Thirty-one scientists urge marine cloud brightening research and note that sulfur in ship fuels formerly reduced Earth’s energy imbalance by at least 4%.
Jeff Haley
March 20, 2024

Following a conference of researchers working on Marine Cloud Brightening, 31 authors have published in Science Magazine a call for an accelerated research program with a summary of each aspect to be researched.  The method of Marine Cloud Brightening is to spray tiny droplets of sea water into the air over oceans, forming tiny sea salt particles that make bright clouds a few hundred meters over the water.  

The authors note that, until 2020 when sulfur in ship fuel- was removed to reduce harmful pollution, sulfur particles in ship exhaust caused an increase in marine cloud brightness that is no longer present, causing global warming to accelerate since 2020. The authors estimate that the sulfur had previously reduced the global energy imbalance by at least .06 watts per square meter.  

For the five years of 2015 through 2019, James Hansen and others measured Earth’s energy imbalance at 1.1 watts per square meter and trending to 1.3 watts per square meter from 2020 to October 2023.

Thus, if we can put into the exhaust of all ocean-going ships tiny droplets of sea water that are as effective at brightening marine clouds as sulfur was, this should eliminate at least 4% of Earth’s energy imbalance.  Marine cloud brightening was done in the same places by nearly identical methods for a century before 2020, and sea salt aerosols are abundant in the marine air layer, so we know that the risk of undesirable side effects is insignificant.

Because the ships are traversing the oceans anyway and the added cost of pumping sea water to spray into the exhaust is small, this method will be far more cost effective than any previously proposed method of marine cloud brightening.  If it can solve a small part of the problem of Earth’s energy imbalance, it will likely reduce damages from global warming by far more than the cost and will be worth doing, even if larger scale marine cloud brightening is never undertaken.

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