Year in Review: Carbon dioxide levels pass milestone

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Even as skeptics continued to doubt human-caused climate change, scientists grew more confident than ever this year that people are driving global warming.

In September, the Intergovernmental Panel on Climate Change reported that it is 95 to 100 percent certain that human activity — largely fossil fuel burning — is the main cause of rising temperatures since the 1950s (SN Online: 9/27/13).

The IPCC also dismissed a common argument that the apparent slowdown in global warming over the last 15 years is evidence that humans aren’t altering climate.