Key words :
climate change,
warmth
,climate change
,autumn 2006
,climate reconstructions
,documentary data
,europe
Autumn 2006 is Very Likely the Warmest of Over More Than Half a Millennium
23 Dec, 2006 05:03 pm
Detailed insight into high-resolution temporal and spatial patterns of climate change during previous centuries is essential for assessing the degree to which late 20th/early 21st century changes may be unusual in the light of pre-industrial natural climate variability. Regional and temporal high-resolution reconstructions show important climatic features, such as regionally very hot or cool summers or autumns and very mild or cold winters or springs that may be masked in a hemispheric or global reconstruction [1,2]. Thus, regional studies and reconstructions of climate change are critically important when climate impacts are evaluated.
Past temperature variations for spring and autumn have not been investigated so far neither at hemispheric nor continental scales due to limited information in climate proxies for these seasons. In a recent approach, Xoplaki et al. [1] combined long monthly instrumental temperature time series from Europe and temperature index series derived from documentary evidence (written sources, historical information, phenological evidence, etc., [3]) to reconstruct statistically the temperature distribution over European land areas for each month (back to 1659) and each season (1500-1658). , Such analyses are always an interdisciplinary approach including climatologists, historians, physicists, statisticians, modellers and scientists from adjacent fields that optimally incorporate their knowledge for a common understanding of past climate change and climate change impacts [3]. The statistical model using long instrumental data and indexed temperature information derived from documentary evidence is calibrated to [conditions in] the 20th century instrumental data and then applied to reconstruct European climate back in time. Apart from the reconstructions, the results also provide uncertainties inherent in those reconstructions taking into account unexplained variance in the instrumental calibration period, partly uncertainties in the documentary data as well as the decrease of data back in time.
We have updated the data of Xoplaki et al. (2005) using monthly values of September, October and November 2005 and 2006 using data from NASA Goddard Institute for Space Studies (http://data.giss.nasa.gov/gistemp/maps/). The updated data indicate that the autumn of 2006 (September-November average) over European land areas was very likely the warmest for at least the last half millennium. The seasonal anomaly averaged all over Europe was around 2.5°C higher when compared to the autumns of the period 1971-2000. Autumn 2006 was the warmest autumn on record in Belgium, the Netherlands, the United Kingdom, parts of Ireland, Denmark, southern Norway and southern Sweden, Switzerland, Germany, as well as most parts of Austria.. In those areas, the temperature anomaly exceeded 3 to 4 times the 1971-2000 standard deviation. Only the southern central and eastern part of Europe including southern Italy, Albania, Bulgaria and Greece did not show much difference to the long-term mean. It was drier from southern France over Italy to the Balkans, Greece and western Turkey and wetter in parts of western and northern Europe. A glance at the large scale autumn 2006 temperature distribution indicates that most areas over the Northern Hemisphere were warmer than usual, except for the US and parts of northern Russia.
Rather unusual is the fact, that all three single autumn months were much warmer than the long-term mean and contributed to the overall autumn warmth. The previous warmest autumns covering the last 507 years were in 1938, 1772 and 2000. The autumn of 2006 however, exceeds those values clearly, [which is also true] when the uncertainties of the earlier reconstructions are taken into consideration. In the context of the last half millennium, the warmest autumn decade occurred in 1997-2006 (0.7°C warmer than the 1971-2000 mean), while the mildest 30-year period for autumn was in 1977-2006 (0.3°C warmer than in 1971-2000). There is also a significant warming trend of European scale autumn temperatures over the last 30 years. The strongest autumn warming over that period was experienced over Scandinavia and the British Isles. It is interesting to note that the previous autumn warming from World War 1 to the late 1930s did also show strongest warming over northern Europe. The physical understanding and the role of internal and external forcings at decadal to multidecadal scale during different periods to understand continental scale climate change is a challenge for future research.
Extreme climate anomalies for a single season, such as the hot European summer 2003 or the warm autumn of 2006, cannot be easily pinned to a single cause. However, the autumn warming trend over the past few decades, including the currently warmest conditions in the context of the past, are both in agreement with the general warming trend over the Northern Hemisphere, also during other seasons over similar periods. Recent studies describe evidence that indicates an anthropogenic influence on surface temperature during the last decades at continental and subcontinental scales.
