What is the current thinking regarding "Atmospheric Carbon Clearing Time": 300 years, 900

[mark_in_seattle]

THESIS:
Reducing Co2 emissions toward zero (except for us all exhaling) is a necessary goal but hardly sufficient. Even if we were all perfect zero Co2 emission angels, our future is bleak unless we can terraform our planet to shorten earth's natural "Atmospheric Carbon Clearing Time".

It's a given that "terraforming" is a politically incorrect word these days. This is nothing new for the engineering and technology development guild these past couple millennium. We are often required to be the adults in the room ... especially if our prior work a few centuries ago inadvertently created the problem.


BACKGROUND:
If everyone had the opportunity to drive an electric car like my affordable Nissan LEAF, cleanly generated all their required energy, flew nowhere until carbon neutral jet fuel is available ... yada, yada, if we achieved all that green goodness in 10 years, the earth's temp would keep increasing for at least 300 - 700 years more because the excess Co2 already in the atmosphere isn't going anywhere until three major natural processes sequester it and they take approx 300 years, 700 years and 1,200 years to complete depending on which scientific journal article you read. This is the dirty little secret of climate science. Ask an oceanographer as I have, they are the best informed and know the math (ocean phytoplankton sequesters approx 58% of Co2, more than any other natural carbon sink). Google: Atmospheric Carbon Clearing Time, or similar as the subject is too extensive to do justice in this post.

QUESTION:
So what terraforming proposals seem viable/practical near term to the eng-tips-com forum members ? My top choice is enhanced phytoplankton ecology, which is what I spend some hours in retirement pursuing ... YMMV.

Thank-you.

 

[GregLocock]

One factor in this is the half life of CO2 in the atmosphere. A very simple model suggests it could be as little as 40 years, and I've seen other estimates of the same order. The way I worked it out was to look at the total CO2 emissions since 1880, and the change in atmospheric CO2 mass (loosely ppm*atmosphere mass), over that period, from which it is easy to work out the rate of deposition back into the carbon cycle. A half life model may not be appropriate, of course, most chemical reactions are proportional to the concentration of the reagents. Your number looks alarmist and silly in that context, or I have made a grave error.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[mark_in_seattle]

I am probably not qualified to consider the merits of your "...half life of Co2 in the atmosphere ..." conjecture, but I will research it as you suggest, thank-you. Can only add that the science journal articles I've read on the topic of atmospheric carbon clearing time have all concluded it will take at least several hundred years (precisely how many years like most science, is debated constantly).

One NOAA scientist I spoke with here in Seattle two years ago during a public open house at their lab, was almost brought to tears when I asked him about the Co2 clearing time issue. He said it is such a depressing topic most of his colleagues refrain from discussing it, but they know the underlying data quite well in oceanography, probably as I've stated earlier: ocean phytoplankton are the earth's biggest carbon sink. He seemed visibly relieved and astonished that an amateur outside of the discipline was aware enough to ask about this sensitive issue in climate science. He unburdened himself, talking about it at length for 10+ minutes.

Oceanography had another bombshell in the science Journal NATURE a few years back when 22(?) co-authors published a study that reviewed 110 years of ocean phytoplankton population data (very difficult task due to seasonal and decade long cycle variations) and concluded the earth's ocean phytoplankton biomass has declined steadily by 32% on a trend line since 1910. The article caused a sensation and generated a flurry of critical interest and heated debate. The authors accepted the critique and spent another two years re-analyzing all the data as well as additional data-sets. Their new result: not 32% --> 33.4% was the newest best analysis. Seeing the enhanced methodology the critics were mum and just as terrified as everyone else .... can you remember the plot line of the movie "Soylent Green": the oceans were secretly dying. I have that image in my head when I spend time working on practical processes to enhance ocean phytoplankton habitat.

 

[rb1957]

we have to be so careful in "terraforming" the planet. We do it unintentionally, and so many of our previous attempts to "fix" the environment have meant with such stellar success (usually back-fire).

Harebrained schemes include ...
1) seeding the atmosphere with particles (to reduce solar heating),
2) erecting sunshades in orbit. (At least these could be retracted).

another day in paradise, or is paradise one day closer ?

 

3) introducing non-native species
4) almost anything the US Army Corps of Engineers touches

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

I humbly enquire:

Do EVs require zero resources and materials to construct?
What surfaces are these EVs driving on?
Have their tires stopped generating crumb?
How many Chevy Volt sales are needed to cancel out one monster pickup with a belching diesel engine?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[moltenmetal]

ironic_metallurgist:

Good, disinterested 3rd party LCAs have been done, and EVs are fabulous in net overall lifecycle terms, relative to what they replace. They are not "zero emissions because nothing is, but that's not a fair comparison, it's a nirvana fallacy argument against anything new.

 

[moltenmetal]

mark_in_seattle the answer to your OP question is "It's complicated".

Just how complicated? I suggest taking a look at this carbon inventory animation which is most instructive about where the extra carbon came from and how it ended up being distributed among the various reservoirs- atmosphere, shallow oceans, deep oceans, biosphere etc.

https://www.youtube.com/watch?v=dwVsD9CiokY&ab_channel=RobertRohde

The figure I've been using is a half-life between emission of about 100 yrs, meaning that 300 yrs would be 3 halvings leaving a small residual, but that isn't a number I could hang my hat on.

 

moltenmetal,

Much depends on local circumstances, primarily how electricity is generated.

The net benefit for CO2 emissions is much smaller than most people assume (and I emphasize 'assume' as opposed to 'know'). I have a retired associate whose entire career was spent doing technology discovery and LCA, and that was the conclusion of his deep dive study. I see the main benefit being the reduction of harmful IC emissions in congested urban areas.

In the near term we can make a far bigger dent by toughening CAFE rules (and eliminating the many ridiculous loopholes), banning non-commercial and leisure diesels outright (I know, not exactly CO2), and investing in public transport. Oh, and stop the enormous subsidies to Big Oil.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[mark_in_seattle]

Thank you to all who have posted replies so far. Good info and a useful survey of opinions on the subject.

@ironic metallurgist
We can disagree on the cost/benefit considerations of personal transportation vs. public transportation, which I am guessing is one of your points: that EV's still require invested energy to produce. I live in the Pacific NW of the United States where hydropower is a major source of our electric grid, so in my limited case the electricity I use to propel our LEAF down the road is cleaner than even a Prius.

*** Are Most Public Transit Systems Really More Efficient than Private Vehicles ??? ***
You certainly could counter that when I drive alone in any vehicle it is more wasteful than public transit, however a Google consultant and big advocate for public transportation doing extensive research to assess the market opportunities for switching from owning personal vehicles to a shared vehicle ownership model (using Google driverless cars probably) in comparison to (shared) public transit was astonished to discover most public transit in America is less carbon efficient than driving a large SUV ! How is this possible ? Follow the data, I think you will find it compelling and as unexpected as I did (full disclosure: in Seattle I was a volunteer and donor to the Seattle Monorail Project started by my friend Dick Falkenbury - so I loved electricity powered public transit).

Turns out most transit systems run their buses (or light rail trains ..etc) many more hours than they carry a sufficiently large number of passengers to be efficient compared to a smaller lighter private vehicle. There are a few exceptions of good efficient public transit, which I will explain later. Many commuters experience that buses and subways are full at rush hour, but are not around to see how drastically ridership falls off system wide for the hours in-between, and worse yet, the buses run nearly empty for a surprisingly large number of hours in the early morning and late evening, burning fuel or using electricity generated by fossil fuel all the while. The US National Transportation Admin(?) keeps lots of data on this sort of thing: average number of passengers per mile, ridership at various times of day, fuel used at diff hours of operation ...etc, and for the past few decades as a gov agency they are big funders of public transit.

According the the National Transit agency, our own King County Metro bus service in the Seattle metro area has among the worst fuel per passenger mile records in the US: only 2.3 passengers per mile averaged over the entire system, during all hours of operation, on all bus routes (some years it's been 1.7 passengers/mile). And worse yet, our local Metro admin decided 20 years ago to use large buses only for all routes, at all active hours, selling off our medium size buses and even reducing the number of electric trolley buses ... go figure. And these large buses driving around at non-peak transit times with only 2-to-3 passengers onboard are heavy and burn lots of fuel. Starting and stopping at traffic lights or to pickup the few riders is very energy expensive compared to traveling along at cruising speed, or driving a personal vehicle 1/20th the weight of a city bus.

