The march toward a greener global economy is headed into a more difficult second phase that will aim to replace carbon as an energy source, said panelists during the Bloomberg New Economy Forum.

Companies including Honeywell International and Schneider Electricare offering solutions to reduce carbon emissions in commercial buildings, the petrochemical industry and transportation that are being adopted now, which constitutes the first phase. But the replacement of carbon-based energy will be more difficult and require more breakthroughs, said Honeywell CEO Darius Adamczyk.

“The short-term technologies are here and frankly more of those should be used,” Adamczyk said. “But we also have to address the longer term and how we displace the use of carbon with other forms of energy.”

The move to a sustainable economy is well on its way as governments and investors agree it’s in their best interest to fund green projects and wean themselves off carbon, said Christiana Figueres, vice chair of the Global Covenant of Mayors for Climate and Energy. Still, the pace is too slow, she said.

“My concern is no longer about the direction.” Figueres said. “My concern is speed and scale, and we are far from the speed and scale we need.”

Honeywell said it’s seeking alternatives to carbon with investments in hydrogen fuel cells to power drones and technology to power electric aircraft, which Adamczyk said will likely become a reality in two to four years. Schneider Electric is banking on electricity, powered by renewable sources and smart grids, as the main solution for reducing emissions in buildings, said CEO Jean-Pascal Tricoire.

By deploying new technologies that have been developed just in the last five years, global temperatures could be kept from rising 1.5 °C, he said.

“The problem is not technology anymore, it’s about adoption and decisions,” said Tricoire.

The New Economy Forum is organized by Bloomberg Media Group, a division of Bloomberg, the parent company of Bloomberg News.