Sea Level Rise: Why We Care, Part 3

In the last post (Part 2), I started to connect climate change to sea level, focusing on how very small increases in ocean temperature can lead to meaningful changes in sea level via expansion of water.  In this post, Part 3, I want to draw a connection between climate change and the other big process that drives most of the climate driven sea level rise projected for the coming decades:  The addition of new water to the ocean basins.

This component of sea level rise is similarly straight-forward (like the thermosteric effect) and driven by processes that we tend to interact with on a day-to-day basis:  If you warm up ice, it melts.  In this particular case we are particularly concerned with large masses of ice grounded on land, things like glaciers perched on mountains or at the edges of ice sheets:

Global map of glaciers (in blue) from the Randolph Glacier Inventory.  See https://earthobservatory.nasa.gov/images/83918

As well as ice sheets (in white in the map above) in Greenland and Antarctica.  As these masses of ice melt, and since they are perched on land masses, when they melt the meltwater flows into the ocean basins, effectively filling them.  Details about how these big masses of ice melt (and also how quickly) are one of the primary sources of uncertainty in sea level rise projections, and compound uncertainties just about climate change (i.e. even if we knew exactly how certain emissions scenarios would influence future temperature, we still wouldn't know exactly how much melt that change in temperature in either the air or water would cause).

What we do know, though, is that these big masses of ice ARE currently melting in a net, long-term sense.  The GRACE satellite mission launched in 2002, and provides near-continuous monitoring of the gravitational forces exerted by the mass of the Earth.  Here is the thing - as these big masses of ice melt, they lose mass.  Therefore their gravitational attraction changes, which can be measured by this satellite mission.  As a consequence you get data like this for Greenland:

Courtesy of NASA: https://svs.gsfc.nasa.gov/30879

or this one for Antarctica:

Thank you NASA!  https://svs.gsfc.nasa.gov/30880

And both of these allows us to assess how much mass is lost or gained from these big masses of ice (and also where it is lost from...which is also interesting and tells a story).  By way of reference, melting roughly 362 Gt of ice leads to 1 mm of global average sea level rise.  Lets play a quick numbers game:  If these masses of ice continue to melt at the same rate as they have since 2002, contributing something like 1.5 to 2 mm/yr to global average sea level...well that will be hard but probably manageable.   That leads us to something like 1/2 a foot of sea level rise by 2100 (from the ice alone...).  The concern though, is that these ice sheets are only just getting started (and there is some evidence for that), and that the possible contributions from Antarctica alone by 2100 may measured in multiple feet.

Its worth noting that sea ice, which is frequently covered as a climate change indicator, does NOT play a direct role in driving long-term sea level change (which isn't technically totally true...but the influence is very small).  It is frozen in the ocean, and therefore displaces seawater.  However, sea ice likely plays a role in buttressing glaciers and ice sheets, slowing them down a bit as they flow into the ocean. 

Sea Level Rise: Why We Care, Part 2

In my last post I attempted to lay the groundwork and evidence that I look to that supports the concept of anthropogenic climate change.  In this post I want to connect climate change to sea level.  That connection, in my mind, is pretty straight-forward and rests on some pretty familiar processes.  

First, though, lets review.  The fundamental idea behind climate change is that as we add greenhouse gases to the atmosphere, especially those that are long-lived (like carbon dioxide), we increase their concentration in the atmosphere.  Those gases then start doing what they are supposed to do...they begin trapping extra heat in the atmosphere.  To be clear, there is a good bit of very fair debate about what is called "sensitivity", that gets at how much warming we should expect from a given increase in the concentration of greenhouse gases.  These are critical questions to address, and I'm no expert on the details (though there are a number of excellent summaries available).  Rather I tend to trust the train of logic that I've laid out thus far...we know that gases like carbon dioxide are greenhouse gases, we know that we are actively transferring carbon from the ground into the atmosphere, and as such its reasonable to expect that this transfer is likely to influence global climate, and lead to warming.  There is also compelling analysis that suggests that we can actually observe the earth system absorbing extra heat energy.  

