Short-Term Cooling from La Niña

Lisa MooreThis 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.

Global Seasonal Temperatures, 1950-2008

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

La Niña and El Niño: What Are They?

La Niña is essentially the opposite of the warming pattern known as El Niño. Both are year-to-year phenomena related to ocean circulation in the tropical Pacific, and both affect weather patterns worldwide.

Winds over the tropical Pacific generally blow from east to west, causing warm surface water to pool in the western tropical Pacific. But every few years, an opposing westerly wind pushes the warm pool of water eastward, making surface waters in the eastern tropical Pacific unusually warm. During this shift, called El Niño, heat from the water is transferred to the atmosphere, so air temperatures tend to be warmer.

La Niña affects the eastern tropical Pacific in the opposite way. Winds and ocean currents bring cold, deep water to the surface. The cool water acts as a heat sink, so air temperatures tend to be cooler.

La Niña conditions began developing last year, and yet 2007 was still one of the warmest years on record!

La Niña conditions typically last only a year or two. In contrast, greenhouse gases can warm the atmosphere for centuries. So unless we start making big cuts in emissions, the long-term trend will be warming.

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  1. kenzrw
    Posted March 24, 2008 at 6:11 pm | Permalink

    So, La Nina and El Nino contribute to global temperatures? That seems to imply that humans do not cause all of climate change, unless we also cause the winds to shift and the El Nino-La Nina cycles, doesn’t it? I know the general trend is that the global temperatures are warming, but if you look at this chart that was in the NYTimes on March 2, if you took away the El Nino and La Nina effects, the general warming trend would be much smoother and appears to be just a natural climatic warming. The record warm year of 1998 would not have occurred, for instance. Considering this, are human’s contribution to climate change less than what’s been published? Certainly we aren’t causing ALL the changes.

  2. kenzrw
    Posted March 24, 2008 at 6:26 pm | Permalink

    Also, something that Climate 411 touched on in a post last year, black carbon (soot) appears to be a major contributor to global warming (as high as 60 percent), and is caused by diesel fumes in the US and burning of wood and coal for homes, mainly in China and India. Soot is NOT Carbon Dioxide as it only stays in the atmosphere a few days and if we could cut out soot, warming would not be nearly as much as with CO2 alone. Cutting out soot would also be a ‘quick fix’ to slow down warming, so people could see results much sooner. Here’s the peer-reviewed article from March 24:

  3. Posted March 25, 2008 at 12:46 pm | Permalink

    Hi kenzrw,

    Scientists don’t say it’s one or the other. BOTH natural and manmade factors affect climate, but it is clear that most of the warming over the past 50 years is due to human activities. Short-term variation (for example, season to season, as affected by Earth’s orbit, or year-to-year, as affected by ENSO) is heavily influenced by natural factors. Human-induced global warming is over a longer time period, of decades to centuries. The human signal is emerging from the natural noise.

    The abstract of the black carbon (soot) article is here. It’s a great review paper, highlighting the importance of cutting all sources of warming pollution (though we can’t ignore CO2!).

  4. kenzrw
    Posted March 25, 2008 at 3:43 pm | Permalink

    I think these year to year, season to season natural climate changes really make it hard for the average public to understand the long-term warming trend and is why I wince when I see reports that say ‘so and so’s heat wave this past week is caused by global warming’ instead of telling the public that no short-term heat extreme can be blamed on AGW anymore than last winter’s very cold spell means global cooling is imminent.

    I think quick action on soot reduction can get the publc much more enegenic and accepting of controls on greenhouse gases than a longer-term CO2 reduction since they can see immendiate results. My opinion, anyway.

  5. Posted March 25, 2008 at 4:33 pm | Permalink

    I agree, it is irresponsible (and incorrect) to say that global warming caused any single extreme event. It is more accurate to say that global warming increases the probability of extreme events occurring. James Hansen’s analogy (at least I think it was his) is that it’s like weighting dice to roll sixes. You can’t say that every six is due to the change, but the chance of getting a six is increased.

    I also agree that quick results such as the health benefits from cleaner air are very appealing. And from a climate perspective, cleaning up soot is a good bridge strategy for making a quick impact on global warming while we ramp up low-CO2 technologies.

