The ocean is absorbing less carbon dioxide
Premier among their many unscientific beliefs, deniers cling to the notion that some magical negative feedback will avert serious climate impacts. Sadly, we will need magic to save humanity if we foolishly decide to listen to the deniers and to keep ignoring the one negative feedback that science says can certainly save humanity — simply reducing greenhouse gas emissions.
The scientific reality based on actual observations (not to mention the paleoclimate record) is that the climate models are not underestimating negative feedbacks — the models are wildly underestimating the positive or amplifying feedbacks. Among the greatest concerns is the growing evidence that the major carbon sinks are saturating, that a greater and greater fraction of human emissions will end up in the atmosphere.
A new study in Geophysical Research Letters ($ub. req’d), “Sudden, considerable reduction in recent uptake of anthropogenic CO2 by the East/Japan Sea,” finds,
The results presented in this paper indicate that the rate of CO2 accumulation in the deepest basin of the East/Japan Sea has considerably decreased over the transition period between 1992-1999 and 1999-2007.
The authors explain to the U.K.’s Guardian why this is an amplifying feedback, why warming is diminishing the ability of the ocean sink to absorb CO2:
The world’s oceans soak up about 11bn tonnes of human carbon dioxide pollution each year, about a quarter of all produced, and even a slight weakening of this natural process would leave significantly more CO2 in the atmosphere. That would require countries to adopt much stricter emissions targets to prevent dangerous rises in temperature.
Kitack Lee, an associate professor at Pohang University of Science and Technology, who led the research, says the discovery is the “very first observation that directly relates ocean CO2 uptake change to ocean warming”.
He says the warmer conditions disrupt a process known as “ventilation” — the way seawater flows and mixes and drags absorbed CO2 from surface waters to the depths. He warns that the effect is probably not confined to the Sea of Japan. It could also affect CO2 uptake in the Atlantic and Southern oceans.
“Our result … unequivocally demonstrated that oceanic uptake of CO2 has been directly affected by warming-induced weakening of vertical ventilation,” he says …
Lee adds: “In other words, the increase in atmospheric temperature due to global warming can profoundly influence the ocean ventilation, thereby decreasing the uptake rate of CO2.”
This study matches other recent research on ocean sink saturation. In 2007, the BBC reported, “The amount of carbon dioxide being absorbed by the world’s oceans has reduced” based on more than 90,000 ship-based measurements of CO2 absorption over ten years. The Global Carbon Project analysis of the “natural land and ocean CO2 sinks” finds:
… the efficiency of these sinks in removing CO2 has decreased by 5% over the last 50 years, and will continue to do so in the future. That is, 50 years ago, for every ton of CO2 emitted to the atmosphere, natural sinks removed 600 kg. Currently, the sinks are removing only 550 kg for every ton of CO2 emitted, and this amount is falling.
Equally ominous, many existing carbon sinks are increasing their emissions because of global warming — and the major climate models are missing these key amplifying feedbacks.
These myriad unmodeled amplifying feedbacks support the analysis that the climate is much more sensitive to changes in greenhouse gas emissions and other “forcings” than the IPCC models have been saying. In turn, this suggests that a doubling of atmospheric concentrations of carbon dioxide from preindustrial levels to 550 ppm will ultimately warm the planet far more than 3°C, as NASA’s James Hansen argues (see ‘Long-term’ climate sensitivity of 6°C for doubled CO2).
A number of major studies looking at paleoclimate data come to the same conclusion. Here are three:
- Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature ($ub. req’d), found Arctic temperatures almost beyond imagination — above 23°C (74°F) — temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.
- A second study, published in Geophysical Research Letters ($ub. req’d), looked at temperature and atmospheric changes during the Middle Ages. This 2006 study found that the effect of amplifying feedbacks in the climate system — where global warming boosts atmospheric CO2 levels — “will promote warming by an extra 15 percent to 78 percent on a century-scale” compared to typical estimates by the U.N.’s Intergovernmental Panel on Climate Change. The study notes these results may even be “conservative” because they ignore other greenhouse gases such as methane, whose levels will likely be boosted as temperatures warm.
- The third study, published in Geophysical Research Letters ($ub. req’d), looked at temperature and atmospheric changes during the past 400,000 years. This study found evidence for significant increases in both CO2 and methane (CH4) levels as temperatures rise. The conclusion: If our current climate models correctly accounted for such “missing feedbacks,” then “we would be predicting a significantly greater increase in global warming than is currently forecast over the next century and beyond” — as much as 1.5°C warmer this century alone.
Yes, natural negative feedbacks exist that would “eventually” absorb any excess carbon dioxide, but as one of the authors of a 2008 Nature Geosciences article explained, “not for hundreds of thousands of years” (see “Humans boosting CO2 14,000 times faster than nature, overwhelming slow negative feedbacks“).
As one recent study of the water vapor feedback concluded:
The existence of a strong and positive water-vapor feedback means that projected business-as-usual greenhouse-gas emissions over the next century are virtually guaranteed to produce warming of several degrees Celsius. The only way that will not happen is if a strong, negative, and currently unknown feedback is discovered somewhere in our climate system.
In short, absent the magical deus ex machin
a negative feedback, we are facing catastrophic 5-7°C warming by 2100 on our current emissions path, just as the Hadley Center recently warned.
Truly only one negative feedback in the planet’s overall carbon cycle can act with sufficient speed and strength to avert catastrophic climate impacts: The dominant carbon-based life form on this planet will have to respond to the already painfully clear impacts of our carbon emissions by slashing those emissions sharply and eventually running the planet on carbon-negative power.
The time for this negative feedback is now.