[the_gastropod]

And then the whole melting of sea ice thing. Sea ice is pretty much the whitest/most reflective surface on the planet. It then melts into the darkest/most absorbent surface on the planet.

Are there any stabilizing forces we know about? I only ever hear about these types of positive feedback loops, and it scares the hell out of me.

[rgbrenner]

Here are a few:

increased temp > increased evaporation > increased cloud coverage which reflects more sunlight

increased co2 > increased tree growth

increased co2 > increased algae, plankton growth to absorb co2... other marine animals will also feed on these, increasing their mass, and when they die, they'll sink to the bottom, where they'll mostly remain.

increased co2 > increased diffusion into seawater.. clams, oysters, etc combine this carbon with calcium to produce shells.. and when they die, they accumulate on the sea floor eventually turning into rock.

Unfortunately, the fact that co2 in the atmosphere is growing indicates we're overwhelming these.. I take zero comfort in the fact that these exists.. it actually makes me nervous because once they reach their maximum, co2 will start growing even more rapidly.. and then it'll be so much worse.

[themgt]

Not only is CO2 continuing to rise, but it's rate of growth appears to be accelerating, from ~1.5ppm/year in the 80s/90s to 2ppm/year earlier this decade and now as much as 2.5-3ppm/year average now.

If this continues, we'll hit 420ppm within a couple years, 430ppm maybe 4 years after that, over 440ppm if not nearing 450ppm by the end of the 2020s with no slowdown in sight.

Truly, truly alarming.

http://mlg.eng.cam.ac.uk/carl/words/carbon.html

[pdonis]

> increased evaporation > increased cloud coverage which reflects more sunlight

Also increased evaporation > increased latent heat transport to upper atmosphere where it can more easily escape to space. According to the numbers in Kiehl & Trenberth's global energy budget, total latent heat transport is about 80 W/m^2, which means a 5 percent increase in it would entirely cancel out the increased radiative forcing from a doubling of CO2. This is a negative feedback that I don't see discussed much at all.

> the fact that co2 in the atmosphere is growing indicates we're overwhelming these

No, it doesn't, it just indicates different timescales for CO2 emissions vs. uptake.

[TheSpiceIsLife]

>> the fact that co2 in the atmosphere is growing indicates we're overwhelming these

>No, it doesn't, it just indicates different timescales for CO2 emissions vs. uptake.

It's not clear to me what the distinction is you're trying to make here? If the time scale for emissions vs. uptake is different such that emissions are exceeding uptake capacity due to the different timescales, isn't the previous comment correct?

[pdonis]

> It's not clear to me what the distinction is you're trying to make here?

If the uptake timescale is longer, uptake will catch up to emissions over time (I realize I didn't make that sufficiently clear in my previous post), so CO2 growth does not indicate that uptake has reached "maximum", which is what the post I responded to was claiming.

[TheSpiceIsLife]

If uptake capacity is decreasing and CO2 emissions are increasing, which I'm lead to believe is the case, and atmospheric and oceanic CO2 levels are increasing, which I'm also lead to believe the case...

Then I don't understand where you're coming from?

[pdonis]

> If uptake capacity is decreasing

I never said that, and I don't think it's true. The timescale I was referring to is the timescale for uptake capacity to respond to a change in CO2 levels. For example, trees grow and reproduce more slowly than CO2 levels have been changing, so the increase in uptake from tree growth and reproduction takes some time to respond to an increase in CO2. But that doesn't mean it never responds. It does; uptake capacity does increase.

[baq]

One slight problem is that we know there were turtles and palm trees in the arctic 50My ago.

[rad88]

Have you looked at Project Vesta? It's a proposal to create olivine beaches around the tropics to boost sequestration due to rock weathering. I think it's somewhat disputed because rock weathering in a surf happens at a different rate than normal, but their analysis is that if "only" 2 percent of tropical beaches were covered in olivine the weathering would counteract current emissions. I can't tell how serious this proposal is and am curious to hear from anyone who knows more about this process.

https://projectvesta.org/

[mrskitch]

I’ve seen this thrown around as well, and would love to hear more. I’m interested in helping the project since it’s about the only one that has stood up to any scrutiny that I’ve seen

[goodname]

increased evaporation - water vapor is a potent green house gas

increased co2 > increased diffusion into seawater - isnt acidity of the ocean increasing, making it more difficult for the shelled sea life to even develop?

