The Changing Ocean in the CeNCOOS Region

Are the ocean and coastal climate of Northern and Central California changing? This page summarizes the types of ocean changes to look for, how they could happen, and what recent and historic scientific information tells us. We also discuss forecasts by scientists about these ocean changes and how the ocean in turn may impact coastal climate, economies and wildlife.

Explore the links and images below to discover what scientists are finding and what it may mean.  Many different programs are working to monitor and share information on the changing ocean and climate in California. Much of this page was guided by the findings of the report: "Climate Change Impacts: Gulf of the Farallones and Cordell Bank National Marine Sanctuaries", a report created with help from CeNCOOS partners and staff.

What is CeNCOOS Doing to Inform Our Region on this Issue?

  • Funding stations collecting data useful for detecting ocean and coastal changes
  • Promoting partnerships among researchers and managers to discuss how data can be used for planning
  • Providing data and analysis through our website
  • Sharing information and resources with the Bay Area Ecosystem Climate Change Consortium
  • Working with local partners to run a Monterey Bay Climate Change Adaptation Workshop in November 2011
  • Linking shellfish growers to information on ocean acidification

What Changes Could be Happening to the California Ocean and Coast?

Topics: Sea Level | Ocean Temperature | Ocean Acidification | Waves and Storms | Coastal Upwelling | Air Temperature | Coastal Rivers and Streams | Sources Cited

Sea level trends

Monthly-averaged sea levels from San Francisco from 1855 through 2008. The red line shows a smoothed version that suppresses the influence of short and longer-period oscillations such as ENSO episodes and the Pacific Decadal Oscillation. (Figure contributed by Larry Breaker, MLML). View expanded image.

NOAA sea level map NOAA coastal sea level trends map (30+ yrs of data). Go to webpage.
Ocean Temperature Plots

NODC-NOAA 1880-2010 Global Sea Surface Temperature Anomaly (top). Click to enlarge

Graphs of ocean temperature recorded by Hopkins Marine Station in Pacific Grove, CA. A plot of data from 1920-2010 (top, provided by Larry Breaker) shows a slight increase, while data from 2002-10 suggests a slight decrease (bottom). Click images to enlarge.
Ocean pH and pco2 trends
Measurements of pCO2 and pH were collected on ship transects from 1993-2008 in Monterey Bay. Trendlines show CO2 increased in ocean water and the atmosphere (top) while pH decreased in Monterey Bay and Hawaii waters (bottom). Plots provided by Dr. Francisco Chavez (MBARI). Click to enlarge
Wave height trends
Trends in wave height (cm/decade) for regions along the major ship routes of the global ocean for 1950 to 2002. Red areas are increasing, blue are decreasing. Only significant wave height trends are shown. Adapted from Gulev and Grigorieva (2004). IPCC. Click to enlarge

CeNCOOS online product with daily wave heights for comparison with a long-term average since 1997 at a NDBC buoy offshore Pt. Reyes, CA. Go to the webpage.
Coastal Upwelling trends

Trends of coastal upwelling derived from the HadISST dataset (Rayner et al., 2003) for the period 1960-2006. There was a significant increase in upwelling. Figure from Narayan et al. 2010. Click to enlarge image.
Air Temperature and Coastal Fog Trends

Trends in air temperature records from select locations near the coast from San Francisco to Los Angeles (top) and central valley/coastal hills (bottom) 1970-2005. Rate of change for the daily temp range is provided on the plot. From Lebassi et al. (2009).Click images to enlarge.

