Seaver Wang Profile picture
Jun 8, 2020 17 tweets 5 min read Read on X
Okay, it’s #WorldOceansDay, so let’s talk about ocean deoxygenation.

To be clear, in no way is the human oxygen supply threatened by ocean deoxygenation.

THREAD

Our current atmospheric oxygen levels accumulated over the long geologic history of the Earth. This Atlantic article communicates the science behind this beautifully: (1)

theatlantic.com/science/archiv…
It’s more accurate to say that 80% of the oxygen humans breathe *came* (note use of past tense) from ocean plant life. The overwhelming majority of that oxygen was built up over incredibly long timescales by algae that lived hundreds of millions of years ago. (2) Image
Oxygen production by the plants and algae living today is of negligible influence upon the 21% of our atmosphere that is made up of oxygen, particularly as today’s photosynthetic oxygen *production* is balanced by biological *consumption* of oxygen via respiration. (3)
No matter what happens to the Amazon or ocean algae, humans will not be in any danger of suffocation.

Nor will the ocean as a whole run out of oxygen, because the atmosphere is *where the ocean gets oxygen from*, via mixing and absorption (4).
Ocean deoxygenation is often pretty misunderstood by the media and public. Yes, ocean oxygen levels have decreased as a result of climate change, but no sudden, movie-like apocalypse awaits, sorry to disappoint. (5)
First, let’s clarify how much ocean deoxygenation we’re actually talking about.

Schmidtko et al (2017)’s seminal paper found a total global ocean oxygen loss since 1960 of 2%. (6)

nature.com/articles/natur…
Ocean models are uncertain but predict global oxygen declines of 1-7% by end-of-century. Long et al (2016) for instance calculated a decline of ~4% by 2100 under a worst-case emissions scenario. (7)

agupubs.onlinelibrary.wiley.com/doi/full/10.10…
Severe deoxygenation is a regional phenomenon. Often occurs in coastal zones w upwelling, like off the west coasts of continents. Many oxygen minimum zones (OMZs) are naturally-occuring, although they are expanding due to human activity and warming. (8)

sci-hub.tw/https://www.na…
Oxygen minima are also typically restricted to particular ocean layers (100-1800m, avg ocean depth is 3.7 km).

sciencedirect.com/science/articl…

In many regions of the world, ocean oxygen concentrations have barely budged. (Figure from Schmidtko et al 2017) (9)
The upper hundred or so meters of the surface ocean are mixed by contact with the atmosphere, wind, waves, and thus are generally very rich in oxygen and rarely experience anoxic conditions.

Low-oxygen conditions can also be seasonal rather than year-round (10)
Nor are OMZs utterly devoid of marine life. Fish, zooplankton can survive in more O2-rich surface layer. If anything, OMZs are often partly caused by a surplus of algae at the surface that produce biomass that decomposes deeper down, consuming oxygen below. (11)
On the other hand, OMZs severely affect benthic organisms (crabs, shellfish, sessile fauna) that move too slowly or can't move at all to escape low-oxygen conditions. (12)
Will regions that are currently OMZs get hit harder by climate change? Absolutely. This will alter ecosystems, reduce fishery productivity, and have important physiological effects for marine life. Don’t get me wrong - ocean deoxygenation is an important climate impact. (13)
What I’m more pushing back against is the misperception that the *entire* ocean ecosystem is on the brink of suffocation, which is not the case. Nor is it the case that the oxygen in the air that we breathe today is under threat. (14)
Ultimately, expansion of OMZs is a byproduct of climate change and human activity. Some oxygen depletion could be alleviated by better managing agricultural nutrient pollution on land. The degree to which we act on climate can also greatly reduce future impacts. (END)
PS: Forgot to actually attach the Schmidtko et al 2017 figure I mentioned in tweet 9 - here it is: Image

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More from @wang_seaver

Apr 25
To supply low-carbon power to a grid via nuclear, solar, wind, or grid batteries, how much material must we dig up to build those power plants?
Answer: far less than for fossil fuels, with nuclear needing the least mining. New @TheBTI report by my team:
thebreakthrough.org/issues/energy/…
Image
Big takeaways:
Coal? Digs ~1.18 million kgs of rock+coal per GWh for fuel only
Solar+wind have improved much in last 10 yrs
Nuclear still needs least mining + critical minerals per GWh
Cu, steel, Ni, Li, U, Ag offer ways to improve mining footprint further
thebreakthrough.org/issues/energy/…
What inspired this analysis? Energy transition mining remains divisive, but discussions often cite flawed or out-of-date data, or end up handwavy. For this analysis, we wanted to make an up-to-date comparison, w transparent methodology using public sources
apps.openei.org/REMPD/
Read 24 tweets
Jan 28
From 2018 to 2023, silver use in solar PV cells has dropped by around half! (h/t @solar_chase)

Indeed academic papers (incl my own) tend to lean several yrs out of date. But industry intel is often paywalled, hence my habit of obnoxiously saving whatever nuggets I come across. Image
This is a clear example of why getting the stamp of peer-review doesn't mean something is right or the golden truth of science.

