System Earth 13b

Anthropogenic perturbation

Misha Velthuis

m.velthuis@uva.nl

Fri 29 Nov 2024

Where are we?

CO2 during Phanerozoic

CO2 since PETM

Last centuries

Fossil fuels and land use change

It's happening in our lifetime

Fossil fuels in comparison

How do we know it's fossil carbon?

Neurath Power Station, next to the Garzweiler mine.

Figure 2.3 from Chapter 2 of the WG1 report of AR4 of IPCC (link)

Isoptopes #1

Photosynthesis prefers C12 over C13

Fossil fuels have a relatively low C13:C12 ratio

Burning fossil fuels should lower the C13:C12 ratio of carbon in the atmosphere.

That is indeed what we observe (see red line in graph).

Refresher of how to interpret δ¹³C (using image from δ¹⁸O):

(Note that δ¹³C is declining, but they flipped the y-axis).

Isotopes #2

Without anthropogenic perturbation, because of natural C14 production and decay in the atmosphere, the atmosphere has a certain C14/C ratio.

When carbon gets buried, over time the C14 decays (into N14).

Burning the fossil carbon that is devoid of C14, should lower the C14/C of the atmosphere.

That is indeed what we observe.

Decline in oxygen

The combustion of fossil fuels consumes oxygen.

Indeed, we see atmospheric oxygen levels go down (in tandem with CO2 emissions).

Also: we see the oxygen levels go down more strongly in the northern hemisphere than in the southern hemisphere which is where most of the burning takes place.

This shows in the graph on the left:

Canada is pink
Australia is blue

Because of the larger land mass (and therefore biomass) in the northern hemisphere, the amplitude of the oxygen fluctuation is higher in the northern hemisphere than in the southern hemisphere. This itself has nothing to do with fossil fuel combustion.

Because most of the combustion of fossil fuels takes place in the northern hemisphere, the oxygen levels will be relatively low in the northern hemisphere (which will cause a NH-SH gradient, that will produce a northward flux). The average oxygen level of pink (declining) trend (Canada) does appear lower than the avere level the blue (declining) trend (Australia).

What happens to all this carbon?

Short term: atmosphere, ocean, land

C in the atmosphere

C captured in biomass

C in oceans

Longer timescale:
restored ocean uptake
and sedimentary rock

Carbonate dissolution restores pH

Higher pH means deeper "carbonate compensation depth": together with bioturbation of ocean floor = ocean floor dissolution.

This restores carbonate ion concentrations, i.e. the ocean's buffer.

Reaction 3 moves to the left. In absolute terms (moles) H₃O⁺ decreases as much as HCO₃^- increases.

But because pH is still relatively high (i.e. low H₃O⁺ concentration), relatively, the H₃O⁺ concentration declines more than that the HCO₃^- concentration increases. So the product of H₃O⁺ and HCO₃^- (the right side of reaction 2) decreases. So reaction 2 moves to the right. (= uptake of CO2).

This allows the ocean to "return" to previous levels of CO2 uptake.

C in sedimentary rock

Partition over time

Share in atmosphere increases

The future of the planet #1

Two main sources of uncertainty

Play with different scenarios

The past as the key to the future #1

The past as the key to the future #2

Wet-bulb temperature

Brannen:

"Wet-bulb temperatures of 35 degrees Celsius or higher are lethal to humanity" (p. 256 of 406).

What is wet-bulb temperature?

The temperature you'll have in a certain environment (air temperature), when you're fully covered in sweat/water that is ready to evaporate.

We cool down through the evaporation of sweat.
When it's 35°C outside, our skin will be significantly colder because of this sweating.
The higher the relative humidity, the slower the sweat/water will evaporate, the less this "cooling trick" works.
So the wet-bulb temperature increases when the air temperature increases, but also increases when the relative humidity increases, because the higher relative humidity makes it harder to lose heat through evaporation.

Bottom line: when it gets very hot, and the air is very humid, people are unable to get rid of the heat that they need to get rid of, and then they die.

From wiki:

"The wet-bulb temperature (WBT) is a temperature that can be measured by a thermometer covered in cloth which has been soaked in water at ambient temperature (a wet-bulb thermometer) and over which air is passed. At 100% relative humidity, the wet-bulb temperature is equal to the air temperature (dry-bulb temperature); at lower humidity the wet-bulb temperature is lower than dry-bulb temperature because of evaporative cooling."

Map from: Lucas, R. A., Epstein, Y., & Kjellstrom, T. (2014). Excessive occupational heat exposure: a significant ergonomic challenge and health risk for current and future workers. Extreme physiology & medicine, 3, 1-8.

