Tomorrow is International Day of Climate Action. A site called 350.org, backed by some of the biggest names in the environmentalism movement, is calling for us to participate in one of the day’s 4,300 events in 170 countries aimed at raising awareness about climate change. 350.org says it will be “the most widespread day of political action in history.” It might be cool to be a part of that, so I’ll list some of the activities planned in Captivate markets in case anyone wants to join in. But first: Why is it called “350.org”?

They got the “350” from the concept, which I first heard of through James Hansen, that to maintain life as we know it atmospheric CO2 levels cannot exceed 350 parts per million for any extended time. Unfortunately, we’re already beyond that level and pushing closer to 400 ppm every day. So in order to get us back down, Hansen and others say, we have to take pretty drastic steps, such as cutting out coal use and replanting vast swaths of forest.

While the International Day of Climate Action isn’t about getting us to immediately stop using coal, it is about making people think about the ramifications of their actions, even the simplest ones, like flicking on a light switch (which draws electricity from your local power plant, which is probably powered by coal).

So take part. It’s a simple action, it’ll give you something fun to do on a Saturday, and it just may, when all is said and done, help save the planet. Check here for all U.S. events, or simply peruse these:

New York City
The 350.org organizing team will gather in Times Square, where the giant video screens will display “350” representations from around the world.

Philadelphia
In what will be a common theme Saturday, participants on Independence Mall will form a giant “350,” as well as hear from speakers such as city green czarina Katherine Gayewski and “environmental heavyweight” Ray Anderson.

San Francisco
The Justin Herman Plaza/Ferry Building is the site for the San Fran gathering, where cyclists completing a 350km route will rally with surfers, artists, poets and activists.

Seattle
You know you’ve always wanted to take part in one of those “Thriller” dance-a-thons. Now’s your chance. Admittedly, the link to climate is pretty weak here, but, hey, it’s probably gonna be fun.

Washington, D.C.A march to Lafayette Park will be followed by participants forming a giant "circle of hope" across from the White House. This "O" will serve as third in a series of 3, 5, and 0 photos taken from around the world.

Welcome to another of Green Among Gray’s periodic green news roundups, in which I list a few items when I don’t have a proper blog post prepared there is more than just one big thing to talk about.

Fuel Economy Guide
The EPA and the Department of Energy have unveiled the 2010 Fuel Economy Guide, which tells you what you can expect to pay for fuel for 2010 model year vehicles.

As I said last year, one of the coolest things about the guide is that it’s mobile-accessible, so you can look through data while you’re at a dealership checking out cars.

Toyota’s Prius once again tops the charts, at 51/48 mpg (up from last year’s 48/45), followed by Honda’s Civic Hybrid at 40/45.

The EPA also lists the worst vehicles for fuel efficiency. Among the bottom-feeders: the Lamborghini Murcielago, at 8/13 (which is why I don’t own one) and the Bentley Azure at 9/15.

And in an interesting side-note, the EPA names the most efficient vehicles it’s ever certified. The leader? A minivan!

It’s the 2000 Nissan Altra EV (above), an electric vehicle that got the equivalent of 123 mpg. Who knew? Previous records like this should be falling soon, though, with the likes of Chevy Volt and Nissan Leaf on the horizon.

Animal die-off numbers
Animals around the US die off for any number of reasons, some alarming – they can be a predictor of a bigger problem, such as a human health threat – some just a natural course.

The National Wildlife Health Center tracks these wildlife mortality events to allow any number of government agencies – or just regular folks like you and me – to better understand them and try to stem them, as necessary.

If you’re a nature lover, it’s interesting to read up on this stuff. And if not – why aren’t you!? Get out there and observe! You’ll love it, I swear.

Check out the most recent list of animal die-offs to see if there are any near your particular stroll-through-the-woods area. These reports offer eye-opening data, like the fact that botulism is wiping out thousands of water fowl across the US, or that millions of amphibians are dying of fungal infections.

Green restaurants
One particularly burgeoning sector of the green movement is the organic restaurant. They’ve sprouted all around the country, offering fresh, local food to legions of diners who care about how their eating habits impact the environment (or maybe they only care about eating yummy stuff; either way, organic restaurants fit the bill).

Over the coming weeks, Green Among Gray will focus on a few of these restaurants in various Captivate cities. Stay tuned.

Pres. Obama has declared October National Energy Awareness Month to “recognize the contributions of individuals, organizations, and companies that are committed to advancing energy innovation and efficiency.”

Now, I know what you’re thinking, my mega-sophisticated, hyper-jaded urbanite readers: “Oh goody – this hard-hitting presidential proclamation will really take care of things.”

But don’t be so quick to snark – Obama’s followed up this hollow announcement with something substantial: An executive order mandating federal agencies set a greenhouse gas emissions reduction target for 2020 within 90 days. Among requirements are a 30% reduction in government vehicles’ petroleum use and a 26% improvement in water efficiency.

So Obama’s helping take care of the “organizations” aspect he refers to in his Energy Awareness Month declaration; it’s up to each of us to take care of the “individuals.” What are you going to do to help advance energy innovation and efficiency?

Not sure? Start here.