One of the most hyped of the catastrophic consequences climate alarmists claim will result from predicted CO2-induced global warming is the rise in sea level we are told will result from the melting of glacial ice and the thermal expansion of ocean water. Thanks to the contribution of a newly-recognized negative feedback factor, however, this tale of gloom and doom may not play out quite the way we have been led to believe it will.
Surmising the existence of this heretofore unheralded phenomenon, Choi et al. (2001) descended upon the coastal marshes of the St. Marks National Wildlife Refuge in Wakulla County, Florida, USA. There they took numerous plant and soil samples along a transect stretching from low marsh to middle marsh to high marsh, which finally grades into upland forest. Back in the laboratory, they measured the carbon contents of these samples along with their stable carbon isotope ratios.
In the low marsh, which is the oldest part of the wetland, the total organic carbon content in the upper 86 cm of soil averaged 29 ± 3.6 kg/m2. In the middle marsh, the carbon content of the same depth of soil averaged 15 ± 3.6 kg/m2; and in the high marsh, the soil carbon content averaged 13 ± 6.0 kg/m2. In comparison, the soils of the adjacent forests contained only 5 to 10 kg/m2 organic carbon. Relative to the mean of the upland forest, therefore, the high marsh contained 73% more soil organic carbon, the middle marsh 100% more, and the low marsh 287% more.
From the results of the stable carbon isotope ratios obtained at different depths within the soil profiles of the several sites, the scientists determined there had been a shift in the local vegetation over the past hundred years characteristic of what would be expected by rising sea levels and consequent inundation of the land. That is, what was once high marsh had become middle marsh and then low marsh; and throughout this transformation of the landscape, soil carbon contents had grown ever larger as the sea invaded the land.
But how does it happen? "The increased accumulation of soil organic carbon," in the words of Choi et al., "is the result of reduced decomposition and increased primary production," two phenomena that are also promoted by atmospheric CO2 enrichment, as we have noted in earlier installments of this series of reports. In the specific wetland studied by the scientists, for example, productivity increased from 243 g/m2/year in the high marsh to 595 g/m2/year in the middle marsh to 949 g/m2/year in the low marsh. In addition, other studies of marshes in the same general area have indicated they are four to five times more productive than the adjacent upland forests (Krucznski et al., 1978; Hsieh, 1996) and that their soils store fully ten times more organic carbon than do those of the forests (Coultas, 1996).
What are the implications of these findings? To quote Choi et al., "carbon is being sequestrated into soils as coastal wetland evolves from high marsh to low marsh," i.e., as sea level rises, which, the scientists say, "would provide a significant sink for atmospheric carbon dioxide," again, as sea level rises. Consequently, if the natural rate of sea level rise continues unabated - or accelerates somewhat in response to additional natural warming, as we continue to recover from the global chill of the Little Ice Age and move further into the Modern Warm Period - there will likely be a significant increase in the rate of removal of CO2 from the atmosphere as a consequence of this important negative feedback, which would tend to temper the warming and reduce the rate of sea level rise.
The bottom line, therefore, is one we have seen time and time again. Earth's enormously complex climate system is chock full of negative feedback mechanisms that operate in such a way as to continuously maintain the planet's temperature within the narrow range required for the continued existence of life. Furthermore, life itself plays a major role in this enterprise, one avenue of which is enhancing biological carbon sequestration in the face of both rising temperatures and sea levels.
| Dr. Sherwood B. Idso | Dr. Keith E. Idso |
References
Choi, Y., Wang, Y., Hsieh, Y.-P. and Robinson, L. 2001. Vegetation succession and carbon sequestration in a coastal wetland in northwest Florida: Evidence from carbon isotopes. Global Biogeochemical Cycles 15: 311-319.
Coultas, C.L. 1996. Soils of the intertidal marshes of Florida's Gulf Coast. In Coultas, C.L. and Hsieh, Y.-P. (Eds.), Ecology and Management of Tidal Marshes, St. Lucie Press, Delray, FL, pp. 53-75.
Hsieh, Y.E.P. 1996. Assessing aboveground net primary production of vascular plants in marshes. Estuaries 19: 82-85.
Krucznski, W.I., Subrahmanyam, C.B. and Drake, S.H. 1978. Studies on the plant community of a north Florida salt marsh. Bulletin of Marine Science 28: 316-334.