2006 might be regarded as the year of climate change hysteria or perhaps the year where we had to get serious about attribution and what is and is not global warming.
Certainly one could not help but notice various bouts of unseasonal cold weather this year with frosts affecting fruit crops in Tasmania, juxtaposed with record high temperatures of late in western Queensland and Russia.
Following a press release from the World Meteorological Society , a regular commentator at this blog Sid Reynolds questioned whether the WMO has infra-red rose coloured glasses and can only see when warm records are broken, having previously listed an impressive slew of recent record breaking cold events.
THE STATISTICS OF EXTREMES
There is a perception that the climate change story selects record breaking events to suit its argument and ignores the cold extremes.
So how do we view extreme events. What’s fair and what’s not?
Certainly global warming theory does not say all weather will be suspended and all temperatures from here on, everywhere in the world, will be always warmer every moment of every day.
It does not say there will never ever be another cold spell – or even a record-breaking cold event.
Realclimate gives a cold overview on record breaking events: “In statistics, there is a large volume of literature on record-breaking behaviour, and statistically stationary systems will produce new record-breaking events from time to time. On the other hand, one would expect to see more new record-breaking events in a changing climate: when the mean temperature level rises new temperatures will surpass past record-highs”.
In short, the probability of cold extreme events should decrease over time.
REGIONAL COLD ANOMALIES
Inner continental Antarctica has cooled compared with a warming on the Antarctica peninsula and surrounding ocean.
The issue is discussed in ‘Interpretation of Recent Southern Hemisphere Climate Change’ by Thompson and Solomon
in Science 3 May 2002: 895, DOI: 10.1126/science.1069270 .
For a graphic view of that trend visit http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17257.
HISTORIC COLD ANOMALIES
What about periodic cold extremes in recent centuries?
A very recent study published in Nature shows how changes in the thermohaline circulation may have contributed to the Little Ice Age .
From around 1200 until 1850, during which average temperatures across the Northern Hemisphere dipped by around 1 °C, the strength of the Gulf Stream also slackened by up to 10%, oceanographers report. The Gulf Stream, which is part of a vast pattern of currents nicknamed the ocean conveyor belt, carries warm surface waters from the tropical Atlantic northeastwards towards Europe. The reduced flow that occurred during medieval times would have transported less heat, contributing to the icy conditions that persisted until Victorian times.
The ultimate cold event in an ice age. Despite popular opinion the current orbital positions make that unlikely for millennia.
THE PRESENT DAY
What studies of extremes do we have of our contemporary climate? Anthropogenic global warming theory would indicate a reduction in the frequency of cold events (but not disappearance).
Where we have decent long term data this is exactly what’s been happening !
From: Frich, P., Alexander, L.V., Della-Marta, P., Gleason, B., Haylock, M., Klein Tank, A.M.G. and Peterson, T. (2002). Observed coherent changes in climatic extremes during the second half of the twentieth century. Climate Research, 19, 193-212. http://www.int-res.com/articles/cr2002/19/c019p193.pdf
From: Changes in Climate Extremes Over the Australian Region and New Zealand During the Twentieth Century.
There has been another, more recent study, involving much of east Asia and Australasia also showing statistically reduced frequency of cold extremes: http://www3.interscience.wiley.com/cgi-bin/abstract/110573943/ABSTRACT .
What do state of the art climate models say about cold air outbreaks (CAOs) in a greenhouse world?
Various studies indicate that although in many areas CAOs will decrease, in some areas there will be little change. How counterintuitive. So the global atmosphere is a complex thing – local circulation changes may override as basic aspects of greenhouse forcing for some areas:
Interestingly, temperatures are expected to warm over the source regions of the CAOs and the coverage of snow and ice are projected to correspondingly decrease. However, the models do not necessarily project a corresponding decrease in the number of cold air outbreaks in all regions.
From: Changes in Cold air outbreak days from a GCM ensemble run. The behavior of extreme cold-air outbreaks in a greenhouse-warmed world. Stephen J. Vavrus, University of Wisconsin, Madison, WI; and J. E. Walsh, D. Portis, and W. L. Chapman. http://igloo.atmos.uiuc.edu/CAO/mrcm.freq.abs.diff.gif
In conclusion, one still should expect to see periodic cold extreme events in a greenhouse world.
Exact climatology will vary from place to place depending on circulation patterns.
A simplistic assumption that cold extremes will disappear and be replaced with only hot extremes is not what the science is showing. However, in general, a greenhouse world should have a higher frequency of heatwave events compared to the current climate, and a reduction in the frequency of cold extremes would be expected. This seems to be already occurring.
This contribution from Luke has been significantly shortened. In particular I have deleted some of the technical argument/abstracts from technical paper to make the post more readable. I hope some of this information finds its way into the thread through comment and discussion.