To Fertilize, or Not to Fertilize

Global warming is “unequivocal,” the Intergovernmental Panel on Climate Change (IPCC) reported in November 2007. Human actions—particularly the burning of fossil fuels—have dramatically raised carbon dioxide and other greenhouse gases in the atmosphere, leading our planet toward “abrupt or irreversible climate changes and impacts,’’ the IPCC said. New, stronger scientific evidence indicates that these impacts may be larger than projected and come sooner than previously expected.

The IPCC, representing scientists from all over the world, shared with Al Gore the 2007 Nobel Peace Prize, which helped ramp up public and political attention to the urgency of taking action on climate change. Meanwhile, some action has been spurred by a combination of international treaties such as the Kyoto Protocol, national policies, and economic forces. From 2005 to 2006, carbon-emissions trading markets tripled, from $10 billion to $30 billion worldwide.

All this has renewed interest in finding ways not only to reduce carbon dioxide emissions but also to remove excess carbon from the atmosphere and sequester it in land-based “sinks” (such as forests), or in the ocean. That has rekindled a spotlight on the oceans’ role in regulating carbon dioxide and climate on our planet.

In the constant exchange between air and sea, carbon dioxide gas enters the oceans and can turn into other inorganic carbon forms. Atmospheric carbon dioxide, an essential ingredient for photosynthesis, is also used by marine phytoplankton, the microscopic plants that account for about half of all the photosynthesis that occurs on Earth. When these phytoplankton die or are eaten, their organic carbon can sink and be sequestered in the deep sea.

In the 1990s, a scientist named John Martin promulgated the “iron hypothesis,” suggesting that if we add small amounts of iron, an essential nutrient, to certain ocean areas, we might turn up the knob on the oceans’ productivity, producing more phytoplankton and maybe decreasing the level of heat-trapping carbon dioxide gas in the atmosphere. Scientists have tested the iron hypothesis in laboratories and in the field for more than a decade. They have verified that iron can stimulate productivity, but it may not necessarily increase long-term ocean carbon storage. Now several companies are embarking on commercial ventures to fertilize the ocean and sell carbon credits for removing carbon dioxide from the atmosphere.

But surely a solution couldn’t be as simple as adding iron “fertilizer” on a large scale to the oceans? Even the most optimistic estimates suggest that ocean iron fertilization could compensate for only a small fraction of total human carbon emissions, and only if we fertilize vast tracts of the ocean. What would be the consequences to ocean ecology and chemistry? Who should regulate and verify an ocean iron fertilization project? Should commercial iron fertilization be allowed to proceed cautiously in a framework of scientific monitoring? Or should it be prohibited given the potential environmental harm and the inherent uncertainties involved in manipulating complex biological systems?

To explore these questions, we set out with a modest goal of bringing together a diverse group of natural and social scientists, policymakers, economists, legal experts, environmental groups, and journalists to spend two days in September 2007 discussing iron, carbon, and plankton in the oceans. We shared what we know about iron’s role in stimulating plankton blooms and increasing ocean carbon storage; about the impacts on the oceans’ ecosystems, chemistry, and circulation; about evidence revealing how the ocean and climate worked in the past; and about computer models that tell us something about how they may operate in the future. We also discussed who might be involved in regulating the high seas, and what economic markets were interested in ocean iron fertilization as a possible method to offset carbon emissions.

We also heard that we don’t understand all of the possible impacts, and we can’t yet predict the full range of consequences of larger-scale ocean iron manipulations. To varying degrees, this is true of all strategies for dealing with climate change: We will have to move forward with uncertainties, whether we simply do nothing or actively pursue some set of strategies.

To make intelligent choices among alternative strategies, we need to assess their likely costs, benefits, and uncertainties. Toward that end, we came together with many different perspectives on what we know and what we would like to know about ocean iron fertilization. We did not come together to approve or disapprove of any particular commercial or research plans. The articles in this volume of Oceanus assemble much of the research and many of the different perspectives on ocean iron fertilization that were presented at our conference.

We hope our conference and this collection of articles shed some light on ocean iron fertilization, an often misunderstood, oversold, and oversensationalized process that has been occurring naturally for millions of years. With new international regulations and public/private partnerships emerging to fund and possibly profit from ocean iron fertilization, the time may be right to pursue a middle ground of longer and larger scientific experiments to improve understanding of ocean iron fertilization and the oceans’ potential for storing carbon.