Global greenhouse gas emissions will nearly double by 2050 under current policies unless urgent action is taken, the International Energy Agency has warned.

Issuing a stark assessment this week at a London environmental conference, the energy policy advisory group said failure to develop fossil fuel alternatives quickly will put the world on an irreversible course to a catastrophic long-term temperature increase of 6 degrees Celsius.

"Under current policies, we estimate that energy use and (carbon dioxide) emissions would increase by a third by 2020, and almost double by 2050," said IEA Deputy Executive Director Richard Jones.

"This would likely send global temperatures at least 6 degrees higher. Such an outcome would confront future generations with significant economic, environmental and energy security hardships," he added.

The grim forecast was delivered at the third annual Clean Energy Ministerial, which brought together ministers from 23 governments for discussions on clean energy progress and opportunities.

"It is my hope that they heed our warning of insufficient progress, and act to seize the security, economic and environmental benefits that a clean-energy transition can bring," Jones said.

While "a few" clean energy technologies were already capable of helping limit global warming to the United Nations' 2-degree target, "most clean energy technologies are not on track" to make the contributions necessary for that goal, the IEA report said.

It noted while onshore wind power has seen a 27 percent average annual growth rate since 2002 and that the cost of solar photovoltaic systems had been reduced by 75 percent in just three years, "halting progress at best" is being made on other vital forms of alternative energy.

Included in that category was carbon capture and storage, through which CO2 is removed from the smokestacks of fossil fuel-burning power plants and pumped into underground formations for long-term storage.

"(CCS) is not seeing the necessary rates of investment to develop full scale demonstration projects and nearly half of new coal-fired power plants are still being built with inefficient technology," Jones said.

The meeting was attended by British Energy Secretary Ed Davey, who noted that investments in renewable energy projects fell off markedly in the first quarter, the BBC reported.

"The risk is that recession delays low-carbon investment, leaving us a high-carbon legacy even when the global economy recovers, making meaningful action on climate change more expensive," he said.

Davey used the occasion to unveil a $57 million fund aimed a helping small businesses make buildings more energy efficient through use of advanced lighting, heat pumps and ventilation technologies, the broadcaster said.

"We are committed to ensuring the U.K. meets its 2050 climate objective, which has been designed to limit global temperature increases to around 2 degrees," added Greg Barker, British energy and climate change minister. "In order to reduce our emissions by 80 percent by 2050, we need to accelerate progress in the development of clean energy technologies."

World Wildlife Federation global climate and energy initiative leader Samantha Smith said the IEA report lays out a credible scenario, asserting that the "de-carbonizing our energy systems and moving towards renewable forms of energy is an absolute necessity."

But she added the assessment also provides an opportunity.

"Recent WWF research shows that a large-scale transition to renewable energy globally can be done with today's technology, to provide energy for the entire world's population."

Smith called on the United States and Canada to emulate Britain -- and even Mexico -- in passing climate change laws and to "embrace renewable energy, too."