Sea change: Climate change is causing a profound transformation of our oceans

Oceans cover approximately 70% of the Earth’s surface and play a major role in local weather and global climate patterns.  Greenhouse gasses, produced by human activities, trap heat from the sun causing global average temperature increases.  Water (i.e. our oceans) has an amazing ability to absorb that heat, but the effects of increased ocean temperatures have profound impacts on humans and the environment.  Four major, measurable characteristics of the ocean are changing as a result of human activities:

  • Ocean heating and increased sea-surface temperature
  • Sea level
  • Coastal flooding
  • Ocean acidity

Ocean heating and sea-surface temperature

As greenhouse gases trap more and more heat within our atmosphere, the oceans are warming at an alarming rate.  Over the past 100 years, the overall ocean temperature has risen 0.1°C (0.18°F) when averaged between the surface and 700 meters (2,300 feet)(http://ocean.nationalgeographic.com/ocean/explore/pristine-seas/critical-issues-sea-temperature-rise).  The increase in ocean temperatures has been especially great at the surface, where there has been as much as a 4°C rise between 1901 and 2015. A rise in the overall ocean temperature causes changes in sea level and alters ocean currents. The biological consequences of global sea temperature increases include (but are not limited to) changes in species distributions and migration patterns, altered behavior, novel interactions between species and species extinctions.

sea-surface-temp-download2-2016

Sea level

Over the past century, the increased rate of sea level rise is a clear response to human activities and global climate change.  Sea levels have fluctuated throughout geologic history but the rate of sea level rise over the past 100 years is unprecedented.  As global temperatures increase, land ice melts, expands, and flows into the ocean.  The current rate of global sea level rise has accelerated to over 2.5 cm (1 in) per decade.  Along parts of the east coast of the U.S., sea levels have risen more than 20 cm (8 inches) between 1960 and 2015.  Rising seas have inundated some historically dry lands and wetlands, reduced the buffer provided by barrier islands, and reduced or eliminated habitat for some species.

sea-level-download1-2016

Coastal flooding

To most people, a rise in sea level of 2.5 cm per decade might sound like small increases, but when considering over 3 billion people live within 60 km of the coast, the potential effects of rising seas are staggering (interactive map https://www.arcgis.com/home/webmap/viewer.html?webmap=26e3d28ef2494aea88596109740fdf5f&extent=-130.5726,24.5943,-65.6654,49.6585).  In many east coast communities along the U.S. mid-Atlantic, high tides and strong winds are all it takes to cause nuisance flooding (inundation of roads, swamping of houses and basements).  In New York, between 2005 and 2014, there were 157 days reported at nuisance flood levels – twice that of the previous decade (https://www.theguardian.com/environment/2016/feb/23/us-coastal-cities-flooding-climate-change-sea-level-study).  In 2015, there was an estimated $46 billion dollars of damage caused by climate disasters (including flooding) in the U.S. (http://www.chicagotribune.com/news/nationworld/ct-climate-change-disasters-cost-20170110-story.html).

coastal-flooding-download1-2016

Ocean acidity

As a consequence of humans’ industrial and agricultural activities (e.g. burning fossil fuels), the amount of carbon dioxide in the atmosphere has risen dramatically.  The world’s oceans absorb roughly 25% of this carbon dioxide annually, so as atmospheric levels increase, so do ocean levels.  This increase in dissolved carbon dioxide has led to chemical changes in the ocean and an overall lowering of the pH.  This process is called ocean acidification.  Over the past 200 years, the world’s oceans have become 30% more acidic (http://ocean.si.edu/ocean-acidification).  This increase in ocean acidity is having a large impact on marine life, and is affecting biological processes such as reproduction, growth, chemical communications and more.  Coral reefs and shelled animals (including oysters, mussels, clams, sea urchins and starfish) are particularly impacted, because they are composed of calcium carbonate, which can be dissolved by increases in acidity.

This graph shows rising levels of carbon dioxide (CO2) in the atmosphere, rising CO2 levels in the ocean, and decreasing pH in the water off the coast of Hawaii.  Credit: NOAA PMEL Carbon Program

 

 

WOA05_GLODAP_del_pH_AYool

Estimated change in sea water pH caused by human created CO 2 between the 1700s and the 1990s, from the Global Ocean Data Analysis Project (GLODAP) and the World Ocean Atlas

 

Global climate change is happening as a result of human activities.  Marine ecosystems are the largest ecosystems in the world and they are rapidly changing as a result of human activities.  International climate agreements, such as the Paris Climate Accords are essential step towards reducing greenhouse gas emissions around the world.  Read more about the effects of climate change of our oceans…

https://www.epa.gov/climate-indicators/oceans

http://ocean.si.edu/ocean-acidification

 

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