4 Degrees Celsius, 30 Percent

This morning I saw this tweet, which is a quote from a Bloomberg News article:

“In the absence of efforts to curb emissions, the earth could warm by 2 degrees by 2050, cutting global gross domestic product by 2.5% to 7.5%, Oxford estimates. Longer term, a rise in temperatures of 4 degrees by 2100 could cut output by as much as 30%.”

And I thought, as I have thought before when I've heard similar pronouncements from economists, That makes no sense. If global temperatures go higher than they've ever been since Homo sapiens existed, let alone since there was human civilization, let alone industrial civilization and civil society, there's no way to put a number on how much the economy will decline, and even if there was, it's not 30 percent. 90 percent? 99 percent?

Like, how would we even know how much it has declined if global communication breaks down completely because there's a nuclear war caused by global unrest as climate refugees flee and nuke-holding governments are destabilized by nationalist and fascist governments?

That's about as far as I got, though, before the day began. 

Then later, I saw this tweet by Naomi Klein responding to the Bloomberg story and the economists' pronouncements:

The hubris is what gets me: these economists have no idea what 2 degree of warming will cost us. Systems are already breaking down in non-linear ways with 1 degree. Imagining that we can manage 4 degrees without total breakdown is insane. Of course no mention of the cost in lives.

The thread of responses to Klein also contains many worth absorbing:

"This cascade of events may tip the entire Earth system into a new mode of operation," said co-author Hans Joachim Schellnhuber, Director of the Potsdam Institute. The "carrying capacity" of a 4C or 5C world could drop to a billion people."
Extinction Rebellion MA

To start with, some economists predicted what would be the economic cost of human extinction. This is what comes out of having left economics to mathematicians, and left moral philosophy out.
Marco Senatore

I’m an economist. My opinion is that every econ graduate program should require a minimum amount of basic natural sciences coursework, especially physics and biology. A failure to understand the real-world implications of their models and results can lead to serious damage.
Julie Pierce

They seem so unable to consider any secondary effects. A 30% output loss means mass famine. Wars and social breakdown happen in such things. You don't get 30% quietly starving to death while 70% just chug along productively.
@DanFmTo

“It’s going to be awful when output is cut by 30%” is a strange way of discussing our extinction.
@Matthew_Lief

We really have lost the plot now. Based on the best evidence it's now cheaper to act. Don't even worry about lives, moral issues, or future of humanity. It is just economically cheaper to act. There is literally no argument not to act, except that you don't believe experts.
Dave Wiltshire

Indeed. There's a quote from WWII that says "It'd be cheaper and less damaging to the economy to just let the nazis win." Darned if I can find the source right now though. Very apt.
@ScienceNotDogma

I am not a climatologist. But as a microbiologist, I do know what the melting of arctic ice and the releasing of germs from permafrost can do to modern human population as we have never encountered some of these viruses and bacteria before. We are NOT immune.
AllOfUs

The impact costs are already mounting, escalating out of control, across the human and environmental systems and generations. They have to see this, in which case they are unethical at best and thieves at worst. #WakeUp #riskmanagement is not a belief system! #ActOnClimate
Jerry33

And concepts like GDP growth are entirely nebulous for most people – who aren’t beneficiaries of our runaway capitalist system. We know climate change is going to cost lives, homes and biodiversity, yet those real costs are juxtaposed with growth as if it’s an equal moral value.
@theRealT_Train

The wealthy are already aligning themselves with climate change. They do not want to let the cat out of the bag until they are in position to capitalize on it.
@DonDon15516330

Economists seem more isolated from the bodies of knowledge produced in other fields than the members of almost any other discipline. It’s frustrating since the sphere of “the economic” does not have any precise social boundary.
Dan Kervick

The complexity involved in predictions like this are maddening, and we delude ourselves by making authoritative-sounding claims like this. The truth is harder: We really don't know just how bad it can get. Do we have to wait and find out?
Trevor Sutherland

Indeed economics does not optimise for sustainability or human welfare. For a brief period some climate change effects create short-term opportunities; ice-free Artic navigation, arms deals for the extra conflicts caused by displaced populations, storm defences etc.
TenPastTwo

Because if they look at that the numbers would be telling them about an almost completely locked in genocide of the majority of the human race, and if they acknowledge THAT the sustainably sourced guillotines might start to appear even earlier.
@nextcontext

Economists are mere ideologues in mathematical-looking disguise. I stopped paying attention to them many years ago, except to reject through evidence their invariably incomplete, biased and wrong assumptions.
@BCNThomson

Direct your attention to this Turkish artichoke farmer who asks: what happens when the seasons no longer work?
@gimleteyeLA

It's a total crap shoot. With precious little time, profiteers will look to gain wealth, the unenlightened will continue to deny, some will wring their hands and wait for the rapture and the rest, with herculean efforts embrace, improve and implement changes required to sustain. VOTE
@edgewoman3000

I know these low-ball percentages are at least partly because these economists are afraid of sounding crazy, because that's how I feel, and I'm not in a conservative academic field.

This is why we need not just activists but science fiction (so-called cli-fi) writers to visualize these negative scenarios and show the existential danger. And their opposite, people who write and create other works showing the type of world we can build that's connected and based on cooperation and regeneration instead of competition and extraction.