” Cool periods produce greater climatic instability. Climatic events are then more extreme.
Climate is a worldwide, integrated system. Significant changes cannot take place in one part without other changes occurring in other places.
At the outer edge of the polar cap of cold air is a region of maximum temperature contrast. This produces west winds in the upper air that flow about the pole in a circumpolar vortex. The jetstream lies over the contrast region. Around the outer edge are the eddies known as subtropical anticyclones. These anticyclones are critical, for their sinking air produces the subtropical deserts of the world, and their position and movement strongly influence the location and duration of the monsoons. The polar air contracts in summer. The subtropical anticyclones move poleward and moist air penetrates the continents producing the monsoons. But the polar air can be more dominant or less dominant over a longer time than seasons‐thus major climate changes.
From about 1945 we have been returning to a time when polar air is more dominant, a time more like the period from A.D. 1200 to 1400 and from A.D. 1600 to 1900. The average temperature of the Northern Hemisphere has declined nearly as much as it rose in the first part of our century. The growing season in England has diminished by two weeks. The frequency of droughts in northwest India has begun to increase. The Soviet Union is experiencing successive years of trauma in its agriculture.
Climatic theory is not now sufficiently developed to give a definitive prediction of what the immediate future holds for us‐in fact, whether this cooler regime will continue. However, the records show that such coolings in the past millenium lasted not less than 40 years, nor has the hemispheric climate returned to the original state in less than 70 years. Thus, it would appear that the coming decade will be either like the last few years, or cooler. It will not be like the unusual 1931–1960 warmer period.
The last few years saw the following: In 1972 and in 1974 crop losses caused by climate, weaker monsoons in India, a monsoon failure in West Africa, drought in the Soviet Union, and climatic abnormalities that shook and are shaking the confidence of North American agriculture.”
via Real Climate Science
May 27, 2022