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Climate Change & Global Warming
Does the Ocean Climate Vary Over Time?
On land, we do not always have the same weather patterns. That is, conditions do not match the climatology. Summers may be warmer or cooler than average. Winters may have more snow than usual. Droughts and heat waves occur. We call this "interannual variability". Differences from the average values are called anomalies. Anomalies can be positive (greater than the mean) or negative (less than the mean). The ocean climate also has interannual variability.
In addition to seasonal and intra-annual (less than annual) variations, there are multiyear patterns of variability. Ocean conditions fluctuate on various time scales. El Niño and La Niña events can occur every 3 to 5 years. Their anomalous effects usually last one to two years in the atmosphere, and often longer in parts of the ocean. Ocean conditions that stay above or below the long-term average for about 10 to 20 years are termed decadal-scale patterns. Sometimes sudden changes in decadal-scale patterns occur that are called "regime shifts". The average ocean conditions before a regime shift are different from the average conditions after the shift. A large regime shift occurred in the North Pacific Ocean about 1976, affecting both the physical state of the ocean and the structure of marine ecosystems and populations of fish such as salmon in the North Pacific Ocean.
Click on image to enlarge
Click on image to enlarge
Climate change often is characterized by summaries such as time series of national or global averages of temperature, which imply that climate change is uniform in space for the entire planet. In fact measurements and computer models show the trends in factors that describe climate, such as temperature and precipitation, vary regionally. For example, the global average temperature has risen by about 0.6°C (1.0°F) over the past century (IPCC 1996). However some subarctic regions have experienced greater than 1.5°C warming since the middle of this century (IPCC 1996). Other areas, such as portions of the North Pacific Ocean, are now actually cooler than they were 50 years ago.
