Saturday, March 14, 2015

Climate Change Part 17: Impacts on the Ocean

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.


UN Coastal Atlas:

Under a Green Sky author Peter Ward (outlines the evidence that ocean stratification was related to mass extinction), on Vimeo

Gulf of Maine Research Institute on ocean acidification: