Fertilizing the Ocean to Slow Global Warming

Professor Wingenter: We are proposing a quite limited iron fertilization of the Southern Ocean (SO) based on a large scale iron fertilization project we took measurements on. Our initial estimates indicate that if the concentration of iron were brought up from about 0.3 nanoMolar to about 1 nM in an area of about 2 percent of the SO, we should be able to increase emissions of dimethyl sulfide (DMS) by 20 percent which would lead to more cloud particles and increased cloud reflectivity resulting in an extra 3 watt m-2 of energy reflected to space. This loss of energy would result in about a 2 degree Celsius reduction in temperature in the region. This would lower the temperature in the Southern Hemisphere a few tenths of a degree and also reduce the flow of ice from Antarctica.

Iron fertilization much beyond this amount would simply cool the region to much and would shut down the vertical mixing in the SO and the resulting stratification would severally alter ecosystems and alter ocean and atmospheric circulation. Any thought of large-scale iron fertilization of the Southern Ocean for carbon sequestration is completely impractical simple because we would induce an ice age because of the changes in cloud reflectivity.

We could also apply limited iron fertilization to the equatorial Pacific, another high nutrient/low chlorophyll region and gain some additional cooling.

S: How could it be implemented for practical purposes?

OW: In the case of the Southern Ocean about 30 ships would be needed to distribute the iron sulfate over a month long period at the start of the growing season. The cost would be about $10 million to $100 million dollars each year. The higher amount would allow for more monitoring and measurements by scientists to quickly discover if some unwanted and unintended consequence were happening and the program would need to be stopped.

It should be noted that our proposal must be optimized by using coupled ocean-atmosphere-ice sheet models in order to get the desired cooling with the least of amount of iron applied. After this limited iron fertilization over fairly large portion of the Southern Ocean can be tried. If this proposal were to be implemented, I foresee scientist from many countries and from several related disciplines would be needed to provide prudent planning and oversight of the project.

S: What do you think of the controversy surrounding geoengineering and the fact that it might be used as an excuse not to cut greenhouse gas emissions?

OW: This is potentially a serious problem. The intention of our 2 percent solution is cool the planet a few tenths of a degree in order to prevent a runaway greenhouse effect until a solution for greenhouse gases is found. Our proposal cannot be viewed as a substitute for reducing greenhouse gases. Our goal is to delay the tipping point by ten or twenty years by this time, hopefully, humankind will have drastically cut CO2 emissions or developed long term CO2 sequestration. Our university is actively exploring this too. Jim Hansen of NASA Goddard Space Flight Center estimates that if climate forcing brought on by about 450 ppmv of CO2 could increase atmospheric water vapor enough leading to a strong positive feedback cycle whereby the increased water vapor leads to higher temperatures and then greater water vapor. This could start in about 9 years.

I feel we have much of the technology already to greatly reduce fossil fuel burning. It saddens me to see houses being built with no regarding for passive solar heating or cooling. Such a simple and elegant approach. How did humans lose this knowledge? I would like to see a program where companies would sell their fluorescent light bulbs at cost and the retailers would also not make a profit. I would like a program were donations could be made to purchase these energy saving light bulbs for low income people. If as much money were invested on the purchase of these bulbs, it is likely that new coal burning power plants would not be needed for years or even decades.

Study available here

Interview by: Clementine Fullias