So lets, finally, get in to the connection to sea level.  Extra heat energy retained in the global system should lead to warming, and so we would expect to find that warming in the atmosphere, and also in the ocean.  This warming is linked to two processes that are the most important processes for driving sea level rise.  Lets walk through each in turn.

First, as ocean water warms, it expands (known as the "thermosteric effect"), and it really doesn't take much of an increase in temperature to drive meaningful sea level rise.  It is easy to see that, because the oceans are deep, the very small expansion of water expected with that small increase in temperature leads to meaningful changes in sea level.  Lets walk through this example that I use with my introductory Oceanography classes.  First, we are going to visualize an imaginary ocean is 1 meter on each side, but is 4000 m deep (the average depth, roughly, of the global ocean) - this just makes our math easier.  Our ocean sits in a basin.  Here is my hand-drawn rendition of this ocean:

We are also going to imagine that this ocean has a temperature of 4C (roughly the average temperature of the global ocean), and a salinity of 35 psu (roughly the average salinity of the global ocean).  We can then use a density calculator to estimate the density of the water in our ocean.  I come up with 1027.786 kg/cubic meter.  We need this density, because what I want to do now is calculate the total mass of water in our ocean, which we can do if we know the density and the volume of our ocean (density has a very simple definition and equation).  We've got both, and can easily come up with the mass:  4,111,144 kg.  Our ocean is heavy. 

Okay, now lets warm our ocean up by just 1C.  This isn't much, but is within the range of end of century possibilities for the global ocean.  In fact, measurements suggest that the surface of the ocean has already warmed up by around 1C since the beginning of the 20th century, some of which is likely due to anthropogenic climate change:

Its worth noting here that the ocean is FAR HARDER to warm up then the atmosphere, both because its mass is so large, and also because water has a much higher heat capacity then air.  So here is our warmer ocean:

You will note that with the temperature increase, the density of our water has gone down a bit...a very small bit...but a little.  We've expanded our water ever so slightly, so a unit volume of it weighs just a tiny bit less.  We also haven't added or removed any water from our ocean, so we have not changed the mass...and we've got the new density, so we can solve for the new volume of water again using our very simple density equation.  I come up with 4000.432 cubic meters.  Our ocean has a new volume.  Now, since our ocean is only 1 meter on a side its easy to figure out that our expanded ocean must go up by 0.43 meters due to this very small increase in temperature.  0.43 meters is roughly a foot and a half...not much relative to the depth of the ocean, but relevant when we start to think about all of the development and value that we've put right at the edge of the ocean.  By increasing the ocean's temperature just a bit, we've suddenly started to bring the ocean's into contact with a lot of value - homes, infrastructure, habitats, roads, etc. - that we never intended to be in contact with the ocean.  Its also worth noting that a foot and a half of thermosteric sea level rise is roughly consistent with end of century projections.

So that is the first big component or process connecting climate change to sea level rise.  Remember in this example we kept the mass of the ocean the same as we warmed it up.  There is another big component driving sea level projections though, one that adds new water to the ocean basins.  We will get to that one next, in Part 3.

Sea Level Rise: Why We Care, Part 1

Just a few weeks ago we published an updated sea level assessment for Washington State, for which I was the lead author.  We anticipated a small splash when we released our assessment, and indeed were covered in a variety of print, radio and TV outlets:

Along with that coverage came a smattering of emails from people around the state, most of them just from individuals, and some appreciative, some dismissive, and some thoughtful.  One stuck out for me for its honest skepticism:

"With all due respect, how do we know that this is not fake news? I think a lot of us out here are very skeptical of this kind of reporting and these studies because we don't understand what it's based on and bias."

We intentionally didn't dive too deeply in our report into the basis for the concept of climate-driven sea level rise - that wasn't the purpose of the document.  However, I figured I would at least take a crack at starting to address the question implicit in the comment above on this blog.  I frame that question as follows:  "Why is sea level rise a thing?  We have enough stuff to worry about, so why should I care?"  The full answer to this question is well beyond the scope of this blog, and my expertise.  There are probably hundreds, if not thousands, of papers that, together over decades, put together the full story of the connections between greenhouse gases and changes in sea level, but the story that I'm going to tell in multiple parts is my simple way of thinking about that question.