This Western Regional Climate Center plot shows central coast 1895-2010 annual air temperature variation from a 1949-2005 mean. A running mean line (average of 5 yrs before and after each point) is also included. Click to enlarge image

Plot created by Johnstone and Dawson (2010). Fog frequency, the percentage of the year that fog existed, was combined from two locations with similar trends to get a Northern California index (black line on plot). A peak in fog was in 1951 and low in 1997 are depicted. Copyright (2010) National Academy of Sciences, U.S.A.. Click to enlarge image

Coastal Freshwater trends

This Western Regional Climate Center plot shows central coast 1895-2010 annual rainfall variation from a 1949-2005 mean. A running mean line (average of 5 yrs before and after each point) is also included. Click to enlarge image

1. Sea Level

Cause: Major changes in ocean volume, raising or lowering sea level on the coast, result from two main factors. Melting of ice on land near the poles adds water to the sea. Less obviously, water expands as it warms, so the more heat energy the ocean absorbs, the more space its water requires (Domingues et al. 2008).

Recent Data: Sea level recorded at a water level station at the mouth of San Francisco Bay is considerably higher today than a century ago (see image at right). However, as of 2008, sea level at this station and some other areas of central and northern California have been stable or even decreasing since 2000. Explanations for this sea level drop include the trend toward colder ocean temperatures along the California coast beginning in 2000, possibly the result of a shift to the cooler ocean water phase of the Pacific Decadal Oscillation (PDO) or increases in coastal upwelling (discussed in sections 2 and 5 below). As the ocean cools it contracts, which tends to lower sea level. Increased movement of ocean surface water from the coast to further offshore due to increased upwelling also contributes to lower sea levels. Sea level rise in California may once again resume with the the next PDO shift, decreases in upwelling or an increase in ice melt entering the ocean from the land near the Artic or Antarctic (see Ramp et al. 2009 CeNCOOS story for more). See the NOAA Coastal Sea Level Trends Map webpage for long-term sea level rise in your area.

Projections: Sea level is forecast to rise 15 inches (40 cm) by 2050 and 55 inches (140 cm) by 2100 based on medium-high CO2 emissions (Rahmstorf 2007, Cayan et al. 2008). Although California state managers are using these estimates, which assume an accelarated sea level rise in the near future. These projections include much uncertainty, including how long the current sea level decrease will last in California and other factors such as differences in tectonic uplift rates along the coast.

Impacts: Even a very small amount of sea level rise can result in inundation of huge areas of low-lying land. Sea level rise can lead to increased: coastal flooding, shoreline erosion, disruption of ecosystems and saltwater intrusion. All of these will threaten homes, businesses and more! See the Cal-adapt interactive sea level maps showing potential California coastal inundation in your area.

2. Ocean Temperature

Cause: The ocean, which covers 70% of the planet, stores about 90% of the Earth's heat entering the atmoshphere from the sun. The heat absorbed by ocean water is released over long periods of time. Heat absorbed by the ocean is moved from one place to another, but it does not disappear. If the ocean absorbs more heat than it releases, the temperature will increase. Conversely, less heat absorption will lead to cooler ocean. However, wind patterns, ocean circulation and other factors such as upwelling play a large role in how cold the ocean will be in your area.

Recent Data: Global sea surface temperature anomalies, or differences from average, have generally increased in the last century (see plot on right column), while the temperatures off California during this same period have increased marginally (Palacios et al. 2004). In fact, nearshore central and northern California waters have been cooling since at least 2002 (see plot on right column) and possibly since 1980 (Garcia-Reyes and Largier 2010). This trend may be due to increased upwelling winds bringing colder waters from depth (see section 5).

- The CeNCOOS Data Portal (CDP) provides real-time and historic temperature (and other) data collected from shore stations and buoys in our region.

- Plots of current vs. historic temperatures in Monterey Bay (from MBARI buoy)

Projections: Researchers are currently studying long-term ocean temperature trends to identify patterns and potential causes for changes in order to predict future conditions. It has been suggested that global climate pattern changes are responsible for the recent cooling trend in the ocean off California. If true, California would continue to see colder ocean temperatures well into the future.

Impacts: Ocean temperature effect everything from coastal weather (see section 6)to ocean ecosystems. Marine life must attempt to adapt to changing temperatures or migrate to other areas (if possible). Changes may favor certain species, which may not be benefitial to humans living near and using the ocean.

