1998 Year of the Ocean Impacts of Global Climate Change 



Status of the Relevant Science and Technical Base 



The ocean interior has a huge capacity to transport and sequester heat, fresh water, and 

 CO, exchanged with the atmosphere at the sea surface. Ocean transports of these play a large role 

 in the present climate and its variability. Coupled ocean-atmospheric models used to predict 

 global temperature changes have shown that the ocean sequestration has the potential to delay the 

 impact of greenhouse gas emissions and thus affect changes in atmospheric conditions. These 

 latter changes occur both directly by the oceanic uptake of 30-60 percent of the anthropogenic 

 COt currently produced, thereby attenuating the atmospheric COj increase, and indirectly by 

 buffering the atmospheric temperature increase due to the ocean's large thermal mass. 



The present state of models and sparse observations are factors that lead to uncertainties 

 in estimates of oceanic transport, uptake and sequestration. For example, the current coupled 

 General Circulation Models (GCMs) used to simulate climate change fail to produce long-term 

 trends in Pacific sea-surface temperature. Observationally, three estimates of the transport of heat 

 from south to north at 24°N in the Atlantic show a steady rise from 1957 through 1992. 

 Available data can not resolve if these changes represent a natural or an anthropogenic induced 

 trend and/or whether they are biased by an unresolved annual signal. Furthermore, the 

 uncertainty in ocean dissolve inorganic carbon uptake is 40 percent of the total (2.0 billion 

 metric tons of carbon per year). These uncertainties must be reduced if confidence in CO, 

 warming scenarios is to increase. 



Models complemented by observations provide the means to distinguish between natural 

 variability on decadal to centennial time-scales and anthropogenic climate change. For example, 

 a recent modeling study looked at a long term record of observed and simulated atmospheric 

 temperature and found the rates of recent increases in temperature in both data sets to be similar. 

 These rates are unprecedented in terms of the longer model record suggesting that the recent 

 increases could be related to CO, effects. 



An effective approach to improve the representation of climatically important ocean 

 processes in models is to test hypotheses on the dynamics of naturally occurring, coupled air-sea 

 interactions that are found in models and observations. Several candidate hypotheses exist. For 

 example, a model forced only by seasonally varying solar radiation at the top of the atmosphere 

 includes coupling on decadal time scales between two atmospheric patterns — a connection 

 between the Pacific and North America known as the PNA pattern and a North Atlantic pattern 

 known as the North Atlantic Oscillation (NAO) — and the upper layers of the northern 

 hemisphere middle latitude ocean. The NAO is a seesaw pattern in sea-level pressure with nodes 

 over the Bermuda High and Icelandic Low. Both atmospheric features have been shown to have 

 significant impact on U.S. and European climate on many time scales. On decadal time scales 

 this could mean multiple years of weather regimes, like drought in the Southwestern United 

 States or floods in the South Atlantic states. Observational studies of coupled air-sea interactions 

 using recently collected data find similarities between the measurements and the coupled model 

 results on decadal time scales in both the North Atlantic and Pacific basins. However, the 



G-20 



