Dear EarthTalk: In recent years the hotel industry began to green up operations, but has it yet gone beyond leaving out little cards to encourage you to re-use your towels and linens? -- Mason Singer, St. Louis, Mo.

Some hotels and hotel chains take sustainability more seriously than others, but the industry as a whole has certainly become greener in recent years. Those little cards may seem like token environmentalism, but they can actually result in significant water, waste and cost reductions. The website Economically Sound reported that a 150-room hotel can conserve 72,000 gallons of water and 480 gallons of laundry soap every year by placing the cards in its guest rooms. The Marriott chain reported saving as much as 17 percent in hot water and sewer costs at its hotels thanks to implementation of its linen reuse program.

While many hotels and chains print up their own cards, thousands more purchase them from the Green Hotels Association, a nonprofit launched two decades ago to bring together hotels around the U.S. and elsewhere that share a commitment to the environment and sustainable use of natural resources. The organization's Catalog of Environmental Products for the Lodging Industry contains a wide range of environmentally friendly energy- and water-saving products. For example, 500 laminated copies of the group's bestselling card (asking guests to consider not having sheets changed every day) costs hoteliers just $200. Another example is the toilet tank fill diverter, which saves about 3/4 of a gallon of water per flush while remaining invisible to guests. The little gadgets cost hotels around $1 and as such pay for themselves in no time thanks to reduced water bills. The catalog also features dispensers that eliminate the waste of stocking every bathroom with soap bars and little bottles of hair and skin care products.

Another group promoting a greener hospitality industry is the World Travel & Tourism Council, which works to improve the quality of tourism around the world. Under its Environment Initiative, WTTC aims to solidify a global vision on how the tourism industry can foster sustainable development. It has been especially proactive around the mitigation of carbon emissions and last year, along with the International Tourism Partnership and 12 major hotel chains including Hilton, Hyatt, Marriott and Starwood, launched the Hotel Carbon Measurement Initiative, which aims to help hotels reduce, measure and communicate their carbon footprints. This is particularly relevant, says WTTC, for hotels' corporate clients who want to quantify the carbon footprints of their hotel stays, meetings and events.

Another positive trend is the Four Seasons' 10 Million Trees Initiative. The hotel chain is celebrating its 50th anniversary by planting 10 million trees across the 34 countries in which it operates with the hope that the effort will help combat deforestation and global warming and attract more customers concerned about the state of the planet.

Beyond what the major chains are doing, eco lodges run by or in partnership with native people or tribes have popped up all over the tropics and beyond; examples include Guludo Beach Lodge in Mozambique, Africa, and Posada Amazonas in the Peruvian Amazon. Staying at such a place is a good way to ensure that locals can benefit from tourism and not be tempted to pillage their region's natural resource base.

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Dear EarthTalk: The world added its 7-billionth person in 2011, but the news came and went quickly while Charlie Sheen news kept on and on. But isn't population growth the "elephant in the room" that needs serious attention? Can you outline the major impacts of unchecked population growth and what if anything is being done to try to arrest it? -- Aaron Rodriguez, Tucson, Ariz.

Unchecked human population growth could be a recipe for doom for the planet and its inhabitants. And it has reached staggering levels in recent years -- the number of people on the planet has doubled from 3.5 billion to 7 billion in just a half century. While we've made great strides in educating people around the world about family planning and birth control, the global fertility rate still hovers around 2.5 children per woman. At that rate, population will grow to 11 billion by 2050 and nearly 27 billion by 2100.

While such a scenario is unlikely given that fertility rates tend to decline as countries develop and modernize, the prospect of a planet with tens of billions of people on it is scary indeed. The first widely published pundit on the potential impacts of too much human population growth was Englishman Thomas Malthus, whose 1798 "An Essay on the Principle of Human Population" warned that violence, genocide, nasty weather, disease epidemics and pestilence would be precursors to widespread famine in a world with too many humans.

"The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race," he wrote.

History views Malthus as an extremist and many would argue that, despite population having swelled some seven times since his day, we have so far managed to avert a planet-wide "Malthusian catastrophe" whereby population has simply outpaced our ability to feed ourselves. Nonetheless, a 2007 UNICEF report indicated that 10.9 million children under 5-years-old die each year around the world, with malnutrition and other hunger-related diseases responsible for 60 percent of the tragedy. And a 2009 World Health Organization and UNICEF study found that some 24,000 children in developing countries were dying each day from preventable causes like diarrhea resulting from lack of access to clean water for drinking and sanitation.

The most obvious issue with seven billion of us here is our profligate consumption of dwindling natural resources and the waste and pollution generated in the process. A recent joint study by the World Wildlife Fund and the Worldwatch Institute found that humans now use 20 percent more renewable resources than can be replaced each year. And while many would say that climate change has eclipsed overpopulation as the major issue of the day, others counter that atmospheric temperatures wouldn't be growing nearly as much if there weren't so darn many of us burning so many fossil fuels.

Human population numbers are predicted to trend downward around the world within a few generations. This so-called "demographic transition" is already underway in the U.S. and other developed countries where fertility rates have dropped due to lower infant mortality, increased urbanization and wider access to contraceptives. Given that fertility rates drop as countries develop, and that lesser developed countries have begun to leapfrog ahead in their urbanization and adoption of technology, the United Nations Population Fund predicts that population may peak in the late 21st century and then begin to shrink.

EarthTalk is by Roddy Scheer and Doug Moss of E -- The Environmental Magazine ( Send questions to