Thursday, September 26, 2013

Things You Should Know About Sea Level Rise

The sea is coming!  The sea is coming!

Sea is for Cookie- get it?  (Also, this is totally the background for my work computer.) Source

Let's talk a little about sea level rise today, shall we?  In my job, I deal with sea level rise (SLR) a lot.  This is great, because it means some cities/states/other areas get it and are willing to pay us to help them
start preparing.  Sadly, there are still plenty of people out there who are in denial or actually think the science is wrong. (I went to a conference last year where a guy gave a presentation about how sea level rise isn't happening- to a room full of coastal engineers... know your audience, dude!  I just kept texting my coworkers asking if this guy was for real.  So bizarre).

So you don't end up being that guy, here are some things you should know...

What is sea level rise anyway?
Well, with or without humans, the oceans would rise and fall as global temperatures change.  For instance, during the Ice Age, lots of water froze on land and formed giant glaciers.  That meant that there was less water in the ocean.  On top of that, the water that was left in the ocean took up less space (not by a lot, but enough... remember back to physics class? when molecules get cold, they slow down.  They bump into each other less, so they take up a smaller amount of volume.  Heat them up and they use the energy to bounce around and the substance expands- that's called thermal expansion).

Molecules doing the thermal expansion dance. Source
So less water in the ocean + less space taken up by the remaining water = low sea levels.  Sea levels were estimated to be 125-135 METERS(!) lower than present at the maximum of the last Ice Age (NRC 2012).   On the flip side, when things get hot, the glaciers on the land melt*, the extra water goes in the ocean, all that water expands because it's warmer (and more energetic), and like an overfull bathtub, things start getting wet.

Wait, but then how much of this sea level rise thing is my fault?
Most of it.  Or at least, you probably aren't helping the situation.  While the non-believers the non-understanders** will argue that global warming is just part of the earth's normal fluctuations, truth is, since the Industrial Revolution we've been making a mess with all of our new-fangled inventions.  While cars are sweet and they help us get around, they burn fossil fuels which release greenhouse gases into the atmosphere.  You've heard about those greenhouse gases, right? Like water vapor, carbon dioxide, methane, nitrous oxide, and ozone?  Well greenhouse gases work kind of like lots of little mirrors.  When the sun shines on us here on earth, the light and heat bounce off the ground and back towards space.  The gases in the atmosphere reflect some of this light/heat back to earth again- like a giant blanket keeping in our body heat.  Now greenhouse gases are super important for us- earth would be too cold for our existence without them.  But put too many little energy mirrors in the atmosphere, and it's like having too many blankets on- we don't release enough heat out into space, and we get HOT.

The other big thing we humans have messed up on, is getting rid of some important greenhouse gas absorbers.  Like forests. And wetlands.  Remember back to elementary school again- plants breathe carbon dioxide (one of those greenhouse gases we're talking about) and exhale oxygen- the reverse of what our bodies do, and an important process for a healthy earth.  So when we cut down entire rainforests, or dry out wetlands, we're releasing all of the carbon dioxide the plants were holding out into the atmosphere.  I'll get more into the awesomeness of wetlands in another post, but even the soils of wetlands hold a ton of carbon for us!!  

So yes, this is your fault (and everyone else's).  Since the Industrial Revolution, there's been a 40% increase in atmospheric carbon dioxide! (wikipedia) That's a lot.  The earth is getting hotter, so all that stuff we talked about in the question above is changing ocean water levels. Additionally, when we pump water out of the ground (which we do a lot these days) it usually ends up in the ocean- more water that wouldn't be there if it wasn't for us.  While this plays a smaller role than thermal expansion and melting ice, it's still not helping.

Okay, I feel horrible.  Let's just stop everything and save the earth!
Sure thing- I'm with ya.  Although it's impossible, let's just say we do stop all our polluting ways TODAY.  Because of everything we've done historically, the oceans will keep rising to get into equilibrium with the warmer atmosphere we've created.  Isn't that crazy?  Thanks a lot great-grandpa.

