Low-impact vacations.

It's vacation season again, the time for sunblock, snorkeling, and surf, while trying to see the world with 760 million other international travelers. All that tourism has a major environmental impact: a typical cruise ship dumps more than 750,000 liters of raw sewage each week, and commercial aircraft emitted nearly 230 million tons of carbon dioxide in the United States alone in 2003. Yet many tourists want to do the right thing. How can you enjoy yourself without, as the punk band the Sex Pistols put it, "a cheap holiday in other people's misery"? Here are some points to consider:

What kind of holiday do you want? There are many ways to add environmental and social value to your trip, whether it includes volunteering at an organic farm, helping rebuild temples, or trekking through a nature reserve. When planning your vacation, says Martha Honey of The International Ecotourism Society (TIES), consider that ecotourism minimizes impact, provides direct financial benefits for conservation and for local people, respects local culture, is sensitive to the host country's political environment and social climate, and supports human rights and international labor agreements.

How can you trust green claims? There are more than 60 tourism certification programs worldwide, some with standards so loose they verge on greenwashing. At the global level, Green Globe "is a pretty credible label, but their for-profit focus has limited the uptake of their program, in my opinion," says Brian Mullis of Sustainable Travel International. The International Organization for Standardization, meanwhile, provides third-party certification of environmental management systems (so-called ISO 14001 standards), but doesn't state specific performance criteria for tourism-related or other businesses. However, three large regional networks in the Americas, Europe, and Asia have earned the respect of Mullis and others, and can put you in contact with credible ecotour operators, hotels, and activities:

The Rainforest Alliance has partnerships with tour operators in 25 countries, including the United States, Mexico, and Brazil, to launch its Sustainable Tourism Certification Network of the Americas. Baseline standards include environmental impact assessments, staff training, environmental monitoring, biodiversity conservation, and benefits to local communities. (See eco-indextourism.org.) VISIT (visit21.net) is a network of ecolabeling programs that has certified tour operators in many European countries. TIES (ecotourism.org) recently initiated a loose network of tour operators, hoteliers, student travelers, academics, and professionals in the Asia-Pacific region, centered around a bimonthly newsletter that emphasizes ecotourism certification, associations, training, and education.

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Other steps toward greener travel:

* Talk to people who have previously traveled to your destination and search local newspapers online for tourism or ecotourism news.

* Confirm that eco-friendly features listed on hotels' and tour operators' websites are real or actually under development.

* Ask hotels if they have an environmental policy, are third-party certified, allow reuse of sheets and towels, and offer recycling as well as other resource-saving features. Asking also shows hotels there is a demand for greener practices.

* Look for philanthropic options that offer opportunities to provide medical assistance, educational materials, construction help, or other needed services. Check out habitat.org, crtp.net, operationcrossroadsafrica.org, crossculturalsolutions.org, airline amb.org, travelersphilanthropy.org, and alternativebreaks.org.

* When possible, take trains; if you have to fly, go non-stop. Offset travel-related carbon emissions by supporting alternative energy projects at atmosfair.de, betterworldclub.com/links/offsets.htm, or nativeenergy.com.

Would it just be best if people stayed out of sensitive ecosystems? Not if they're threatened by poverty, according to TIES' Martha Honey. Responsible ecotravel, including volunteering, can help support local economies, indigenous communities, and critical conservation efforts, while minimizing the overall impact on the natural world.

Additional information on ecotourism is available at the following websites: thegreenguide.com, sustainabletourism.org, adventurecouncil.com, tourismfortomorrow.com, sustainabletravelinternational.org, ecoclub.com, responsibletravel.com, and worldsurface.com.

P.W. McRandle is Senior Research Editor of The Green Guide, published by The Green Guide Institute, which provides the research for this department.

Visit the Worldwatch online consumption portal at www.worldwatch.org/ww/consumption/.