Recent research has emphasized that “critical mysteries remain” in our ability to quantify or even understand carbon cycle processes as they relate to Earth’s water bodies. Observational constraints prevent the detection of an anthropogenic signal in ocean carbon uptake trends on decadal timescales (McKinley et al., 2017). Many new papers even contradict the IPCC-endorsed conclusion that the oceans are a net sink for CO2 emission rather than a net natural source.
The “We Had No Idea” Terrestrial Carbon Cycle
Since the mid-1980s, the Earth’s coasts and land area have been expanding (Donchyts et al., 2016), meaning there is more land mass above sea level today than there was three decades ago. Sea level rise has not been rapid enough to keep pace with the natural shifts in Earth’s geological processes.
Net growth in global land and soil area could significantly affect the Earth’s carbon budget, especially since “Earth’s soil is releasing roughly nine times more carbon dioxide to the atmosphere than all human activities combined” (Carey et al., 2017).
Scientists frequently “discover” terrestrial locations that are new, unaccounted for sources of natural CO2 emission that “we had no idea” about. They also routinely “discover” terrestrial surfaces that are deemed new CO2 net sinks that they never knew existed (Bastin et al., 2017).
Furthermore, scientists acknowledge that “the heterogeneous and sparsely measured terrestrial biosphere cannot be directly measured” (McKinley et al., 2017).
With new carbon sources and sinks “discovered” on a routine basis, as well as the very limited availability of direct measurements, why should there be any confidence that our land area carbon budget estimates are reliable?
Earth’s Water Bodies: “A Mechanistic Understanding of Carbon Sink Variability Requires Substantial Additional Elucidation”
Scientists have recently acknowledged that “critical mysteries remain” in ocean carbon uptake processes such that we lack a “detailed, quantitative, and mechanistic understanding of how the ocean carbon sink works” (McKinley et al., 2017).
Observational constraints do not even allow us to confirm that the alleged ocean carbon sink has been growing in recent decades due to anthropogenic emissions.
“That the growth of the partial pressure of CO2 gas in the atmosphere ( pCO2 atm) drives a growing oceanic sink is consistent with our basic understanding that, as the globally averaged atmosphere-to-ocean pCO2 gradient increases, carbon accumulation in the ocean will occur at an increasing rate. This behavior has been illustrated clearly with models forced with only historically observed increases in pCO2 atm and no climate variability or change (Graven et al. 2012, Ciais et al. 2013). Nonetheless, critical mysteries remain and weigh heavily on our ability to quantify relationships between the perturbed global carbon cycle and climate change.”
“The current inability to accurately quantify the mean CO2 sink regionally or locally also suggests that present-day observational constraints are inadequate to support a detailed, quantitative, and mechanistic understanding of how the ocean carbon sink works and how it is responding to intensifying climate change. This lack of mechanistic understanding implies that our ability to model (Roy et al. 2011, Ciais et al. 2013, Frolicher et al. 2015, Randerson et al. 2015), and thus to project the future ocean carbon sink, including feedbacks caused by warming and other climate change, is seriously limited.”
“First, substantial uncertainty remains on the mean sink (∼30% of the total flux). Formally, the quantitative estimate of the 1980–1989 sink (−2.0 ± 0.7 Pg C y−1) is not statistically distinguishable from that for 2000–2009 (−2.3 ± 0.7 Pg C y−1). Reducing this uncertainty is absolutely critical to global partitioning of anthropogenic carbon sources and sinks. Each year, the Global Carbon Project (http://www.globalcarbonproject.org) estimates global sources and sinks of carbon, but because the heterogeneous and sparsely measured terrestrial biosphere cannot be directly measured, its flux is estimated by difference from estimated anthropogenic sources and the ocean sink (Le Quer´ e et al. 2015). In these budgets, land use change uncertainty is at least 50% of the mean flux, and uncertainty is growing for emissions from fossil fuel burning and cement manufacture (Ciais et al. 2013). Reduction in ocean sink uncertainty could therefore help to compensate from a global budgeting perspective.”