So are we doomed to be water-logged in the near future?
No, not really.  Even with the worst-case scenarios, things won't get too crazy for a while.  It's all about the acceleration of these things.  Right now, the global rate of SLR is 1.7 mm/yr- not too bad.  By 2030, we'll still only see 8-23 cm (3-9 in) of SLR since 2000.  But at 2050 it's likely to be 18-48 cm (7-19 in), and in 2100, we're looking at 50-140 cm (20-55) or 1.4 meters (4.6 ft) of SLR (NRC 2012)! 

Okay, 14 inches of SLR by 2050.  What does that really look like?
Well, conveniently for you, my dear reader, my co-worker Jeremy did some time traveling to show you what sea level rise is going to look like.

Jeremy back in 2000 - 0 in of SLR

Jeremy in 2050- 14 in of SLR

Jeremy in 2100- 55 in of SLR

Jeremy in 2100+ - ?

Those estimates are kind of all over the place. What do you have to say about that?
Well the scientists don't know everything at this point.  Will our political leaders lead us to decrease our greenhouse gas emissions?  Will developing countries put in an effort to reduce their emissions, or just say heck with you guys- it's our turn now! Will there be a turning point where all sorts of physical processes occur at once and accelerate the changes (like changing ocean currents or large chunks of ice melting at once)?  There are still a lot of unknowns.  With the data being collecting now, SLR science and it's models will vastly improve in the next 10 years.

Ok, so the sea is rising and it's our fault.  So what?
This is going to be a big issue for coastal communities going forward.  Natural systems are smart, and will try to adjust to changing sea levels, however we've done a really good job at boxing in most of those systems.  If you've ever driven along Highway 1 in San Francisco, you've probably seen the sand that blows on to the road.  This is the beach and dunes's attempt at moving upslope in response to SLR.  Marshes do something similar (they actually accumulate more sediment to raise up, but if they can't do that fast enough, they too will try to move up slope).  So when we build roads along the water, or houses, or other infrastructure (water treatment plants, pipes, buildings), we're setting ourselves up for a fight with nature.

And while we're smart, you know who generally wins these battles? Nature.  She's usually easier to just go along with.  Move your roads when they start falling into the water.  Move your house.  You can build a wall to keep out the ocean (another topic I'll get into in another post), but you're probably going to be spending a lot of money, and you'll just be putting off the inevitable.  And even if you do win the battle, you're probably destroying a valuable habitat/resource like a beach or wetland.  So just move- it'll be okay.   


This has been great!  How can I learn more!
I've included some links at the bottom of this report of some of the more recent scientific papers on sea level rise.  And of course, if you have any questions, please feel free to ask them in the comments below.

Thanks for listening and learning with me today!

*For a while I was spending a lot of time wondering about the glaciers in the water.  Since ice is less dense than water, (ever try freezing something in a ramekin and then forgetting this part of physics and getting really sad over your broken ramekin? (this may have just happened to me) Same process- water expands, and the greater volume breaks your ramekin.  Remember, density = mass/volume.  So if your mass stays the same, and your volume goes up, your density decrease- thus water expands when it freezes and is therefore less dense) Where were we? Oh right.  Since ice is less dense than water, if it melts, the volume actually decreases.  With glaciers, the majority of ice is underwater, so I thought, heck maybe we should melt the glaciers to stop sea level rise! Then the voluminous ice will shrink to water when it's melted, and our bathtub volume will decrease.  Great plan, except the ice on land also melts and runs into the ocean, and your bathtub overflows. Sad.  So to summarize, it's the ice on land that's really important.

**I hate that- "believers."  Like science is a belief and not based on data. Like all the scientists got together and said, "let's pull one over on everyone else" and invented this stuff.  This isn't a belief-system, people!

A special thanks to Jeremy and Nena for pictures and proof-reading!

(1) NRC 2012 (National Research Council) -currently the go-to paper for SLR on the west coast of the US
US Army Corp of Engineers on SLR
Intergovernmental Panel on Climate Change (IPCC 2007)

Vermeer and Rahmstorf 2009 -important paper that is cited a lot in SLR discussions

1 comment:

  1. But wait, as everyone knows the earth is flat and if the earth is flat, won't the excess water just run off! Great post Lindz!