This post is by Sheryl Canter, an online writer and editorial manager at Environmental Defense Fund.

How much do different sectors of the U.S. economy contribute to greenhouse gas emissions, and how much does this vary by region? That's a complicated question, but you can see the answer at a glance through a nifty, interactive map on the New York Times Web site.

A bar across the top gives the overview by sector - electric, transportation, industrial, residential, and commercial. Click on a bar to see the breakdown by state, shown on a map of the U.S. via proportionally-sized circles. When you hover your mouse on a circle, you see text with the state name and million metric tons of emissions.

If you'd like to dig into the numbers in full, gory detail, check out the latest U.S. Greenhouse Gas Inventory Report.

In the previous post, I described which gases are important and what activities they come from. But we can also learn a lot by looking at regional patterns in how those gases are emitted.

For example, most deforestation occurs in poor tropical countries (in fact, in many of these countries deforestation is a much larger source of CO₂ than fossil fuel use). In contrast, most CO₂ emissions from fossil fuel use come from the developed countries.

As I described in an earlier post, the U.S. is the largest emitter in the world, both today and historically. Next let's take a closer look at the U.S. greenhouse gas pie.

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We keep talking about the need to reduce the greenhouse gas we produce. But how do these gases get in the atmosphere? To answer that question we need to look at what I like to call the "greenhouse gas pie," and it turns out there are lots of ways to slice it up.

One way is to slice the pie up by the type of gases we're talking about. There are dozens of human-produced greenhouse gases, three of them get special attention: carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). Here's why.

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This is the third installment of a four-part series to be published each Wednesday on Action Needed to Stop Global Warming.

1. How Warm is Too Warm?
2. Worldwide Emissions Target
3. U.S. Emissions Target
4. Technologies to Get Us There

In Part 1 of this series, I defined the global tipping point as the melting of the Greenland ice sheet, which could cause sea levels to rise 20 feet. In Part 2, I showed by how much global emissions of carbon dioxide (CO₂) must drop to avoid this tipping point. They must start to decline around 2020, drop 50 percent by 2050, and drop at least 75 percent by the end of the century.

Meeting these global emissions targets will require a global effort. Even if the U.S. and other developed countries were to cut their emissions to zero, global emissions would likely exceed the targets by mid-century. This is because of the rapid rise in emissions from China and other developing countries.

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This is the second installment of a four-part series to be published each Wednesday on Action Needed to Stop Global Warming.

1. How Warm is Too Warm?
2. Worldwide Emissions Target
3. U.S. Emissions Target
4. Technologies to Get Us There

In Part 1 of this series, we described why scientists and policy-makers have identified the melting of the Greenland ice sheet, which would lead to a 20-foot rise in sea level, as the tipping point that must not be crossed. To stay below the tipping point, average global temperatures must not rise more than 3.6^oF above pre-industrial temperatures, or 2.3^oF above current temperatures.Today we consider how global emissions of greenhouse gases must change over the coming century to stay below that tipping point.

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