  6. kenzrw
    Posted March 25, 2008 at 5:10 pm | Permalink

    I agree 100 percent. I like that dice analogy.

  7. johnmashey
    Posted March 26, 2008 at 8:52 pm | Permalink

    One must always be careful of short-term vs long-term tradeoffs.

    The issue is that CO2 and soot are very different:

    a) Soot ~ emission rate. if you can drive the mission rate down, you see immediate results. Soot, sulfatss, etc drop out of the atmopshere quickly, and are only around because they get replenished.

    b) CO2 ~ concentration in atmosphere, and it takes a long time for natural processes to lower it significantly, even if we stopped emitting it today.

    c) this was nicely covered in:

  8. koday
    Posted March 27, 2008 at 12:39 pm | Permalink

    I liked the original NYT temperature-El Nino-La Nina chart so much, that I reproduced it as an example of effective data visualization. The chart and downloadable Excel workbook are available at this link:

    In trying to understand global warming, I have recreated a number of published charts in downloadable Excel workbooks. These charts and data are available at this link:

    D Kelly O’Day

  9. oligarchynot
    Posted April 2, 2008 at 4:31 pm | Permalink

    Taking action to prevent the destruction of our beloved home — Planet Earth — must start with each individual and the choices each of us make daily. If each of us becomes committed to changing our wasteful habits, and act on that commitment, we will have an instantaneous revolution that will “trickle up” to our governments and big business.

    It is a waste of critical time to sit around denying the validity of global warming or thinking that we can’t have an effect as individuals and must wait on our governments to take action or blame the business world for causing the problem. They will follow us where we go since we are their bread and butter. The actions of one individual combined with the actions of many other individuals will be revolutionary in its effect.

  10. alexj
    Posted April 5, 2008 at 12:34 am | Permalink

    It does seem that many people don’t get the difference between interannual weather fluctuation and global climate change. Global climate variability has been relatively modest during the holocene. Now the concern is about rapid change during this populous, biodiverse interglacial period. On soot, from what I’ve read it has stronger regional effects (like intensifying glacial melt in the Himalayas), but not so much globally. Particulates and sulfate aerosols can also provide a shorter-term cooling effect/partial offset of global warming when suspended at high altitudes.

  11. kenzrw
    Posted April 5, 2008 at 7:53 am | Permalink

    Has everyone seen this BBC story regarding the UN’s World Meteorolgical Organization report regarding La Nina and short term cooling? They headline that ‘global warming dips year’ and that the ‘natural’ El Nina is responsible. The story also states that global temperatures have not risen in 10 years, since 1998, but that the decade as whole was the warmest on record, although no one year was warmer than the El Nino induced warming of 1998.

    The UN WMO goes on to state that they forecast a new record warm year will be observed within 5 years.

    My question and concern regarding this is why the IPCC and the papers they reviewed didn’t take these natural ocean warm and cool periods into account? Or did they? I’m sure the public is getting more confused all the time since the media has been saying over and over that the planet is warming, all caused my humans. Now a natural force, La Nina, comes along and slows this warming, so in many people’s mind this means that humans may not be playing as big a role in climate change as has been hyped.

  12. Posted April 7, 2008 at 4:32 pm | Permalink

    Scientists, including the IPCC, certainly know about and include natural climate variation in their study of climate change. It’s an essential part of climate, after all! For example, see my earlier post about how scientists are learning to model natural climate variability.

    It’s important to keep time scales in mind. Short-term variation (a couple of years), both up and down, is normal. But the longer term trend (over decades) is clearly up. That upward trend is the influence of all the extra greenhouse gases we’re producing – the human signal is emerging from the natural noise.

  13. kenzrw
    Posted April 7, 2008 at 5:18 pm | Permalink

    I remember that previous post now…in fact I commented on it in 2007. Still, the general public has a short-term memory mentality….so if they see some cooling in the short term, it’s hard to convince them to take immediate action for a longer-term result, in my opinion.

