The author of today’s post, Sheryl Canter, is an Online Writer and Editorial Manager for the Climate 411 blog.at Environmental Defense.

When it’s apple season here in New York and the green markets are overflowing, for a store to ship in apples from Washington State or New Zealand burns fuel for no good reason. Local food is fresher, tastes better, and supports the community. And locally produced food often results in lower greenhouse gas emissions - but not always. The greenhouse gas calculation is complicated, and you can’t assume that if a crop is produced locally, greenhouse gas emissions are lower.

For starters, the term "food mile" is itself problematic. A mile travelled by a large truck full of groceries is not the same as a mile travelled by a mini-van carrying a crate of carrots. A report published by DEFRA [PDF], Britain’s environment and farming ministry, says it’s more useful to think in terms of "food-vehicle miles" (the miles travelled by vehicles carrying food) and food-tonne miles (which considers the tonnage being carried).

The DEFRA report contains several counterintuitive findings:

• Trucking in tomatoes from Spain during the winter produces less greenhouse gas emissions than growing them in heated greenhouses in Britain.
• A shift towards local food systems might actually increase the number of food-vehicle miles travelled. This is because supermarket-based food systems have central distribution depots, short supply chains, and big full trucks. In local food systems, food is distributed in a larger number of smaller, less efficiently packed vehicles.

But the DEFRA report is not the last word on the subject. The Leopold Center for Sustainable Agriculture found different results in its 2001 study "Food, Fuel and Freeways." They reported that conventional food systems used 4 to 17 times more fuel and emitted 5 to 17 times more CO2 than local and regional food systems, depending on the system and truck type.

A Lincoln University study [PDF] included elements they called "factor inputs and externalities" in analyzing the impact of food miles - for example, the amount of water and fertilizer used, harvesting and storage techniques, means of transport, and dozens of other aspects of cultivation. They found that lamb raised on New Zealand’s lush pastures and shipped 11,000 miles by boat to Britain produced 1,520 pounds of CO2 per ton, while British lamb produced 6,280 pounds. The reason? British pastures provide poorer grazing, forcing farmers to use feed. They found similar results for dairy products and fruit.

There’s a push for "food miles" labeling in both the U.S. and Europe. North Carolina State University’s Center for Environmental Farming Systems is working with FoodLogiQ to develop a pilot program in North Carolina with an eye towards national implementation. Local food is fresher and supports the community, so a locale label can tell you that much. But "local" doesn’t necessarily mean lower greenhouse gas emissions. That depends largely on how the food is produced and transported. Just knowing where the food was produced doesn’t tell you that.

Read more posts on Environmental Defense’s Climate 411 blog.

Chicagoan Betty Schlatter, a self-described nonathelete, traded in her van for a bike.By Leslie Valentine, Writer/Editor at Environmental Defense

National Bike-to-Work Week is May 14-18, and there's no better time to start doing just that. Here's why. Besides the glorious spring weather, bicycling instead of driving pays off: you save gas money, avoid traffic jams, get exercise, help curb global warming pollution and often save time, too.

Consider these facts:

• If everyone who lives within 5 miles of their workplace left the car at home and cycled to work just once a week, we would prevent nearly 5 million tons of global warming pollution every year — that's like taking about a million cars off the road.
• Pedaling to work 30 minutes a day or even twice a week is a great way to get more exercise while helping reduce unhealthy air pollution. Nearly two-thirds of American adults are either overweight or obese, and cases of Type 2 diabetes are at epidemic proportions.

If you're hesitant about taking the leap, take some pointers from these five commuters who pedal to their jobs nearly every day in Austin, Chicago, Long Beach, CA, New York City and Washington, D.C. From a nurse-midwife who downshifted to a carless life and the photographer who uses his bike to lug pounds of gear to shoots, to the father of two young sons who bikes to work to live simply and economically – each has their own story to tell.

Biking used to be commonplace, and it's surging again

Early in the 20th century, bicycling to run errands or to work was common in the United States. Even in the 1940s, people often biked to make short utilitarian trips. But bicycling and walking increasingly took a back seat to driving in the 1950s and 60s, with the advent of the high-speed Interstate Highway System.
Today, bicycling to work is enjoying a rebirth. Some 2 million Americans cycle to work or use a bike as part of their job (nearly 10 million walk to work). Bicycling trips have doubled since 1990. (Read the full story.)

Growing bike-friendly options can entice more people to bike

National surveys indicate many more adults would bike to work if they had safe routes, secure parking and changing facilities. Cities and states across the country are responding. From spread-out cities like Houston to dense urban centers like Chicago and New York, more bike lanes, paths and greenways are in the works or on the drawing boards. (Take our survey and let us know if you bike to work, and if not, why not.)

Bike transit centers are proliferating across the country, too. They offer convenient, locked facilities to store bicycles at train and bus depots, so commuters can combine pedal power and mass transit.

But the picture is not all rosy. Although more people are bicycling more, more people are driving more too. The percentage of bicycling trips has barely budged in relation to driving.

That's where you come in. Consider biking to work at least one day a week and see what a difference it can make.

See how five other cyclists manage the daily commute.

Cross posted from Climate411.org, a blog by Environmental Defense's chief scientist, Bill Chameides.

Tons of CO2 pollution. We are always hearing about how many tons of CO2 pollution we emit. The average American car emits about seven tons of CO2 in a year; the average American family, about 24 tons; the United States as a whole, over seven billion tons; and worldwide, almost 30 billion tons. The Virgin Earth Challenge offers $25 million to whoever can economically remove one billion tons of CO2 from the atmosphere each year.

But what is a ton of CO2?

