Will Global Warming Weaken The North American Monsoon?

South Western Monsoon explodes on the Horison

Arizona gets most of its rain from thunderstorms during the summer, a period called the North American monsoon (see Arizona Monsoon for background and the anatomy of thunderstorms). By government decree, the monsoon season lasts from June 15 through September 30. In actuality, rains usually start in early July following the rain-dance ceremony of the Tohono O’odham people. In 2017, there were unusually heavy rains in July and below normal rain in August and September.

Researchers from Princeton University, using a new precipitation model, claim that global warming will decrease the rain of the monsoon. From the abstract of their paper published in Nature:

Future changes in the North American monsoon, a circulation system that brings abundant summer rains to vast areas of the North American Southwest, could have significant consequences for regional water resources. How this monsoon will change with increasing greenhouse gases, however, remains unclear, not least because coarse horizontal resolution and systematic sea-surface temperature biases limit the reliability of its numerical model simulations. Here we investigate the monsoon response to increased atmospheric carbon dioxide (CO2) concentrations using a 50-km-resolution global climate model which features a realistic representation of the monsoon climatology and its synoptic-scale variability. It is found that the monsoon response to CO2 doubling is sensitive to sea-surface temperature biases. When minimizing these biases, the model projects a robust reduction in monsoonal precipitation over the southwestern United States, contrasting with previous multi-model assessments.

Let’s see how this model premise has worked so far:

The graph below, from NOAA data, shows that year-to-year precipitation varies quit a bit. The overall trend is for increasing precipitation with global warming, not a decrease.
A plot of annual precipitation reflects the high temperatures and drought conditions of the first half of the 20th Century, but there is no apparent trend for more recent warming.

This new model, as all climate models, assumes that carbon dioxide is the major forcing of global temperature, an assumption for which there is no physical evidence.


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9 Comments on "Will Global Warming Weaken The North American Monsoon?"

  1. Albert Lannon | October 15, 2017 at 7:50 am |

    What I’ve noticed is that the summer storm cells are smaller and more intense, and that what happens in Tucson has nothing to do with what happens where I live, in Picture Rocks. We got very little monsoon rain this summer with the result that stands of cacti dozens of years old collapsed and died. Just sayin’….

  2. Tony Davis has a front page story in the Arizona Daily Star about this study. It is mostly computer speculation with little attention to real data.

  3. Mike Putfus | October 15, 2017 at 8:52 am |

    The weather will change every second as it has from the start of this planet if you want it to or not.

  4. “How this monsoon will change … remains unclear.” This is a quote from the published paper. It is nice to see an article on “climate change” with an honest headline!

  5. SilverTones | October 15, 2017 at 2:00 pm |

    The honest way to present model results is to incorporate a discussion of uncertainty right from the get go. What is the base case assumptions and sensitivities around those assumptions. Then go back to your conceptual model and question if there are alternative explanations. Mr. Davis’ article left the discussion of uncertainty to the last inch of his 2-page story. How many will read the article in its entirety and pick up on the fact that the researches acknowledge the results reflect one model and are the subject of some uncertainty?

  6. according to the weather man, weather is now a ‘monster’ it’s not just ‘rain anymore’ – when it was JULY it was the wettest thing since water – now Lannon says it didn’t rain at his house – must be the Russians weaponizing the weather and who hasn’t heard of HARP – it’s equal amount of light and day everywhere we go – just divided differently. When I was a kid the storms would hit the entire city – of course the population then was 147,000 and you could see the edge of the world from Swan road, what is now Wilmot are buildings simply didn’t exist.. Picture Rocks, heck they may well have been still drawing some of them – it was way out by the mine – and only a few crazy people lived there, guess somethings don’t change.

  7. I can answer the question posed in the title of this article: No, probably not.

  8. I also can answer the question posed in the title of this article: No.

Comments are closed.