ITCZ Shifting

26 Apr 2017

At ... it seems HH Lamb is haunting climate science again. At this link we are told the Intertropical Convergence Zone (ITCZ) can shift, and has done throughout history. The ITCZ is a band of tropical rain. It changes its position in response to the path of the Sun, following its zenith. This determines wet and dry periods in the tropics and sub tropics over the full year. It also affects the monsoon rains over SE Asia and central America. In other words it is responsible for the ups and downs in the fortunes of the Maya - periods of drought (a disaster) and periods of wet weather (crops thrive). Now, scientists in Zurich are saying the migration of the ITCZ is sensitive to small changes in global temperature (rather than the historical big changes) in a paper published in Scientific Reports (2017). In particular, they say that between 1450 and 1850 a switch in the ITCZ brought drought to normally wet regions and flooding to normally dry regions. We may note this roughly corresponds to the Little Ice Age - which was not a universally cold period but one of a colder on average temperature, with swings in climate and rainfall etc. Apparently, part of the shift affects the North Atlantic Oscillation (or in response to the shift) and the weather in western and central Europe. Rainfall tends to increase over southern Europe leaving the northern zone open to colder weather with an origin in the Arctic. This information was readily available by reading HH Lamb's books and articles from the mid 20th century - but appears to be presented as a new study finding (for the computer generation). The bottom line, of course, is that the Little Ice Age was not as disastrous as glaciers in the Alps suggest, or so they seem to think, but a rather benign cooling episode. Therefore we are all doomed and we are going to die because the world is warming and climate is changing, and even just a slight change in temperature is catastrophic. Get your fur coat out of the attic - and the long johns from the bottom of the wardrobe. Meanwhile, the BBC is telling gardeners today, on radio and TV, that gardens in the south are going to be subject to drought in the near future as a result of global warming (even as the sleet and snow runs across the eastern side of the country and temperature drop low at night threatening apple and cherry blossom). Apparently, we are going to have a climate like Mexico according to one wag. Northern Mexico is a desert for a reason - it lies in a band that runs around the globe where rainfall is low and winds are in short supply. Is he seriously suggesting southern Britain is going to move to the latitude of the Sahara? Southern Mexico is in the sub tropics - so he can't possibly be referring to that part of the earth system. It would be an even bigger shift in latitude.