Clearing Up Confusion: The Recent Cold Snap and Global Warming

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.

NOAA map of worldwide temperatures

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.

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  1. Posted January 20, 2010 at 5:24 pm | Permalink

    There will definitely be variations from year to year. I think that's the most important thing here. I think it's the easiest for people to understand.

    And, surely, on average, extreme events will increase over time as the Earth warms.

    This, I think is where we get alot of our "Day After" movies. This is the second winter in which (well, of course it's not over yet, but … ) we've received very little snow. We've had some bitter cold weather (extreme events), but overall, it has been a fairly mild winter.

  2. Lynn Vincentnathan
    Posted January 21, 2010 at 10:33 am | Permalink

    Dr. James Hansen, head climate scientist at NASA, has addressed this very issue in "If It’s That Warm, How Come It’s So Damned Cold?" in his end of year summary, in which he says that 2009 is tied for the 2nd warmest year since record-keeping began.


    Earlier I needed info on this to respond to the well-oiled media smirking about climate change and the cold weather, and someone at gave me these links (the "strongly negative arctic oscillation" phrase now helps me to make it sound as if I know of which I speak :) ):

    The cold weather in much of the northern temperate zone is due to a strongly negative phase of the arctic oscillation. NSIDC has a discussion of current conditions:

    [I'll put the rest in the next post, since it said my comment looked too spammy]

  3. Lynn Vincentnathan
    Posted January 21, 2010 at 10:38 am | Permalink

    Here is the rest in a series of posts (since it's still to spammy) from that kind RC poster that helped me out (the maps take time to figure out, but are great):

    Global anomaly maps are available at (e.g.)

    (still too spammy) take that last link & replace the last section with:

    This will help begin to show the difference between weather and climate (more stats & long time span in climate)

  4. Lynn Vincentnathan
    Posted January 21, 2010 at 10:39 am | Permalink
  5. Posted January 23, 2010 at 9:20 am | Permalink

    Sorry, 10,000 years of Ice-core data says this is a hoax. If you really want the weather to cool down, maybe you should stop blowing hot air.

  6. Posted January 23, 2010 at 10:06 am | Permalink

    My data goes back 10,000 years, how far back does yours go?

    There was no industrialization to bring the planet out of it's last six ice ages, but if you're still not convinced this is a scam, I have some carbon credits to sell you.

  7. Posted January 26, 2010 at 3:06 pm | Permalink

    Thank you very much, because you are spreading the facts about this topic . Buy essay and custom papers if want know much more!

  8. Posted January 27, 2010 at 10:02 am | Permalink

    in my country, Indonesia.
    the last few years the weather becomes extreme, not like the american winter but a long summer and there many storms. The main cause, in my opinion is global warming.
    It's right???

  9. James Wang
    Posted January 28, 2010 at 3:28 pm | Permalink

    Christopher Zurcher,
    Thanks for your comment. Keep in mind that the winter conditions (mild or cold) in one area may not be representative of _global_ conditions, which is what global warming is about. However, recent years have indeed been relatively warm on a global basis. 2009 tied with 2006 as the fifth warmest year on record on a global average according to NOAA, and the 2000-2009 decade is the warmest on record, see
    (According to NASA's analysis, 2009 was tied for second warmest.
    But the difference in rankings isn't statistically significant.)

  10. James Wang
    Posted January 28, 2010 at 3:44 pm | Permalink

    Hi "stop global warming",
    I'm not very familiar with the climate conditions in Indonesia, but there have indeed been changes in atmospheric circulation patterns in the tropics that scientists are still trying to understand. For example, the tropical zone appears to have expanded over recent decades, along with a shift in hot, descending winds towards the poles. (These descending areas are where most of the world's deserts occur.)
    I know also that El Nino-La Nina cycles strongly influence the weather conditions in Indonesia, with droughts occurring during El Nino years. Again, scientists are trying to better understand whether these cycles are changing and whether global warming is influencing them.
    Finally, a warmer atmosphere can mean heavier rainfall, so that may be contributing to more intense rainstorms in Indonesia.

  11. James Wang
    Posted February 25, 2010 at 5:54 pm | Permalink

    Hi Lynn Vincentnathan,

    Thanks a lot, belatedly, for your comments and the interesting links and temperature maps. They do help put the recent weather in perspective. Perhaps the comments didn't show up right away because of that "spammy" problem.

  12. Everybody
    Posted March 6, 2010 at 9:42 am | Permalink

    im not that old or a prof. so my question is a simple one. you say:"Climate refers to the average weather over a long period". so my question now is: what is a long period?
    is it a hour? a year? 100 years? and why you dont go more back in the past like Epididymus did?
    thanks and i hope i get a answer soon.

  13. Elizabeth M
    Posted March 15, 2010 at 7:41 am | Permalink

    Most of the scientists use a 30 year period of 'average weather' against which to compare data. So, for instance, global average temperatures are often compared to the 30 year average frm 1961 to 1990 or 1971 to 2000. So one cold period of 2 months, in places which might represent 10% in total of the total globe's surface, would not make a significant difference to this 'average weather'.

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