An increasing trend of warm autumns or an increase of extreme warm European autumns (that is also very likely a scenario for the future) can have impacts on the phenology. For instance, some flowering trees, such as horse chestnuts, may spring into blossom before winter arrives. That can cause problems later in the year. Also butterflies, migratory birds and other animals may face troubles if they miss the signal to reduce their activity for the winter or do leave too late in warmer areas. A disruption in the common pattern between food availability and temperature could also cause starvation.
In summary, the new 507 years European scale autumn surface temperature time series provides evidence of current European climate change. Comparing recent temperature changes with those of the past and taking into account uncertainties in the reconstruction shows that the autumn of 2006 is very likely the warmest over more than half a millennium. Furthermore, the late 20th and early 21st century warmth very likely exceeds that of any time during at least the past five centuries with similar results having been found for the other seasons. The high-resolution reconstruction also sheds light on the spatial structure of regional temperature anomalies and extremes at monthly to seasonal resolutions back in time.
The European seasonal temperature data can be downloaded from the NOAA Paleo Climatology program:
http://www.ncdc.noaa.gov/paleo/pubs/xoplaki2005/xoplaki2005.html
[Author’s Note: Important work on those documentary weather and climate information to obtain temperature and precipitation for European areas have been done for instance by Emmanuel Le Roy Ladurie (Paris), Christian Pfister (University of Bern); Rudolf Brázdil (University of Brno); Ruediger Glaser (University of Freiburg); Mariano Barriendos (University of Barcelona); Ricardo Garcia Herrera (University of Madrid); Fernando Rodrigo (Unversity of Almeria); Maria Joao Alcoforado (University of Lisbon); Dario Camuffo (University of Padova); Rajmund Przybylak (Nicolaus Copernicus University, Torun); Lajos Racz (Szeged); Judit Bartholy (Eötvös Loránd University, Budapest) Astrid Ogilvie (INSTAAR); Aryan van Engelen (KNMI) and many others. Those data are the most reliable sources of independent temperature reconstructions prior to the late seventeenth/early eighteenth centuries to reconstruct monthly and seasonal spring and autumn temperature fields over Europe back to AD 1500 [see for instance [3] and references therein. Typical indicators for warm autumns from the past (before instrumental information) in central Europe are for instance an extended growing season, re-blossoming of plants, no reports about snow in low altitudes from September to November (e.g. Pfister, 1999, Wetternachhersage, Haupt Bern)]
References:
[1] Xoplaki, E., Luterbacher, J., Paeth, H., Dietrich, D., Steiner N., Grosjean, M., and Wanner, H., 2005: European spring and autumn temperature variability and change of extremes over the last half millennium. Geophys. Res. Lett. 32, L15713.
[2] Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M., and H. Wanner, 2004: European seasonal and annual temperature variability, trends and extremes since 1500. Science. 303, 1499-1503.
[3] Brázdil, R., Pfister, C., Wanner, H., von Storch, H., and Luterbacher, J., 2005: Historical climatology in Europe – The State of the Art, Climatic Change, 70, 363 - 430.
Key words :
First some facts to the temperature pick in 1938. Actually, the strong warming started at the end of WWI in 1918, extremely pronounced at Spitsbergen, as B.J. Birkeland observed in 1930 (?Temperaturvariationen auf Spitzbergen?, Meteorologische Zeitschrift, June 1930, p. 234-236). While this warming showed significant effect in Greenland from about 1920 to 1932, in Europe the temperature increased until 1938, respectively August/September 1939 until WWII started. The two events even got names: ?Greening if Greenland? and ?Warming of Europe?, (see for details: http://www.seaclimate.com , and http://www.1ocean-1climate.com ). WWII ended the temperature rise in Europe followed by a four decade long decrease of global temperature (ditto), which started with three of the coldest winters in North Europe for more than 100 years, namely 1939/40, 1940/41, and 1941/42, due to naval warfare in the North Sea and Baltic Sea (ditto).
