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UN Panel: ‘Extremely Likely’ Earth’s Rapid Warming Is Caused by Humans

September 27, 2013 at 12:00 AM EDT


JUDY WOODRUFF: We return to the latest assessment on global climate change.

It comes from the U.N.’s Intergovernmental Panel on Climate Change, or IPCC, which last issued a series of reports in 2007. The scientists who wrote it won the Nobel Peace Prize for the warnings they raised and the evidence they presented. The newest work includes more predictions and examples of what’s already happening.

We take a closer look, starting with this report from Tom Clarke of Independent Television News.

TOM CLARKE: Two-hundred and fifty scientists, 195 governments and thousand of pages of analysis all conclude the world is warming, not just the atmosphere, the oceans, too, and only a rapid reduction in greenhouse gas emissions has any real chance of turning back the tide.

THOMAS STOCKER, Co-Chair, Intergovernmental Panel on Climate Change: Human influence on the climate system is clear. Climate change challenges the two primary resources of humans and ecosystems: land and water.

TOM CLARKE: This six-yearly update of the science concludes temperatures have risen by almost a degree over the past century. It is extremely likely that global warming seen since 1950 is manmade. It predicts global average temperatures are likely to rise between 1.5 and 4.5 degrees by 2100.

And sea levels, says the IPCC, have been rising faster since Victorian times than at any point in the last two millennia. Time travel down Isambard Kingdom Brunel’s Great Western Main Line, and you can see why that’s important.

This seawall was built to protect the railway from a one-in-a-100-year storm event. Now, since Victorian times, when the railway was built, sea level has already risen about 19 centimeters. Based on today’s IPCC report, the sea is going to come up by an additional 26 to 82 centimeters. That means, by 2100, what is today a one-in-100-year storm will be an annual occurrence.

The report also gives short shrift to an observed lack of land surface temperature increases since a very hot year in 1998. Skeptical observers claim that shows global warming has stopped.

EMILY SHUCKBURGH, British Antarctic Survey: Well, first of all, it’s important to understand what’s been happening. So, temperatures are still at record levels. Each of the last three decades have been successively warmer, and it’s that longer-term trend which is important for whether or not we’re changing our climate. And the overwhelming evidence is that we are.

TOM CLARKE: Not everything is more certain. This report concludes the impact of warming on extreme weather, like hurricanes and floods, is less clear than researchers previously thought.

As best as the facts can be established, this report lays them down, and they should be viewed, say scientists, in the knowledge that, since their last report in 2007, we have pumped 200 billion more tons of CO2 into the atmosphere.

JUDY WOODRUFF: And a note of clarification about Tom Clarke’s story: It explained the potential rise in temperature when measured with the Celsius scale. Using the Fahrenheit metric, the panel said temperatures could rise by 2.7 to 8.1 degrees.