Less than a month after world leaders meeting in Paris signed a sweeping deal to fight climate change, a major question looms: Who will pay for the plan? Curbing the planet’s carbon emissions and shifting away from fossil fuels will require investments on the order of $1 trillion a year — more than triple what the world now spends on solar, wind and other renewable energy supplies.

With that clean energy investment gap in mind, over 500 global investors gathered at the United Nations headquarters in New York City Wednesday in the first major meeting since the U.N. climate summit in Paris last month. Ban Ki-moon, the U.N. secretary-general, urged attendees at the Investor Summit on Climate Risk — including institutional investors, state treasurers and corporate executives — to at least double their climate-related investments within the next five years.

“I call on the investor community to build on the strong momentum from Paris and seize the opportunities for clean energy growth,” he told the group of investors, who together represent more than $22 trillion in financial assets. “Sustainable, clean energy is growing, but not nearly fast enough to prevent excessive global warming that would trigger profound economic disruption and human suffering.”

Former Vice President Al Gore and Michael R. Bloomberg, the former New York City mayor and a possible U.S. presidential candidate, were both set to speak at the investor summit, along with the U.N. climate chief Christiana Figueres and senior French cabinet minister Ségolène Royal. 

Figueres, who is widely credited with assuring a successful outcome in Paris, said investment decisions over the next five years would be critical for accelerating the pace of climate action. "All of that is going to decide the quality of the energy and the global economy for the next 35 years, and hence the quality of life for everyone else for hundreds of years," she said in her opening remarks.

"The proverbial 'follow the money' is really true here," Figueres added. "We know that you cannot manage what you cannot measure, but you also cannot build what you do not finance."

At Wednesday’s gathering, investors were expected to discuss four broad themes, including "decarbonizing" investment portfolios to include fewer fossil fuel companies, as well as the push to make publicly traded companies disclose more details about their carbon emissions and exposure to climate regulations. The group also planned to discuss broader climate policies, including a price on carbon dioxide emissions, and how to boost investments for clean energy technologies.

Under the Paris deal, the leaders of nearly 200 nations agreed to limit the rise in global average temperatures to “well below” 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. To do that, the energy sector alone must invest $13.5 trillion in energy efficiency and low-carbon technologies from now through 2030, or roughly $1 trillion a year, the International Energy Agency estimated.

Clean energy investments last year, by comparison, totaled nearly $330 billion, Bloomberg New Energy Finance found in a recent report. The 2015 investment was the highest ever for the renewables sector, driven by a surge in spending from China, the United States, India and countries in Africa and Latin America.

Investments rose despite the plunge in crude oil prices, which analysts and investors feared could sap enthusiasm for lower-carbon technologies. The price of oil has dropped by 70 percent over the last 18 months due to a persistent oversupply of crude and slower demand growth from China. But solar and wind power, which are used in power generation, don’t always compete directly with petroleum, which is used for transportation as well as power generation; and the technologies are becoming increasingly cost competitive with coal and natural gas power plants, industry experts said.

Still, with crude prices expected to stay low this year — the World Bank forecast prices of $37 a barrel in 2016 — interest in zero-emissions vehicles and alternative fuels, like cellulosic ethanol, is expected to wane. That could slow the shift away from cheap gasoline-powered cars and diesel-driven transportation. And a cheaper market for fossil fuels in general could make carbon-cutting policies politically unpopular.

Fatih Birol, executive director of the International Energy Agency, told the New York Times this week that the lure of cheap fossil fuels is a “litmus test” for governments that will show "whether or not they are serious about what they have done in Paris.”

For large and institutional investors, however, the drop in oil prices hasn’t swayed their interest in confronting the risks that climate change poses to their portfolios, said Mindy Lubber, president of Ceres, the sustainability organization behind Wednesday’s summit.

“They believe acting on climate is a global economic imperative,” she said.

Lubber said that wasn’t necessarily the case around 12 years ago, when Ceres held its first Investor Summit on Climate Risk. The event in late 2003 drew around 300 investors and chief investment officers, but Lubber said participants came reluctantly. “They wanted to know if they could send their environmental interns instead, and we said no,” she recalled.

This year, the summit has a wait list of more than 100 people as the world awakens to the threats of climate change and the effects of carbon-cutting policies on today’s energy industries.

“All of them realize that climate risk is a financial risk,” Lubber said, albeit one that affects companies in different ways.

Indeed, investors with their toes in California’s large agricultural industry are exposed to the brutal drought that has sapped fields dry, destroyed crops and livestock, and cost farmers around $2.7 billion in the last year alone. Individuals or funds with a stake in seaside real estate face rising risks of property loss due to rising sea levels and extreme weather events. A shareholder in Peabody Energy, the world’s biggest private sector coal company, has seen its value plunge by over 90 percent in the last year as the U.S. coal sector struggles with crippling debts, more stringent power plant regulations and the plunging price of natural gas, which many utilities can easily switch to from coal.

“The impact on portfolios across the economy can now be felt and now be seen as severe,” Lubber said. “So how will the investment community transition to a low-carbon future, and what does that mean for fossil fuel investment? That’s the gist of what people are discussing.”