Tip: read the first chapter of the "Ministry for the Future" (and the rest is very moving as well).

“If warmings of 10°C were really to occur in the next three centuries, the area of land likely rendered uninhabitable by heat stress would dwarf that affected by rising sea level.”

Organize and resist

The future of the planet #2

Longer term

100,000 years

Even longer term

800 million years

Over time, the sun is getting less young, and less faint. (As in, the irradiation the earth will receive from the sun will continue to increase. See the "Faint young sun paradox" in Kump et al.).

Silicate weathering is expected to steadily increase, while volcanism is expected to remain (on large timescales) constant.

As a result, the atmospheric CO2 concentration is expected to steadily decline. Up to the point where photosynthesis becomes impossible.

The planet will become increasingly shrubby, barren, and brown until about 800 million years from now, when carbon dioxide will drop below 10 parts per million. When this happens, photosynthesis—and thus plant life—will become impossible. When plant life disappears, so too will the animals that depend on them for food and oxygen.

Brannen on the "poetic symmetry of the story of life on earth":

"Long after animals have wandered the earth, and even after the dramatic microcosm of the eukaryotic microbe universe is gone, bacteria will inherit the planet for a few hundred million years more, just as it was in the beginning."

And a longer quote:

"On a red dune overlooking a salt flat more than 300 feet thick and extending thousands of miles, the red sun swells enormously in the sky, though hazily through the Venus-like atmosphere. It’s hundreds of degrees out, and the withering toxic haze makes it hard to believe that this was once a verdant world, teeming with biology. The showy pageantry of complex life is long over, and the former splendor of the oceans and jungles is petrified and buried deep underfoot in limestones, in coal tableaus, and in fossils that no one will ever study. In 1.6 billion years, in the face of a pitilessly hostile and temperamental star, conditions on the planet will become so inimical to life, even deep underground, that bacteria will be extinguished. On the other side of this last mass extinction is eternity. Peter Ward and Donald Brownlee have noted the poetic symmetry to this story of life on earth, where multicellular life, eukaryotes, and prokaryotes will take a bow in the reverse order that they first appeared onstage."

System Earth 13b

Anthropogenic perturbation

Misha Velthuis

m.velthuis@uva.nl

Fri 29 Nov 2024

Where are we?

CO2 during Phanerozoic

CO2 since PETM

Last centuries

Fossil fuels and land use change

It's happening in our lifetime

Fossil fuels in comparison

How do we know it's fossil carbon?

What happens to all this carbon?

Short term: atmosphere, ocean, land

C in the atmosphere

C captured in biomass

C in oceans

Longer timescale:
restored ocean uptake
and sedimentary rock

Carbonate dissolution restores pH

C in sedimentary rock

Partition over time

Share in atmosphere increases

The future of the planet #1

Two main sources of uncertainty

Play with different scenarios

The past as the key to the future #1

The past as the key to the future #2

Wet-bulb temperature

Organize and resist

The future of the planet #2

Longer term

Even longer term

Being local
feeling lucky

Lucky #1:
Life exists

Lucky #2:
Strong negative feedback loops
have saved "us" multiple times

Lucky #3:
Still: multiple close calls

Coincidence?

Let's enjoy it while it lasts,
while fighting for it to last

System Earth 13b

Anthropogenic perturbation

Misha Velthuis

m.velthuis@uva.nl

Fri 29 Nov 2024

Where are we?

CO2 during Phanerozoic

CO2 since PETM

Last centuries

Fossil fuels and land use change

It's happening in our lifetime

Fossil fuels in comparison

How do we know it's fossil carbon?

What happens to all this carbon?

Short term: atmosphere, ocean, land

C in the atmosphere

C captured in biomass

C in oceans

Longer timescale:restored ocean uptakeand sedimentary rock

Carbonate dissolution restores pH

C in sedimentary rock

Partition over time

Share in atmosphere increases

The future of the planet #1

Two main sources of uncertainty

Play with different scenarios

The past as the key to the future #1

The past as the key to the future #2

Wet-bulb temperature

Organize and resist

The future of the planet #2

Longer term

Even longer term

Being localfeeling lucky

Lucky #1:Life exists

Lucky #2:Strong negative feedback loopshave saved "us" multiple times

Lucky #3:Still: multiple close calls

Coincidence?

Let's enjoy it while it lasts,while fighting for it to last

Longer timescale:
restored ocean uptake
and sedimentary rock

Being local
feeling lucky

Lucky #1:
Life exists

Lucky #2:
Strong negative feedback loops
have saved "us" multiple times

Lucky #3:
Still: multiple close calls

Let's enjoy it while it lasts,
while fighting for it to last