Without aggressive action now, it will be hard to keep greenhouse gas emissions in check long term, U.S. Energy Secretary Ernest Moniz said.

A report from the Intergovernmental Panel on Climate Change warns international efforts to reduce carbon emissions are short of what's needed to keep expected temperature increases in check. Greenhouse gas emissions would have to be close to zero by the end of the century to keep changing weather patterns from growing more severe.

"The IPCC report notes that it will be substantially more difficult to maintain low greenhouse gas concentrations in the long term if we do not act aggressively now," Moniz said in a statement Sunday.

IPCC Co-Chairman Ottmar Edenhofer said the dangers from climate change are clear.

"To avoid dangerous interference with the climate system, we need to move away from business as usual," he said in a statement.

The IPCC said the burning of fossil fuels was a top contributor to high levels of greenhouse gases in the atmosphere.

British Energy Secretary Ed Davey said in renewable energy targets were more important than ever given the IPCC's warning.

"The science has spoken," he said. "Left unchecked, climate change will have far reaching consequences for our society."

Moniz said his government was looking to bring sources of renewable energy online faster and to curb emissions from the transportation sector. European leaders are working to have renewable energy account for 20 percent of their energy mix by 2020.