This post is by James Wang, Ph.D., a climate scientist at Environmental Defense Fund.

Last summer we saw record-shattering shrinkage of Arctic sea ice caused, in part, by human-induced global warming. Last week I listened in on a NASA briefing on polar sea ice, and this year looks no better.

This winter was relatively cold due to a strong La Niña, so the Arctic saw a modest increase in overall sea ice (slightly above the record low of 2005-2006, but still below the long-term average). However, the older, thicker ice that lasts through the summer has declined sharply, and this is very worrying.

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

A huge Antarctic ice berg - seven times the size of Manhattan - is close to breaking off, supported only by a thin strip of ice hanging between two islands.

Part of the Wilkins Ice Shelf, the berg was captured in satellite and video images by British Antarctic Survey (BAS), which said, "It is another identifiable impact of climate change on the Antarctic environment."

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

According to NOAA's National Climatic Data Center, this past winter was the coolest since 2001. A single season can't determine a long-term trend any more than a single month can (see my previous post, "Did Global Warming Stop in January?"). But the recent cooler temperatures do offer an opportunity to talk about La Niña - a climate pattern that causes short-term cooling.

This winter's La Niña is the strongest (coldest) since 1989, so we'd expect the weather to be cooler than usual. But even so, the cooling didn't come close to offsetting the warming of the past 50-100 years. As you can see in the graph below, the cooling barely takes us back to 2001.

Data source: NASA. Each dot is a three-month period (season).

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

On Monday, the Washington Post reported that new studies say carbon output must be near zero to avert danger. They referred to two recent studies, one published in Geophysical Research Letters and one in the journal Global Biogeochemical Cycles.

I asked the scientists here at EDF about this. It turns out what's missing from the Washington Post article is the time frame. Yes, we have to bring emissions to near zero, but it doesn't have to be tomorrow. And moreover, this isn't news!

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This post is by Scott Anderson, an attorney and senior policy advisor at the Environmental Defense Fund. It's the second in a three-part series on carbon sequestration - storing carbon or carbon dioxide (CO₂) in soils, trees, geological formations, and oceans.

1. Biological Sequestration
2. Geological Sequestration
3. Ocean Sequestration

To stop global warming, the U.S. must substantially move away from carbon-emitting fossil fuels to clean renewable energy. But a transition of this magnitude takes time. Right now this country is heavily dependent on coal for electricity, and traditional coal plants are none too clean.

How do we stop global warming while renewable technologies to meet our energy needs are still under development? Part of the answer may lie in an emerging transition technology called Carbon dioxide (CO₂) Capture and Storage (CCS). The idea behind CCS is to capture the CO₂ from industrial processes like coal plants, and then store it in deep geological formations.

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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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