This leads to the second point of Dr. Xoplaki?s findings, that ?the strongest autumn warming most recently was experienced over Scandinavia and the British Isles?. When analyzing the ?Warming of Europe? from 1918 to 1939, the warming increased year by year from the North Cape toward the South. ?Something? must have caused this specific regional climatic event. The causation may be linked to changes in the ?interior? of the Norwegian Sea (ditto). The other option is the increased use of screw driven vessels in the North Sea and Baltic Sea. Since the end of the sailing ship area, the number of ships, their draught, and their speed has increased considerably over the last 150 years. Their impact on the water temperature structure over the seasons is considerable. Particularly the high latitude of North Sea and Baltic Sea makes them particular sensitive to ?external? forcing by movements of vessels. Linking the causation of the pronounced warming in Europe from 1918-1939 and ?over the last 30 years? (see: Dr. Xoplaki) is worth serious considerations. That Scandinavia and the British Isles show the strongest autumn warming is a particularly strong supporting aspect.
The article says "The updated data indicate that the autumn of 2006 (September-November average) over European land areas was very likely the warmest for at least the last half millennium."
That is not the same as the headline,
[Response] Mr Burns is correct as the headline and my statement do not exactely mean the same. I followed the guidance notes of the IPCC Fourth Assessment Report on Addressing Uncertainties (see http://www.ipcc.ch/activity/uncertaintyguidancenote.pdf). The likelihood scale (Table 4) refers to a probabilistic assessment of some well defined outcome having occurred. In this context, very likely means > 90% probability . This 'mislead' is based on the change of my suggested title, which was: 'How extreme was the European autumn of 2006 in the context of the past half millennium?' Obviously this headline was too long and has been changed to the title above. I hope it is not too late to change it : 'Autumn 2006 was very likely the Warmest of Over More Than Half a Millennium' or 'How extreme was the European autumn of 2006 in the context of the past half millennium?'
What has forthcoming Northern Hemisphere winter 2006/07 in common with war winter 1939/40? By first glance we find that both winters see an El Ni?o event, a natural phenomenon in the Equatorial Pacific. By a second assessment, the climate stability is tested by anthropogenic ?field experiments?. For many years science is claiming that the industrial release of ?greenhouse gases? are changing global climate. In winter 1939/40 Europe saw a much more decisive climate change experiment, by thousand naval ships sailing and fighting in the North Sea and Baltic Sea since WWII commenced on September 1st, 1939.
The naval war experiment immediately produced significant results. After autumn 1772 the autumn 1938 had been the warmest for a half millennium (see article above). Although since the end of WWI Europe had been getting warmer every year (Chapter D, at http://www.warchangesclimate.com), suddenly Northern Europe was back into the Little Ice Age, respectively experienced the coldest winter for more than 100 years. The dramatic change is well demonstrated by the mean temperatures in the city Hamburg in North Germany, which is close to the North-, and Baltic Sea. From early December 1939 to end of March 1940 the temperatures were about 6-10 degrees Celsius lower than the long-term mean temperatures (corresponding graphic on: www.1ocean-1climate, with corresponding text). The arctic winter was felt from Finland, to England, France, Switzerland, and Eastern Europe until March 1940. The climate change experiment by naval war proved to be a full success.
Now 67 years later, the Pacific has again an El Ni?o event, albeit a small one, but the autumn 2006 was the warmest for 500 years (see article above), and also the December 2006 was unusual warm. More than 20?C was the temperature difference at New Year Eve in Hamburg this year 2006/07, than back in 1939/40. Was this difference caused by naval war alone, or did also the 1939 El Ni?o event contributed, as S. Br?nnimann, et. al (FN) claimed recently in a Nature article? The article concludes: ?The results suggest that the global climate anomaly in 1940 to 1942 ? previously poorly documented ? constitutes a key period for our understanding of large-scale climate variability and global El Ni?o effects.? Comparing the weather conditions than and now, the answer to the conclusion would be clearly no.
The authors of the referred Nature article received great attention in the international press two years ago. The discussion on the impact of greenhouse gases is getting ?hotter? day by day. Should we any longer ignore the huge ?field experiments? by naval war during WWI and WWII? We think not. Why were the two following war winters in Europe also arctic? Why was there a period of global cooling for four decades since war winter 1939/40?
FN) S. Br?nnimann, et. al, Extreme climate of the global troposphere and stratosphere in 1940-42 related to El Ni?o, Nature, Vol. 431, 21 October 2004, p. 971-974.