Our bitter cold winter has become one of the hottest topics of conversation in America.

Specifically, people are talking about how a severe cold snap can occur at the same time as global warming. If you haven’t seen it yet, check out the debate on the Washington Post website.  In this post, I’ll try to clear up two of the issues that emerged from that debate:

1. What does a particular cold spell say about global warming, and
2. If the recent cold spell doesn’t disprove global warming, does that also mean that other kinds of extreme weather, like heat waves, aren't caused by global warming?

Climate versus weather

All of the Post’s panelists were careful enough to explain the difference between weather and climate: Climate refers to the average weather over a long period. For the most part, they did not fall for the common mistake of interpreting a cold spell as evidence against global warming.

Here's what's been happening with the weather recently: There have indeed been below-average temperatures recently in much of the eastern U.S. and in parts of Europe, Russia, northern China, and northern India. But at the same time, there were above-average temperatures in the western U.S., eastern Canada and Greenland, some other parts of the Arctic, North Africa and Central Asia, as this map shows.

This distinct pattern of temperatures was caused by an unusually persistent version of an atmospheric flow pattern known as a “Greenland block.”  This Greenland block diverted frigid Arctic air far to the south in eastern North America and Europe. (More about it on the Weather Channel: "Why So Cold? Blame the Greenland Block.")

It’s important to look at weather events like cold snaps in context—we can have a relatively brief spell of cold weather in certain regions even while the global climate is warming.  All the evidence shows that the world overall has been warming over the past several decades. (See a chart in a post on this same topic by Lisa Moore in 2008.)

So how do we know if the climate is warming? We look at a wide range of long-term trends. Along with rising air and ocean temperatures, the other signs of a warming climate include rising sea level, retreat of glaciers in most regions, rapid shrinkage of summer sea ice in the Arctic, and shifts in species distributions and seasonal behavior.

Global warming does cause more extreme weather

Although the Post’s panelists were accurate on the first issue, there could have been more discussion on the fact that global warming does have an effect on some kinds of extreme weather. One of the panelists even claimed that extreme events like heat waves cannot be used as evidence of global warming. That is wrong, so let's look at how the frequency and intensity of certain extreme weather events are expected to increase under global warming.

Records indicate that there has already been an increase in intensity and frequency of heat waves and heavy rainfall in many parts of the world over the past several decades.  (See “Frequently Asked Question” number 3.3 excerpted from the 2007 IPCC report [PDF].)  Why? Global warming drives a rise in average temperature and atmospheric moisture, promoting more heat waves and torrential downpours. On top of that, changes in atmospheric circulation patterns caused by global warming are also thought to contribute to stronger heat waves.

There will still be variations from year to year, but on average, these extreme events will increase over time as the Earth warms.  On the other hand, extremely cold temperatures are becoming less common — but can still occur — as heat builds up in the climate system.

Of course, individual weather events should not be blamed on global warming, just as an individual cold snap doesn’t disprove global warming. EDF has been careful not to attribute individual events to global warming.  Instead, we point to examples of what we expect to see more and more of in the future if we don’t fight global warming.

And with the trends in extreme weather we’re already seeing, that future ain’t lookin’ pretty.

NOAA just released a terrific scientific report that explains, in plain English, the current and projected effects of climate change on the U.S. The nonpartisan report, prepared by the 13-agency U.S. Global Change Research Program, tells a grim but important story, clearly and with lots of powerful maps and charts. I encourage you to check it out to see how climate change will affect your area of the country.

Here are some of the "business-as-usual" projections that my colleagues and I find most striking and disturbing:

You think August is hot now?

By the end of this century, we could be in for much more severe summers all across the country.

• If you live in New Hampshire, summer could feel like it does today in North Carolina (p.107).
• If you live in Michigan, brace yourself for summers that feel like today's summers in Oklahoma (p 117).
• And if you live in Texas, you now experience 10 to 20 days a year over 100 °F. By the last two decades of this century, look for 100 such days – that's more than three months (p. 90).
• In 1995, Chicago suffered a heat wave that killed more than 700 people. Chicagoans could experience that kind of relentless heat up to three times a year (p. 117).
• The Southwest, including cities like Los Angeles and Phoenix, will face worse and more frequent droughts, as spring rains decline by as much as half, snowpacks shrink and melt earlier, and water evaporates more rapidly (p. 129-130).

People who live on the coasts could be a lot closer to the shore

Sea level is projected to rise up to 3 to 4 feet. Here's what that means for various parts of the country:

• Portions of New York City and Boston could be regularly flooded by storms and even high tides (p. 150).
• On the Gulf Coast, approximately 2,400 miles of roads and 250 miles of freight rails are likely to be permanently flooded (p. 62). This area is home to seven of the nation's ten largest ports and much of our oil and gas industry.
• Some coastal freshwater sources will be contaminated with saltwater, meaning we can no longer use them for drinking water without expensive desalinization (p. 47)

Your grandchildren will miss out on local icons and specialties

The foods and activities that define different parts of the country are changing.

