Warming Summers Not Causing Colder Winters


A recent news clipping on the research of an international climate scientist claimed rising temperatures during the other three seasons are actually cooling off winters in North America –all because of snowfalls in Siberia and an atmosphere pressure pattern in high latitudes called the Arctic Oscillation (AO).

The argument that is being made is that the recent warmer summers (due to global warming) are causing more negative Arctic Oscillation, which in turn causes colder winters in North America and Europe. This is totally opposite to what the IPCC predicted.

Here is what the actual abstract to an article called Arctic Warming, Increasing Snow Cover & Widespread Boreal Winter Cooling by Judah L. Cohen et al 2012 in the Environmental Research Letter said:

The most up to date consensus from global climate models predicts warming in the Northern Hemisphere (NH) high latitudes to middle latitudes during boreal winter. However, recent trends in observed NH winter surface temperatures diverge from these projections. For the last two decades, large-scale cooling trends have existed instead across large stretches of eastern North America and northern Eurasia. We argue that this unforeseen trend is probably not due to internal variability alone. Instead, evidence suggests that summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover, which dynamically induces large-scale wintertime cooling. Understanding this counterintuitive response to radiative warming of the climate system has the potential for improving climate predictions at seasonal and longer timescales.”

I like the words ”most up to date consensus from global warming models” and “recent trends in observed NH winter surface temperatures diverge from these projections”. In plain English the AGW scientists are finally admitting that even their latest climate models are wrong with respect to global warming. I give the above authors credit for finally admitting what most of us have known for some time.

Also the statement “For the last two decades, large-scale cooling trends have existed instead across large stretches of eastern North America and northern Eurasia “seems overstating the cooling. There has not been large-scale cooling for 2 decades, only the last 10 years in North America – as noted below-  and in Europe only the last 4-5 years.

As has been recently reported by this writer on this blog and at Anthony Watts on WUWT, the summers in both the contiguous US and Canada have not warmed but have actually cooled in US and the trend is quite flat in Canada over the last 10 years. Therefore warmer summers cannot be causing more negative AO and colder winters.

The colder winters are more likely due to changing spatial pattern of more cooler water in the North East Pacific than in the Central and North West Pacific Ocean, especially since 2007 (see PDO) and more recently the slow cooling of the Atlantic Ocean (see AMO) here.

While it is true that a negative AO can result in cooler winters, what causes the AO to cycle unpredictably is not yet clearly understood. Scientists have been unable to predict AO levels for more than a week or two. Whatever has been causing AO to cycle or to be negative, it has been causing this for at least a century and probably much longer – our records only go back to about 1899. This not a new phenomena caused by recent global warming. Below is a plot of winter AO provided by Jiaso.Washington.edu for the years 1899-2002.


More recent AO Index data after 2002 to 2011 can be found at NOAA:


Here is how the winter AO has varied during past warming and cooling phases of this planet for the last century:

1900s decade: 7 positive, 3 negative AO winters

WARMING PHASE [temperatures rising] 1910 -1939
1910s 6 positive, 4 negative
1920s 8 positive, 2 negative
1930s 6 positive, 4 negative
TOTAL 20 positive, 10 negative

COOLING PHASE [temperatures dropping] 1940 -1969
1940s 4 positive, 6 negative
1950s 4 positive, 6 negative
1960s 4 positive, 6 negative
TOTAL 12 positive, 18 negative

WARMING PHASE [temperatures rising] 1970- 1999
1970s 5 positive, 5 negative
1980s 5 positive, 5 negative
1990s 7 positive3 negative
TOTAL 17 , 13 negative


2010s 6 positive, 4 negative (temperatures have been declining slightly during the past decade)
2010 negative AO WINTER
2011 positive AO winter

Final Comments

It would appear that the Winter AO Index has a significant impact on global winter temperatures. During recent two 30 year global warming phases there were more positive (warm) AO winters than negative (cold) AO winters and almost twice as many. During 30 year global cooling phases, there are more negative AO winters than positive AO winters and about 50% more. During individual peak warm decades (1920s and 1990s) there were 2 to 4 times as many positive AO winters as negative AO winters. During individual peak cooling decades [1940s, 1950’s and 1960s, there were 50% more negative AO winters.

Clearly the recent negative AO winters are not new phenomena caused by warmer summers due to global warming but is a continuing natural climate process that has been ongoing for centuries. A recent extreme cold spell in Canada during January 2012 was happening with mostly positive AO, so we have a lot to understand about our climate. There seems to be no end to some climate scientists trying to tie every climate phenomena, however small or varied, to global warming.

13 responses to “Warming Summers Not Causing Colder Winters”

  1. Edward.

    Undoubtedly the Arctic Oscillation plays a big part in how winter rolls out over the NH, the Atlantic oscillation, the Atlantic conveyor, the Jet stream and definitely not forgetting the PDO – it all effects and affects greatly our winter weather.

    Observing the ‘kinks’ in the AO and how it reflects the winter here in Britain is a fascination in itself – if you look at the second figure and note the plunge into the negative at the end of 2010 – it closely correlates with the coldest December in Britain since 1895 – not conclusive by any means but better than IPCC models which are predicated upon a deeply flawed fiction.