The most crucial round of peer review is really the permanent, continuous reactions/feedback from other experts once a study is actually publicly read.
I had assumed 10g per watt in my @Joule_CP paper, and had thought afterwards that might've been generous--but now it's right on the money.

Where I was way off was concrete, which is no longer used to anchor solar mountings in most utility-scale plants.

sciencedirect.com/science/articl…
Read 4 tweets
Aug 15, 2023
Finally found time yesterday evening to take an unofficial satellite's-eye-view tour of the quasi-legendary Spruce Pine ultra-high-purity quartz mine in North Carolina.

It'd be an understatement to say this mine is currently key to the semiconductor + solar PV industries. 🧵 Image
IIRC, there's no other ultra-high-purity quartz mine of this scale, creating quite the potential bottleneck. A fire at a Spruce Pine facility may have contributed to the 2008 spike in polysilicon prices that arguably set off the last decade's solar boom.

Ultra-high-purity quartz is used for chip factory tools + crucibles used to contain molten silicon during manufacturing of ultrapure monocrystalline silicon ingots for chips + solar PV wafers via the Czochralski process. Pure quartz reduces impurities in the resulting product. Image
Read 11 tweets
Jul 27, 2023
Expanding energy access + clean energy in Asia + Africa won’t be as easy as many high-profile “100% renewable” papers suggest.

My new analysis shows how 100% RE models on Asia/Africa assume implausibly low costs + overlook key infrastructure challenges.

thebreakthrough.org/issues/energy/…
A flashy review paper from @ChristianOnRE + coauthors allegedly compiling hundreds of “100% renewable energy system” studies worldwide has received a lot of recent attention.

But this isn’t as big/rigorous of a field as such stated numbers might imply.

https://t.co/L23TRAoo9C
Image
Given my interests in Asia climate/energy policy, I noticed this review generating buzz early on, and was keen to dig deeper.

I noticed some funny things at a first glance (see linked thread), but over the past months I found much more serious issues...

Read 27 tweets
Jul 26, 2023
Untangling @enricomariutti's solar PV CO2 analysis as quoted by Shellenberger, Part 2

To his great credit, Enrico has made his calculations available, emphasizing he has nothing to hide.

In the same spirit I agreed to take a close look--and I think I've isolated the key issues. Image
I’m going to work through these numbers step by step below.

I’ve made a copy of Enrico’s calculations sheet that I’ll share here in case anybody else wants to take a look. Fair warning, the units change often and are not clearly denoted:

https://t.co/JvyYOngSGLdocs.google.com/spreadsheets/d…
Image
LIFETIME GENERATION:

Enrico uses the full equivalent hours method here, assuming generation at full capacity for the equivalent of 1137 hours/yr in Italy. Other key factors include 25 year lifetime, module degradation at 2% the 1st year + 0.5%/yr thereafter, and 5.6% grid losses Image
Read 20 tweets
Jul 25, 2023
I think this solar PV CO2 analysis from @enricomariutti promoted by Shellenberger is too high for reasons I'll point out.

Mariutti gives range of 170-250 g/kWh (!!)
Many literature estimates range 12-80 g/kWh
My rough estimate of upper-end is maybe a bit more than 72 g/kWh
I think Mariutti is correct to point out that much of the LCA literature is not sufficiently accounting for more CO2-intensive Chinese manufacturing.

But Mariutti then bases electricity inputs for silicon supply chain on a 2006 study

Mariutti's calcs: https://t.co/f8PBWRYC11enricomariutti.it/the-dirty-secr…
Image
I can appreciate why he likes the transparency of the 2006 study? But this misses the past 17 years of learning-by-doing as the solar-grade polysilicon sector has scaled many times over.

He takes 1.61 GWh/MWp as the electricity input for solar-grade polysilicon, for instance.
Read 16 tweets

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