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Under (high) pressure
Folks who look at weather maps regularly will notice that there is often a big H near or directly over Arizona. That H is how meteorologists represent areas of high pressure.
High pressure often creates clear, dry conditions that offer a greater opportunity for things to heat up. Arizona is under the influence of a persistent area of high pressure. Some persistent highs have catchy names like the Bermuda High that hangs around the East Coast of the United States. Our high is known as the Eastern Pacific subtropical high-pressure system.
The system isn’t always right overhead, but it never goes too far.
“On the weather time scale it gets shoved out of the way,” Crimmins said. “It builds north, gets shoved south, wanders off to the east or whatever. Climatologically, that high-pressure system is really close to Arizona just about all year long. We’re always under the influence of this sinking air.”
The system's wandering plays a big role in monsoon conditions. When it moves far enough east it helps bring moisture into the area from the Gulf of California, which fuels summer storms.
The system is also a factor in the heat wave we're expecting this weekend. High-pressure systems can vary in strength and the persistent high over the Southwest is expected to intensify in the coming days. High temperatures in Phoenix could top 115 degrees Sunday and could reach 120 Monday.
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In 1967 Hansen went to work for NASA’s Goddard Institute for Space Studies, in New York City, where he continued his research on planetary problems. Around 1970, some scientists suspected Earth was entering a period of global cooling. Decades prior, the brilliant Serbian mathematician Milutin Milankovitch had explained how our world warms and cools on roughly 100,000-year cycles due to its slowly changing position relative to the Sun. Milankovitch’s theory suggested Earth should be just beginning to head into its next ice age cycle. The surface temperature data gathered by Mitchell seemed to agree; the record showed that Earth experienced a period of cooling (by about 0.3°C) from 1940 through 1970. Of course, Mitchell was only collecting data over a fraction of the Northern Hemisphere—from 20 to 90 degrees North latitude. Still, the result drew public attention and a number of speculative articles about Earth’s coming ice age appeared in newspapers and magazines.
https://earthobservatory.nasa.gov/Features/GISSTemperature/giss_temperature2.php
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CLIMATIC PHENOMENA AND THE STATE OF THE ART
Since the late 1960s, a number of foreboding climatic predictions has appeared in various climatic, meterological, and geological periodicals, consistently following one of two themes.
A global climatic change was underway global climatic change would create worldwide agriculture failures in the 1970s.
Most meteorologists argued that they could not find any justification for these predictions.
The climatologists who argued for the proposition could not provide definitive
causal explanations for their hypothesis.
Early in the 1970s a series of adverse climatic anomalies occurred:
The world's snow and ice cover had increased by at least 10 to 15 percent.
In the eastern Canadian area of' the Arctic Greenland, below normal temperatures were recorded for 19 consecutive months. Nothing like this had happened in the last 100 years.
The Moscow region suffered its worst drought in three to five hundred years.
Drought occurred in Central America, the sub-Sahara, South Asia, China, and
Australia.
Massive floods took place in the midwestem United States.
Within a single year, adversity had visited almost every nation on the globe...
The western world's leadlng climatologists have confirmed reports of a detrimental global climatic change [cooling]. The stability of most nations is based upon a dependable source of food, but this stability will not be possible under the new cllmatic era. A forecast by the University of Wisconsin projects that the Earth's climate is returning to that of the neo·boreal era (1600-1850) - an era of drought, famine, and political unrest in the western world....
Scientists are confident that unless man is able to effectively modify the climate, the northern regions, such as Canada, the European part of the Soviet Union, and major areas in northern China, will again be covered with 100 to 200 feet of ice and snow. That this will occur within the next 2,500 years they are quite positive; that it may occur sooner is open to speculation...
http://www.governmentattic.org/18docs/CIAclimateResearchIntellProbs_1974.pdf
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The New York Times
Scientists Ask Why World Climate Is Changing; Major Cooling May Be Ahead; Scientists Ponder Why World's Climate Is Changing; a Major Cooling Widely Considered to Be Inevitable
By WALTER SULLIVAN
May 21, 1975
http://www.wmconnolley.org.uk/sci/iceage/ny-times-1975-05-21.pdf