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Extreme Weather is Linked to Global Warming, a New Study Suggests

In 2013, a blocking pattern over Alaska caused a record-breaking heat wave. Credit: Photo by Jesse Allen and Jeff Schmatltz, using data from theLand Processes Distributed Active Archive Center(LPDAAC) and theLANCE/EOSDIS Rapid Response

In 2013, a blocking pattern over Alaska caused a record-breaking heat wave. Credit: Earth Observatory

Extreme weather is becoming much more common. Heat waves and heavy rains are escalating, food crops are being damaged, human beings are being displaced due to flooding and animals are migrating toward the poles or going extinct.

Although it has been postulated that these extreme weather events may be due to climate change, a new study has found much better evidence.

The research shows blocking patterns — high-pressure systems that become immobile for days or even weeks, causing extreme heat waves and torrential rain — may have doubled in summers over the last decade.

“Since 2000, we have seen a cluster of these events,” lead author Dim Doumou told The Gaurdian earlier this month. “When these high-altitude waves become quasi-stationary, then we see more extreme weather at the surface. It is especially noticeable for heat extremes.”

It was a blocking pattern that led to the heat wave in Alaska in 2013, and to the devastating floods in Colorado last summer.

These blocking patterns are associated with the jet stream, the fast flowing winds high in Earth’s atmosphere at latitudes between 30 and 60 degrees. Sometimes the flow weakens, and the winds can dip down into more southern latitudes. These excursions lead to blocking patterns.

And the jet stream is becoming “wavier,” with steeper troughs and higher ridges.

The climatologists analyzed 35 years of wind data amassed from satellites, ships, weather stations, and meteorological balloons. They found that a warming Arctic creates and amplifies the conditions that lead to jet stream excursions, therefore raising the chances for long-duration extreme events, like droughts, floods, and heat waves.

That said the climatologists were unable to see a direct causal link between climate change and extreme weather. Ordinarily we think about “cause” in a simple sense in which one thing fully brings about another. But the Colorado floods, for example, were partially caused by moisture from the tropics, a blocking pattern, and past wildfires that increased the risk of runoff.

So there is a difference between “direct causation” and “systematic causation.” The latter is not direct, but it is no less real. In this study, the team noticed that the rise in blocking patterns correlates closely with the extra heating being delivered to the Arctic by climate change. Statistically speaking, the two seem to go hand in hand.

But the team does hypothesize a direct causal link. The jet streams are driven by the difference in temperature between the poles and the equator. So because the Arctic is warming more quickly than lower latitudes, the temperature difference is declining, providing less energy for the jet stream and causing it to meander.

Although the study shows a correlation — not causation — between more frequent blocking patterns (and therefore extreme weather) and Arctic warming, it is a solid step forward in understanding how the two are related.

The article has been published in the journal Proceedings of the National Academies of Science (PNAS).

To see why Universe Today writes about climate change, please read a past article on the subject.

About 

Shannon Hall is a freelance science journalist. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. Currently, she is working toward a second M.S. from NYU's Science, Health and Environmental Reporting program. You can follow her on Twitter @ShannonWHall.

Comments on this entry are closed.

  • FarAwayLongAgo August 26, 2014, 10:33 AM

    Oh, yeah!
    Skip the space theme, spend this blog on one sided political propaganda instead.

    The little fact that the temperature hasn’t increased at all since 1998 doesn’t matter, right? Somehow the CO2 magically in itself directly causes “extreme weather” without affecting the temperature. And extreme weather is by the way is not at all becoming more common. But some people don’t care about being wrong.

    Could anything happen which would make the climate doomsday believers change their minds? Could someone mention any kind of statistics which could make them accept that their religious belief is not true? Like if the temperature didn’t increase at all during the next 20 years either, would that in any way cause them to change their pre-programmed little minds?

    • Hops August 26, 2014, 12:57 PM

      What do you mean by “the temperature?”

      The Earth is not like a turkey in the oven that you stick a thermometer in.

      The Arctic is warming rapidly. But if you take a global average, it dilutes the impact of the Arctic warming because the atmosphere over the oceans, especially in the southern hemisphere, hasn’t warmed as much, for now.

      Regarding 1998, riddle me this: have we warmed since 1996? Have we warmed since 2000? And if the answer is “yes,” how can that be?

    • TTC August 26, 2014, 3:51 PM

      But but but… The Earth is in the universe. The Earth is in space. So we should cover it in an astronomy blog, right?

      I mean, astronomers study Earth climate, right?

    • Adrian Morgan August 26, 2014, 8:12 PM

      You can always tell someone is doing “one sided political propaganda” when they repeat claims like “the temperature hasn’t increased at all since 1998″ no matter how many times the claims have been debunked.

