CLIMATE CHANGE AND OCEAN ACIDIFICATION

TWO FORCES TO BE RECKONED WITH

Puget Sound is facing unprecedented environmental changes. Not only is there evidence for a changing climate in the Pacific Northwest, but the global ocean that influences Puget Sound is undergoing acidification. Environmental changes associated with climate change and ocean acidification will continue, although there are still many unknowns that remain to be addressed. Climate change and ocean acidification have the potential to profoundly affect ecosystems, and many, if not all, of the Vital Signs are likely to be affected in one way or another.

Climate change

The term “climate change” refers to the long-term change in weather around the world. Human activities have increased atmospheric levels of greenhouse gases (carbon dioxide, methane, and nitrous oxide) to levels unprecedented in at least the past 800,000 years. This increase in greenhouse gases has had repercussions on the climate; these changes are expected to accelerate in the coming years, with increasing impacts on local ecosystems, human economies, and cultures. As the climate changes, scientists expect that local patterns in temperature, precipitation, and humidity—both averages and extreme events—will change.

The climate is changing in the Pacific Northwest

There is compelling evidence of long-term change in the regional climate, water resources, and local sea level, even considering large natural variations. Already observed changes include higher air temperature, decreased glacial area and spring snowpack, earlier peak streamflows in many rivers, and rising sea level at most locations in and around Puget Sound.

Projections for future climate change depend in part on the ability to foresee greenhouse gas emissions, which will in turn be determined by society’s choices about energy sources and use. To forecast future climate, scientists use a range of low to high greenhouse gas emissions scenarios. All scenarios indicate continued warming in the Pacific Northwest in general, and Puget Sound in particular. However, natural variability will remain an important feature of global and regional climate, at times amplifying or counteracting the long-term trends caused by rising greenhouse gas emissions.

OBSERVED CHANGES IN THE PAST CENTURY
PREDICTED CHANGES IN THE NEXT CENTURY
  • Air temperature increased by about +1.3°F between 1895 and 2011
    • Even warmer temperatures, more extremes in weather, more droughts
    • Precipitation totals (rain or snow) stayed about the same, with no significant trend
    • Small changes in precipitation, with heavy rainfall becoming more extreme
    • Snowpack thinned, glacial area decreased, most Washington glaciers are in decline
    • Spring snowpack will decline
    • Streamflows are peaking earlier in the year for many snowmelt-influenced rivers in the Pacific Northwest as a result of decreased snow accumulation and earlier spring melt
    • Streamflows will peak even earlier
    • Winter streamflow will increase
    • Summer streamflow will decrease
    • More floods
    • Lower summer low flows
    • Sea level is rising at most locations. Local sea level changes range from a decline along the northwest Olympic peninsula, a region experiencing uplift, to sea level rise in parts of the Puget Sound and the outer coast where land is subsiding
    • Coastal areas in Washington will experience sea level rise, with perhaps the exception of areas like the northwest Olympic Peninsula, where the land is uplifting
    • Ocean temperature trends vary with location. In the Strait of Georgia and West of Vancouver Island: significant warming observed. Average for top 330 ft was +0.4°F/decade between 1970 and 2005
    • Ocean temperature offshore of Washington will continue to go up, by about +2°F by the 2040s (2030-2059, relative to 1970-1999) for a medium greenhouse gas scenario

    ocean acidification

    The term “ocean acidification” refers to a long-term change in seawater pH toward the acidic end of the pH scale. Ocean acidification is caused as carbon dioxide (CO2) from the atmosphere dissolves into seawater. Over time, the addition of CO2 causes changes in seawater chemistry, lowering the pH and reducing the carbonate ion concentrations of the seawater. Ocean acidification will increase as fossil fuel combustion and deforestation continue to add CO2 to the atmosphere.

    The acidity of the global ocean has increased by about 26 percent since 1750. The acidity is projected to further increase roughly 100 to 150 percent by 2100 relative to pre-industrial levels. Ocean waters on the outer coast of Washington and the Puget Sound have seen an acidity increase of about 10 to 40 percent since 1800 (decline in pH of 0.05 to 0.15).

    Ocean acidification is a reality in the Pacific Northwest

    Significant effects of rising atmospheric CO2 from human sources are detectable in Pacific Northwest waters now, and these effects will continue to grow as CO2 continues to increase. The Puget Sound and adjacent Pacific Northwest marine waters are particularly vulnerable to ocean acidification due to the combination of several factors that affect the dissolved CO2 concentration, pH, and aragonite saturation state of seawater. These can include the amount of global CO2 in the atmosphere, the emission of other acidic gases besides CO2, the high rates of plankton growth that ultimately drive oxygen down and release CO2 via respiration in the water column, runoff of nutrients that fuel plankton growth, and upwelling off the Washington coast that brings nutrient-rich and low pH waters up to the surface. Through ocean circulation, these waters eventually can make their way into Puget Sound.

    Oceanic waters at depths of 150 to 300 meters on the coast of Washington naturally have higher dissolved CO2 concentrations than surface waters, due to respiration. Upwelling causes this water to rise upward closer to the surface where it mixes with the increased dissolved CO2 from the atmosphere. This results in waters that are more corrosive than during pre-industrial times. Current atmospheric CO2 concentrations cause an increase in coastal surface water corrosive conditions from 11 to 33 percent of the time.

    Puget Sound waters meet federal and state water quality standards in terms of pH. However, southern Hood Canal and the Whidbey Basin are of particular concern because pH levels there are among the lowest in Puget Sound, partially because the high productivity leads to high biological respiration rates producing more CO2, which adds to the atmospheric CO2 signal.

    Impacts on species

    Direct changes to marine water quality will occur as seawater pH declines and corrosiveness increases. These changes will alter biological communities in Puget Sound. Species that build shells or other internal structures from calcium, such as molluscs, crustaceans, and echinoderms are affected by corrosive conditions, with negative consequences on shell formation, survivorship, or reproduction. Of the species likely to be affected, molluscs have so far received the most attention. Laboratory tests have shown impacts on Olympia oysters, pteropods (also known as sea angels and sea butterflies), red urchins, and northern abalone. Combining two or more stressors—for example, high temperature and low pH or aragonite saturation state—can cause more harm than either stressor alone. While most marine organisms can tolerate a range of environmental conditions, at some point their tolerance fails. Evidence of conditions in Puget Sound that exceed the tolerance of some native species—pteropods, for instance—have been detected.

    Corrosive conditions are particularly of concern to the shellfish industry in Puget Sound, which depends on good water quality to grow oysters, clams, and mussels. Already, this industry has had to make changes to its culture practices to adapt to lower pH water.

    Ecosystem-based models suggest that changes to crustacean abundance—especially copepods, a kind of zooplankton—will have a strong impact on overall food web structure. Not only would Vital Sign indicators such as the Marine Water Condition Index and harvestable shellfish beds be among those impacted by ocean acidification, but also planktivorous forage fish and those species higher up in the food web, such as salmon and marine birds that depend on forage fish for food.

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