U.S. Secretary of State John Kerry on Sunday defended the climate accord finalized after two weeks of talks in Paris, stating that the deal sent a “very clear signal” to the world that “people are moving in to low carbon, no carbon, alternative, renewable energy.” Kerry’s comments were in response to criticism by the prominent climate scientist James Hansen who called the Paris talks “a fraud.”

“I understand the criticisms of the agreement because it doesn’t have a mandatory scheme and it doesn’t have a compliance enforcement mechanism. That’s true,” Kerry said, in an interview with ABC News’ George Stephanopoulos broadcast Sunday. “But we have 186 countries, for the first time in history, all submitting independent plans that they have laid down, which are real, for reducing emissions. And what it does, in my judgment, more than anything else -- there is a uniform standard of transparency. And therefore, we will know what everybody is doing.”

Hansen, a former NASA scientist who rose to prominence in 1988 when he first brought global attention to anthropogenic climate change and the role of greenhouse gases in global warming, had, on Saturday, slammed the multinational climate talks in Paris for failing to discuss putting a price on greenhouse gas emissions -- a so-called carbon tax.

James Hansen James Hansen stands behind a mock grave in the grounds of Coventry Cathedral during a climate change day of action in Coventry, central England March, March 19, 2009. Photo: Reuters/Darren Staples

“It’s just bulls--- for them to say -- ‘We’ll have a 2C warming target and then try to do a little better every five years,’” Hansen told the Guardian Saturday. “It’s just worthless words. There is no action, just promises. As long as fossil fuels appear to be the cheapest fuels out there, they will be continued to be burned.”

The 31-page agreement, released Saturday, aims to limit the increase in the global average temperature to well below 2 degrees Celsius above preindustrial levels, and even urges countries to pursue efforts to limit the temperature rise to the much more ambitious 1.5 degree Celsius target. However, while the agreement legally requires countries to come back every five years with new reduction targets, it imposes no sanctions on those who fail to follow through their pledges. Nor does it mention the idea of a carbon tax, which many now believe is the only way to efficiently cut greenhouse gas emissions.

“The economic cost of a business as usual approach to emissions is incalculable. It will become questionable whether global governance will break down,” Hansen told the Guardian. “You’re talking about hundreds of millions of climate refugees from places such as Pakistan and China. We just can’t let that happen.”

In the interview, Hansen also hit out at U.S. President Barack Obama, accusing him of failing to live up to his promises.

“We all foolishly had such high hopes for Obama, to articulate things, to be like Roosevelt and have fireside chats to explain to the public why we need to have a rising fee on carbon in order to move to clean energy,” Hansen said. “But he’s not particularly good at that. He didn’t make it a priority and now it’s too late for him.”