The Google consultant calculated that compared to the poor efficiency stats of most US public transit systems, driving a large SUV was more eco-friendly than riding a bus during average times of the service day on most US public transit systems. You could argue as he did, that since the buses are moving along their scheduled route regardless of whether you choose to ride or not, even if there are just a tiny number of riders, then your weight on that bus doesn't add much to the already wasteful fuel burn. However, the consultant, again prior to his research, a big fan of transit, concluded that to be energy efficient in competition with private vehicles (or shared ones) US public transit needed to emulate Asian transit systems which run at much higher ridership for a larger percentage of the service day. If the capacity utilization is high - the data shows transit systems are more efficient than private vehicles. Problem is only a few transit systems in the US meet this high capacity utilization to be considered energy efficient per passenger mile served. My brother lives in Boston, with one of the systems cited as very eco-friendly: the Boston Metro Commuter Rail system. Their secret: run all the commuter rail cars you have during peak rush hour windows and then park a large number of them on side-tracks during all other hours of the day, bringing a few more back-online to serve any unexpected demand. Like Asian commuter systems, the NY City subway is similarly efficient due to high capacity utilization. A few medium and small cities are efficient because they follow the same logic as Boston Commuter Rail: park the buses, trains when ridership is low and allow longer service time between stations, don't burn fuel needlessly to maintain the illusion of efficient service.

Probably more than you wanted to know, but I needed to provide some background if advancing a counter-intuitive claim: most (but not all) US public transit is not as energy efficient as driving a private vehicle. Believe me, as a strong monorail transit advocate I had to re-read the report several times and trackdown footnotes before altering my opinion on transit. Automated monorail systems are very popular in Asia and could be useful in the US too, but we have to manage their operation wisely.

 

[mark_in_seattle]

@moltenmetal
I watched the YouTube video at the link you provided, with the animation of the complex Carbon Cycle... useful. Thank you. FYI, as complex as that video demonstrated, in comparison, a similar animation of the various and myriad ocean carbon cycles modeled by oceanographers would require a large 8k theatre projection system ... studying them makes my head hurt, but I do my best.

Since becoming invested in this question: to terraform or not to terraform problem, I have been gathering a mountain of research papers to study the carbon cycle and atmospheric carbon clearing time with extra emphasis on the various ocean based components. I study the ocean based parts of the carbon cycle because that is the area I think I might be able to contribute a useful mechanical engineering solution. Carbon-Clearing-Time is probably very similar to your "carbon half-life" issue. Most of the science journal debate on this technical climate issue, I can only dimly follow in depth. Though, just like learning to program embedded computer control systems in the late 1970's forward, if you read things you only partially understand, eventually a higher percentage of it starts to make sense and then you can make progress.

Based on all these research papers and lectures I have attended at the University of Washington Oceanography dept (we donate a small annual gift to the university and they send me invitations to lectures in subjects I show interest), I have come to believe the years required to pull, sequester, atmospheric Co2 is much higher than a century or even two you mention for carbon-half-life. Reversing the Earth's average global temp rise could take 300-700 years as mentioned previously because the natural processes that sequester Co2 require more time than we took dumping carbon into the air. So maybe the topic I am reading is a bit different than data you have seen. Because you have brought it to my attention I will look specifically for science journal articles that mention: "carbon half-life" and report back here as time allows (next week will be busy helping my brother the doctor evaluate VC term sheets for his medical services startup - a good task to have, wish him luck improving healthcare and reducing costs).

For other folks who replied and cited concern over the unfortunate ability of us humans to inadvertently make things worse not better when we "engineer" nature, I do share your apprehension. Even small experiments have to be evaluated by skeptics and peer reviewed by those with demonstrated knowledge in the field, all in an open and transparent manner. Balance this caution with the real threat our dumping Co2 into the atmosphere has caused. It will continue to harm countless species we share the planet with. If we can find a way to use existing natural processes to reduce the harm from ongoing centuries in the future to only decades then it is worth exploring.

Also note regarding ocean phytoplankton, the foundational base of the ocean food chain, the science and data are clear, something has been reducing/destroying ocean phytoplankton colonies by approx 30% for the past 110 years for which we have data. This is yet another canary in our ironic coal mine. Ocean species will continue to die if we do nothing about improving carbon sequestration just as over-fishing has brought many species to the brink of extinction. Doing something recklessly would be really bad, doing nothing is a guaranteed disaster which future generations will curse us for.

 

Public transit is so difficult and expensive because it has to overcome a century of infrastructural inertia favouring the personal luxury vehicle (often transporting only one commuter), at the expense of all else. In other words, cities are effectively built to physically block out new rail-based systems. But it is the mindset inertia of ourselves and of institutions that is the most difficult thing to overcome. Think about it: the automobile has greater human rights than most humans.

And when we compare cost of EVs with anything else, we need to consider the entire system cost in all its aspects, past, present and future. It is a habit of promoters to be thermodynamically dishonest. We need to consider far more than how the electricity is generated; that is only a fraction of the total cost. At the end of the day, EVs are a mitigation but will have negligible impact on forestalling the present crisis.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."