Climate change and sea level rise

How long can you tread water?

It’s become almost a daily bluster: articles bemoaning the reality of climate change and how it is going to destroy the earth and lead to the end of life as we know it.

Don’t get me wrong: I am a true believer regarding climate change and human contributions to the process. I am, after all, a scientist who tries to keep an open mind and pay very close attention to the world around me.

But… the climate is always changing, and the only reason we’re getting worked up about it now is because the inevitable effects are starting to impact our status quo, and force us to make changes that — as a technological and resource-hungry species — we would rather not be forced to make.

It seems like nearly everything that needs a villain is being blamed on climate change: Too little rain, too much rain; too hot, too cold; too many wildfires; too many hurricanes; tornadoes at Christmas… dogs and cats together. The list goes on and on. It could make one either go tharn, or begin to doubt that any of this has validity (an approach taken by far too many as an easy way out of the dilemma).

So, let’s keep it simple for today and focus on a single effect: a rise in sea level.

Before we start, there are a few givens that we should all be able to agree upon:

• We are pumping carbon out of the ground, combining it with oxygen, and returning it to the atmosphere as carbon dioxide. Click here for an earlier post (cleverly titled “Climate Change?”) that summarizes the science regarding this.

• Carbon dioxide is a proven “greenhouse gas” that disrupts the global energy balance; causing more heat to be retained at and near the surface.

• The surface of the planet is warming. This observation is fully supported by all available (and peer-reviewed) data, and even makes sense from a scientific standpoint.

• The cryosphere is continuing to melt, and return its water from the solid phase into the liquid. Click here for an “Introduction to Glaciers: Ice with an Attitude”.

• This additional water will end up in the ocean.

• This will cause sea level to rise (post hoc ergo propter hoc, as Poppy would again remind us).

• This rise in sea level will flood low-lying coastal areas.

• Humans have always loved to live near the beach (and still do).

So… sea level is going to rise and and flood coastal areas. This will surely have an unfortunate impact on the billion or so beach dwellers of today, but should they expect anything different? As I said at the beginning of this rant, the climate is always changing, glaciers advance and retreat, and coastal areas are exposed and flooded, and then exposed and flooded again… and again… and again.

Consider the end of the last ice age and the reality of the transition from an icebox earth to what we had at, let’s say, the birth of Christ (or Mohammed or Buddha or whomever you want — plus or minus a thousand years doesn’t really affect the discussion enough to matter).

Twenty thousand years ago the ice age was fully advanced — there was a mile of ice over what is now Detroit for God’s sake. But the climate changed, the planet warmed, the ice melted, and sea level rose.

I would imagine that the need and desire to live near the beach was even greater at that time: a moderated climate, abundant sources of food, ease of transportation, communication routes — oh yeah, living at the beach may be a choice now, but it was the source of life back then.

But… the climate changed and the ice melted. There is still some debate regarding the specifics, but it seems reasonable to conclude the following: enough ice melted to raise global sea level by — at a minimum — four hundred feet. (Now may be a good time to remember that this is a vertical distance — the horizontal flooding of the coastal areas would obviously be much different; the severity controlled locally by the shape of the land.)

This flooding would have drowned the low-elevation continental shelves (refer to the images of Asia and the Gulf of Mexico, above, to see what was likely submerged in those two areas). Anyone living at the beach at the time would have had a problem! This much is pretty obvious…

The timing needed to complete this transition is a bit more problematic, and estimates vary greatly. However, most glaciologists seem to agree that, in round numbers, the rise in sea level (and flooding of the coastlines) occurred over a very short span of earthtime. Let’s use two thousand years in our estimate to make the math easy — it was probably quicker than that, but, really, I think you’ll get the point.

Hmmm… four hundred feet in two thousand years converts to 0.2 foot per year (again, a vertical measurement). Doesn’t sound like much, so who cares?

But these two inches per year of vertical rise can translate into many feet horizontal, again depending on the shape of the land. And since we’re often talking about a passive continental margin with gentle relief, this can result in tens to hundreds (to even thousands) of feet across the surface. (Click here for an earlier post that touches on the different types of continental margins.)

Extend this out to a generation and what we have is two feet or more of vertical sea level rise from birth to childbearing age (and now we may be talking about miles of horizontal displacement per lifetime!). And then another two feet of rise during the next generation, and then the next, and the next, and the next… for a hundred generations.

What this translates into is that for two thousand years, most of humanity was on the move — heading away from the coastline in order to keep in front of the water continually flooding their settlements. Actually, they were probably more like temporary campsites than established communities.

So what evidence, if any, exists that all of us can relate to?

It’s amazing that so many cultures have legends of a flood lost in the haze of antiquity. Christians credit Noah and his ark for allowing animal (and human) life to continue, but there are literally hundreds of other myths that follow the same theme: an angry deity (the most common villain) sends a bunch of water and drowns out nearly all of us. I could include a passel of links here, but just log into your favorite search engine and search for “flood legends” — you’ll get as many as you can handle.

So is the melting of the glaciers at the close of the last ice age responsible for the flood myths? I surely cannot confirm one way or the other, but the concept certainly checks several of my personal boxes.

BTW: Speaking of God… Just because we may be able to link the flooding myths to a natural earth process — in this case the ending of an ice age and the resulting submergence of coastlines across the globe — doesn’t mean that God (or whichever deity you choose to blame) wasn’t responsible. What better way to express his or her dissatisfaction with humankind than to disrupt the complacency of their lives, and what better way to do that than to force them out of their homes and onto the road for a hundred generations!

At least God left the Christians a way out, whether they wanted it or not. As He is reported to have asked a hesitant and skeptical Noah: “How long can you tread water?”

Anyway, so how does any of this relate to these days of modern times? Like much of everything else in the earth sciences, there are so many variables that it’s impossible to know anything for sure. But… I do think that it’s probably appropriate that there are so many RVs and mobile home parks in Florida.