Two ocean hot spots have been linked to the hottest summers on record for the central United States, in 1934 and 1936. Those two summers and the "Dust Bowl" that saw farming devastated were accompanied by the worst drought in America of the last 1,000 years.

In 1934, giant dust storms and drought covered more than 75 percent of the country and affected 27 states severely. Silt from storms even covered the decks of ships 200 miles off the east coast. 

In the years afterward, over-farming was blamed but new research instead blames unusually warm sea surface temperatures. In the Pacific, there were anomalously warm ocean temperatures along the coastline of the Gulf of Alaska stretching down as far as Los Angeles, while a relatively small area of the Atlantic Ocean off the coast of Maine and Nova Scotia was also unusually warm and combined they reduced spring rainfall and created perfect conditions for hot temperatures to develop in the heart of the U.S.

Yes, this was worse. Credit: University of Illinois

To reach their conclusion, researchers compared the large-scale climate conditions in 1934 and 1936 with those of the extensive recent hot drought years of 2011 and 2012 to see if there were any similarities to the dust bowl years. They found that in 2011 and 2012 while there were definitely warm ocean temperatures off the coast of Nova Scotia and Maine, the same was not true along the coastline of the Gulf of Alaska, where ocean temperatures were below normal.

Instead, in the mega-drought of 80 years ago, unusual ocean warming in two regions compounded the impacts on the atmosphere and pressure gradients across the continental US, profoundly changing the weather systems during the spring and summers. The Atlantic warming off Nova Scotia and Maine meant southerly winds shifted further north-east and the transport of moist air from the Gulf of Mexico northward into the Central US was weakened. At the same time, the Pacific Ocean warming expanded a large Pacific high that also contributed to reduced transport of moist air into the central US - that meant higher summer temperatures that came after reduced spring rainfall, which led to atmospheric dust over Western North America once summer was underway and a positive feedback loop that intensified the high pressure system even further.

So we can complain about the drought happening right now, but it seems odder that there hasn't been a repeat of those Dust Bowl years due to climate change.