US Secretary of State John Kerry Thursday urged nations to set ambitious goals to curb greenhouse gases, warning climate change deniers that gambling with the Earth's future was a risky business as "there is no Planet B."

"We have nine short months to come together around the kind of agreement that will put us on the right path," Kerry said ahead of a key UN climate change conference to be held in Paris in December.

Countries, which are tasked with trying to limit the rise in global temperatures to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels, have until March 31 to announce their commitment to cutting greenhouse gas emissions.

The United States, which accounts for 12 percent of global emissions, has announced it plans to reduce them by 26-28 percent in 2025 compared with their level in 2005.

"If we fail, future generations will not and should not forgive those who ignore this moment, no matter their reasoning," said Kerry, long a passionate environmental advocate, adding that "for decades now the science has been screaming at us."

"Future generations will judge our effort, not just as a policy failure, but as a collective, moral failure of historic consequence," he told the Atlantic Council.

"And they will want to know how world leaders could possibly have been so blind, or so ignorant, or so ideological, or so dysfunctional, and, frankly, so stubborn that we failed to act on knowledge that was confirmed by so many scientists in so many studies over such a long period of time."

The top US diplomat, who during more than two years in office has given a number of major climate change speeches, sought to convince skeptics by making an economic argument for developing alternative energy sources like wind and solar power.

"Clean energy is not only a solution to climate change. Guess what? It's also one of the greatest economic opportunities of all time," Kerry said.

"The global energy market of the future is poised to be the largest market the world has ever known. We're talking about a $6 trillion market today with four to five billion users today. That will grow to nine billion users over the next few decades."

And he predicted that by 2035 investment in the energy sector was expected to reach some $17 trillion -- more than the entire current GDP of China.

But investing in new technology to bring renewable energy sources to every community meant governments would have to "phase out wasteful fossil fuel subsidies" to dirty power sources such as oil and coal, he said.

"Gambling with the future of Earth itself when we know full well what the outcome would be is beyond reckless; it is just plain immoral, and it is a risk that no one should take," Kerry said.

"And we need to face reality: There is no Planet B."