Can we trust empirical marine DMS parameterisations within projections of future climate?

[摘要] Dimethylsulphide (DMS) is a globally important aerosol precurser. In 1987Charlson and others proposed that an increase in DMS production by certainphytoplankton species in response to a warming climate could stimulateincreased aerosol formation, increasing the lower-atmosphere's albedo, andpromoting cooling. Despite two decades of research, the global significanceof this negative climate feedback remains contentious. It is thereforeimperative that schemes are developed and tested, which allow for therealistic incorporation of phytoplankton DMS production into Earth Systemmodels. Using these models we can investigate the DMS-climate feedback andreduce uncertainty surrounding projections of future climate. Here we examinetwo empirical DMS parameterisations within the context of an Earth Systemmodel and find them to perform marginally better than the standard DMSclimatology at predicting observations from an independent global dataset. Wethen question whether parameterisations based on our present understanding ofDMS production by phytoplankton, and simple enough to incorporate into globalclimate models, can be shown to enhance the future predictive capacity ofthose models. This is an important question to ask now, as results fromincreasingly complex Earth System models lead us into the 5th assessment ofclimate science by the Intergovernmental Panel on Climate Change. Comparingobserved and predicted inter-annual variability, we suggest that futureclimate projections may underestimate the magnitude of surface ocean DMSchange. Unfortunately this conclusion relies on a relatively small dataset,in which observed inter-annual variability may be exaggerated by biases insample collection. We therefore encourage the observational community to makerepeat measurements of sea-surface DMS concentrations an important focus, andhighlight areas of apparent high inter-annual variability where samplingmight be carried out. Finally, we assess future projections from twosimilarly valid empirical DMS schemes, and demonstrate contrasting results.We therefore conclude that the use of empirical DMS parameterisations withinsimulations of future climate should be undertaken only with carefulappreciation of the caveats discussed.

[学科分类] 地球化学与岩石