And that's all you need to know. This is yet another example of what I now call pointless science.

But if we reach 750 ppm, "Tricho has the potential to gobble up all its available resources, which could trigger die-offs of the microorganism and the higher organisms that depend on it."

Summing up, the nitrogen-fixing cyanobacteria Trichodesmium goes haywire after we reach 750 parts-per-million (ppm) of carbon dioxide in the atmosphere. Quoting Science Daily, "Trichodesmium (called "Tricho" for short by researchers) is one of the few organisms in the ocean that can "fix" atmospheric nitrogen gas, making it available to other organisms. It is crucial because all life — from algae to whales — needs nitrogen to grow."

Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean.

Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown.

There's a new paper out called Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide (Nature Communications, September 1, 2015). Here's the abstract, though you can find a more readable summary at Science Daily.

Why is this study and hundreds of others just like it pointless? Let's work through it.

The Southern Cal and Woods Hole researchers looked at the response of Trichodesmium at 750 ppm CO2. That's nearly a doubling of current levels.

There are only two questions to consider: 1) will CO2 ever reach 750 in the atmosphere? and 2) if it does, then what?

First, it is highly unlikely that we will get to 750 ppm. Economic growth (population and productivity growth) drives anthropogenic emissions.The amount of economic growth required to get to that level of CO2 is extremely unlikely to occur for reasons far too numerous to get into here.

Humans make the standard optimistic assumption that growth can continue indefinitely. Thus they discount how much they have fucked up the biosphere up to this point, and how much they will fuck it up in the next 30 or 40 years. Yet, growth is assumed to continue despite severe, ongoing degradation of the biosphere in which human civilization is embedded.

If we humans add 3 parts-per-million of CO2 to the atmosphere now and for a long time to come, it would take 117 years of steady cumulative economic growth to get to 750. Now, how many of you think that's going to happen? Give me a show of hands.

But let us suppose, contrary to everything we currently know, we reach 750 ppm sometime earlier than 117 years from now, perhaps, say, only 50 years from now in 2065. That could happen if certain positive climate feedbacks occur earlier than expected and are much, much stronger than expected. That would push up CO2 levels well above what anthropogenic emissions alone could achieve.

Or maybe, and very unexpectedly, the ocean carbon sink crashes, or the terrestrial carbon sink crashes, and thus one of these does not take up carbon at anything like current rates. As a result, carbon would accumulate in the atmosphere far faster than it does now. That could get us to 750 too.

You can mix and match these kinds of scenarios to your heart's content, but it doesn't make any practical difference in the end.

OK, now we're at 750 ppm in the year 2065, or whatever. So what's going on?

Nothing! Regarding research on the future ocean, no further research will confirm these results because the University of Southern California and the Woods Hole Oceanographic Institution do not exist. Let me say it again: do not exist. If we're at 750 in the year 2065, there will be no spring football practice at Southern Cal (video below). At 750, global industrial civilization no longer exists. There are scattered remnants, but who cares at that point?

Yes, Trichodesmium is probably going haywire in the oceans, but any surviving humans are too busy foraging for edible food and potable water to give a damn about it. Nobody is handing out grants to study this particular cyanobacteria, that's for sure. The few remaining fish care, but nobody is considering them. They're on their own.

If the point of this typical "business as usual" research is to show that humans could really fuck up future marine ecosystems in a big way, well, I think we already know that, don't we? Or maybe the point of this research is to obviate the need for any such research in the future (i.e., render all such BAU research pointless).

If the point of this research is too keep these scientists gainfully employed, well, OK, I can certainly understand that. On the other hand, I don't see how modeling impossible anthropogenic emissions scenarios or scenarios which mean the End of Everything constitute useful employment.

If the point of this research is to inform policymakers about future risks, we already know that policymakers never consider this kind of research in making "decisions" (using that term loosely) about future climate policy. That rationalization is a delusional self-serving story scientists cling to so they can keep themselves gainfully employed modeling practically impossible or catastrophic End-of-the World scenarios.

And so, by a process of elimination, we have reached the question implicit in the title: what's the point of this research?

Damned if I know.