3. Ocean Acidification

Cause: World oceans have absorbed almost one-half (~525 billion tons) of human-released carbon dioxide (CO2) emissions since the Industrial Revolution. This has moderated the effect of greenhouse gas emissions, but it is chemically altering the oceans 100 times more rapidly than it has changed in the last 650,000 years (Rogelj et al. 2009). CO2 absorbed in ocean waters in high enough amounts can raise the pH level (a measure of acidity). This is important because as seawater becomes more acidic, the amount of dissolved carbonate available for calcium carbonate shell and skeleton formation – important to corals, plankton and shellfish – decreases.

Recent Data: Ocean pH is currently decreasing and CO2 is increasing (possibly faster than in the atmosphere) in California and global ocean waters (see image at right). CeNCOOS is taking hourly measurements of pH at shore stations in Humboldt Bay and Trinidad (in partnership with at Humboldt State University). Monterey Bay Aquarium Research Institute (MBARI) deployed two ocean acidification monitoring buoys at the north end of Monterey Bay in April 2011, CeNCOOS displays the MBARI data.

Projections: Acidity will continue to increase with increased CO2 emissions, but it is unknown whether the ocean will continue to absorb CO2 at the same rate it has in the past. Negative impacts on shell forming sea life may increase slowly or accelerate beyond an unknown threshold point. Photosynthetic organisms living in oceans may increase as CO2 becomes more available.

Impacts: More acidic oceans may impact animals eaten by humans (clams, oysters etc.), important habitat forming organisms like coral reefs (yes there are corals in California!), and plankton species that are food for many fish species and other wildlife like whales. Impacts may have already been seen by aquaculture businesses on the West Coast of the U.S.. Read more about this problem:
- Climatide article "Discovery of the year: ocean acidification is happening NOW"
- UC Davis experiments show shellfish growth is impacted when raised in more acidic water
- West Coast Ocean Acidification Shellfish Workshop report
- NOAA Report on Pacific Oysters and Ocean Observing
In addition, larger and more frequent algal blooms occuring in California and the northwest in recent years may be partially due to increased CO2 levels in the ocean.

4. Waves and Storm Events

Cause: Before reaching California, storms cross the Pacific Ocean and are greatly affected by the ocean itself. Higher sea surface temperatures in the open Pacific (far offshore) can lead to greater wave heights on the U. S. West Coast (Graham and Diaz 2001). El Niño and La Niña events generate large storms in the Pacific, often leading to large waves in California (Allan and Komar 2006). El Niño events cause a shift to a more southerly angle of approach for storm systems hitting the California coast, leading to larger storms (Storlazzi and Griggs 2000). Major storms bring large waves as well as heavy rainfall and high winds. Variation in local winds near the coast of California not associated with storms can also change the pattern and size of waves reaching the shoreline throughout the year.

Recent Data: Bromirski et al. (2003) showed a significant increase in intense winter storms since 1950 using San Francisco Bay water level data from 1858 to 2000. Data collected on shipping routes show waves got higher from 1950-2002 along the U.S. West Coast including California (see wave height map at right). Based on a buoy network operating along the US Pacific Coast since the 1980s, and voluntary observer ship data, northern California's waves have increased by an average rate of about 1.5-2 cm per year. Increases in wave heights for central California are not statistically significant (Wingfield and Storlazzi 2007). The change in mean wave height in northern California is largely attributable to an increase in peak storm waves as opposed to average waves throughout the year (Menendez et al. 2008). A CeNCOOS product for comparing northern California today's wave height with long-term averages is available through our website (see this product on right column).

Projections: If ocean temperatures continue to increase, more intense storms with larger waves, erosion and runoff will result. El Nino and La Nina years will continue to have the largest storms in the future. Resulting coastal erosion is estimated to reach nearly 50 square km by 2100 (PWA 2009a).

Impacts: The observed long-term increase in wave heights (particularly extreme wave heights) poses significant risks. Since El Niño events typically bring the largest recorded waves (Seymour 1998) and occur in late winter when most beaches are at their narrowest width, they are often the cause for the majority of coastal erosion, flooding, and property loss (Wingfield and Storlazzi 2007). Coastal erosion will cause damage to coastal homes and businesses and could increase risks for public use of coastal areas. Larger waves may impact certain sensitive ocean species and habitats. Changes in patterns of beach sand movement, estuary mouth structure and ocean inundation to coastal areas may also occur.

5. Coastal Upwelling

Cause: Coastal ocean upwelling is a feature of the northern and central Califonia coast that creates a productive ocean ecosystem and supports extensive and diverse fisheries. Upwelling results from the offshore transport of near-surface water (known as Ekman transport) due to alongshore winds from the north and the influence of the earth’s rotation (the coriolis effect). This water is replaced with cold, salty, nutrient rich water from depths below. Changes in patterns of coastal winds can alter the strength and timing of upwelling events.

Recent Data: Upwelling is increasing in central California and possibly beyond (García-Reyes and Largier 2010, Narayan et al. 2010, see figure at right). Data from the last 30 years collected by oceanographic buoys and coastal stations indicate increased winds and colder coastal ocean waters. As the earth warms, the land is expected to heat up faster than the ocean, likely increasing alongshore winds in coastal California that drive upwelling (Mendelssohn and Schwing 2002, Garcia-Reyes and Largier 2010). Increased upwelling may have contruted significantly to recent cooler ocean surface temperatures along the California coast.

Projections: Upwelling will continue to increase as the North American continent warms if the current pattern continues.

Impacts: Increased supply of nutrients to light-filled surface waters could create more productive ecosystems but also could cause more harmful algal blooms. There is the potential for increased transport of plankton and fish/invertebrate eggs/larvae to offshore waters where survival is more difficult for some species. Nearshore surface waters on the California coast will likely become colder.

6. Air Temperatures - Ocean Impacts

Cause: The temperature of the ocean offshore California has a strong effect on coastal California air temperatures. Coastal upwelling and other factors explain why the coast is often much cooler than inland California during spring and summer. Therefore, if ocean temperatures change, coastal air temperatures may follow. Another factor that can affect coastal air temperatures is fog, which often shrouds the California coastal areas from late spring to early fall. This 'advection' fog forms when warm, moisture laden air from far offshore California condenses as it is blown across the band of cold ocean surface along the coast. Therefore, recent colder ocean temperatures might be expected to increase coastl fog, in turn decreasing air temperatures.

Recent Data: A recent study by Lebassi et al. (2009) indicates that summer air temperatures at inland sites of California are warming while coastal low lying areas have actually cooled since the late 1940s (see graphs at right). However, data from the Western Regional Climate Center indicates central coast temperatures increased from 1950-97 and decreased through 2010 (see image on right column). Differences in these time-series may be due to locations of sampling stations, but both suggest air temperatures are currently decreasing on the central coast. Johnstone and Dawson (2010) analyzed cloud ceiling height data from Arcata and Monterey, California, from 1951 to 2008 (see image at right). There was a decrease in fog from the mid-70's through the late 90's, during a period of generally warmer ocean temperatures. Since 2002, when water temperatures began decreasing off coastal California, the same study showed fog has been fluctuating from year to year. Other data show onshore movement of marine air (winds) has increased recently. Therefore it is possible that the lower ocean temperatures combined with increased winds blowing cool air onto the coastal areas has resulted in decreased air temperatures. CeNCOOS supports weather stations along the coast monitoring air temperatures.

Projections: Potentially drastic changes in clouds, wind and air temperatures in coastal California.

Impacts: Changes in cloud cover, wind patterns and air temperatures may alter coastal agricultural practices and ocean ecosystems.

