On the March 20 edition of Fox News' Your World -- during a segment featuring the on-screen graphic: “Al Gore and Global Warming: Is His Information Accurate?” -- host Neil Cavuto questioned the reliability of data showing that the recent increase in the Earth's average surface temperature surpasses that of other warming periods during the past four centuries. Cavuto and his guest, meteorologist Larry Cosgrove, both falsely claimed that such comparisons are misleading because the data are not “reliable” beyond “about 100 years.” Yet a June 2006 report by the National Academy of Sciences (NAS) determined “with a high level of confidence” that during the last few decades of the 20th century, the Earth's average surface temperature was higher than any other period in the last 400 years.

From the NAS report, titled “Surface Temperature Reconstructions for the Last 2,000 Years”:

It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries. This statement is justified by the consistency of the evidence from a wide variety of geographically diverse proxies.

From the March 20 edition of Fox News' Your World with Neil Cavuto:

ANNA AURILIO (U.S. Public Interest Research Group federal legislative director): Well, Neil, the top climate scientists say something's really happening. We've got cherry blossoms in January. As Larry [Cosgrove] pointed out, the polar bears are drowning, the ice that they depend on is melting. And again, the good news is, the things --

CAVUTO: But how do you know -- wait, wait, how do you know that wasn't occurring 150 years ago? Reliable statistics we have now go back only about 100 years, right?

AURILIO: Well, no, I mean, if we go back to the great explorers of the Earth, they were always looking for a Northwest Passage through the Arctic Sea ice. This goes back hundreds of years. This year, for the first time --

CAVUTO: But you don't have accurate --

AURILIO: -- people were actually able to find it.

CAVUTO: But you don't have accurate measurements of what the Earth's temperature was even more than a century ago, right?

AURILIO: Actually, the International Panel on Climate Change, which is the world's top climate scientists, say that the Earth's temperature and the carbon buildup in the atmosphere, more importantly, is higher than it's been in 20,000 years. And they know that from all the --

CAVUTO: Do you buy that Larry? Is it the highest it's been in 20,000 years?

COSGROVE: And again, I have to disagree, Anna, simply because the data, as Neil pointed out, is not reliable beyond about 100 years.

And I'll take it one step further. Let's go further back to when the Norse settled Greenland. Now, think about that. It's very tough to settle an ice, rock-bound community, but they were doing farming in Greenland many, many hundreds of years ago. Why? Because the climate had warmed sufficiently to allow that.

My bottom line is this: Yes, carbon emissions may be hurting the atmosphere. It may be inducing --

CAVUTO: OK.

COSGROVE: -- some global warming, but is it doing it all? I don't think so. I think there's a natural cycle.

CAVUTO: All right. Larry and Anna, I want to get you both back here. You both argue your points very well. Thank you.

Aurilio's statement that “the International Panel on Climate Change, which is the world's top climate scientists, say that the Earth's temperature and the carbon buildup in the atmosphere, more importantly, is higher than it's been in 20,000 years” may be a reference to the IPCC's latest report on climate change. The report's “Summary for Policymakers” states:

The atmospheric concentration of carbon dioxide (CO2) has increased by 31% since 1750. The present CO2 concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years.