Michael E. Mann
Michael E. Mann is a noted climate scientist and Distinguished Professor of Atmospheric Science at Pennsylvania State University. From the transcript of his Q&A with Steve Curwood for PRI's Living on Earth:
CURWOOD: So, you're famous research-wise for doing what some folks would call paleoclimate work. That is, you look back at what happened hundreds, thousands of years ago to say what might be happening in the future. Talk to me about that. And why did you become intrigued with that?--Marshal Zeringue
MANN: Yeah. So what we did is we used all the natural archives that we could get our hands on: tree rings, of course, tell us something about past conditions related to tree growth -- rainfall and temperature. So we can glean information about climate from the thickness and even the density of the rings in tree cores from sort of continental, extratropical locations. Tropical trees aren't useful for tree ring research. So you're only getting information really from the extratropical continents, and that's not the whole planet, right? So you need to fill in those gaps. Well, we do that by using other data like ice cores, which come from high latitudes or even in some cases the tropics, at very high elevations, like Mount Kilimanjaro or in the Andes. So now you're starting to fill in those gaps. You've got the tropics, you've got the polar regions, then the oceans; well, we can turn to corals. The calcium carbonate skeleton of a coral contains, typically, annual growth rings. And we can look at the isotopes of oxygen in those growth rings; that tells us something about the seawater that that coral was growing in. And so what our project was about was taking this increasingly rich information coming from scientists around the world producing these different kinds of records, and assimilating them into a single reconstruction of past large-scale temperature patterns around the globe. Now to us, the most interesting thing about those reconstructions was what we could learn about the regional patterns of past climate -- the El Nino phenomenon; what happened during the largest prehistoric eruptions. It was those sort of regional patterns that we were really interested in, what they could teach us about climate dynamics. But what ended up becoming by far the single most prominent aspect of that research was what happens when you average over all of the regions, you average away a lot of those interesting details. And you come up with one number for each year, the average temperature of the Northern Hemisphere. And we could plot that back in time. And when you do that, what you see is that it was relatively warm about 1000 years ago. And then we descended into the depths of the Little Ice Age, in the 17-, 18-, 1900s; and then we see this warming spike, of the past century. And it is so sharp that it takes us well outside of the range that we see over the past thousand years. So laid on its side, it looks like, you know, the sports implement that we refer to as a hockey stick. And that's...[read on]
