Why it is frightening — Iron fertilization of the ocean

Dr. Arnd Bernaerts
3 min readSep 16


The proposal to introduce iron filings into the oceans in order to reduce global warming due to the expected climate catastrophes comes up regularly. Few days ago the Opinion section of the New York Time, picked up the issue under the title: “Iron Dust Could Reverse the Course of Climate Change” written by John T Preston, Dennis Bushnell and Anthony Michaels (online, September 14th, 2023) (1). Straight forward they claim: “As crazy as it might sound, geoengineering the oceans by adding iron — in effect, fertilizing them — may offer the best, most effective and most affordable way not just to slow the march of global warming but to reverse its course by directly drawing carbon out of the atmosphere.”

This is frightening. By the extent they discuss the matter it also shocking, by demonstration how little they understand about the principle features of the oceans. Let’s start with a few excerpts from the Authors opinion, which seems to mainly based on assumptions and believe.

They acknowledge that the little is known about the long-term result by iron fertilization, as too little and short-term experiments, often lasting only months, and had been tiny relative to the vastness and variability of the ocean. Thus a lot of key questions remain, including how long the carbon would stay in the ocean..

They believe that more experiments and patches at least 200 to 500 miles in diameter, over multiple years would indicate long term impacts. Not necessarily because it would have an impact on a number of ocean parameters, as for example, significantly alter terrestrial and oceanic life forms, or ocean currents, or increase in oxygen-deprived dead zones in the ocean where toxin-producing microbes thrive. Many others are not even known or considered. Even the “patches” would not stay at the location of the experiment but move, in horizontal direction and vertically. Not having addressed this point may already indicate that the authors see the ocean as too static.

The authors opinion is shocking because they ignore the that any geoengineering the oceans to combat global warming has to observe and acknowledge that the oceans mean temperatures are merely about + 4°Celsius (39,2° Fahrenheit). To get cold water from lower ocean level to the surface would be easy and at low costs. It would not be without risks, but those would be minor in comparison with fertilizing the sea. How easily man can substantially cold the atmosphere, one has only the understand the reasons for the global cooling of the Northern Hemisphere from winter 1919/40 to the mid-1970th, cause by naval war in the North- and Baltic Sea, the North Atlantic since 1941 and in the North Pacific since 1942 until 1945. https://www.seaclimate.com/

Not understanding this cooling period thoroughly, but loosely discussing ocean affairs and climate change, should be not accepted. The suggestion, combatting an alleged escalating climate catastrophe by ocean geoengineering without sufficiently understanding the oceans, is frightening

The authors conclude their opinion as it follows:
We urgently need more aggressive measures to reduce atmospheric carbon on a large scale. Whatever questions ocean fertilization presents, they pale compared with what we already know about the escalating climate catastrophe if we continue on our current path.

(1) https://www.nytimes.com/2023/09/14/opinion/geoengineering-climate-change-ocean.html?searchResultPosition=1