Addressing a packed press conference here on Thursday, Mr. Kerry who is en route Colombia, made a 35 minute speech which was more like a political statement where he slammed climate sceptics and emphasized that no single country, not even the United States, can solve this problem or foot this bill alone.

He said there is no time to sit around going back and forth about whose responsibility it is to act. It’s everyone’s responsibility, because it’s the net amount of carbon that matters, not each country’s share,” he said.

He accepted that the biggest emitters, including the United States have to contribute more to the solution. And only those nations who step up and respond to this threat can legitimately lay claim to any mantle of leadership and global responsibility. And yes, if you’re a big, developed nation and you’re not helping to lead, then you are part of the problem, he declared. He called for giant, measurable, clear steps forward and concrete actions and ambitious commitments.

However, he also issued a warning to developing countries to act, saying that while industrialized countries have to play a major role in reducing emissions, that doesn’t mean that other nations are just free to go off and repeat the mistakes of the past and that “they somehow have a free pass to go to the levels that we’ve been at where we understand the danger.”

“We have to remember that today more than half of global emissions – more than half – are coming from developing nations. So it is imperative that they act, too, “he said.

Speaking of the urgency to combat climate change, he said it ranked equally with the array of global threats– terrorism, extremism, epidemics, poverty, and nuclear proliferation – all challenges that know no borders. An ambitious agreement in Paris is not an option, it’s an urgent necessity and he was optimistic that the world can get there.

And while no one here believes that a global climate agreement is going to be the silver bullet that eliminates this threat, he said it certainly won’t be eliminated without an agreement. Now you don’t need a PhD to see for yourself that the world is already changing, Mr. Kerry said and listed out various impacts of climate change and extreme events. He blamed “bad habits’’ for the current state of affairs but pointed out that the challenge that may be immense but it’s not insurmountable.

Unlike some other problems this one already has a ready-made solution which is energy policy, he said. The energy market today is a $6 trillion dollar market with 4 to 5 billion users today, and it’s going to go up to that 9 billion users.

There is still time to come together as a global community and make the right energy choices. Science shows that at this moment there still is a window and there is time to change course and avoid the worst consequences – but the window is closing quickly, he cautioned.

The United States and other industrial nations have contributed significantly to this problem, he said and they recognize the responsibility they have now to lead the global response.