• Some western ski resorts could face a 90 percent decrease in snowpack, making the country's most iconic ski locations just shades of what they are today (p. 133).
• Thanksgiving might no longer include cranberries produced in the Northeast's cranberry bogs (p. 73).
• In the Northwest, salmon will be driven out of about one-third of their habitat. We could start to see the changes in the next ten years (p. 137).

This very thorough scientific report paints a bleak picture of what life will be like in this country if we let pollution continue at today's rate. The report's good news is that if we act now, we can avoid the most severe consequences. But the more sobering news is that even if we cut emissions aggressively, not everything in this report can be avoided. This is a first step toward understanding how to prepare for the coming changes.

The American Clean Energy and Security Act, which would take us off the "business-as-usual" path, will come in front of the U.S. House for a vote in a matter of days. This report gives our leaders yet another reason to do the right thing for our country's future.

This post is by Amy Hardberger, an attorney with EDF's Texas Office's Climate/Air and Water programs.

Hurricane Ike storm surge hits Jetty East, by Flickr user eh3k.

For some, it’s hard to care about global warming because its impacts on everyday life aren’t obvious. It’s too abstract. It’s not tangible. It’s too wonky. It’s just not real enough.

Well, what if you learned that global warming could literally push you out of your home? Is that real enough for you?

Texas cities Houston and Galveston just got a wake-up call – conservative estimates of sea level rise due to climate change will displace 78 percent of households over the next 100 years in Galveston County alone, according to a new study that EDF and the British Consulate-General commissioned from the Harte Research Institute at Texas A&M Corpus Christi.

And that's the conservative estimate. In a business-as-usual scenario, Galveston-area sea levels could rise as much as 1.5 meters in the next 100 years, which could displace more than 100,000 households and create more than $12 billion in infrastructure losses for Houston and Galveston.  Rising sea levels will also damage at least 23 public facilities, industrial sites and water treatments plants, begging many questions about where to move or how to protect these sites. (See a related post on sea level rise.)

For cities like Galveston, which is still rebuilding from Hurricane Ike, these findings reinforce the notion that planning for how to adapt to climate changes or mitigate their effects is critical. Current discussions have centered around building a large, expensive and likely ineffective “Ike Dike” to protect the city from future storm surges, though there are likely more realistic adaptation measures that will make people safer quicker. Passing federal climate legislation and ramping up local municipal energy efficiency are surely the most effective ways to begin reducing the rate of sea level rise.

So, for all of you out there who don’t think global warming could happen to you, take a hard look at the harsh reality that these coastal communities face.

Have Hurricanes Gustav and Hanna gotten you thinking about the possible link between hurricanes and climate change?

Check out our hurricane and clilmate change overview for the straight facts from EDF climate scientists. And Peter Black shares eye-opening maps over on ClimateAtlas.

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

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.

Read more »

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

It's been raining a lot in some parts of the world. In Northern India, Bangladesh, and Nepal, the worst rains in decades have devastated tea and rice crops, killed at least 3000 to 4000 people, and affected tens of millions of people since June. Great tracts of land are under water. Crop land has been destroyed; people are hungry. And the weather forecast says rain.

Click image to view original page.

Torrential rains also have caused severe flooding in Korea, Uganda, and Sudan. In North Korea, over 600 people are dead or missing, 170,000 people displaced, and almost 1 million people affected. In Sudan, 200,000 are homeless from floods. India, itself reeling, sent $250,000 in aid to flood-ravaged Uganda.

Is this all from global warming?

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The author of today's post, Bill Chameides, Ph.D., is Chief Scientist at Environmental Defense.

A week or so ago I wrote about all the recent extreme weather in the United States. Well, it's not just happening here. Great Britain is being hit by the worst flooding in decades, and it keeps on raining. A heatwave blanketing south-eastern Europe has killed hundreds of people, and out-of-control wildfires are burning across Greece.

Is this global warming? It's impossible to say for sure what causes a particular weather event, but global warming does make extreme weather events more likely. Whether or not the events in Europe are due to global warming, I do think the Europeans are, unfortunately, getting a taste of things to come. For more, visit our Web page on global warming and extreme weather.

With all that's going on in the world, it's easy to miss weather events. So you may not have noticed that U.S. weather patterns the last few months have been quite extreme and worrying.

From NOAA's National Climatic Data Center

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Today's post is by Bill Chameides, Chief Scientist at Environmental Defense.

The hurricane season began on June 1, and we are all waiting with some dread to see what this year will bring. Will it be a relatively mild season like last year, a devastating one like 2005, or something in between? An ominous sign is that we have already seen two tropical storms in the region: Andrea, which formed almost a month before the season began, and Barry, which formed on the first day of the season.

Last week I read that Oman was hit by Tropical Cyclone Gonu. ("Hurricane", "typhoon", and "cyclone" are all names for the same thing.) I know that Asia and Australia are regularly hit by tropical storms, but the Arabian Peninsula? Is that normal? I didn't know, so I decided to do a little investigating. Here's what I learned.

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