A response to the report of the Harvard University ‘Dim the Sun’ project

Contributed by Ray Garnett & Madhav Khandekar © 2021

In reading the recent press release on Harvard University’s proposal to combat human induced global warming by dimming the sun we are taken aback. Such a project would likely have harmful effects on world grain production. Crops such as rice, wheat and corn need solar radiation, heat units etc. to mature. Other noteworthy factors related to this proposal are as follows:

1) Spraying sulfate aerosols into the lower stratosphere would only add to what is already happening with respect to extremely low solar activity as documented by Svensmark and Friis-Christenson in 1997 and 2017. Low solar activity is associated with increased incoming cosmic rays that play a role in cloud seeding increasing global cloud cover. We reference their work in our 2020 publication entitled Is Diminishing solar activity detrimental to Canadian Prairie Agriculture? We found a loss of about 100 growing degree days over the Canadian prairies for the period 1985-2019 during the May to August growing season.

2) The following graph, courtesy of Roy Spencer, reveals 0.6ºC loss of temperature in the Global Lower Atmosphere in the past 15 months. This is most likely attributable to recent low solar activity. In 2019, 2020 and 2021 there has been an average of 4.8, 3.0 and 15.2 sunspots/month respectively. The long-term average is closer to 60.


3) A 70-year study of rice yields in Japan found that mean July-August temperatures below 21.5º C. reduced yields. Rice is the world’s most staple crop and needs lots of warm/hot weather. In countries such as India, Vietnam and Thailand where 2.5 bln people live the mean temperature in the monsoon season is often in the range of 30-32ºC and higher.

4) In 2019 U.S. corn crop was adversely affected by too much rain at planting and by adverse weather towards harvest. At May 19th, 2019 the U.S. crop was 49% planted and 19% emerged vs the 5-yr. average of 80% and 49% respectively. Corn denting approaching harvest was 10% behind average. Dimming the sun would only exacerbate such problems. Similar effects can be expected with crops grown in Argentina and Russia.

5) Please also consider the very recent cold extremes in grain growing areas of India and U.S. So far in the current 2020/21 U.S. hard red winter wheat growing season numerous cold records have fallen. The calamity in Texas is most notable. Over the Canadian prairies in 2009 a mere 2 sunspots/month has been linked to the coldest May-July temperatures in decades.

6) In summary, such climate engineering or ‘climate intervention’, must be done with utmost concern for possible adverse effects on humanity, agriculture and ecology. In the case of Dimming the Sun, one has to question how well it was thought out. Dimming the Sun for purposes of fighting human induced global warming in cold countries of Northern Europe as well as Canada’s cold weather climate makes no sense.

Please see our 2020 peer reviewed publication “Is Diminishing Solar Activity Detrimental to Canadian Prairie Agriculture?”


  1. Karabar

    Not to mention the effect on Vitamin D production within each human body. Some in the medical field maintain that there is no “cold and flu season”, but that what we actualllyexperience is a “Vitamin D DEFICIENCY season”. Vitamin D is essential in maintenance of an optimal immune system.

  2. Patrick Hunt

    Worst still, if the world is naturally entering a cold spell as predicted by the Milankovitch Cycles, then this would make matters worse, not better. I think it is a dim idea.

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