People keep saying to me, I thought CO2 is a gas. How can a gas have weight? I explain that CO2 is made up of atoms, and atoms have mass, and with gravity mass has weight. As often as not, my explanation is met with a blank stare. So let me try a different tack.

Picture a football field, and then imagine a round balloon with one end lined up on the goal line and the other on the 10 yards line – that is, a balloon with a diameter of 10 yards. If that balloon were filled with CO2, it would weigh about 1 ton; it would be a 1-ton CO2 balloon.

In 2006 an American family emitted the equivalent of 24 CO2 balloons by powering their home, driving their cars and flying. If you lined those balloons from end-to-end they would go from goal line to goal line almost two-and-a-half times – 240 yards!

Within a year or two, a little more than half of those CO2 balloons will be absorbed from the atmosphere into the ocean or trees. Unfortunately, the rest of the balloons will hang around for a very long time. One hundred years from now there will still be almost half a football field of CO2 balloons left to overheat the earth. And that's just the CO2 from one family in 2006. There will also be CO2 balloons from 2007, 2008, and so on.

In total, Americans were responsible for more than seven billion CO2 balloons in 2006. Lined up end to end they would circle the earth 1,600 times, and the number grows each year. Isn't it about time we start taking the CO2 out of some of those balloons?

Do you have ways of your own to imagine what a ton of CO2 looks like? If so, post them here!

By John DeCicco, Environmental Defense automotive expert

American cars and light trucks are a huge source of global warming pollution. U.S. autos emit more than 333 million tons of carbon dioxide each year, roughly one-fifth of the nation's total carbon dioxide emissions. In 2004, U.S. cars and light trucks traveled 2.7 trillion miles. That's equal to 10 million trips from the earth to the moon.

Any serious effort to fight global warming must include cutting auto emissions.

The good news? There are a lot of simple steps you can take to cut your car's emissions – and when you cut your emissions you'll also be saving yourself money at the pump.

Before we get to the tips, I can't resist reminding you that your most important leverage comes when you decide to buy a car (or not!). Unless you live in an urban area with good walking, biking and transit options, you're likely to be one of the over 200 million Americans who rely on a car. The best advice is simple: choose the most fuel-efficient vehicle that meets your needs and fits your budget. Choosing your car as if the health of the planet depends on it means giving fuel efficiency greater priority than higher horsepower, extra size and all the "creature comforts" that most auto advertising seduces us to think are oh-so-important. Yahoo!'s Green Ratings are an easy way to compare cars.

But most of the time, of course, we are using the car we have, and there are in fact lots of ways to make the best of it, environmentally speaking. Here are some tips to get you started:

Drive efficiently

• Lighten up! Carrying around an extra 100 pounds in your car reduces your fuel economy by up to two percent. Take with you only what you need and be sure to place luggage inside instead of in the trunk or on the roof to minimize drag and maximize your mileage.
• Take it easy. Nine out of 10 doctors and engineers agree—aggressive driving wastes fuel, not to mention increases stress and accidents! Rapid acceleration and braking reduces gas mileage and can burn an extra 125 gallons of gas per year. Even if the person driving in front of you hasn't seen our tips list, hold your horsepower and keep your cool. And keep your distance, too: tailgating means more fuel-wasting braking, and is one of the worst safety hazards as well.
• Keep it slow. In highway travel, exceeding the speed limit by a mere five mph results in an average fuel economy loss of six percent. You're not on the NASCAR circuit. This is commuting, not racing.
• Don't be an American idle. Idling for more than 10 seconds uses more gas and emits more global warming pollution than restarting your car! Also, the best way to warm up a car in winter months is to drive it. When the temperature is below freezing, give it 30 seconds—that's all you need.
• Hot fun in the summer time. Air conditioning can decrease your fuel efficiency by as much as 12 percent in stop-and-go traffic, so consider cracking the windows. But at high speeds, driving with the windows open can decrease the overall efficiency of the vehicle. At higher speeds, you can use the vents to get a good air flow. On the hottest days keep your AC on low.

Maintain your car

• Don't be tune deaf. Keeping your engine properly tuned can save you up to 165 gallons of gas per year. Checking spark plugs, oxygen sensors, air filters, hoses and belts are a few examples of maintenance that can result in big savings. (Energy Information Administration’s U.S. Retail Gasoline Prices)
• Keep up the pressure. Low tire pressure wastes over two million gallons of gasoline in the United States—every day! Save about a tank of gas a year by keeping your tires properly inflated. And make sure to have your tires correctly aligned to maximize fuel economy.
• Go grease lightning. Thicker than required oil will reduce your gas mileage, because it takes more energy to push through thick oil than it does through thinner oil. Check your owner's manual for the recommended weight, and ask for it specifically when you get your oil changed.

Drive less

• Combine trips. Cutting a 20 mile trip out of your schedule each week can reduce your global warming pollution by more than 1,200 pounds a year and save you over $100 in gas expenses.
• Telecommute once a week. If all commuters worked from home just one day a week, we could save 5.85 billion gallons of oil and cut over 65 million metric tons of carbon dioxide each year.
• Share a ride. Carpool and use public transportation when possible. If you share rides and use other means to get to work, you'll save yourself money, reduce congestion on the roads and cut your global warming pollution.
• Just park it. And keep it there. If you’re going to several stores in the same strip mall, don’t move your car. Walk.
• Gotta wear shades. In summer, park in the shade. Use windshield shades to keep summer heat from baking your car and to help keep frost away in the winter.
• Move your feet. Walk, ride a bike or take the train when your car isn’t needed.
• Avoid the rush. Plan trips during off hours when fewer cars are clogging the roads.