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:
JANUARY, FEBRUARY, MARCH AVERAGE AO INDEX
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
POTENTIAL COOLING PHASE? 2010-2030
2010s 6 positive, 4 negative (temperatures have been declining slightly during the past decade)
2010 negative AO WINTER
2011 positive AO winter
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.