Note: This program first aired on February 28, 2014.
We’ve come to the part of the climate change story that
really matters. What is going to happen? What will the world look like for your
kids and grand kids? How will it be different than it is today?
When we look at the ocean, the impacts of climate change are
vast and many. The ocean covers 70% of the surface of the planet, and its’
medium, water has all the unique properties that make this planet hospitable to
life. So you should expect anything that affects climate will affect the ocean
in a big way, and it does.
Sea level rise is one of the first things people think of
when they ponder the impacts of climate change. Some 44% of people world wide
live within 150 km of the coastline, here in the US, that number is over 50%.
The coastline though is an arbitrary location, relatively stable in the past
few hundred years, our time frame for the modern world. The location of the
coast is the result of a combination of factors; the amount of water in the
ocean, the volume of the water in the ocean,
and the level of the land, and it turns out all of these factors are
dynamic. The current climate event is increasing both the mass and volume of
the ocean. By melting land based fresh water ice caps (both large and small) the
total amount of liquid water in the ocean is increasing, and as we all know,
when you over fill a glass, it spills out. A second issue is at play, thermal
expansion. As water warms the molecules spread out more, so the same mass of
water will take up more space. Not only are we putting more water into the
ocean, that water is getting bigger because it is warming up, increasing the
volume of the ocean. How high will it go? The IPCC’s last projection was for
approximately 0.4 and 0.7 meters of average sea level rise between now and
2100. Currently sea levels are rising at a rate of 3mm a year.
Things in the ocean are responding to changing water
temperatures the same way things on land are to changing terrestrial climatic
conditions, those that can move to keep up with their water temperature of
choice are doing so. This is one of the main reasons we haven’t had a winter
shrimp fishery here in the Gulf of Maine for the past couple of years. The
commercially harvested Northern Shrimp (Pandalus borealis) are at the southern
edge of their range here in Maine. Warming Gulf of Maine water is interfering
with their reproduction, and populations have collapsed here as a result.
As ocean waters warm, ocean circulation is affected,
particularly the vertical circulation that brings nutrients to the surface, and
oxygen rich water to the bottom of the ocean. Increased warming at the surface
creates a warm surface layer, effectively putting a cap on top of the ocean
that prevents these vertical mixing currents (this is what happens on a small
scale on the west coast of South America during an El Nino event). With no
nutrients at the surface primary productivity drops dramatically. With no
oxygen replenishment at the bottom, the bottom goes hypoxic. There is evidence
from the fossil record that this kind of situation has happened before, and
let’s just say, it wasn’t good.
The final elephant in the room is of course ocean acidification.
This is a chemical phenomenon directly related to the increase in atmospheric
carbon dioxide. As levels rise in the atmosphere, they correspondingly rise (by
diffusion) in the ocean as well. When carbon dioxide mixes with sea water it
forms carbonic acid, and uses up carbonate ions in the process. Carbonate ions
are what calcium carbonate are made of, and animals that use calcium carbonate
in their shells are very negatively impacted. Unfortunately those organisms
happen to be important in the food chain, provide significant ecosystem
services and are a significant part of many fishing dependent economies.
So you see, the impacts of climate change on the ocean are
numerous and diverse and what happens on land also happens in the sea. There’s
no place to hide. We’ll see what this really means for us next week.
References:
UN Coastal Atlas:
IPCC 2013 report on Sea Level Rise: http://www.ipcc.ch/pdf/unfccc/cop19/3_gregory13sbsta.pdf
Island nations in threat: http://www.japantimes.co.jp/life/2013/09/06/environment/pacific-islands-fighting-for-survival-as-sea-levels-rise/#.VOzFv8bhJJM
Northern Shrimp in Maine: http://www.pressherald.com/2014/11/07/shrimp-depletion-in-gulf-of-maine-part-of-a-pattern-across-globe/
Under a Green Sky author Peter Ward (outlines the evidence
that ocean stratification was related to mass extinction), on Vimeo https://vimeo.com/64407973
Gulf of Maine Research Institute on ocean acidification: http://www.gmri.org/news/waypoints/ocean-acidification-growing-concern-gulf-maine
NOAA on Gulf of Maine ocean acidification: http://oceanacidification.noaa.gov/WhatsNew/OANews/CurrentNews/TabId/552/ArtMID/1344/ArticleID/9991/Study-shows-Gulf-of-Maine-likely-to-be-more-sensitive-to-ocean-acidification-.aspx
