what countries can do when they stand together.

The meeting comes at a somber time for France, two weeks after militants linked to the ISIS terror group killed 130 people around Paris. Fears of more attacks have prompted extra-high security and a crackdown on environmental protests -- and threaten to eclipse longer-term concerns about rising seas and increasingly extreme weather linked to global warming.

Dozens of leaders streaming into Paris, including President Barack Obama, paid their respects at sites linked to the attacks. Obama, in a late-night visit, placed a single flower outside the concert hall where dozens were killed, and bowed his head in silence.

Gathering for the talks near Le Bourget airfield, just north of the city, the leaders also held a moment of silence for victims of recent attacks in France, Lebanon, Iraq, Tunisia and Mali.

"We stand with Paris," said U.N. climate change agency chief Christina Figueres. "The city of light, now more than ever, is a beacon of hope for the world."

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Addressing negotiators, she added: "The eyes of millions of people around the world are on you."

The clock is ticking in large part because after world leaders leave Monday negotiators have limited time to strike a deal. Already, 181 nations have made pledges to combat carbon dioxide pollution.

"We just have 11 short days before us," French Foreign Minister Laurent Fabius said as he took over as president of the negotiations. "Success is not yet assured, but it is within our grasp ... The eyes of the world are upon us and there are great hopes."

Added the outgoing president, Peruvian Environment Minister Manuel Pulgar-Vidal: "We can show to the world that we can work together against climate change and against global terrorism."

U.N. Secretary-General Ban Ki-moon and French President Francois Hollande greeted heads of state and government from around the world as they arrived for the talks. The leaders were giving speeches about what their countries are doing to reduce emissions and slow climate change.

"Consider the needs of the youngest generation," Britain's Prince Charles said. "Because none of us should assume that for our today, they should give up tomorrow."

Wide Paris-area highways usually packed with commuters were cordoned off to clear the way for all the VIPs. Riot police vans and plainclothes officers were stationed around the capital and by the national stadium, one of the targets of the Nov. 13 attacks that is near the climate conference venue.

The conference is aimed at the most far-reaching deal ever to tackle global warming. The last major agreement, the 1997 Kyoto Protocol, required only rich countries to cut emissions, and the U.S. never signed on.

Among several sticking points is money -- how much rich countries should invest to help poor countries cope with climate change, how much should be invested in renewable energy, and how much traditional oil and gas producers stand to lose if countries agree to forever reduce emissions.

With that in mind, at least 19 governments and 28 leading world investors were announcing billions of dollars in investments to research and develop clean energy technology, with the goal of making it cheaper.

Backers include Obama, Microsoft co-founder Bill Gates, Facebook founder Mark Zuckerberg, billionaires George Soros and Saudi Prince Alaweed bin Talal, and Jack Ma of China's Alibaba.

Under the initiative, 19 countries  pledge to double their spending on low- or no-carbon energy over the next five years. They currently spend about $10 billion a year, about half of that from the U.S., Brian Deese, senior adviser to Obama on climate and energy issues, told reporters in Washington.

Gates, the "intellectual architect" of the effort, committed $1 billion of his own money, U.S. Energy Secretary Ernest Moniz said.

"We'll work to mobilize support to help the most vulnerable countries expand clean energy and adapt to the effects of climate change we can no longer avoid," Obama wrote on his Facebook page.