"Those who choose to ignore or dispute the science so clearly laid out in this report do so at great risk for all of us and for our kids and grandkids," Kerry said.
The UN's Intergovernmental Panel on Climate Change (IPCC) said today that time is running out to limit global warming to two degrees Celsius (3.6 degrees Fahrenheit), and that current trends in carbon emissions heralded disaster.
Kerry said the report issued in Copenhagen was a fresh warning, "another canary in the coal mine".
"The longer we are stuck in a debate over ideology and politics, the more the costs of inaction grow and grow," he said.
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The report - the first overview by the Nobel-winning organisation since 2007 - comes ahead of UN talks in Lima next month to pave the way to a 2015 pact in Paris to limit warming to a safer two degrees Celsius.
"The bottom line is that our planet is warming due to human actions, the damage is already visible, and the challenge requires ambitious, decisive and immediate action," Kerry said.
"We're seeing more and more extreme weather and climate events, whether it's storm surges, devastating heat waves, and torrential rain, across the globe," Kerry said. "It's not a coincidence."
Earth, the panel warned, is on a likely trajectory for at least four degrees Celsius warming by 2100 over pre-industrial times - recipe for worsening drought, flood, rising seas and species extinction.