Climate 411

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.