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

Scientists use some technical terms in discussing climate change that can cause confusion. Two that are especially useful to know are "forcing" and "feedback".

You’ll hear these terms a lot in discussions of how human activity impacts climate – and especially when the topic turns to the melting Arctic. If you know what they mean, you’ll have a much better understanding of the dynamics behind climate change.

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

January 2008 was the coldest month in several years, according to the scientific groups that track global temperature. Is it true, as DailyTech concludes, that January’s cold "wipes out a century of warming"? Has global warming stopped?

In a word, no. A single month does not make for a climate trend. Let’s look at the data.

Source: Raw data from the U.K.’s Met Office Hadley Centre (see description of data).

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

In a comment on my Global Warming Crib Sheet, johnmashey asked if I could say something about the lifetimes of greenhouse gases – that is, how long different greenhouse gases stay in the atmosphere. Great idea! Here’s a whole post on it.

Many people don’t realize that the greenhouse gases we emit can stay in the atmosphere for decades, centuries or even millennia. That’s why it’s so important that we cap emissions as soon as possible.

Here’s a table showing a selection of greenhouse gases, their global warming potential (GWP), and their lifetimes:

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

The science behind global warming is, well, science, and it can get pretty technical. By how many degrees has the globe already warmed? How much more can it warm before we’re in trouble? How much carbon dioxide is in the air now, and how much more can we afford to emit before risking climate catastrophe? Which are the most important greenhouse gases? And what do all those funny abbreviations mean?

Below you will find a handy crib sheet that gives you all these numbers and more.

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

The term "tipping point" refers to a critical threshold at which a small change can qualitatively alter the state of a system. For example, when temperature reaches 32°F, ice changes into water. There also are "tipping points" in global warming. The best known is the Greenland Ice Sheet, which could begin a slow, irreversible meltdown if global temperature passes a certain threshold.

Last week, climate researchers published a paper that examines Earth systems in danger of passing tipping points due to human activity. They call these "tipping elements", and highlight nine such systems from around the world. They say the greatest threat is to the Arctic, followed by the Greenland Ice Sheet. Here’s the list.

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This post is by Sheryl Canter, an Online Writer and Editorial Manager at Environmental Defense.

The U.S. Environmental Protection Agency (EPA) has come out with a neat new calculator that can make sense of all those arbitrary-sounding greenhouse gas numbers.

What does a metric ton of carbon dioxide look like? The calculator shows a dozen different equivalencies, such as 114 gallons of consumed gasoline, 2.3 barrels of oil, or 0.01 acres of forest preserved from deforestation. And it’s not limited to metric tons or CO₂. You also can try different amounts and different greenhouse gases.

The EPA developed the calculator to help people in communicating about reduction targets, but it’s useful to anyone trying to get a handle on the numbers.

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

Yesterday, an unusually ferocious winter tornado system killed at least 55 people in five Southern states, and destroyed over a thousand homes and businesses. Usually tornadoes touch down for 20 minutes then come back up, but these were rare "long-track" tornadoes that stayed on the ground for 30 to 50 miles.

Lots of recent research indicates that global warming increases the intensity of hurricanes. Could it also affect tornadoes? It’s too early to tell, but scientists are starting to look.

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

The results are in for 2007, and it was a warm one. How warm? It depends who you ask. According to NASA, 2007 was the second warmest year on record. NOAA’s analysis put it in fifth place. The University of East Anglia’s Climatic Research Unit (CRU) ranked it eighth.

The results differ because it’s not as straightforward as you might think to take the temperature of the globe. There are many subtleties to consider.

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

Last week, scientists published a study about global warming and hurricanes in the U.S. The authors found a weak downward trend in the number of landfalling U.S. hurricanes, but concluded that future trends will depend on the spatial distribution of ocean warming.

In its coverage of the study, the Miami Herald said that "global warming actually is diminishing the number of hurricanes that strike Florida and the rest of the United States – and the phenomenon is likely to continue." This is not exactly what the study said. Here’s the full scoop.

Atlantic hurricane tracks, 1980-2005.

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

On January 13, Nature Geoscience published an article that reports large increases in ice loss from West Antarctica over the past 10 years. It’s a sobering result that’s in line with earlier, independent studies.

But then why do some people say that Antarctic ice is growing?

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