I am working on a story that takes place roughly 2000 years after a worst-case-scenario climate apocalypse. It revolves around a society located in present-day Glacier Bay National Park on the Alaska/BC border.

I should note that in my world building, on top of the normal climate apocalypse which devastated society 2000 years ago, there is an alien race that has also been terraforming the earth for hundreds of years now, changing the atmosphere to make the climate even warmer. (I don't know if it matters but these aliens are also raising the oxygen level of the atmosphere to something similar to what existed in the Carboniferous period, primarily because I want to justify the existence of genetically engineered giant dragonflies.)

So given all that, I'm hoping to get some advice on how the landscape would have realistically transformed. I've been working off the assumption that by then the glaciers would have cut U-shaped valleys that run down the mountain into the ocean, in some places ending in fjords. However I'm unsure if 2k years is a realistic timeframe for that, and I'm curious if the rapid warming of the climate would actually melt the glaciers entirely before the glacial troughs have a chance to reach the ocean. Although it's worth pointing out that in most pictures I could find, lots of these glaciers appear to be pretty close to sea-level already.

To be hyper-specific, I want to know about the area where the "Melburn glacier" and the "Grand Pacific glacier" meet, and I'm especially interested in knowing whether I'm being realistic in assuming that the melting of those glaciers, combined with rising sea-levels, would create a waterway that connects the Tarr Inlet to the Tatshenshini River (Or at least levels the landscape to the degree that it would be easy for people to create an artificial canal there that connects the two bodies of water.)

To be more general, I'm curious about realistic projections for the climate and ecosystem of this area, the effects of glacial melting, and the effect that rising sea-levels would have on the unique landscape of Glacier bay and the surrounding area.

(Thanks for reading, I'm really excited to have discovered this website!)

For clarity, when I say "normal climate apocalypse" I mean the current projection for climate change with the assumption that there is absolutely no major effort to reduce carbon emissions or seriously curb any of the excesses of industry over the next century. (Hi, I'm extremely pessimistic about the current political and economic system.)

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    $\begingroup$ (1) Glaciers cut U-shaped valleys while they are glaciers. If they melt, they don't cut U-shaped valleys, they cut V-shaped valleys just like any other river. (2) Whethere 20 or 200 or 2000 years is enough depends heavily on what you mean by "normal climate apocalypse". (3) Fjords are made by the sea rising and invading pre-existing river valleys. $\endgroup$ – AlexP Mar 28 at 22:09
  • $\begingroup$ So it sounds like a rapidly melting glacier would leave behind a u-shaped valley that abruptly narrows and deepens into a v-shaped river-valley. Is there a word for that, or a good real-world example of what it looks like? $\endgroup$ – DemonLung Mar 28 at 22:18
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    $\begingroup$ They result of river erosion cutting down the floor of a previous glacial valley is usually called a (river) notch or inner gorge. ("Notch" more usually means a narrow pass between two peaks.) ("Inner gorge" is a wide catching term, and can refer to any subsequent erosion which deepens a valley.) $\endgroup$ – AlexP Mar 28 at 22:33
  • $\begingroup$ Aren't we in the middle of an ice age? Those aliens will be in for a big surprise! $\endgroup$ – elemtilas Apr 9 at 21:30

Extremely hot rainforest over U-shaped valleys with thin rivers in the middle

So here's an estimate of the warming rate around the world per century:

enter image description here

The area with your national park is warming at ~2-2.5 degrees F per century, or ~1-1.5 degree C per century. Just taking the simple extrapolation maths here, in 2000 years, it's going to be 25 degrees C warmer. This seems extreme and I'm questioning the validity of the extrapolation, but you've included aliens helping with the warming, so this is plausible, lets assume its true.

This area currently is getting July temperatures of Average Max 17, Average Min 9 (degrees C), and January temperatures Average Max 0, Average Min -6. Adding 25 to that and we're looking at July Average Max 42, Min 34. That's extreme, and that's your average. You're average July day exceeds the Australian definition of a heatwave. My city (Adelaide Australia), which has seen 47.7 degree days, has an official summer average of 29/17. You're 13 degrees above this, so you may have the occasional 60 degree C (140 F) day. 25/19 will be your typical winter temperature, which is a Sydney December.

"Bikini weather" is your winter. "Hide in the shade by the water and only go out at night" is your summer. I'd also expect frequent summer storms but lack the knowledge to calculate their intensity accurately.

Trees and shrubs will survive, but they'll be a different breed to what is currently there, think palm trees, or other rainforest-like trees shielding areas from the heat, where underneath vegetation can survive the hot summers. The ice will be a heatsink for a while, but it'll retreat up into the mountains, to be replaced with a longer river. It won't be a desert due to the rivers, I'm thinking hot rainforest.

In the timeframes we're talking here, the change in erosion from glacial (U shaped) to river (V shaped) will be in the order of meters (a V shaped stream in a U shaped valley). A quick skim of the wikipedia page I'm seeing that tectonics and human activity causes rock erosion an order of magnitude faster than water does - the pacific plate and north american plate intersect about here, and both Canada and USA would probably want to drill it for oil.

Sea level rise is approximately 30cm per century. This works out to about 6m after 2000 years. Messing around with the Google Maps Cycle directions (which shows elevations over a route), it seems the majority of the national park is above 12m above sea level, suggesting the whole park wont be flooded by sea unless tectonics do something unexpected.

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    $\begingroup$ Wow, I've been writing it like it has Northern California's current climate, but that's extreme! Maybe I need to have the alien terraforming push the temperature in the other direction, lol. Thanks for such a thoughtful answer. This is great, this website rules. $\endgroup$ – DemonLung Mar 29 at 2:36
  • $\begingroup$ "about 6m after 2000 years" - this is not the "worst-case-scenario climate apocalypse". Worst case is a runaway global warming with all glaciers (including Antarctica) melting well before 2000 years mark. $\endgroup$ – Alexander Mar 29 at 18:46
  • $\begingroup$ Good point, and I'm being purposely vague about the nature of this climate apocalypse because it's so far in the past for my story as to not be super pertinent. All that matters is that it hits the reset button on human civilization. But I'm reading that all the ice melting would mean about 70m of sea level rise. So I guess I have a potential realistic sea-level-rise range of anything in between 6 and 70 meters, lol. That gives me a lot of wiggle room. $\endgroup$ – DemonLung Mar 29 at 19:09

I would add to Ash's answer two things:

  • Retreating glaciers will enhance landslide risk. The ice restrains the land underneath and when that restraint is removed, the land will then slough off. If it happens to dump all that earth into a fjord, you get a mini-tsunami which can be quite destructive.
  • If you are interested in details about the topography of a particular area, a lot of the data you'd need is public as long as you're handy with a GIS. Daniel Farinotti and coworkers have published estimates of the thickness of glaciers worldwide. They're indexed according to the Randolph Glacier Inventory. You can get surface elevation maps from the US Geological Survey although there are other good sources as well.

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