By Jim Steele

Why have major coral bleaching events occurred during EL Nino events?

During an El Nino, warm water stored in the Pacific Warm Pool of the Coral Triangle sloshes eastward. That lowers the ocean temperatures in the western Pacific and raises temperatures in the eastern Pacific (illustration A). It also shifts the centers of convection eastward and the resulting changes in atmospheric circulation cause downward air flow typical of heat domes and clearer skies over the western Pacific and Atlantic Ocean (Illustration D). That causes more intense solar radiation and coral light stress.

Due to the biochemistry governing photosynthesis, high light stress causes the increased production of dangerous oxidants (aka ROS: Reactive Oxygen Species). Dangerous oxidants damage living tissues, which is why all organisms naturally produce and ingest anti-oxidants. So, when corals’ symbiotic algae produce too much ROS and overwhelm a coral’s natural anti-oxidant systems, to prevent further damage, the coral eject their symbiotic algae and that causes bleaching.

As peer reviewed science explains, “The most likely explanation to the commonest form of mass coral bleaching involves the production of Reactive Oxygen Species associated with Photosystem I of photosynthesis (and to some extent Photosystem II): namely superoxide (O2- ), hydrogen peroxide (H2O2) and singlet oxygen.”

See“A Review: The Role of Reactive Oxygen Species in Mass Coral Bleaching Szabó (2020)

Alarmist scientists with a global warming agenda (i.e. Hughes, or Hoegh-Guldberg) always tell click-bait media the same narrative, that global warming is the main cause of bleaching. But increased solar radiation creates both high light stress and heat stress and heat stress can affect the efficiency of the corals’ antioxidant protection. So, both excess heat and light can increase the accumulation of ROS.

Which is the primary cause?

Unfortunately, rarely have studies satisfactorily separated the two factors. But those that have suggest light stress is the main factor. For example read: Antioxidant responses to heat and light stress differ with habitat in a common reef coral Hawkins (2015). For the species Stylophora pistillata they state,

“Overall, changes in enzymatic antioxidant activity in the symbionts were driven primarily by irradiance rather than temperature, and responses were similar across depth groups. Taken together, our results suggest that in the absence of light stress, heating of 1C/day to 4C above ambient, is not sufficient to induce a substantial oxidative challenge”.

That’s why regions of reduced cloud cover during El Nino events correlate with so-called “global bleaching events” that happened in 1998, 2010, and 2014-2017 and now 2023-24.

Major eastern-Pacific El Nino events also happened in 1997–98, 2014–16, and 2023–24 and a Modoki El Nino 2009-2010. As seen in illustration B’s white circles, the death rate from bleaching during the 2023–24 El Nino, is associated with regions where El Nino induced atmospheric subsidence and reduced cloud cover that increases light stress.

The alarmists seeking power can’t control solar radiation, but they want to control the public’s use of energy. So, they unscientifically ignore changes in clooud cover choosing to blame global warming for coral bleaching and evidence that rising CO2 is killing coral! Alarmists deny the science!