Filed under: Altithermal, book, climate change, Hot Earth Dreams, Speculation | Tags: California High Altithermal, Hot Earth Dreams
One of the things that bugs me is that, about half the time when I dawdle on writing something, new facts emerge that change everything. That’s happened here a bit.
This is part one of a series of blog posts about California in the High Altithermal, and here I’m focusing on the environment. What I’m doing is taking the ideas from Hot Earth Dreams and working to show what might happen in one specific spot, in this case, the area currently defined as the state of California, over a specific time period, in this case, the High Altithermal.
My goal is to show how climate change happens over time, because different things happen on different scales, and that makes the future a lot messier. It’s not meant to scare people, but rather to give us a way to intellectually examine this model of the future, and figure out how people and other organisms will adapt.
If you’ve already read the book, you know the basic global scenario for the High Altithermal, which will run from 2100 CE (when our greenhouse gas emissions from fossil fuels stop) to 3600 CE (when the East Antarctic ice sheet finishes melting, and sea level tops out at 65 meters above the current level). These dates aren’t hard: we don’t know when we’ll finish binging on fossil fuels, what Arctic methane is going to do, or whether or even if the entire East Antarctic ice sheet will melt. But that’s the scenario I’m using here. During the first 200 years of the High Altithermal, global average temperatures climb from +3oC (we’re currently at +1oC) to +8oC, and the Greenland and West Antarctic ice sheets melt, raising sea levels by about 16 meters over those 200 years. From 2300 CE on, global average temperatures stabilize, and then start to fall 1-2oC over the next 1,300 years, while the sea continues to rise as the East Antarctic ice sheet melts away.
In this post, I’ll cover sea level rise, climate, and rivers and dams. This is necessary background, and I’m breaking it up into multiple posts so you don’t have to read a 7,000 word essay.
Sea Level Rise
If you want to see a rough visualization of sea level rise, I personally use http://geology.com/sea-level-rise/, and I use the +13 m setting as my proxy for around 2300 CE, and +60 m for 3600 CE. It’s not perfect (since it blues areas under the given elevation, whether or not they’re connected to the ocean), but it’s workable.
At +13 meters, the map shows two big changes: the Imperial Valley (which is actually below sea level) floods through the Salton Sea and Coachella to Indio, and the San Francisco Bay extends through the Sacramento/San Joaquin Delta to flood most of Sacramento, up to somewhere around Yuba City and Colusa in the north, and down west of Modesto in the South. That’s a lot of good farmland gone, and (not that the California canals would be working) it also severs the water link between northern California and southern California, since the critical pipes and infrastructure are all in the Delta. Existing ports all flood, but you’d expect that.
At +60 meters, the Gulf of California, doesn’t extend much further north, but it gets a bit wider, swallowing more of the former Imperial Valley. A good chunk of south and central Los Angeles floods, leaving the local hills as islands in a shallow and junk-strewn sea. Up north, San Francisco remains as an island (the peninsula is inundated through the trough of the San Andreas Fault), but the Central Valley is inundated from southwest of Fresno in the south to Chico in the north, with the current Sutter Buttes as a cute little round island in the northern bay. Now, not all this will be ocean. I suspect the edges will be full of salt marshes and mudflats, as I explain below.
If you want to have fun, google Hadley Cells. In the most abstract sense, these run from the equator to about 30o poleward, and are due to, well that’s where it gets complicated, and I’m not going to get into it here. It has to do with how the heat coming of the equator gets dissipated and how dry air creates deserts at around 30o N and S. The edges of the Hadley Cells are dynamic over the course of the year as it is, but there’s a widespread notion among climatologists that the Hadley Cells are broadening with climate change, meaning that their poleward boundaries are moving closer to the poles, perhaps 2-5o since 1979, but that perhaps they’re also weakening. The key thing here is that dry air. Without dry air, as California heats up, it will become more tropical and jungly. With the hot air, it means that the Sonoran and Vizcaino deserts are moving up into California. How far? I don’t yet have a good answer: if the current boundary is 32oN, that’s about the latitude of Ensenada. San Francisco is up at 38oN, halfway up the state, and according to one model, the edge of the Hadley Cell will stop somewhere around there in 2300 CE, before perhaps sliding south 2-3 degrees by 3600 CE. It’s safe to say that Los Angeles will become a true desert, and it’s probably safe to say that the southern Central Valley (aka the San Joaquin Valley) will be desert. It mostly is already, due to the rain shadow effects of the Coast Ranges. Still, the northern part of the state will be outside the Hadley cell, and that’s where things get interesting, because they will be fairly tropical up to, again, about the latitude of Chico. It appears that California will be desert in the south and tropical to subtropical in the north. Go figure.