[pdonis]

> increased evaporation - water vapor is a potent green house gas

But its lifetime in the atmosphere is very short; the evaporated water vapor condenses in the upper atmosphere into clouds and precipitation.

What longer term numbers I have seen indicate that the average water vapor content of the atmosphere has been roughly constant during the warming of the last half century or so.

[labster]

More importantly there is tons and tons of water in the atmosphere, even in so-called dry places. There’s just no wiggle room in the water vapor spectral bands, optical path is pretty constant.

We will probably get more water vapor in the future but most of the PWAT ends up in clouds. And that’s where the feedbacks get interesting, cloud height is very important to radiative balance and there are a couple of indirect effects to consider too.

[ouid]

microplastics aggregate in longer lived predators organisms, killing sharks before plankton. Lowering the maximum size of animal paradoxically increases total biomass, though it's unclear by how much, and it's a pretty unstable proposition at its core what happens to humans in a mass extinction of large organisms.

[DennisP]

Based on geological history, the negative feedbacks seem predominant for small perturbations, but if you push things a little too hard the positive feedbacks take over. It's happened before several times; a little initial heating from orbital variations, which leads to greenhouse gas emissions, which leads to the global average temperature going up several degrees. A good explanation of the evidence for this is in James Hansen's Storms of My Grandchildren.

People have long thought the threshold to be around 2 degrees C, but now some are thinking it's more like 1.5. The CO2 level everybody agreed was safe was 350 ppm.

[mlyle]

(and then obviously negative feedback takes back over, as we don't run away to infinite or zero temperature).

[easymodex]

I suppose, but before that happens the environment could get very, very unpleasant for humans (and animals in general).

[mlyle]

Yah, the point is if we draw a set of hills with bumps and stable equilibria for a ball to roll down-- there is resistance to perturbation near an initial point, and then a sufficient "nudge" to get over a hill and roll somewhere else... but the ball always ends up in a stable region at the bottom of a hill.

How different a place that new equilibrium is ... is open to debate and not really known. What climate scientists have shown is that it can be, and likely is, pretty bad.

[nostrademons]

The primary negative feedback loop is increased photosynthesis. As CO2 concentrations rise, there's more carbon in the air that can support plant life. There also tends to be both more sunlight (warmer air can support more water vapor before it precipitates into clouds) and more water (in absolute terms, from increased evaporation).

Note that in the near term, the negative feedback of photosynthesis may be overwhelmed by changes in ecosystems: if the climate changes rapidly, whole forests may find themselves in a different biome, ocean circulation patterns may change, more freshwater may enter estuaries, etc. Plants evolve quickly, though, and most of their carbon sequestration is through algae and seaweed with short lifespans.

[vonmoltke]

Unfortunately, I think human land use is impeding that feedback mechanism, as there are large portions of land area that are not allowed to freely green up anymore.

[nostrademons]

That'll change as human-caused global warming results in widespread crop failures and migration of people. We're at the top of the food pyramid; change an ecosystem and (most of) humanity is the first to go. It only takes about one human generation for an ecosystem to recover after humans leave: Chernobyl and the Korean DMZ are among the most pristine environments on earth now.

This is probably cold comfort for the billions of people that will die.

[jussij]

And you can add to that list several natural forces as well.

For example, the Australia tropical rain forest, which by it's definition is wet, never has to deal with fire.

But this year that change as some parts of the Australian rain forest experienced bush fires.

If that trend continues then those ecosystem will struggle to survive as they have not evolved to deal with fire on a regular basis.

[BurningFrog]

I keep hearing forests are on the rise lately, as the world urbanizes: https://www.theglobeandmail.com/opinion/we-are-making-the-gl...

[chimi]

Global Dimming is caused by pollution emitted into the air. This has caused a decline in the Pan Evaporation rate. Meaning, less water is evaporating now than decades prior.

My concern is, if we stop polluting the environment and the global dimming is stopped, then climate change will get much worse.

Global Dimming might explain why the climate hasn't changed as much as some would expect.