By JR on Thursday, October 13, 2016
Cold waves and the jump in European temperatures
An excerpt below of a study based on long records of temperature held in various European cities. The analysis showed 8 "cold waves" from 1750 to 2000 and explained these as incursions of Arctic air. So the record is one of alternating cooling and warming, not the climate stability preached by Warmists such as Michael Mann. Climate change is natural and cyclic, in other words.
Another finding, however, was of a temperature "jump" of a full degree in one recent 3 year period. There was however no corresponding jump in CO2 so once again we see a disjunction between CO2 and temperature. It is oscillations in Arctic air currents that cause European temperature change, not CO2
Much of European history has been marked by the effects of such irruptions of arctic air into a region that is habitually under the influence of warm Atlantic air – to which, consequently, European agriculture and economy has been adapted. But at the end of the 20th century, an anomalous and very rapid warm shift in surface temperatures occurred that has been described as a “jump” in the temperature record. Over just a 3-year period from 1987-1990, SAT anomalies inceased rapidly over about a full degree.
Regional SAT was maintained through to the end of the record in 2014 at a higher mean temperature than had been recorded during the previous century. One may choose to ignore it and simply draw a trend line from 1890 to 2015 – or one may choose to interpret the record differently, as here: both positions are valid and in the present state of climate science your choice will largely depend on your confidence in the reliability of simulation modelling of complex Earth systems.
The flowering dates of plant communities in Britan, analysed for their response to long-term change in the Central England surface air temperature record, responded closely to this regime shift. The fit between ambient temperature and flowering dates (both at community level and for individual species) is excellent over each 25-year segment of the entire record back to the 1750s. The series terminates in a very clear 15-day advance in the dates of community flowering after 1985 that was maintained to the end of the record in 2008.
Such a rapid change in surface air temperature over this large region is compatible neither with anthropogenic nor with volcanic forcing, but is consistent with the expected result of an equally major and rapid change in the distribution of atmospheric pressure over the entire North Atlantic-Arctic region.
This is indicated by change in the values of both the wintertime NAO and the Arctic Oscillation (northern annular mode of Hurrell) which together describe the state of the polar vortex north of the mid-latitude jet stream; when polar surface pressure is low (positive AO index) this flows strongly and consistently, with relatively weak meanders, so that cold polar air tends not to intrude down into mid-latitude Europe. But when polar surface pressure is high (negative AO index) the jet stream weakens and meanders more strongly, so that cold polar air is routinely carried down into mid-latitudes. Because of the existence of the western mountain ranges in North America that perturb its flow, the jet stream has a preferred number and location of southerly waves appropriate to each state of the AO. Periods of strongly negative AO are, in western Europe, associated with irruptions of cold polar air, as occurred rather commonly in the period 1935-45, discussed above.
Major warm excursions in surface air temperatures on the Japanese islands have already been noted for these same years (see plots for two rural stations on p. NN) and although these excursions were brief and cooling set in after only a single peak warm year, they were peraps related to the same rapid change in the value of the Arctic Oscillation after 1985. Changes in the AO has consequences for the strength of the winter westerlies that bring cold air from central Asia down across the Japanese islands, affecting winter temperatures generally in East Asia; this effect is modified by the strength of western Pacific cyclonic activity, and the 1985-1990 warm event over Japan (see p. NN) appears to have been the result of complex interaction between these two processes.