      • mewo August 27, 2014, 8:57 PM

        Or when they have to pick 1998 specifically, because neither 1997 or 1999 will do the job for them.

  • Paul Gracey August 26, 2014, 11:24 AM

    As is all too common these days the mention of climate, even on a science based forum such as this one brings the bad science partisan comments out right away. Believe what you want ‘FarAway’. This article is being quite fair about the complexities involved and your comment begins right away with denigration undeserved by it.
    I worked over twenty years ago on Earth Science satellite instruments designed to get at the truth of global climate change when that knowledge was much less certain than it is today. The trend these satellites have revealed in the intervening years continues to point to the the excessive warming of the Arctic regions atypical of previous patterns.
    Perhaps the stridency of your comment suggests that you are becoming more desperate in the effort to hold on to your cherished beliefs?

    • FarAwayLongAgo August 26, 2014, 12:27 PM

      Would two more decades without any “global warming” in any way affect your premise that human industry is causing Doomsday and should be abolished? Can anything happen which could in any way affect your premise which is equal to your conclusion? Is your belief system in any way possible to test scientifically? Why do you not use any kind of reasoning between your assumption and your conclusion?

      How do you explain that no temperature increase since 1998 now allegedly has cause terrible extreme weather? Is NO CLIMATE CHANGE also an immediate danger to the existence of life on Earth? Do 99% of climate scientists really have a consensus that CO2 in itself, even without any temperature effects, causes extreme weather and melts polar ices???

      • Hops August 26, 2014, 3:06 PM

        “Can anything happen which could in any way affect your premise which is equal to your conclusion? ”

        If it got markedly colder. If you look at chart of global average temperature (lower troposphere) there used to be times when the temperature dropped over periods of a decade or more.

        Doesn’t seem to happen any more. Flat is the new down.

  • Denver August 26, 2014, 3:43 PM

    2000 years ago the Romans reported vineyards in Caledonia (Scotland). Warmer.
    1000 years ago there were thriving Viking dairy farms in Greenland. Warmer
    650 years ago Iceland was surrounded by sea ice for nearly 50 years. Cooler
    238 years ago Washington ordered cannon to be dragged across the frozen Hudson River. Cooler

    Obviously, the climate changes. When it is yet again warm enough for dairy farms to exist in Greenland, and when it has been warm enough for those dairy farms to have existed for nigh unto 500 years . . . then call me about “Global Warming”, because it will finally, finally, be warmer than it is now. For 500 years (850-1250) it was warm enough for dairy farms to exist in Greenland.

    • Hops August 26, 2014, 5:20 PM

      And on top of all these (probably local) variations, we have added a warming trend.

  • Pvt.Pantzov August 26, 2014, 7:21 PM

    no matter one’s stance on climate change, it always makes sense to live cleanly, pollute as little as possible, have efficient combustion, etc…

    it’s not necessary to convince deniers that climate change is real. bypass these people. using science to help reduce emmisions and doing it in a fashion which will not add huge expenses to everyday life (eg: carbon tax) will make most people happy. some will never be happy… ever.

  • Greg August 26, 2014, 8:57 PM

    There have been a few articles also about the Alaska heat wave being driven by warm air riding northwards from the Pacific. See below. http://earthobservatory.nasa.gov/IOTD/view.php?id=83032
    This is a cyclic pattern involving the Pacific ocean and is due reverse in a few years, but global warming may be enhancing it. There is little doubt that it is this intrusion of warm air that is the mechanism causing the increase in the blocking or meandering jet stream resulting in the extreme persistent weather in areas unfortunate enough to have been affected by it.
    I like to look at the problem more simply in that if warm air is intruding further north into the Arctic than normal, then cold air must then be displaced further south than normal elsewhere. The displacement of cold air seems to occur in somewhat unpredictable locations around the globe, but when it happens the cold air mass will sit in the same location for week and months with a weakened jet stream (due to a lower regional temperature gradient) unable to displace it and thereby going on a long detour around it. So the arctic gets warmer in spots while normally warmer areas further south get colder than normal.
    For an analogy just look at what drives arctic fronts in the winter. Cold air gets trapped in the arctic until enough builds up to disperse southward, but usually for a shorter period of time. With warm air invading the arctic this process is disrupted and the cold air has to build up somewhere else, hence the polar vortex migrates further south for much longer period and with somewhat less intensity.

  • rolfingqueen August 26, 2014, 11:25 PM

    Thank you for your explanation
    so many people can’t understand when we get 40 below weather in canada why they say we have global warming
    This explains it easier I would say to them its just weather but the end result is global warming
    rolfing queen

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