Another fun thing is El Nino, and even the IPCC5 predicts that this isn’t going away. If anything, it will intensify, so there will be hot droughts and then hot rainy periods. In the south, this probably means that places like Los Angeles will start looking more like the dry side of the Hawaiian islands. Mountain peaks, where they catch the clouds, may be relatively wet and forested, and this may feed some local rivers (like the Los Angeles River). But the lowlands will be hot and dry, except during El Nino years, when they’ll get pretty wet. This kind of weather is normal now for Central Baja (the Vizcaino Desert) and in the Sonoran desert.
The big change for California is that storms will happen during all parts of the year, not just in the winter. As the seas warm (this will take about 500 years to fully occur, because California gets a lot of deep upwelling, and that takes time to warm), hurricanes will increasingly make it to California. Again, this is normal for Baja, where the storms come rarely, but at any time of the year. This will become normal for all of California, but the north will get a lot more storms.
Rivers and Dams
What makes industrial civilization possible in California are dams on almost all the existing rivers, and this poses an interesting problem: what happens when civilization fails? The dams are reinforced concrete, but it’s not clear how long they’ll last: anything between 50 and 10,000 years have been proposed for different dams.* One problem here is that there’s functional failure, with the spillways and outflows getting clogged with everything from crap to quagga mussels, and there’s physical failure, with the concrete of the dam giving way.
Functional failure will happen first, and what that means is that rivers, including the Colorado, will run dry below the dams if water can’t get through. The downstream channels will stay dry until water overtops the dam, at which point it will spill down the dam face and reflood the dry channels. This will happen even with the Colorado River and Hoover Dam. Normally you’d expect the situation to even out eventually, so that the river flows year-round over the dam. It might, especially as the upstream reservoirs silt up and the dams can hold less water. Still, in the early going at least and especially in southern California, I’d expect most dammed rivers to dry up entirely below dams during droughts, as evaporation keeps the reservoirs from overtopping the dams.
In the fullness of time, the dams will physically fail, each in their own unique way. These failures will cause massive floods downstream, after which each river will start rewilding itself, with spectacular waterfalls cutting through all the layers of silt left behind the dam and dumping this (anoxic at first) mud into the ocean. Rewilded rivers running off the Sierra will make lots of nice mudflats in the Central Valley Bay.
I should point out, as an aside, that there’s a great story hiding here, as the heroes try to reopen the clogged outflows of something like Hoover Dam so that their downstream families can survive. If anyone wants to tell that story, go for it. Any other stories people see?
*EDIT (1/28): I’ve been reading a bit more about dam failure, and the engineers seem to feel that modern dams (post WWII) should be good against physical failure for a century without maintenance, and indefinitely with maintenance and periodic rehabilitation. Again, what this means isn’t clear, because (IIRC) older dams like the Hoover Dam are a lot chunkier than modern dams, but modern dams have better concrete that’s somewhat less prone to all the ailments that concrete gets (basically, beyond freeze-thaw cracking, there’s a rash of chemical reactions which can cause the concrete to expand and crack, and the retaining rods can rust, expand, and crack too). Still, I’d predict that, once dam maintenance ceased, there’d start to be physical damage and possible structural failures within the first 200 years, and definitely within the High Altithermal. Until I read more, I’m no longer buying a 10,000 year lifespan without maintenance and periodic rehab.
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