Changing a light bulb is a start -- but it's not enough. To celebrate Earth Day, take action with this smart advice from the country's leading environmental leaders and activists.

"Earth Day grew out of a period in our history when rivers were on fire, when you couldn't see across the street because of smog, when we started to notice environmentally related birth defects. These were the signs of 150 years of industrialization going south, and the problems were obvious.

"Look, changing a light bulb might sound silly, but think back to World War II, when everyone became a cog in the wheel and played their part. Women like my mother worked in tire factories. People bought war bonds. It was millions of people doing the right thing. And that's what needs to happen now, because this is a war -- a war against flagrant abuse of resources, a war against greenhouse gases. Everyone needs to play a part."

-- Kathleen Rogers, President of Earth Day Network

(Poster courtesy of Joe Wirtheim, victorygardenoftomorrow.com)

"Grow fresh vegetables and meet your neighbors at the same time! Community gardens are as much about beautifying and preserving the land as they are about strengthening local networks.

"For people of all ages, they serve as a natural classroom to demonstrate where food comes from and what it takes to nurture plants and trees. They also act as 'pocket parks' -- green spaces that provide shade, cleaner air, and a place to gather." (Find one near you at communitygarden.org.)

-- Adrian Benepe, New York City Parks Commissioner

"Commit to planting a tree in your yard or neighborhood each year. A properly placed tree can reduce your cooling costs in the summer and improve the overall health, aesthetic, and value of your home.

"Look for these species, because they're some of the best at absorbing and storing carbon dioxide: horse chestnut, black walnut, white pine, Douglas fir, and red oak."

-- Eric Ryan, cofounder of Method home cleaning products

"Between industrial farming practices, fossil-fuel processing plants, packaging, and shipping, our modern food system is said to be responsible for a third of global warming. But we can change that by making better choices.

"Whenever you can, eat organic, eat local, eat seasonally, and turn off the TV and talk to your kids about these things. Plus, isn't it nice to spend a little family time together? We could all use more of that."

-- Chef Ann Cooper, Renegade Lunch Lady

"We manufacture millions of products daily that are destroying our ecological niche. We don't see the connection between the things we purchase and the damage we do to the Earth. 

"1. What we buy is more important than what we do. Look at yogurt containers. We're encouraged to think that recycling them is enough, but that takes care of only 5 percent of their impact on global warming. When companies were pushed to replace plastic tops with foil seals, there was a dramatic drop in waste. Since Stonyfield made the switch in 2003, they've decreased their packaging by more than 100 tons annually. We need to get smart about the ecological impact of what we buy and let companies know we're wise to the game.

"2. Green is not black-and-white. We can buy a T-shirt made from pesticide-free organic cotton, but it takes about 713 gallons of water to grow the cotton for that shirt. GoodGuide.com can tell you how more than 70,000 products stack up in terms of their environmental, health, and social impact in a single rating. You can even scan a product's bar code at the store with your iPhone and a rating will pop up (if one's available).

"3. Spread the word ... to friends, family, online social networks, and most important the companies that are being affected by your actions. We need to push them to lessen the ecological impacts of what they sell -- by letting them know that our purchasing decisions depend on it."

-- Daniel Goleman, psychologist and author of "Ecological Intelligence"

"We need to think of nature as our living room. You don't have to be an uber-adventurer; just step out your back door. Sit in a hammock and enjoy the fresh air. Keep a blanket in your car for impromptu picnics. It doesn't matter what you do outside. Just get out there."

-- Becky Garland, an executive director at the National Wildlife Federation

"Even though there's a farm stand two miles from where I live, I still have a garden right outside my kitchen. It's such a joy to prepare the soil, watch the plants grow, and bring in the harvest. It really keeps you in rhythm with the seasons, and it's a great way to involve the whole family in an activity that teaches kids about the origin of food."

(Once your veggies are harvested, get eco-friendly recipes here.)

-- Myra Goodman, cofounder of Earthbound Farm Organic

"Before you throw something out or recycle it, take a moment to consider where it's going to end up and how it's going to get there. Really think about it. Chances are, it will be placed on a diesel truck and dumped in a poor neighborhood, next to a fossil-fuel-burning power plant. It doesn't matter that you are "recycling" or that your banana peel is "organic" -- it all ends up in the same place.

"Think about how to divert it from the waste stream altogether, whether by composting or finding a second use for it. And hold that image in your head every time you buy something. Once you can visualize that daily waste stream and all the energy used to support it, and you can imagine the impact on the people who live alongside it every day, you'll understand environmental justice a little better."

-- Majora Carter, founder of Sustainable South Bronx

"Encourage your legislator to vote for cap-and-trade legislation, the climate and energy bill that they're trying to pass. First, make it heartfelt. Second, handwrite it. Staffers often think a typed note comes from a website and was generated by a special interest group. I'm very optimistic that we're going to solve this crisis. I think we have everything we need to do it, with the possible exception of political will. Luckily, political will is a renewable resource." 

-- Al Gore, Nobel Prize winner and author of "Our Choice: A Plan to Solve the Climate Crisis"

For more tips on contacting your senator and supporting clean energy legislation, visit repoweramerica.org.

(Recycled newspaper pencils, pictured, from treesmart.com)