In nature, loud colors aren’t usually an afterthought. Mate with me, says many a strutting bird, vibrant plumage on full show. Don’t eat me, shouts the poisonous plant. Yet, for a long time, no one considered that the most noticeable of color displays—the slow, then sudden, wave of warm shades that sweeps through our forests each year—might have its own hidden meaning.

Recently, ABC World News with Charles Gibson reported on studies that link climate change to worsening late-summer allergy seasons. Ragweed plants, scientists assert, are growing larger and producing more--and more potent--pollen because of global warming and increasing carbon dioxide levels in the atmosphere. Since a single ragweed stem generates hundreds of millions of pollen grains that can travel up to 400 miles on the September breeze, that's a grim prospect for the 50 million Americans who already suffer from ragweed allergies.

In New York, it's officially fall. There's a nip in the air, the skies are a crisp blue, and everyone's sleeping better and smiling more, now that those humid, asphalt-scented dog days of summer are over (we hope).

When I was in college and the air got like this, heralding changing leaves and cool afternoons of pickup football in the park, my friends and I would round up a gaggle of girls and head up to Poverty Lane Orchards in Lebanon, N.H., to pick what always ended up being way too many apples; they got made into way too many pies. We always ended those outings feeling uncomfortably stuffed--usually even before the pies, cakes, cookies and muffins came out of the oven. As a tribute to those fond memories, here are a few offerings of green ways to celebrate fall this weekend.

It's not exactly the Tour de France, but for those who care about the environment, a five-day bike race that kicks off tomorrow (September 20) in New York and ends up 300-some miles away in D.C. is one worth noting. Called Climate Ride, it's the first multi-day bike race to raise money and awareness to help tackle global climate change and demand renewable energy legislation. And really, what vehicle makes an argument for economical, carbon-free living (or, at least, transportation) than a bicycle?

One of the best things about traveling in East Africa is the abundance of muchomo, barbecued kebabs of unidentified (but delicious) meat. We ate the muchomo without ever being sure what sort of meat it was. It’s not like anyone would tell you if it were anything less traditional than beef or goat, and I don't think it was—but then, I’m known for mistaking possum for highly seasoned chicken, and “bush meat” (monkeys, duikers, bush pigs, lizards) isn’t so uncommon in rural parts of Africa. 

Let's play a round of free association. If I say "urban bird,"  you might say "pigeon," right? Makes sense. But city planters and parks attract a host of other avian species. If you're itching to know them better, the Cornell Lab of Ornithology is there to help with its "Celebrate Urban Birds!" project.

Believe it or not, occasionally the presidential candidates can offer more than bullying banter. Audubon recently asked the candidates to describe their positions on some important environmental issues (See September-October 2008). On Monday, ScienceDebate 2008, a citizens initiative now signed by hundreds of influential scientific organizations, universities, and individuals, released McCain’s written answers to 14 questions about today’s most pressing scientific concerns. Obama provided answers to the same questions two weeks ago.

Last September, Lehman Brothers announced in a report that “Society may want to pay an insurance premium to reduce the risk of an unforeseeable…catastrophe.” 

That report, oddly enough, had nothing to do with Lehman itself, or with the bank’s sudden collapse yesterday, which sent global stocks into a collective tailspin and prompted presidential candidate Barack Obama to call it “the most serious financial crisis since the Great Depression.”

Black Tuesday (Courtesy FDIC)

Old-growth forests may be invaluable habitat, but they’ve never counted for much on the world’s carbon-budget sheets. As trees age and their growth rates slow, they become “carbon-neutral,” emitting about as much carbon dioxide as they absorb—or so went decades of traditional thinking. By comparison, young adolescent forests, perhaps sprouting on recently logged land, were thought to soak up the most C’s.

As October nears, native asters by the numbers are making their annual appearance in meadows, damp thickets, open woods and along country roads and seashores in the Northeast. There are some 150 aster species in North America and most of them have showy flowers that range from white and pale blue to shades of rose and violet, though never yellow. However, wildflower enthusiasts generally agree that all of the others pale when compared with the New England aster, often found towering over a sea of goldenrod.