    Your comment on ‘the human signal is emerging from the natural noise’ is absolutely right, but the main media organizations are playing it like humans are the ONLY cause of the warming when in fact we are not the only cause. The media ignores facts like La Nina for instance and also ignores severe weather events of the past 100 years, always implying that severe weather today has never happened before, or saying that Hurrican Katrina ‘proves’ global warming, when in fact (according to the National Hurricane Center), Katrina was only a cat 3 when it hit New Orleans and there were numerous more powerful hurricanes in the past 100 years, including the cat 4 Galveston storm of 1900. We have to look at the big picture for sure, but past weather events have to be included in that discussion, as well as short-term cooling caused by La Nina.

    I think Nature will always play a role in climate change, in feedbacks, positive or negative. We don’t know all the answers yet and that’s why billions are still spent on climate research even though according to some, the ‘debate is over’. Research and debate is never over in science.

    If EDF’s more scientifically oriented news and articles would make the national network news, such as your comments above, instead of the blatant alarmism that so many in the media hype, we’d be much farther along in getting the needed caps on emissions that we should impose. Alarmism tends to cause bad short-term policy, like the corn-based ethanol fiasco, which is actually causing MORE global warming, not less (see this weeks’ TIME magazine, for instance).

    Sorry about the long rant, but I feel strongly about telling people ALL the facts of climate change, including the temporary La Nina cooling effect and the fact that we’ve had stormy weather, including heat waves, in the past, not just today.

  14. marsh02
    Posted April 12, 2008 at 2:19 pm | Permalink

    I agree. I too wish that posts such as Dr. Moore’s were more widely distributed. Keep up the excellent work! And post more! I look forward to your posts more than any of the other bloggers’ posts on Climate 411.

  15. bobclive
    Posted April 25, 2008 at 2:05 pm | Permalink

    I agree with Kenzrw

    Changes in the last couple of decades have caused the frequency of El Nino to increase (now coming every two years instead of the average rate of 7 years as in the past) and the La Nina phenomena has almost DISAPPEARED,this same time period also corresponds to a RISE in global temperatures of 0.5C in the last three decades.

    It is suggested that these are a periodic oscillation related to the oceanic distribution of tropical heat. Although a significant natural influence on interannual weather, the temperature effects of the cycle smooth out over years and decades, that might have been the case when they occurred about every 7 years prior to the 1970`s, but not when they occur every TWO years as there is very little time for the temperature to normalise over that short period.

    The Met Office Hadley Centre Coupled4 Model (HadCM2) has suggested than an increase in carbon dioxide in the atmosphere will indeed increase the frequency and intensity of El Niños. However, the third version of that model (HadCM3) does NOT show this; it predicts LITTLE or NO change in how El Niños occur.

    It appears CO2 is NOT the cause.

  16. Posted April 28, 2008 at 11:42 am | Permalink

    Thanks kenzrw for your compliments. It can be difficult to get a nuanced picture out to the public! Like you say, even the nuanced, scientifically based picture is clear enough to warrant action.

    bobclive, there’s a great summary of the relationship between warming and El Nino in this RealClimate post (see the last 3 paragraphs, plus this follow-up post). So you’re right that this is still an area of really active research. However, note that the question is how El Nino responds to warming, not to CO2.

  17. richardschumacher
    Posted June 20, 2008 at 10:28 am | Permalink

    Two key points which are often lost in popular accounts:

    1. Global warming is not the same thing as climate change. The increasing concentration of atmospheric CO2 and other greenhouse gases causes the Earth as a whole to retain more heat. That’s global warming. Climate change is mostly a *consequence* of global warming; climate change is not the principal cause of global warming and it’s not the same thing as global warming.

    2. Another way of saying “the Earth as a whole retains more heat” is “the overall average temperature of the Earth’s oceans and atmosphere increases”. But this does *not* mean that all of the atmosphere and all of the oceans are everywhere getting warmer all of the time. There are local variations, and variations which can last for years. La Nina is one example. La Nina temporarily exposes cold deep ocean water which absorbs much of the global warming heat that would otherwise go into the atmosphere. This temporarily slows or stops the temperature rise of the atmosphere. When La Nina stops, the flow of heat into the deep ocean slows down, and heating of the atmosphere resumes. Lay people commonly think that atmospheric temperature increase is the only signal of global warming, so when global average atmospheric temperature holds steady or drops they mistake it as a sign that global warming has stopped or that it never existed.

    (Obviously this leaves out a lot of detail. An ounce of imprecision saves a ton of explanation.)