1998 Year of the Ocean Impacts of Global Climate Change 



parts of the globe, these waters can cool sufficiently such that the colder temperatures combined 

 with this higher salt content make them denser than the surrounding fresh waters. When this 

 happens, this cold, dense water sinks and enters into the circulation of the deep ocean. The deep 

 currents of the ocean eventually surface, primarily in the North Pacific, where they enter into the 

 surface circulation again. It takes on the order of 700- 1 ,000 years to complete a single circuit of 

 the global ocean (see Figure 6, the "Conveyor BeU"). 



The ocean is not only an immense reservoir of heat and water but also of carbon dioxide 

 (CO2). On geological time scales, marine biological processes act through the uptake of dissolved 

 CO2 (photosynthesis) and its conversion to inorganic carbonate (which is precipitated as 

 carbonate rock (limestone)) as the major control on CO2 distributions in the Earth's 

 biogeochemical system. On time scales of years, marine biological systems, as with faster 

 growing terrestrial systems, equilibrate fairly rapidly with carbon dioxide in the atmosphere. On 

 longer time scales, transfer of CO2 to woody vegetation, soils, and transfer to the deep ocean 

 removes CO2 from the atmospheric system. The oceanic sink of CO2 is considerably larger than 

 the terrestrial sink. While 10-20 percent of the CO2 emitted to the atmosphere by man's activities 

 has been sequestered by terrestrial processes, some 40 percent of the total COj emitted by man 

 has been removed from the atmosphere relatively permanently by oceanic processes. 



Increased confidence in understanding climate variability, and potential impacts by man 

 on climate can only be obtained through improved representation of ocean climate processes in 

 models, and systematic collection of long-term instrumental observations of climate system 

 variables in the ocean. Key uncertainties limit our ability to detect and project future climate 

 change. In particular, the IPCC 1995 report lists the following as priority topics: 



• "Representation of climate processes in models, especially feedbacks associated with 

 clouds, oceans, sea ice and vegetation, in order to improve projections of rates and 

 regional patterns of climate change." 



• "Systematic collection of long-term instrumental and proxy observations of climate 

 system variables (e.g., solar output, atmospheric energy balance components, 

 hydrological cycles, ocean characteristics, and ecosystem changes) for the purpose of 

 model testing, assessment of temporal and regional variability, and for detection and 

 attribution studies." 



These priorities recognize that predicting climate change resulting from emissions of 

 greenhouse species and formulating future decisions on the possible regulation of these 

 emissions require more accurate models, models which have been adequately tested against a 

 well-designed network of observations. Observations also serve other purposes. Of paramount 

 importance, only observations can detect climate change. In addition, observations can provide 

 increased understanding of climatically important ocean processes. Finally, chemical and 

 physical oceanographic observations provide data needed to separate anthropogenic from natural 

 variability. 



G-18 