It starts here, with the concept of climate change driven by greenhouse gases.  As many have pointed out, from a geologic standpoint this isn't a new thing.  Greenhouse gases have apparently changed the Earth's climate on multiple occasions in the planet's history.  The primary culprit in most (or all??) of those cases, though, wasn't human emissions, but rather large volcanic flows.  Starting a few centuries ago, though, humans started transferring buried carbon from underground, back into the atmosphere, via coal mining, and then the extraction of oil and natural gas.

There were a few observers in the late 1800's and early 1900's that put together the pieces.  The key insights about the heat-absorbing properties of carbon dioxide, water vapor and other greenhouse gases were made by John Tyndall and reported in 1859 (the story of which is wonderfully recounted here).  These observations of the properties of atmospheric gases provided evidence to support hypotheses about a "greenhouse effect" on Earth originally posed in the 1820's by Jean Baptiste Joseph Fourier.  It didn't take too long for someone to make the connection between the properties of gases that John Tyndall described, and the mining of coal that started in earnest in the 1800's...and indeed in 1896 Svante Arrhenius published a paper describing how changes in carbon dioxide concentration in the atmosphere should lead to changes in temperature on the ground.

To me, these early insights about gases and the global system lay the groundwork for two fundamental ideas that, based on their insights, I trust:

1)  The idea of climate change - that greenhouse gases can control, or change, the Earth's climate

2)  That humans are capable of adding those greenhouse gases to the atmosphere via extracting fossil fuels from the ground, and transferring the carbon they hold to the atmosphere.  Its not just volcanoes that can do that.  

From there, rather simply put, the rest is details.  How exactly does carbon move through the Earth system after it is added?  How long does it take for geologic processes to remove carbon?  How much does the ocean absorb?  How much does adding a certain amount of different greenhouse gases to the atmosphere change temperature?  Where and why are there differences around the globe?  How much of warming that we observe is due to greenhouse gas emissions, versus "natural variability"?  The list goes on and on.

There are highlights along the way.  In 1958 Charles David Keeling began to focus on monitoring carbon dioxide in the atmosphere, and his efforts are on-going to the present day:

and clearly demonstrate a trend in carbon dioxide concentration in the atmosphere.  

Also in the 1950's, the development of micro-processors started to lead to rapid advances in the ability to model processes related to Earth's climate, and in the 1990's led to the development of global climate models, which are now widely used in efforts to translate scenarios of future emissions changes into estimates of future greenhouse gas concentration, temperature change, and a slew of other climate impacts.  Climate models are complicated, imperfect and most definitely aren't my expertise, so I find these sorts of layman descriptions helpful:

Climate models, there use, short-comings and applications are probably the key source of confusion about climate change, and perhaps rightly so.

The 1990's and early 2000's marked the emergence of climate assessments - efforts to review, sort, rank and summarize scientific developments about climate change and its associated impacts.  Early on these processes were international, and more recently national, regional and local, and also associated with mitigation or adaptation planning processes.  

I will stop there for now...and we haven't even yet touched sea level.  That is coming up next.  My key take-away from this Part 1, though, is that there is a real basis for the concept of climate driven forced by humans.  There certainly is real and honest debate about the details, but we will start Part 2 with that concept.

The Rock Pile

Extirpation of Pycnopodia?  Not a thing at this site.  Pycnopodia were plentiful and there were more than a few larger specimens.

I had the chance to team up with the Elwha Interagency dive team again this year, for a truncated version of the Elwha dive surveys that we've been conducting since 2008.  With just 5 diving days (Rather than 15 as in previous years) we turned our attention towards surveying priority sites from amongst our set of ~20 locations that we've been able to visit in previous years.  

However, as can often be the case, we also have to contend with losing dive time to bad weather.  We did pretty well this year, but lost our last half a day due to wind chop and swell.  Instead, we used that time to visit a site in Port Angeles Harbor called the "Rock Pile" that requires special access authorization from the USCG.  It is a pretty cool, and great for fish...

Cabezon

Once more...Pycnopodia!

Dermasterias imbricate...a nice big one.

Copper Rockfish (and another Pycnopodia) in the rocks

Notably, we also spotted a GPO, our first since 2016: