This post is by Leslie Valentine, Online Writer and Editor at Environmental Defense.

1

Rank of shrimp in popularity among all types of seafood Americans eat

4.4

Pounds of shrimp the average American consumed in 2006

10%

Share of shrimp sold in the U.S. that comes from the Southeast U.S. (Gulf of Mexico and Atlantic Ocean), where fisheries and farms are held to stricter standards

90%

Share of shrimp sold in the U.S. that comes largely from Southeast Asia and Latin America, where environmental regulations are sometimes lax and often not enforced

33%

Share of U.S. shrimp imports that come from Thailand, our largest single supplier

$4.1 billion

Value of U.S. shrimp imports in 2006, nearly one-third of all seafood imports, compared with coffee imports of $3.1 billion and fossil fuels worth $300 billion

44%

Percentage of worldwide shrimp production that came from farms in 2005

12,000%

Increase in farmed shrimp production between 1975 and 2005. Production ballooned from just over 22,000 tons to more than 2.6 million tons.

3.7 million

Acreage of tropical coastal mangroves estimated to have been converted to shrimp farms, destroying important habitat for fish, birds and people

2

Number of pounds of wild fish it generally takes to produce one pound of farmed shrimp

More on eco-friendly farmed shrimp.

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.

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

Total greenhouse gas emissions from cars and trucks is a function of three factors: amount of driving, fuel economy, and carbon emissions per gallon of fuel (the "three-legged stool [PDF]"). The news media tend to focus on the latter two factors, but how much people drive has a huge impact.

A new report published by the Urban Land Institute says that greenhouse gas emissions cannot be reduced sufficiently by making vehicles more efficient, because growth in driving cancels out improved fuel economy. People also must drive less. And the report’s solution is not just better public transportation.

The way to reduce driving sufficiently, the authors say, is to shift development patterns to favor compact, mixed-land-use neighborhoods where you can walk to school and the grocery store. If you live in a car-dependent area, moving to a walkable area will do more to fight global warming than buying a fuel-efficient hybrid car.

This idea is already being put into action in some areas. New York City is expecting one million more people by the year 2030, and is using rezoning to direct development towards areas with strong transit access.

Environmental Defense helped California’s San Joaquin Valley, which is notorious for bad air quality, implement a similar strategy. The Air Pollution Control Board adopted an incentive program [PDF] that gives developers two choices: reduce the environmental impact by creating sidewalks, bike paths, and nearby schools and commercial districts, or pay a fee for any excess pollution.

Living in a walkable neighborhood has other advantages. Recently released figures from the New York City Department of Health show that New Yorkers tend to live longer than most people in the country — an odd finding considering the lack of fresh air and other hazards. The city’s Commissioner of Public Health thinks it’s because New York is a walking city.

Today’s post is by Leslie Valentine, an editor and writer at Environmental Defense.

When I visit friends and family in other places, whether it’s Portland or Los Angeles, Austin or New York City, I’m always struck by how traffic and commuting inevitably come up in conversation.

Those who live in the central core of a city are grateful they don’t have far to drive, or can walk or ’sub’ it to work. Others trade stories of commutes from hell, driving in bumper-to-bumper traffic on the main route into downtown. Everyone laments how it seems to be getting worse and worse every year in these lively, growing places.

Many growing cities and towns are traffic-choked and plagued by pollution. But population growth accounts for only a small share of increasing road traffic in recent decades.

What’s really going on is that Americans are driving more: We are taking more trips on motorways, making longer trips and driving alone more. More people live in car-dependent suburbs not conducive to walking or transit.

Sadly, incentives are skewed toward car use: "freeways" subsidized by general tax revenue, "free" parking paid for by employers, low mileage drivers subsidizing insurance costs for high mileage drivers, and countless policies favoring low density sprawl over infill mixed-use development. (Read more about our broken transportation system.)

But this has to change. We can’t keep building our way out of traffic jams and pollution with more roads and highways – it just doesn’t work. And the costs to our health and quality of life are too high. Our transportation experts at Environmental Defense have long studied the problems and are working on smart solutions. (Read more about solutions to traffic problems.)

One key is to use existing infrastructure much more efficiently. Incentives like congestion pricing and bus rapid transit lanes are two ways to get traffic moving. With tools like these in place, an existing highway can move more people more quickly with less environmental damage.

Says Environmental Defense regional director Andy Darrell: "Our country is growing, and we’ll always be building something new. The key is to build new communities in ways that decrease dependence on the traditional car and increase opportunities for walking, cycling and innovations like car-sharing, advanced vehicle technologies and new ideas for transit."

Take action: Help support transportation solutions. Earn points for your state for the personal actions that you pledge.

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

Hydrogen fuel cell vehicles got a big boost when President Bush made them part of his 2003 State of the Union address:

Tonight I’m proposing $1.2 billion in research funding so that America can lead the world in developing clean, hydrogen-powered automobiles… With a new national commitment, our scientists and engineers will overcome obstacles to taking these cars from laboratory to showroom, so that the first car driven by a child born today could be powered by hydrogen, and pollution-free.

That generated a lot of interest in hydrogen cars! So what are they, and can they become mainstream in the next 20 years?

Honda FCX fuel-cell car.

Hydrogen fuel cells take in hydrogen and oxygen, and put out water, heat, and electricity - no pollution at all.

Sounds good, but there’s a catch - producing the hydrogen fuel can itself generate significant greenhouse gas emissions and other pollutants. And unfortunately, that’s not the only serious hurdle.

Honda is the first company to put a fuel cell demonstration car into the hands of ordinary consumers. Yet as Steve Ellis, Honda’s Manager of Fuel Cell Vehicles, told me hydrogen-powered cars are not likely to be mainstream for another 10 to 20 years. Many industry analysts put the number at well over 20 years, and some think it will never fly. All agree it’s not a near-term solution.

Chevrolet Sequel fuel-cell car.

Joseph Romm, in "The Hype about Hydrogen, notes five main problems with hydrogen cars as they currently stand:

• They are extremely expensive, currently costing around $1 million (for example, the GM SequelHonda’s FCX). Most of this cost is in the fuel cells. If history is any guide, it will take decades for the cost to come down sufficiently.

• On-board fuel storage is a huge problem - literally - since at room temperature and pressure, hydrogen takes up 3000 times more space than an energy-equivalent amount of gasoline. There are several ways to store hydrogen, but all known approaches are complex and costly. Storing hydrogen as a liquid isn’t practical because it takes so much energy to liquefy and then convert back to gas. Storing it as compressed gas requires 300 to 600 times atmospheric pressure, and even then the tanks take up more than five times the space of a gasoline tank.

A National Academies study [PDF] noted, "In even the best case of improved compression efficiency and high pressure on-board tanks, the energy, space, cost, and weight penalties are formidable." It goes on to recommend that the U.S. "halt efforts on high-pressure tanks and cryogenic liquid storage" since "neither approach can reach DOE targets for energy density". A Department of Energy review reached a similar conclusion.

• There are serious safety issues with hydrogen fuel since it’s among the most flammable substances known. It is vastly easier to ignite than gasoline, and leaks are much harder to detect and control. A cell phone or flashlight could ignite it, as could static electricity or an electric storm a few miles away.

Russell Moy, former Project Manager for hydrogen storage at Ford Motor Company, wrote about this in an article for the Energy Law Journal [PDF]: "Industrial experience has shown that 22 percent of hydrogen accidents are caused by undetected leaks, despite the standard operating procedures… of specially trained hydrogen workers. With this track record, it is difficult to imagine how the general public can manage hydrogen risks acceptably." Chemical Engineer Reuel Sinnar put it even more strongly [PDF]: "A hydrogen car as presently envisioned is a potential suicide bomb that cannot be detected by any of the standard methods that detect explosives."

• Producing hydrogen is expensive and energy-intensive [PDF]. The same energy currently used to create electricity would be used to create hydrogen, and today this mostly involves the use of fossil fuels (see House testimony of Dr. John Heywood of MIT).

Current methods using natural gas produce significant heat-trapping emissions, and there is a serious question of whether a renewable fuel used to create hydrogen wouldn’t be better used to replace electricity now generated from coal, since generating electricity is much more efficient than producing hydrogen power for vehicles.

• There’s no fueling station infrastructure for hydrogen. Building a hydrogen fuel infrastructure will be very expensive. A National Renewable Energy Laboratory report estimates the cost at $837 million [PDF]. Others say it could be tens of billions of dollars.

Companies hesitate to build something so expensive when there are no cars to use it. Similarly, automakers are reluctant to manufacture hydrogen cars when there’s no infrastructure, because consumers won’t buy them if they can’t fuel them. It’s a classic "chicken-and-egg" problem.

There’s another obstacle to infrastructure. Ideally, hydrogen would be produced in a central location so carbon emissions from its manufacture could be efficiently sequestered. But that isn’t set up yet, so initially the hydrogen would be created locally. No one wants to invest large amounts of money in an infrastructure that will be abandoned.

All these problems may be solvable, but it will take time. And you can’t necessarily trust the automakers’ predictions. In 2001, our automobile expert, John DeCicco, Ph.D., wrote an in-depth review of fuel cell vehicles [PDF] for the Society of Automotive Engineers. In it he noted that "Several automakers have pledged the introduction of fuel cell vehicles, including buses, by 2003-2005." It’s 2007, and beyond a few demos I don’t see them yet! Dr. DeCicco considers the hydrogen car an "utterly speculative proposition."

Maybe we’ll have hydrogen fuel cell vehicles by 2030, but in 20 years, who knows? Perhaps some new and better technology will come along, and research into hydrogen power will be abandoned. None of us can know which technology will be the future, but we do know this: the world can’t wait 20 years to reduce carbon dioxide emissions from vehicles. So while the hydrogen car is worth researching for the long term, the heavy emphasis placed on it by the Bush Administration is ill-considered.

So if you’ve been waiting for hydrogen cars to let you off the hook for buying a fuel efficient car and driving it smartly, time to reconsider! It’s the same old smart driving tips for now.

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

Plug-in Hybrid Electric Vehicles, or PHEVs, have been in the news a lot lately (and here on Green Options, too!). It’s an appealing idea - virtually no emissions, just plug in your car at night and go. Plus, the batteries that drive them could store electricity for homes and offices. When cars are parked and plugged in, the electric utility could draw on stored battery power during times of peak demand (with compensation to the car owner).

But will plug-in cars really be ready for widespread use by 2010?

Reading the news, you might think that PHEVs are just around the corner. Toyota just displayed a plug-in version of its Prius. A recent study by the Electric Power Research Institute (EPRI) and the Natural Resource Defense Council (NRDC) says that if plug-in cars are in widespread use from 2010 to 2050, the reduction in greenhouse gas emissions could be dramatic.

Certainly people are trying to make it happen, spurred by inventor/advocates such as Felix Kramer of CalCars.org and others. The Austin City Council has launched a $1 million campaign to promote plug-ins. Google’s philanthropic arm is donating $10 million towards the development of the technology. General Motors made a splash with its Chevy Volt concept in January. Ford has joined the party with a plug-in prototype of its Edge SUV.

But as our automotive expert John DeCicco points out, there are some daunting technical issues. In a briefing before the U.S. Senate [PDF], Advanced Automotive Batteries president Menahem Anderman estimated that plug-ins won’t be generally available for another 10 years. Honda manager John German, also in Senate testimony [PDF], said that the problems with plug-ins were so difficult that Honda wasn’t even going to try.

So what’s going on? Are plug-ins around the corner, 10 years away, or not realistic at all?

The bugaboo is the battery. Here’s a summary of the problems, based on Anderman’s analysis:

1. The plug-in battery will be about 3 to 5 times the size of today’s non-plug-in hybrid batteries, essentially filling the cargo space of an average sedan.
   The weight of this battery will add 200 to 300 lbs. to that of the car, putting a drag on performance and efficiency.
2. The lithium batteries needed to provide adequate performance for plug-ins raise a serious concern about hazardous failure, such as a fire in a home garage, because they need much deeper, full charging than the smaller batteries of today’s hybrids, which are always kept at an intermediate state of charge.
3. The cost of this plug-in battery (at pack level) to carmakers, using present technology, will be 3 to 5 times the average cost of today’s hybrid batteries, i.e. around $5,000 to $7,000 per pack.
4. The life of any battery technology, lithium or otherwise, when used in a plug-in car is not known. There’s a good chance that battery life will be short, meaning costly replacements over the life of a vehicle.

John German points to market problems, as well. He says that unless battery prices drop considerably, the vehicles will be too expensive for broad acceptance. So Honda has instead chosen to focus on hydrogen fuel cell technology.

German closes his statement with some good advice about how the government can help:

It is impossible to predict the pace of technology development and when breakthroughs will or will not occur. Accordingly, technology-specific mandates cannot get us where we need to go. In fact, previous attempts to mandate specific technologies have a poor track record, such as the attempts in the 1990s to promote methanol and the California electric vehicle mandate. The primary effect of technology-specific mandates is to divert precious resources from other development programs that likely are more promising. If there are to be mandates, they should be stated in terms of performance requirements, with incentives and supported by research and development.

So will plug-in hybrids eventually become mainstream? Possibly, but only with sufficient investment in the development of battery technology. Since we can’t know for sure which technologies will work out, it’s best to push ahead on all fronts - including making better use of the technologies already at hand - and not put all our eggs in the plug-in basket.

Editor’s note: We’re pleased to welcome Kira Marchanese to the Green Options blog! Kira, Director of Internet Communications at Environmental Defense, will be taking over for Jessica Bosanko, who’s moving on to other pursuits, including a wonderful-sounding trip with her partner to South America. We’re glad to have Kira on board, and very grateful to Jessica for her time and effort in contributing to Green Options.

Today’s post is by Tom Elson, from Environmental Defense’s Living Cities program.

If you spend time in a dense urban area like New York City, you know the frustrations of gridlocked streets: blocked intersections, horns blaring and tempers flaring. But there’s an invisible cost to traffic, too: the damaging health effects from breathing the air polluted by so many cars and trucks. Vehicles stuck in stop-and-go traffic produce up to three times the pollution of cars moving steadily.

But New York and other metro areas are on the road to clearer streets and clean air. Congestion pricing is one of the innovations that will help them get there.

The idea is simple: at times when the roads are busiest, drivers pay a premium to use them. Think of the way you buy an airline ticket. When you check fares, you get a wide range of prices depending on factors like when you want to fly and how many stops you’re willing to make. We know that flying at convenient times costs more, and we might take a red-eye to save money.

The concept is the same on the road. An electronic toll system collects the fee as drivers enter busiest sections. The system charges drivers more during the busiest times. Those who take mass transit or reschedule their trip can save money. (See more about congestion pricing.)

This isn’t a new idea. London started charging motorists to enter its central business district in 2003 and has seen traffic congestion cut by nearly a third. Sooty particles and nitrogen oxide pollution dropped by roughly a fifth each. Singapore, Stockholm and several cities in Norway have also reduced traffic, travel time and pollution.

The idea is still new enough in this country to raise questions, though, as last week’s debate in New York shows. Critics of congestion pricing worry that boundary neighborhoods – those just outside the pricing zone — will see an increase in traffic and cars trying to park there. Studies in London and Stockholm show otherwise. Those cities limited conflicts around the boundaries by issuing residential parking permits and creating park-and-ride facilities.

Commuters who live in areas with poor public transit fear not being able to drive – but revenue from collecting tolls is generally used to improve transportation. London, for example, raised hundreds of millions of dollars, which it invested in better transit such as new buses. Ridership rose dramatically, and bicycling increased. There, as in other places that have tried this system, skepticism gave way to enthusiastic support for the plan.

This year Mayor Michael Bloomberg embraced congestion pricing and unrolled a plan as part of his sustainability ‘greenprint’ for New York. A remarkably broad coalition of 140 civic, religious, health, business, labor and environmental groups supported the plan, despite strong opposition from some legislators. After intense negotiations, Bloomberg and state leaders agreed to consider a three-year pilot program.

New York City is one of nine finalists for $1.2 billion in federal grants to try congestion pricing and other traffic-busting incentives. Eight other cites — Atlanta, Dallas/Ft. Worth, Denver, Miami, Minneapolis, San Diego, San Francisco and Seattle — are vying for funds by proposing a variety of traffic-reducing tools, from tolling and parking management to express buses to telecommuting support. New York’s is the most comprehensive, with specific traffic-reduction goals leading to substantial cuts in air pollution and real public health benefits.

You can help! If you live in one of the cities trying to implement smart traffic policies, contact your elected officials and ask them to support congestion pricing.

Many a book has seeded, incubated and hatched great change in the world. In fact, Rachel Carson's Silent Spring, which exposed the hazards of pesticides, gave birth to the modern environmental era. From Thoreau's Walden, that staple of English classes, to Dr. Seuss's The Lorax, which inspired many of us as children, the environmental movement has gathered momentum from a slew of informative, visionary and literary works.

Our staff compiled a list of favorites, so this summer, check these out for your next good read.

Here's the list. Vote for the most influential, and tell us what's missing.

Nonfiction

Cadillac Desert: The American West and Its Disappearing Water
Marc Reisner

Collapse
Jared Diamond

The Creation: An Appeal to Save Life on Earth
E.O. Wilson

Desert Solitaire
Edward Abbey

Earth in the Balance: Ecology and the Human Spirit
Al Gore

The Omnivore's Dilemma
Michael Pollan

A Sand County Almanac
Aldo Leopold

Silent Spring
Rachel Carson

Song for a Blue Ocean
Carl Safina

Walden
Henry David Thoreau

Wilderness and the American Mind
Roderick Nash

Fiction

Animal Dreams
Barbara Kingsolver

The Lorax
Dr. Seuss

Again, get more details on the books, vote for your favorite and tell us what's missing.

Barbara Kingsolver's latest book, Animal, Vegetable, Miracle, tells the story of how she and her family lived for a year eating only food they grew themselves or that they purchased from local food-growers.

She was generous enough to take time from her book tour to answer our questions on the importance of keeping in mind that we are what we eat.

Why is buying and eating locally-grown food important?

The shorter the distance between your meal and its point of origin, the more you can know about it. Certain systems of oversight are meant to help you untangle the great unknowns of a complex system: "organically grown," for example, guarantees that a food item was produced without toxic chemicals. But it still may have accrued the same fuel costs of processing and long-distance transport as the conventional counterpart. And if there's profit to be made, corporate agriculture will be involved, with the likely agenda of watering down all standards.

"Locally grown," by contrast, is a designation that's incorruptible. Buying food from growers at small markets or through Community Supported Agriculture (CSAs) is really the only way for most of us to step away from a disordered food system. Food from your neighborhood will likely be whole, unprocessed vegetables, fruits, or animal products grown on small, diversified farms by growers committed to the health of their land. The food is good for you, and the money you spend on it stays in your community, helping to keep those nearby green spaces intact and strengthening your local food economy.

Environmental Defense is working to reform the nation's farm policies, which historically have helped agribusiness rather than family-run farms. What can individuals do to help keep farmers on the land?

We can start by thinking about farmers every time we eat. Our food, however it may have been altered in the interim, was grown somewhere, by someone. Who was it? How did that person use the land? How much of my food dollar went to a farmer, to help support sustainable choices? On average, 85 cents of every food dollar goes to the processors, packagers, advertisers and oil companies who profit handsomely from our lack of regard for soil, water, climate and the future. Farmers have no choice but to respond to consumer demand. They can only grow what we will buy.

Food policy is made, not born. It's not "natural" that organic and whole foods cost more than tallow-fried junk. We choose that through our tacit approval of the Farm Bill that defines food and nutrition policy in this country. We've elected to subsidize corporate commodity farms while leaving small, diversified fruit and vegetable farmers on their own, trying to compete. For organic farmers it's even worse – we make them pay for their own inspection and oversight. If we'd like to flip this over and subsidize healthy rather than unhealthy foods, we can call our legislators and start talking. This is a good time to do it, because the Farm Bill is being renegotiated at this moment.

The experiment chronicled in your book was a major family commitment. Did it change you as a family? How?

Commitment is exactly the right word for it, and that's what made the project valuable to us. For years we had been thinking about the food industry and our part in it. We tried to make choices that were better for the environment and our farmers – but mostly when those choices were pretty easy.

When we made a formal commitment to ourselves (and the world, via a book contract) to spend one year eating only fruits, vegetables, and animal products that were produced locally, it felt something like a marriage ceremony. It pushed us toward a fuller engagement with a way of life we really knew we wanted. It moved us to get to the farmers' market even on Saturday mornings when we didn't exactly feel like it. It helped us pass up the Peruvian asparagus and Bolivian bananas, concentrating instead on whatever wonderful things were coming into season in our own county. We learned to start with incredibly fresh ingredients and cook with the seasons. We learned to sleuth out local products at our supermarket, where we found organic dairy products, cider vinegar, and many other wonderful things produced here in our region. We spent more time as a family in the kitchen, and in the garden. Hoeing weeds is good exercise; inventing recipes is both scientifically and artistically creative; these things added up to time well spent. Our formal year-of-local has ended, but we're still eating locally because we enjoy it. We occasionally buy transported foods (usually something from the ocean) but we now consider that a splurge rather than a daily entitlement.

