The wave of optimism that followed last month’s climate change deal in Paris is wending its way down Wall Street. Investors and financiers meeting in New York this week vowed to harness their trillions of dollars in collective wealth to develop clean energy projects and curb the planet’s carbon emissions.

Whether they actually deliver on that promise could mean the difference between winning and losing the fight against climate change. Only with a dramatic spike in spending — and a total shift away from fossil fuel investments — can countries have a shot at avoiding dangerous levels of global warming, according to policy leaders and climate experts speaking at the Investor Summit on Climate Risk at the United Nations headquarters Wednesday.

“We have the momentum with us. We are winning. But we need you,” former U.S. Vice President Al Gore told a group of over 500 investors, pension fund managers, bankers and business executives over lunch. “This is a moment of extraordinary hope, because the investor community is moving — because the business community is real.”

The financial sector’s participation is considered critical for ensuring the goals of the Paris climate conference are actually achieved. Last December, the leaders of nearly 200 nations agreed to limit the rise of global average temperatures to “well below” 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-Industrial levels.

To hit that target, the world must invest at least $12.1 trillion in renewable electricity — including solar and wind power, battery storage and energy efficiency — within the next 25 years, analysts at Bloomberg New Energy Finance said in a new report. So far, countries are on track to spend $6.9 trillion by 2040, resulting in an investment gap of $5.2 billion, by BNEF’s estimate. Investments in emissions-free vehicles, alternative fuels and sustainable-agriculture practices will add trillions more to the total.

Investors and fund managers at the event pledged to plug that funding hole by backing more renewable energy projects and revisiting their investments in fossil fuel companies or energy-intensive sectors.

“We want to be part of closing that gap,” Thomas DiNapoli, the New York State comptroller, told reporters at the U.N. headquarters. He noted the state this month launched a 10-year, $5 billion Clean Energy Fund to install more solar and wind power in New York. “Investors have put the word out that we’re looking to put more money into these kinds of opportunities, so the opportunities are coming to us,” he said.

The financial industry has transformed from a reluctant bystander on the topic of climate change to an active participant in the past few years.

In the run-up to the Paris climate summit, six major U.S. banks urged world leaders to adopt policies that “recognize the cost of carbon” and “drive innovation in low-carbon energy.” Large pension funds from California to Norway are stripping their portfolios of risky, high-carbon coal companies. Late last year, the first “fossil-free” exchange-traded fund was launched on the New York Stock Exchange. The ETF includes only companies with cleaner-than-average carbon footprints.

Motivations are mostly economic. If countries adopt policies to reduce emissions to nearly zero this century, those who heavily support coal, oil and natural gas will see their returns evaporate. The effects of climate change itself — from rising sea levels to enduring droughts and extreme storms — threaten to disrupt production and trade flows, and drain global economic growth.

Yet for all the conviction and enthusiasm at Wednesday’s summit, the path for delivering a clean energy transformation remains largely uncertain. In many markets around the world, petroleum-based fuels and electricity from coal and natural gas remain cheaper and easier to access than cleaner alternatives. Most investors generally prefer to stick with the safe bets, rather than testing the waters with new financing tools like “green bonds,” or carbon-free investment funds.

Christiana Figueres, the U.N. climate chief, outlined two broad steps that could clear some of those roadblocks: putting a global price on carbon dioxide emissions and compelling companies to publicly disclose more information on how climate regulations could threaten their bottom lines. Photo: Francois Guillot/AFP/Getty Images

“Both of those brought together will be incredible enablers of the speed of transformation,” she said during a panel.

Pricing carbon emissions would effectively penalize polluters and make it more expensive to extract or consume oil, coal and natural gas. Renewable energy, as a result, would gain a competitive price advantage.

About 40 nations and 23 cities, states and regions have adopted or are starting to adopt a price on carbon, either via a direct tax on emissions or through a cap-and-trade system. California and nine East Coast states have cap-and-trade markets in place, although efforts to adopt a national scheme resoundingly failed during the first Obama administration. Exxon Mobil and other energy companies have adopted an internal carbon price to help determine the long-term viability of their exploration projects.

Betty Yee, the California state controller, said a universal price on carbon would make it less risky for the state’s investment funds to direct their dollars to clean energy projects. The California State Teachers’ Retirement System has a goal to invest $3.7 billion in clean energy by 2019. But that amount could reach $9.5 billion under a carbon price, Yee said.

While the policy has gained momentum in the wake of the Paris agreement, the plunge in oil and gas prices over the past year could derail some of those efforts, energy analysts said. Policymakers and the broader public may be less inclined to support regulations that drive up prices when they’re enjoying cheaper gasoline and heating fuel.

“For the clean energy sector, sustained low oil and gas prices are concerning, there’s no question,” said Michael Liebreich, founder of Bloomberg New Energy Finance and chairman of its advisory board.

The push for increased public disclosures is also gathering support from global business leaders and shareholder activists. Proponents say boosting climate disclosures could steer more dollars toward cleaner energy projects by making investors better informed of the risks of investing in fossil fuels.

“What banks and financial institutions choose to finance will make an enormous difference in how people go about getting their energy,” Mary Schapiro, former chairman of the U.S. Securities and Exchange Commission, said during a panel.

Photo: Luke Sharrett/Getty Images

Schapiro adopted the 2010 SEC guidance that requires publicly traded companies to inform investors of their climate risks. She now serves on the Task Force on Climate-Related Financial Disclosures, a new initiative of the Financial Stability Board led by Michael Bloomberg, the billionaire founder of Bloomberg LP and three-term mayor of New York. The task force aims to develop consistent voluntary guidelines for companies providing information to lenders, insurers, investors and other stakeholders.

Yet guidelines and other measures have their limits. A New York investigation into Peabody Energy last year found the St. Louis coal giant, despite the SEC guidance, had not been forthright with investors and regulators about the threats to its business that the company acknowledged behind closed doors.

Peabody’s shares have fallen nearly 96 percent in the past year to around $4 a share as the industry has grappled with rising debt, plunging coal prices and softening demand from the power and steelmaking sectors. The Dow Jones U.S. coal market index has plunged 80 percent in the past year and 95 percent since 2011. In an agreement with New York Attorney General Eric Schneiderman, Peabody agreed to disclose more details about the financial risk it faces from climate change policies and other environmental issues that could limit demand for its coal.

“Understanding those risks is important for investors in decisions about where to allocate capital,” Schapiro said. “Without disclosure you can have no understanding.”

During his impassioned lunch speech, Gore argued that backing clean energy would not only help investors manage their financial risks but also transform the global economy.

He likened the push to invest in lower-carbon energy systems to the industrial expansion that arose in the 1940s during World War II. Clean energy transformation could catapult the global economy by creating jobs and boosting production in the same way the war machine boosted the world from the depths of the Great Depression, Gore said.

“The transition to a low-carbon economy is the greatest opportunity we have to lift the global economy in a sustainable way,” he said.