HH Lamb, Jet Stream Meridionality & Extreme Weather

By Paul Homewood

It will come as no surprise to learn that HH Lamb had plenty to say about meridional jet streams and atmospheric blocking.

Here is an extract from his book, “Climate, History and The Modern World”.

From Chapter 14, Climate Since 1950. (Bear in mind that the book was published in 1982).

ANOTHER TURNING POINT

Over the years since the 1940’s, it has become apparent that many of the tendencies in world climate which marked the previous 50 to 80 years or more have either ceased or changed…. It was only after the Second World War that the benign trend of the climate towards general warming over those previous decades really came in for much scientific discussion and began to attract public notice.

VARIABILITY INCREASES

Such worldwide surveys as have been attempted seem to confirm the increase of variability of temperature and rainfall [since 1950].’’

In Europe, there is a curious change in the pattern of variability: from some time between 1940 and 1960 onwards, the occurrence of extreme seasons – both as regards temperature and rainfall has notably increased.

A worldwide list of the extreme seasons reported since 1960 makes impressive reading. Among the items included:

1960-9 – Driest decade in central Chile since 1770’s and 1790’s.

1962-3 Coldest winter in England since 1740.

1962-5 Driest four-year period in the eastern United States since records began in 1738.

1963-4 Driest winter in England & Wales since 1743; coldest winter over an area from the lower Volga basin and Caspian Sea to the Persian Gulf since 1745.

1965-6 Baltic Sea completely ice covered.

1968 Arctic sea ice half surrounded Iceland for the first time since 1888.

1968-73 Severest phase thus far of the prolonged drought in the Sahel, surpassing all 20thC experience.

1971-2 Coldest winter in more than 200 yrs in parts of European Russia and Turkey: River Tigris frozen over.

1972 Greatest heatwave in the long records for north Finland and northern Russia.

1973-4 Floods beyond all previous recorded experience stretching across the central Australian desert.

1974-5 Mildest winter in England since 1834.

1975-6 Great European drought produced the most severe soil moisture deficit that can be established in the London (Kew) records since 1698.

1975-6 Greatest heatwaves in the records for Denmark, Netherlands and England.

1976-7 Severest winter in the temperature records (which began in 1738) for the eastern United States.

1978-9 Severest winter and lowest temperature recorded in 200 yrs in parts of northern Europe, and perhaps in the Moscow region. Snowfalls also extreme in parts of northern Europe.

This shortened list omits most of the notable events reported in the southern hemisphere and other parts of the world where instrument records do not extend so far back. Cases affecting the intermediate seasons, the springs and autumns, have also been omitted.

These variations, perhaps more than any underlying trend to a warmer or colder climate, create difficulties for the planning age in which we live. They may be associated with the increased meridionality of the general wind circulation, the greater frequency of blocking, of stationary high and low pressure systems, giving prolonged northerly winds in one longitude and southerly winds in another longitude sector in middle latitudes.

Over both hemispheres there has been more blocking in these years… The most remarkable feature seems to be the an intensification of the cyclonic activity in high latitudes near 70-90N, all around the northern polar region. And this presumably has to do with the almost equally remarkable cooling of the Arctic since the 1950’s, which has meant an increase in the thermal gradient between high and middle latitudes.

This describes a situation which is the total opposite of the theory propounded by Jennifer Francis and others, that blocking has increased in the last decade or so as a result of a warmer Arctic and lower thermal gradient. I know who I would believe.