7. Coastal River and Stream Changes

Cause: California precipitation amounts and types (rain vs. snow) as well as river and stream temperatures can be impacted by global changes in the climate. Locally, periods of drought will reduce river flows, while unusually large rainfall events may cause flood events. If the Sierras receive less snowfall and more rain due to warmer air temperatures, the highest flows in major rivers reaching the SF Bay Delta and other areas will be shifted from late spring to earlier in the season. Warmer air temperatures in the Sierras, central valley or coast will tend to increase freshwater temperatures as well. During the dry months in California, the flow from the Sacramento and San Joaquin Rivers to San Francisco Bay and the ocean is primarily due to snowmelt from the snowpack covering the Sierra Nevada range. This snowpack acts as a natural reservoir, delaying runoff from winter precipitation (Kiparsky and Gleick 2005). Northern and Central California coastal rivers and streams flow into the ocean, adding important nutrients as well as unwanted pollutants, but also serving as important migratory pathways for aquatic animals.

Recent Data: Precipitation and monthly mean streamflow throughout California have increased since the early 20th century (Lettenmaier et al. 1994, Mote et al. 2005). Most of this increase in freshwater runoff is apparently due to more extreme single-day precipiation events (Kundzewicz et al. 2007). Global climate models show California precipitation will likely continue to increase, especially in northern California, but the resolution of these models is low (Kim et al. 2002). Analyses by the Dept. of Water Resources (DWR 2006) show a slight increase in precipitation in northern California, as opposed to a decrease for central California from 1890-2002.

Projections: A shift in the timing of peak streamflow events is seen in historical observations and modeling efforts (Stewart et al. 2005). Rising air temperatures will likely result in less snowfall and a retreat of Sierra snow cover in northern and central California. This would lead to an increase in runoff during winter months, a decrease in runoff during spring and summer, and a higher annual peak runoff (Kiparsky and Gleick 2005). Precipitation may become more variable from year to year, while heavy precipitation events will become more prevalent (DWR 2006, Kundzewicz et al. 2007).

Impacts: Coastal freshwater is vital to many components of California's economy and ecology. People rely on coastal freshwater supplies for drinking, household uses, agriculture, etc. More variability in precipitation from year to year may lead to droughts (such as the California drought 2007-09) that will impact coastal society and ecosystems as well as floods that can destroy houses and businesses (such as those seen in 2011). More frequent extreme winter precipitation events and a more rapid melting of Sierra snowpack in spring may lead to increased flooding and changes to estuaries and nearshore ocean systems. Droughts as well as floods are generally not benefitial to coastal freshwater, estuarine and neashore marine animals, including economically important species such as salmon that must return to rivers and streams to reproduce. Increases in freshwater temperatures will also impact species not able to adapt.

What is CeNCOOS Doing to Inform Our Region on this Issue?

  • Funding stations collecting data useful for detecting ocean and coastal changes
  • Promoting partnerships among researchers and managers to discuss how data can be used for planning
  • Providing data and analysis through our website
  • Sharing information and resources with the Bay Area Ecosystem Climate Change Consortium

Sources Cited

Click here to see a list of scientific journal articles and reports used in this webpage.


- "Climate Change Impacts: Gulf of the Farallones and Cordell Bank National Marine Sanctuaries." CeNCOOS partners and staff contributed to and authored parts of this report on potential climate change impacts to habitats and biological communities along the north-central California coast. (7/7/2010)

- Center for Ocean Solutions (COS): Climate Change Impacts

- NOAA Climate Services

- Cal-adapt: Exploring California's Climate Change Research

- Dr. John Largier (UC Davis) presentation on Climate Change and the ocean: Regional Climate Change: Physical Impacts (pdf)

- Live Science article about 2010-11 winter storms - signal of climate change?

- Pacific Marine Environmental Laboratory Carbon Program - Information on Ocean Acidification including Data Portal

- California Department of Water Resources (DWR) Climate Change Webpage

- Questions or comments? Contact CeNCOOS (