“The sum of the available evidence indicates that variability in the ocean carbon sink is significant and is driven primarily by physical processes of upwelling, convection, and advection. Despite evidence for a growing sink when globally integrated (Khatiwala et al. 2009, 2013; Ciais et al. 2013; DeVries 2014), this variability, combined with sparse sampling, means that it is not yet possible to directly confirm from surface observations that long-term growth in the oceanic sink is occurring.”
“Globally integrated variability fluctuates with ENSO. Yet, at regional scales outside the equatorial Pacific, these modes tend to explain less than 20% of the large-scale variance in pCO2 ocean and CO2 flux (McKinley et al. 2004, 2006; Breeden & McKinley 2016), indicating that much variance remains undescribed. Consistent with the limited amount of variance explained, the mechanistic connections of these modes are not well understood, except in the equatorial Pacific with ENSO. In the North Atlantic, a variety of studies have suggested a connection of the NAO and AMO to pCO2 ocean and CO2 fluxes, but whether these changes occur through convection or advection remains an open question. In the Southern Ocean, the SAM has been linked to pCO2 ocean and CO2 fluxes through impacts on wind-driven ventilation and subduction; however, since the mid-2000s, the clear relationship to SAM has substantially weakened (Fay & McKinley 2013, Landschutzer et al. 2015). In the North Pacific, the relative influence of the PDO ¨ as opposed to ENSO requires further study. Particularly as observations in the high latitudes have become more abundant, evidence has grown that climate modes do not adequately explain carbon cycle variability and that mechanistic understanding of carbon sink variability requires substantial additional elucidation.”
“[T]his CESM-LE analysis further illustrates that variability in CO2 flux is large and sufficient to prevent detection of anthropogenic trends in ocean carbon uptake on decadal timescales.”
The Earth’s Water Bodies: Net CO2 Source Or Sink?
Observational analysis has indicated that water bodies release more of their stored CO2 as they warm and retain more of their stored CO2 as they cool.
This has been borne out in Mauna Loa CO2 records as they relate to a “warm water year” versus a “cold water year”.
“The recent increase of the CO2-content of air varies distinctly from year to year, rather independent from the irregular annual increase of global CO2-production from fossil fuel and cement, which has since 1973 decreased from about 4.5 percent to 2.25 percent per year (Rotty 1981). … Indeed the cool upwelling water is not only rich in (anorganic) CO2 but also in nutrients and organisms. (algae) which consume much atmospheric CO2 in organic form, thus reducing the increase in atmospehreic CO2. Conversely the warm water of tropical oceans, with SST near 27°C, is barren, thus leading to a reduction of CO2 uptake by the ocean and greater increase of the CO2. … A crude estimate of these differences is demonstrated by the fact that during the period 1958-1974, the average CO2-increase within five selective years with prevailing cool water only 0.57 ppm/a, while during five years with prevailing warm water it was 1.11 ppm/a. Thus in a a warm water year, more than one Gt (1015 g) carbon is additionally injected into the atmosphere, in comparison to a cold water year.”
The Intergovernmental Panel on Climate Change (IPCC) has nonetheless claimed the oceans are a net carbon sink rather than a net source.
Recent research analysis has challenged this conclusion, including several new (2018) published papers.
Astor et al. (2013), for example, found that 72% of the attribution for the increase in CO2 emission for the studied region arose from warming sea temperatures, and thus they concluded “the ocean is primarily a source of CO2 to the atmosphere”.
A Partial List Of Papers Indicating Earth’s Water Bodies Are A Net Source Of CO2
Below is a very non-comprehensive compilation of 12 recently-published papers that challenge the IPCC conclusion that the oceans function as a net sink for CO2.
This list would appear to support the conclusion that “critical mysteries remain” in our ability to quantify or even understand carbon cycle processes as they relate to Earth’s water bodies.