From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block.


And I'm Audie Cornish.

Whether it's stifling hot or freezing cold, people can agree about the weather. The issue of climate, however, is not so benign. Most scientists who study the Earth say our climate is changing and humans are part of what's making that happen. But to a lot of non-scientists the issue isn't so cut and dried.

NPR's Christopher Joyce reports on the latest attempt by scientists to clarify the question of climate change.

CHRISTOPHER JOYCE, BYLINE: Today, the federal government's top climate scientists announced that 2012 was really hot, among the top 10 hottest years on record. The National Oceanic and Atmospheric Administration issued its annual state of the climate report. Mostly, bad news: rising sea level - check; less sea ice in the Arctic - check; warmer oceans - check.

But then there are places that are cooler and wetter, West Africa for example. And recently, the rise in global temperature seems to have stalled.

Tom Karl runs NOAA's National Climatic Data Center. He says the hard thing about measuring climate change is a close-up view can be misleading. Like last year's record temperatures in the U.S.

TOM KARL: Well, you know, was that just natural variability? But if you compare that then to the whole suite of indicators that scientists are trying to look at, you see, no, that's part of a pattern we're seeing.

JOYCE: NOAA's report describes that warming pattern in 260 pages, without discussing the cause; a second report will talk about that in September. But the American Geophysical Union is ready with an explanation now. The AGU represents some 60,000 scientists who live to study the Earth.

This week, the group issued a two-page statement with the headline, quote, "Humanity is the Major Influence on the Global Climate Change Observed Over The Past 50 Years."

Here's climate scientist Gerald North from Texas A&M University.

GERALD NORTH: We've been looking, what other possible candidates? We just cannot find any other way that this could be happening.

JOYCE: North ran the panel that wrote the new AGU statement, its first in six years. He agrees that things like temperature and sea level do vary a lot, and that gives the long-term climate record a kind of herky-jerky appearance.

NORTH: This thing doesn't just go up continuously but is a kind of ratchet. It goes up, then it steps back a little bit, then goes up some more.

JOYCE: But is this just the scientific community preaching to itself? Well, Amy Clement hopes not. Clement is a climate scientist at the University of Miami. She was on the panel that wrote the new statement.

AMY CLEMENT: Let's say I'm in the supermarket and I'm in line and people say, oh, what do you do. I talk about, I'm a climate scientist. Oh, is global warming happening? And, I mean, that is so well-established in the scientific literature, and somehow the public still has the perception that that is not well-established.

JOYCE: Clement points out that the AGU statement acknowledges that there are still uncertainties about the local effects of a warming planet. But the long-term trend is clear: It's getting warmer.

Christopher Joyce, NPR News.

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