    Judah Cohen’s stuff, is interesting in itself but in synopsis and clinging fastidiously to the idea of MM >CO2= AGW is why it falls down, twisting yourself into ever tighter knots to try to prove that the busted postulation, is still valid, is a waste of the learned Doctor’s time and effort.

    Having said that, the good Prof’ is in the AGU and was at GISS, nuff said.

  2. matti

    I agree with you.
    Uk/CET has just experienced an above normal year in 2010 and the current winter to date has been the same . All this seems to be associated with a positive AO and especailly during December when it was the second highest ever at 2.221 with only December 2006 being higher at 2.282.
    UK as a whole in 2011 had its second warmest annual temperature of 9.63 C since 1910. Only 2006 was higher at 9.73 C.
    NAO was the at 2.52 in December 2011 which was the highest December since 1865. All this follows the coldest NAO of -4.64 in December 2010. So things are very unprdictable. La Nina winters have not been the cold winters or years in UK or Europe more recently as compared to ENSO neutral or El Nino winters .December 2010 was the exception.

    1. Edward.

      Yep! – Matti agree with all of that.

  3. matti

    You neglected to note the author of the article ? You are a busy man .

  4. DirkH

    Interesting graph by NOAA showing the yearly change in temperature. Notice the lack of an upward trend; dispelling the notion of “acceleration”.

  5. matti

    Dirk H

    The HADCRUT 3GL temperature data per Woodfortrees web page shows a least square trend slope increase of 0.00492 C per years since 1861 , really very little change . That represents 1800 months . Can you or I or anyone even detect or measure this . The graph you noted says the same thing really perhaps , the change is insignificant.

    1. DirkH

      I wonder who at NOAA released it.

      He’s probably already dead, uh, I wanted to say neutralized. 😉

  6. matti

    DIRK H

    It would not surprise me if there are individuals in organizationes such as EPA, Met Office ,NOAA/NCDC or NASA who know the real temperature numbers that show no significant global warming has taken place and who know that there is no justification for all the climate alarmism other than to get more free grant money , who do not support the political agenda of their superiors. Once in a while a graph such as you posted gets out . On the other hand maybe the organization has seen the light also and the political pressure has diminished due to a change in government, who now feel it is safe to release some alternate information and points of view . The article that I posted probably would not have been released a year ago.

  7. Piers Corbyn (@Piers_Corbyn)

    The trouble with most standard meteorology ‘explanations’ for seasonal changes or events is they are about DESCRIPTION of weather supposedly controlling description of weather.
    In reality as opposed to computer models external solar-lunar factors drive shifts in the jet stream and extreme events in specific regions – events which models without cause can NEVER foresee. Any long range predictive ‘rules’ produced by standard meteorology are essentially certain to be broken because the real drivers of events change differently and sometimes very abruptly.

    The recent results of our WeatherAction ~3month ahead public forecast test of a set of extreme events are on:
    It reports on our 6 extreme events/situations forecast from October (on Vid) to occur at specific dates and regions up to 13 or so weeks later. The results were superb.

    No amount of “PDO did this..” or “ENSO did that…” can ever predict with this sort of timing and regional detail.

    Thanks Piers

    1. Edward.

      Thank you Piers,

      NOW, I shall go and stand in the dunces corner.

  8. matti


    There seems to be an error message associated with your web page reference ? I cannot get anything meaningful to show up?

    In my opinion, the use of climate making factors like ENSO, PDO , NAO , AO, solar, AMO and volcanic events are major factors to be considered in making longer term or decadal weather forecasts for the Northern Hemisphere . We may not completely understand the solar- ocean – atmosphere link yet but we know that there is a near 60 year climate cycle . The world batting average for accurate short term predictions like inter annual and inter decadal leaves much to be desired yet . You may have a special insight but very little of your approach is documeted for others to properly to comment . Suggest you write an article for this blog to comment on . Good to hear from you.

  9. matti

    I don’t know if anyone else noticed that the authors of the above article claimed that for the last two decades, large –scale cooling trends have existed across large stretches of eastern North America and northern Eurasia. I thought that this may be overstating the winter cooling that far back and for that large an area I looked into this a little more and got a mixed results. According to NCDC there was some cooling in the South Eastern and central US or Ohio Valley between 1988 and 2010 [about -0.67 -0.71 F per decade] but only about 7 years of the 23 year study period showed below average temperatures . North Eastern US showed warming of 0.19F. Southern Canadian winters a shown on their graphs [or south half of the Prairie provinces] had slight cooling but mostly after 2006 and only 7 of the 23 years again showed below average winter temperatures . Canadian Atlantic coast shows no winter cooling trend during this period. Europe as a whole showed warming winter temperatures except the last 3-5 winter but they talk about Northern Eurasia. I don’t have any figures for Asian winters but Moskva winter temperatures showed a slight cooling .Personally I find that most of the winter cooling or flat temperatures have been during the last decade or post 1998 .

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