How "Hot Water" is getting us into Hot Water

One of climate science’s favorite facts and infographics to use to convince people that climate change is real is rising ocean temperatures.  “If the ocean’s average temperature rises by 2⁰C we cannot recover!”  They tell human’s that this will affect marine and coastal eco systems (which is true) and to care about other species outside of humanity.  As is the theme with all of my posts, we are told to care about these topics via buzzwords and declaratives while the science and facts are deemed "too confusing."  So let’s peel back why we need to be worried about ocean temperature outside of the fishes and crustaceans and focus on what we are really after: our future.  As with all of my posts this is not all encompassing and tries to give you a framework to think about the changing climate.

This post will rely on Easy Being Green, Being John Milankovitch, and Deep Ocean Currents , and assumes you have read them.

Photosynthesis

If there is one thing they do not let you get out of grade school without learning these days it is “Photosynthesis!” Plants take in “sunlight” and convert it to “energy”.  While this is not incorrect it is neither the whole, nor most important part of the equation when it comes to climate science.  Here is the chemical reaction for photosynthesis:

CO₂ + H₂O + light ==> CH₂O + O₂

A chemical reaction is kind of like a recipe and this one reads: Take one part Carbon Dioxide, one part Water and mix with light.  After some time you will have a cake made of Sugar (CH₂O) and Oxygen.  Photosynthesis, in terms of climate science, can be seen as a Carbon Dioxide removal mechanism, like a CO₂ sponge.  While Oxygen is also a Greenhouse gas it has a much lower absorption rate for earth’s radiation than Carbon Dioxide (see previous post).  Taking our last blog post into consideration photosynthesis does not technically make the planet cooler, but it prevents it from getting warmer; it slows down the positive feedback machine that is the Greenhouse effect by limiting Carbon Dioxide in the atmosphere. 

What does any of this have to do with ocean temperature?  This is where these little guys come into play:

These tiny organisms are known as “phytoplankton”.  You have most likely spent your life calling them “algae” and spending your summer fending them off from your pool.  The earth is not your swimming pool however and we require the billions of tiny and large algae to live.  It is estimated that 55-85% of all oxygen in the earth’s atmosphere is produced by these little organisms.  While we cannot estimate directly how much CO₂ this process draws out of the atmosphere it is clearly some non-zero number. The difficulty in accessing the information is CO₂ being absorbed and released by the Ocean in many ways and attributing the exact amount of CO₂ absorbed by phytoplankton photosynthesis is currently not possible.  What we need to consider is the effects of rising ocean temperatures on our friend the phytoplankton.  The following video shows changing ocean temperatures alongside the total amount of photosynthetic algae on the ocean’s surface:

You can see that as the ocean cools CO₂ “eating” algae prosper.  They are also most prevalent in areas where we saw deep ocean currents sinking and rising out of the depths (the second part of this blog post).  A warming ocean is not good for algae that remove CO₂ from the atmosphere.  It is also great for algae that do not contribute to this (i.e. red algae and red algae “blooms”) and can push beneficial algae out of the eco system.  Again we are dealing with a positive feedback system as additional man made CO₂ “can” have drastic effects on the global climate.  We have man made greenhouse gas added to the Milankovitch cycles warming the planet, causing algae to consume less greenhouse gas, causing the planet to heat more… etc.

Surface Reactions:

Our next example relies on a little chemistry and a little on our previous post about deep ocean currents.  In addition to our little algae friends eating up the atmosphere’s CO₂ the ocean’s surface itself can react with CO₂  .  Here is an example:

This says that Carbon Dioxide and Water under the right conditions will make Carbonic Acid, Hydrogen and Bicarbonate. If the ocean water simply stayed on top of the ocean some of Carbonic Acid, hydrogen and bicarbonate would spread out through the water, and some would recombine to form CO₂ and H₂O (the opposite reaction).  The Carbonic Acid, hydrogen and bicarbonate would only spread so deep into the ocean as there isn’t any force to spread it out throughout the rest of the ocean. This process would be self-contained in the surface of the ocean however – absorbing and emitting the same amount of CO₂ ; not having much of a changing effect on the climate.  This is where we revisit our first blog posts!

At three places on the globe the surface ocean water is driven to the ocean floor and moved incredibly slowly throughout the globe.  The driving force for the sinking water is density and the driving force for the density is… ocean temperature.  This means that some of the carbonic acid and bicarbonate at these locations is driven all the way to the ocean floor, where it will remain for ~1000 years.  This gives it the entire ocean to distribute the carbonic acid and bicarbonate.  Instead of just the ocean surface and atmosphere we now have the entire ocean to distribute our used CO₂.  The following map shows where in the ocean our CO₂ is “stored”

As expected a majority of CO₂ is found where surface currents sink to the ocean floor in the northern and less so southern poles. This process “buries” many CO₂ sources not just the one in this example.  From our algae example, as algae dies its “corpse” can be turned back into the CO₂ we hoped it was getting rid of and released into the atmosphere.  Algae corpses that get pushed into the deep ocean current however remove this potential CO₂ from the atmosphere all together and “store” it in the ocean.

As discussed in the first blog post rising ocean temperatures slow down the deep ocean currents.  As deep ocean currents slow, the amount of CO₂ consumed by the deep ocean currents lowers, the more CO₂ is in the atmosphere, the warmer the planet gets, the more the deep ocean currents slow… Yet another positive feedback system.

Final Thoughts

Examples like these are why some scientists respond with such hyperbole and hysterics when talking about climate science.  The system in question is based on many, many intricate positive feedback systems that point to a situation that does not get better.  It is not just one input/output that snowballs downhill but many.  The next blog post will talk about current levels of CO₂ in the atmosphere compared to the past, however I will bury the lead a little and tell you our current CO₂ level is almost twice that of any previous time in known history.  While the ice cores can tell us about past climates, no known atmosphere has ever been this greenhouse rich.  We are taking one of the inputs into our feedback system and turning it up to 11, and while the results are likely to be drastic, the scarier part is that they are also unpredictable. 

Sources:

http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYD28M&d2=MY1DMM_CHLORA

 http://earthsky.org/earth/how-much-do-oceans-add-to-worlds-oxygen

http://www.pmel.noaa.gov/co2/story/Ocean+Carbon+Storage