1998 Year of the Ocean Impacts of Global Climate Change 



The ocean and the atmosphere interact on different time scales. As the time scales change 

 from weather time scales (minutes to weeks) to the longer time scales of climate, the interaction 

 between the ocean and the atmosphere changes as more of the ocean becomes involved. Thus, on 

 weather time scales generally only sea surface temperatures (SST) are involved. At time scales of 

 seasons to years, the upper layers of the ocean (a few hundred meters) have an influence, while at 

 time scales of decades and longer the entire ocean plays a role. The transport of heat by surface 

 ocean currents, for example, modifies mid-latitude temperatures across ocean basins so that land 

 areas on the eastern boundaries of ocean basins are generally warmer than areas at the same 

 latitude on the western boundary. 



The purpose of this document is to consider how the ocean influences weather and 

 climate and to address the barriers to progress and the opportunities presented by the 1998 Year 

 of the Ocean to better understand and predict weather and climate variability. This topic includes 

 seasonal to interannual forecasts, as well as prediction of long term climate change such as 

 temperature and sea level. Because this paper spans such a broad array of considerations, it will 

 be split into three parts: seasonal to interannual climate impacts, decadal to centennial climate 

 impacts, and coastal global climate change impacts. The ocean's influence on weather has its 

 largest economic and social impact on coastal areas and will be considered in the coastal section. 



SEASONAL TO INTERANNUAL CLIMATE IMPACTS 



Introductory Considerations 



The ocean's influence on climate can be split into normal seasonal cycle influences and 

 departures from normal. Commerce, agriculture, and industry have all evolved to operate best 

 with normal seasonal changes. However, changes from the seasonal normal, for example floods 

 and droughts, can lead to economic disruptions and human suffering. Thus, predictions of 

 climate differences from the expected or normal pattern on seasonal and longer time scales can 

 be of great importance to society. 



The best understood, strongest, and somewhat consistent interarmual air-sea climate 

 signal comes from the El Nino/Southern Oscillation (ENSO) which originates in the tropical 

 Pacific. Under normal conditions, the prevailing trade winds blow from east to west and thus 

 contribute to higher ocean temperatures in the west. Associated with these temperatures are a 

 higher sea level and deeper thermocline in the west than the east. (The thermocline is the 

 boundary between warmer surface waters and the colder water below.) In addition, convective 

 rainfall is located in the far western Pacific Ocean over the warmer sea surface temperatures (see 

 the upper panel of Figure 2). In a warm episode (El Nifio), the trade winds weaken and warmer 

 water expands eastward, carrying with it portions of the precipitation. This change includes a 

 reduction of the sea level and thermocline depth in the west and an increase in the east (see the 

 lower panel of Figure 2). There are also cold episodes which are generally the inverses of the 

 warm episode shown in the figure. The term ENSO will be used to refer to both a warm and a 



G-8 



