People throughout the U.S. are experiencing strange weather this summer, with scorching heat in the East Coast and Midwest and cooler temperatures in coastal California. What are recent trends across the country, and how much is due to global climate change? What future changes could occur, and is the Bay Area getting colder for good?

Why is This Summer So Cold? 19 July,2011forum

Jan Null, meteorologist in the Department of Geosciences at San Francisco State University
Phil Duffy, chief scientist for Climate Central

  • Chemist151



    NASA reported a collapse of the
    thermosphere in 2009.  A collapse of the
    thermosphere means that the atmosphere was contracting.  This is also
    influence by increased CO2 levels which increases cooling at this altitude due
    to the lack of feedback.  NASA attributed CO as ~10% of the
    influence.  This would put pressure on the mid latitudes of the
    Earth.  Because of this, it would influence the Arctic Oscillation (AO) and warm the Earth.  The
    arctic oscillations influence temperature dramatically around the world by
    oscillating between it’s Negative and Positive phases. 

    In the Positive phase, the high pressure is in the middle latitudes and
    the low pressure in the arctic regions forcing warm air toward the poles from
    the middle latitudes.  This increases global temperatures.  In the
    Negative phase, the high pressure is in the arctic regions and the low pressure
    is in the middle latitudes pushing the cooler air from the upper atmosphere
    onto the poles and then down toward the middle latitudes cooling the Earth.  This is what we’ve been experiencing the past
    40 or so  years with the collapsing
    thermosphere putting an additional pressure on the mid latitudes driving
    warming toward the poles.

    Since the 2008-2009 minimum, the thermosphere has been expanding. 
    This would create a lower pressure on the middle latitudes.  The
    effects of this have been seen.  In the winter of 2009-2010, NOAA had to
    readjust their AO scale from about -2.5 to -4 because a new low in
    the Negative phase was observed.  The reversal between the high pressure on the
    mid latitudes to a low pressure on the mid latitude is most likely causing
    stagnation between the mid latitude and poles as the trend reverses.


    The significance is that the
    thermosphere continues to expand and create a lower pressure on the middle
    latitudes increasing the draw of cool air from the upper atmosphere down to the
    poles and then down to lower latitudes.  We’re currently seeing blizzard
    conditions around the northern hemisphere of the world for the past couple of
    years after the reversal started.  This
    connects cause and effect .

    As this trend continues, we’re likely to begin observing cooling trends over
    the next 40 years or so as this cycle plays out.  On top of that, winters
    should begin stabilizing.  It should also
    be noted that the cooling of the upper atmosphere forces moisture out of the
    atmosphere and the volume force out can account for about 8% of the rise in sea

    • Easy?  Thanks, anyway.

    • Easy-peasy.

    • Anon

      I like it – I may not understand it completely, but it’s good to know what’s going on technically. I really want to understand it more – so, it’s a good start! thank you!

  • Jeremy Traurig

    What about La Nina (last year and early this year) or the Arctic Oscillation or the PDO (Pacific Decadal Oscillation)?

    • PDuffy

      Hi Jeremy,

      I did not get the chance on the air to give you a good answer to this. As you may know, La Nina is associated with relatively cold and dry conditions here. So last year’s La Nina might possibly explain last summer’s coolness. But the La Nina ended months ago, so it can’t explain why it’s colder than average here now. And of course it can’t explain last winter’s greater than average precipitation.

      I do think that the PDO could be the main reason why it has been colder than average here for the past year or so.

  • Arango, Ann

    The 2 recent major earthquakes which were strong enough to cause strong tsunamis were said to cause the Earth to wobble on it’s axis.  Could there events have influenced the weather and climate zones.

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  • It’s unfortunate this conversation veered off the topic so quickly and severely. Jan started saying that the high temperatures inland – which are breaking records – is affecting coastal winds and *perhaps* driving them more strongly onto the coastline, cooling us off. Did I get the gist of that right? Unfortunately I’m not sure because this was not discussed for more than a few minutes – I would have liked to hear more about how these patterns effect one another and play out.  

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