The world’s oceans are warming, including those in B.C. where surface temperatures in recent years have been consistently warmer than the 30-year baseline. More observation and study is needed to track ocean warming and understand its effect on aquatic ecosystems and human settlements.
Authors: Karin Bodtker and Raissa Philibert, Coastal Ocean Research Institute, an Ocean Wise initiative
Reviewer: Peter Chandler, Fisheries & Oceans Canada, Institute of Ocean Sciences, Sidney, B.C.
Banner Photo Credit: Louise Janes (Wikimedia Commons, CC BY-SA 4.0)
The ocean is on a warming trend. Globally, the surface ocean has been warming at a rate of 0.13 degrees Celsius per decade since 1981, and in 2016, it was warmer than the average temperature for the 20th century by 0.75 degrees Celsius.
Average sea surface temperature off the B.C. coast in 2016 was not quite as warm as the two previous years, but it was 1 degree Celsius warmer than the average temperature between 1981 and 2010 (Figure 1). While annual average sea surface temperatures can vary from year to year, a warming trend, averaging approximately 0.1 degrees Celsius per decade, is evident from satellite data, available since 1981. Daily observations made at lighthouse stations along the B.C. coast over the previous 80 to 100 years also show long-term warming trends.
Why is it important?
Ocean temperature, salinity, and chemical properties like pH, a measure of acidity, tell us about the climate of the ocean. Species have long adapted to ocean climates that are typical for the region where they live. Changes to ocean conditions that are outside of the typical range of variability can affect species in many ways. Temperature changes in particular may affect the distribution and abundance, health, and phenology (timing of biologically important processes such as blooms and migration) of marine organisms. These responses are complex and may be influenced by a number of other factors (e.g., time and space scales,species resilience, and addition of other pressures such as changes in predator-prey relationships and human activities).
Changes in the marine ecosystem during unusually warm events can provide some insight into the conditions that may prevail under projected climate change. For example, the increased stratification (separation of warm and cold waters) and reduced mixing of nutrients due to warmer than average temperatures played a role in creating conditions that resulted in lower phytoplankton levels in 2015. Due to the warm events in 2015 and 2016, zooplankton generally found on the south coast were observed much further north than usual.
Changes in geographic range have been observed for many terrestrial, freshwater and marine species, including Pacific salmon, sardines, anchovies, and Pacific hake. Furthermore, species that have evolved together may not respond to climate change to the same extent and at the same rate, leading to changes in predator-prey relationships and effects on species composition that are difficult to predict.
Finally, warmer ocean temperatures have a direct effect on sea level because the volume of water increases as it warms causing sea levels to rise. Increases in sea level will also amplify the risk of coastal flooding (see Sea Level Rise article).
What is the current status?
How warm was 2016 compared to recent history?
If we compare the annual average sea surface temperature in 2016 to the average temperature over a recent 30-year baseline period between 1981 and 2010, we find that temperatures in 2016 were warmer everywhere in the Canadian Pacific Exclusive Economic Zone (EEZ) (Figure 2). The spatial pattern shows differences ranging from about 0.5 to 1.5 degrees Celsius, with the largest differences showing up on Dogfish Banks east of Haida Gwaii, in the middle of Hecate Strait, and in the Broughton archipelago at the north end of Johnstone Strait.
How fast is the ocean warming?
The answer to that question depends on where exactly you take measurements and how far back in time you go to estimate the rate of change. As shown in Figure 1 temperature does not steadily increase year after year but may be above or below average for several years at a time. We looked for statistically significant trends between 1981 and 2016 and found the EEZ to be warming at about 0.1 degrees Celsius per decade (Figure 3). Data from three lighthouse stations and two buoys also showed significant trends with a range in values. The trend at a buoy (46208) located west of Haida Gwaii shows a cooling trend over time between 1981 and 2016. While this may have been related to La Niña events which led to cooler than average surface waters between 2008 and 2012, it reminds us that the spatial variation in sea surface temperature is considerable.
In fact, looking at the time series of annual temperatures back to 1981, we see average values for the EEZ ranging from nine degrees Celsius to about 12 degrees Celsius, and a much larger temperature range (seven degrees Celsius to above 13 degrees Celsius) when we consider values at the individual lighthouses and buoys where data are collected (Figure 4). Trend analysis is also sensitive to the values at the beginning and end of the observation period. For example, if we considered the 30-year interval from 1983 to 2012, the trend in average sea surface temperature across the EEZ would be a decreasing one (Figure 4).
What can you do?
Individual and Organization Actions:
- Help prevent climate change by producing fewer greenhouse gasses. Adopt policies and practices within your organization. Recommended actions include driving less, eating less meat and recycling.
- Eat sustainable seafood to foster healthy and resilient fish populations.
- Learn more about climate change and its implications for B.C. from the Pacific Institute for Climate Solutions online courses: Climate Insights 101 .
Government Actions and Policy:
- Incorporate latest climate change hazard assessments into emergency response planning.
- Protect any cold water “refugia” within rivers. Strengthen regulations that protect riparian areas along streams to keep warming to a minimum.
- Acknowledge that diversity among salmon populations will be critical in helping salmon populations adapt to future climate conditions and develop policy to maintain the diversity.
- Continue to develop monitoring programs in collaboration with non-governmental agencies to advance the scientific understanding of the marine environment.