This post is by Mary Kelly, Attorney and Co-Director, Land, Water, and Wildlife Program at Environmental Defense.

If you've been watching the news, you know we have a climate problem, and you may also know we have a drinking water problem in some parts of the country. What you may not realize is that these two problems are related. Yes, global warming can impact rainfall, but that's not all. The water supply sector uses large amounts of energy to transport, treat, and deliver water. On the flip side, vast quantities of water are required to generate power.

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

Yesterday's New York Times Magazine had an article aptly titled "The Future is Drying Up", about the threats that climate change and booming populations pose to precious water resources in western states. Usually when we think of water and climate change we think of rising sea levels, but climate change is also causing drops in drinking water supplies.

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The author of today's post, Andy Darrell, is Regional Director for the Living Cities program at Environmental Defense.

In 1800, 3 percent of the world's people lived in urban areas. In the last year, that number is likely to have passed 50 percent [PDF]. The world is becoming urbanized at an extremely fast rate, and as the urban population increases, so does urban development.

This presents an opportunity in the fight against global warming, since energy use in buildings accounts for 40 percent of greenhouse gas emissions in the U.S.

You might think it costs a lot more to make a building energy efficient, but it doesn't have to. A building that produces half the usual emissions can cost as little as 1 percent more to build. How can that be?

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

One reason that old-fashioned incandescent light bulbs are such a particularly poor idea in summer is that they put out a lot of heat compared to compact fluorescent light bulbs (CFLs). If you're air conditioning your home, incandescent lights will require your air conditioner to work harder because you're basically heating and cooling the room at the same time.

Some people have translated this into the advice that incandescent light bulbs are good in winter because they supplement the heat to your home, making up for the additional energy they draw. I asked James Wang, Ph.D., a climate scientist at Environmental Defense, to calculate whether this was indeed true. His answer was no. Here's why.

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The author of today's post, Jeffery Greenblatt, Ph.D., is a scientist at Environmental Defense specializing in low-carbon energy technologies.

Consumers and businesses alike complain that it takes years for savings on energy bills to repay the up-front costs of energy efficiency. No longer. As the Wall Street Journal recently reported, lenders have discovered what energy analysts have known for years: loans for energy efficiency improvements are low-risk, because borrowers can "finance" these loans through lower energy payments.

Energy-efficient mortgages have been available for some time, but lenders didn't promote them, and customers resisted the extra inspections and paperwork. Now to get home buyers interested, banks are offering incentives of $500-$1000 off closing costs. Everybody wins: consumers save money, lenders make a profit, and the atmosphere enjoys lower carbon emissions.

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

Carbon offsets are a good idea that, unfortunately, without guidelines, can be implemented badly. The basic idea is to reduce and then offset the carbon emissions produced by your lifestyle by funding projects that reduce carbon emissions elsewhere. This works because, from a global warming perspective, it doesn't matter where the carbon comes from. A reduction anywhere reduces the global total.

But how do you know a given offset is truly reducing carbon emissions?

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

When we think about climate change and the burning of fossil fuels, the discussion often centers around alternative sources of energy. But another key element is energy efficiency - simply using less power. A recent report published titled "The Twin Pillars of Sustainable Energy" says the two should be considered together.

When public policy takes both energy efficiency and renewable energy into account, there can be significant synergies. The report is over 50 pages long with many detailed case studies, but you can find a good summary of the findings on the World Business Council for Sustainable Development Web site.

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

They say knowledge is power. That's the idea behind an interesting innovation in the U.K. called "smart meters" which tell people in real time how much energy their appliances are using, and how much carbon is being emitted as a result. The goal is to change usage patterns by giving immediate feedback.

Energy usage feedback devices are starting to appear in the U.S., as well.

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The author of today's post, John Balbus, M.D., is Chief Health Officer at Environmental Defense.

Compact fluorescent light bulbs (CFLs) use dramatically less energy than incandescent bulbs and reduce greenhouse gas emissions. But they also contain mercury - a dangerous toxin.

What if you drop a CFL and it breaks? How much trouble are you in?

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In large cities such as New York, buildings account for most of the greenhouse gas emissions. The William J. Clinton Foundation has developed a plan to reduce energy usage in buildings, and organized an international coalition of banks and 16 of the world's largest cities to implement it. Billions of dollars have been pledged to address the problem. For details, read the story in the International Herald Tribune.