When my kids are my age, everything about food will be different except for one thing: they will still have to eat. The fuel-intensive food industry of the present, which has come to seem normal to us in recent decades, will become impossible. When people look back on this era, it will surely seem grotesquely indulgent. The next generation will have to return in some way to more local and sustainable food economies. I'm happy to participate in this part of my kids' education, giving them a genuine understanding of food processes. What could be more important?

You're a long-time supporter of Environmental Defense. Is there a particular message you would like to give our audience of online members and activists?

Your members already know, as I do, that Environmental Defense is an effective force for steering this country's environmental policies into a cleaner future. I can only offer individual encouragement, and the promise that small changes in our lives, multiplied by thousands, add up to a revolution. We can't wait for radical conservation measures to be imposed on us by our government – that takes a courage that our political system probably can never muster, no matter who's in charge. The way to look at it, I think, is that WE are in charge, individually and collectively. By proving to myself that my family can learn to live well with less, drastically reducing our food-miles and our carbon footprint, I'm giving myself the courage to require more responsibility from myself, my fellow citizens, and our government.

Thanks so much for your time.

Thank you and thanks to all the other Environmental Defense supporters out there

Looking for more environmentally themed books? Check out the Environmental Defense summer reading list.

Our guest blogger, Sheryl Canter, is an Online Writer and Editorial Manager at Environmental Defense.

If you have a garden, you know the climate is warming. In temperate zones, the last frost in spring comes earlier, and the first frost in fall comes later. The longer growing season may allow you to grow vegetables you never could grow before. But you also may have noticed your weeds are more aggressive, insect pests are more of a problem, and pollen plagues you all summer long. You're not imagining things!

For over 40 years, gardeners have relied on the USDA Plant Hardiness Zone Map as a guide to what they can grow in their area. But the USDA zone map hasn't been updated since 1990, and gardeners have seen detectable shifts since that time.

In 2003, the American Horticultural Society (AHS) updated the zone map with a grant from the USDA, and published a draft of the new map [PDF] in The American Gardener. Based on temperature information from July 1986 to March 2002, the map showed widespread warming, with zones edging northward.

The USDA rejected the new map without explaining why, and said they would update it themselves. Four years have passed and still they have not released a new map. But the National Arbor Day Foundation has just released one, current for 2006. Like the 1990 and 2003 maps, the Arbor Day map is based on 15 years of data. The changes between 1990 and 2006 are dramatic; the U.S. is clearly getting warmer.

Global warming is caused by elevated concentrations of greenhouse gases in the atmosphere - notably carbon dioxide (CO2). Plants use sunlight, water, and CO2 to synthesize the glucose they need to grow - a process called photosynthesis. Thus when CO2 concentrations in the atmosphere increase, it acts as a fertilizer, accelerating plant growth. This may sound good at first, but there's more to the story.

CO2 fertilization affects different plants to different degrees. As Duke University biologists discovered, one plant that loves additional CO2 is poison ivy [PDF]. With increased CO2, poison ivy grows 2.5 times faster, and produces a more potent version of the rash-causing chemical urushiol. Other types of woody vines also grow much faster with higher levels of CO2 - fast enough to strangle and topple trees.

Accelerated plant growth has some other bad side effects. One is increased pollen production, creating misery for asthma and allergy sufferers. A Harvard study [PDF] showed that elevated CO2 concentrations caused up to a 55 percent increase in ragweed pollen production.

Another consequence is that high levels of CO2, while increasing crop yields, decrease the plants' nutritional value. Obviously this is bad for humans eating the plants, but it's also bad for humans growing them. Insects eat dramatically more plant matter when the plants are less nutritious (and ironically, can still starve to death from poor nutrition). Farmers using more pesticides to control infestations will increase pollution in rivers and streams.

So the next time you hear people arguing that global warming will be good for gardeners and farmers, set them straight!