While trumpeting its own audio presentation, Treehugger this week pointed to The Green Room, where the iTunes Music Store has aggregated 23 green-topic podcasts. That is, 23 shows, all of which offer multiple episodes.

I was familiar with some — "Living On Earth" is produced around here (by my friend and former Globie Steve Curwood), and of course NPR has a couple of offerings — but there are also 'casts from all over the world. Some are put out by industry trade groups, which by their nature would be on the bottom of my list. I have a severe podcast overload as it is; I typically have 70 or so pending at any one time:

(My current roster:

* "The Book Show" from ABC Radio National in Australia.

* The New York Times Book Review podcast.

* Talk of the Nation's "Science Friday" from NPR.

* The Commonwealth Club of California.

* "The Writer's Almanac" (a 5-minute-a-day thing by Garrison Keillor that notes calendar points of interest and includes a brief poem).

* "Left, Right, and Center," a fairly civilized political discussion show from KCRW in California featuring Robert Scherer, Arianna Huffington, Tony Blankley, and some guy from the center (Matt something).

* "This American Life," which I do enjoy, though perhaps I would better say "admire." I notice it's rarely the choice I make to listen to, and the episodes just mount up at the bottom of my list.

I decided to sample "TPN: The Cleantech Show" from Australia, and got a fascinating report on an Aussie corporation's product, well past testing and about to go into commercial operation, that is a combination desalination device and clean-energy producer harvesting tidal power. This is particularly valuable in an island nation like Australia, where the population is concentrated at the shore.

Most, if not all, of the 'casts are free, of course.