Last summer, in an unseasonal event, more than 100 miles of Florida’s coast around Tampa Bay became an oxygen-depleted dead zone littered with fish along the nearby shoreline. In the Northwest, Dungeness crabs were washing onto Oregon’s beaches, unable to escape from water that has, in dramatic episodes, become seasonally depleted of oxygen over the past two decades.
Much of the conversation around our climate crisis highlights the emission of greenhouse gases and their effect on warming, precipitation, sea-level rise and ocean acidification. We hear little about the effect of climate change on oxygen levels, particularly in oceans and lakes. But water without adequate oxygen cannot support life, and for the three billion people who depend on coastal fisheries for income, declining ocean oxygen levels are catastrophic.
As ocean and atmospheric scientists focused on climate, we believe that oceanic oxygen levels are the next big casualty of global warming. To stop the situation from worsening, we need to expand our attention to include the perilous state of oceanic oxygen levels—the life-support system of our planet. We need to accelerate ocean-based climate solutions that boost oxygen, including nature-based solutions such as those discussed at the 2021 United Nations Climate Change Conference (COP26) held in Glasgow.
As the amount of carbon dioxide increases in the atmosphere, not only does it warm air by trapping radiation, it warms water. The interplay between oceans and the atmosphere is complex, but to put it simply, oceans have taken up about 90 percent of the excess heat created by climate change during the Anthropocene. Bodies of water can also absorb CO2 and oxygen but only up to a limit: warmer water holds less oxygen. This decrease in oxygen content, coupled with a large-scale die-off of oxygen-generating phytoplankton resulting not just from climate change but from plastic pollution and industrial runoff, compromises ecosystems, asphyxiating marine life and leading to further die-offs. Large swaths of the oceans have lost 10 to 40 percent of their oxygen, and that loss is expected to accelerate with climate change.
The dramatic loss of oxygen from our bodies of water is compounding climate-related feedback mechanisms described by scientists in many fields, hundreds of whom signed the 2018 Kiel Declaration on Ocean Deoxygenation. This declaration has culminated in the new Global Ocean Oxygen Decade, a project under the U.N. Ocean Decade (2021–2030). Yet despite years of research into climate change and its effect on temperature, we know comparatively little about its effect on oxygen levels and what falling oxygen levels, in turn, may do to the wider earth system.
As the financial world invests in climate change solutions, possibly including future geoengineering efforts such as iron fertilization, we run the risk of exacerbating oxygen loss. We need to evaluate potential unintended consequences of climate solutions for the full life-support system.
Beyond enhanced monitoring of oxygen and the establishment of an oxygen-accounting system, such an agenda encompasses fully valuing the ecosystem co-benefits of carbon sequestration by our ocean’s seaweed, seagrasses, mangroves and other wetlands. These so-called blue carbon nature-based solutions are also remarkable at oxygenating our planet through photosynthesis. At COP26 we saw a lot of primarily terrestrial initiatives and commitments, such as for forestry management, that are excellent steps forward. We hope the 2021 climate conference and this year’s COP27 meeting help oceanic nature-based solutions to come into their own, propelled by the U.N. Ocean Decade.
Putting oxygen into the climate story motivates us to do the work to understand the deep systemic changes happening in our complex atmospheric and oceanic systems. Even as we celebrated the return of humpback whales in recent years to an increasingly clean New York Harbor and Hudson River, dead fish clogged the Hudson in the summer as warmer waters carried less oxygen. Ecosystem changes connected to physical and chemical systems-level data may point the way to new approaches to climate solutions—ones that encompass an enhanced understanding of the life-support system of our planet and complement our understanding of drawdown to reduce emissions of CO2. Roughly 40 percent of the world’s people depend on the ocean for their livelihoods. If we do not save marine life from oxygen starvation, we starve ourselves.”