Dissing DAC

[Greg Rau]

https://thebulletin-org.cdn.ampproject.org/c/s/thebulletin.org/2023/12/direct-air-capture-an-expensive-dangerous-distraction-from-real-climate-solutions/amp/

“ All year, the zeitgeist has been building toward technologies that separate carbon dioxide from air, referred to as direct air capture (DAC). In September, the United States Department of Energy awardedOccidental Petroleum a $600 million grant to build a DAC machine. As scientists and entrepreneurs who’ve dedicated our careers to help solve global warming, you might expect us to be happy.

We are not.  The reason is simple: Separating carbon dioxide from air, while technically straightforward, is outrageously expensive. In fighting climate change, the obvious question should always be: How can we avoid the most carbon dioxide per dollar invested?

GR Interesting, coming from the founder of C12, Kurt House, that sought to provide geologic storage for CCS and DAC, https://venturebeat.com/business/c12-energy-captures-45m-for-carbon-sequestration/ , not to mention he was the inventor of electrogeochemical CDR https://pubs.acs.org/doi/10.1021/es0701816

I don’t think the problem is DAC, but the fact that DAC has been gifted Bs of taxpayer $$ as though it is the answer to CDR. Fortunately, private investment is much more willing to diversify and hedge its bets. US gov policy and investment needs to follow suit, fossil fuel lobbyists permitting.

Sent from my iPhone

[Greg Rau]



https://thebulletin-org.cdn.ampproject.org/c/s/thebulletin.org/2023/12/direct-air-capture-an-expensive-dangerous-distraction-from-real-climate-solutions/amp/

“ All year, the zeitgeist has been building toward technologies that separate carbon dioxide from air, referred to as direct air capture (DAC). In September, the United States Department of Energy awardedOccidental Petroleum a $600 million grant to build a DAC machine. As scientists and entrepreneurs who’ve dedicated our careers to help solve global warming, you might expect us to be happy.

We are not.  The reason is simple: Separating carbon dioxide from air, while technically straightforward, is outrageously expensive. In fighting climate change, the obvious question should always be: How can we avoid the most carbon dioxide per dollar invested?”

GR Interesting, coming from Kurt House, the founder of C12 that sought to provide geologic CO2 storage for CCS and DAC, https://venturebeat.com/business/c12-energy-captures-45m-for-carbon-sequestration/ , not to mention he was the inventor of electrogeochemical CDR https://pubs.acs.org/doi/10.1021/es0701816

I don’t think the problem is DAC, but the fact that DAC has been gifted Bs of taxpayer $$ as though it is the answer to CDR. Fortunately, private investment is much more willing to diversify and hedge their bets. US gov policy and investment needs to follow suit, fossil fuel lobbyists permitting.

Sent from my iPhone

[Dan Miller]

My comment posted to the article:

While DAC is very expensive today and only a tiny amount has been deployed, the same thing would have been said about solar PV 25 years ago. Funding DAC is not about reducing the most emissions per dollar today. It is about developing and scaling a technology that is *required* for us to maintain a safe climate. As James Hansen has recently pointed out, we are effectively at 1.5ºC now and may pass 2ºC in the *2030s*! And 2ºC itself is catastrophic.

One of the most important things to know about climate change is that CO2 lasts in the atmosphere for hundreds to thousands of years, so things won't get better when and if we hit net zero. Whatever temperature we are at when we finally stop emitting GHGs, that is the temperature we have for the next 1000 years... if we are lucky and don't pass tipping points first!

So while renewables provide the most bang for the buck, DAC/CDR (and Sunlight Reflection Methods - SRM) are required to pass on a safe climate to our children. Renewables alone won't cut it. But we don't need to take renewable money to pay for DAC, we instead can take some of the $1 trillion in direct fossil fuel subsidies or the $6 trillion in indirect subsidies to pay for it. And if that's not enough, why not trade off cruise ships vs. DAC instead of solar vs. DAC?

While DAC is expensive, the cost of *not* deploying it is far higher than the cost of deploying it.

Dan

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[Ken Caldeira]

It would be nice if people would spend less effort on attacking things other people are doing to try to address the climate problem, and more time focused on the drivers of the emissions that are causing the emissions.

People working on climate solutions do not have to form a circular firing squad.

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[Adam Sacks]

It would also be nice if we generally acknowledged that an overheated Earth has its roots in billions of acres of bare land and general human-civilization mismanagement of the biosphere.  To attribute growing catastrophic collapse of ecosystems worldwide to a single isolated variable is a futile and expensive non-solution - although of course we should reduce/eliminate fossil fuel emissions as well.

Adam

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[Albert Bates]

Dan's analogy to solar PV is inapt (not inept). In his October 12 interview for the Nori Reversing Climate Change podcast (S3 E57), Paul Hawken neatly described how DAC won't and can't follow Moore's Law. https://nori.com/podcasts/reversing-climate-change/S3E57-Is-direct-air-capture-an-energetic-dead-end-w-Paul-Hawken--author-of-Regeneration-Ending-the-Climate-Crisis-in-One-Generation-e2a0f9e

The limiting factor is unlikely to be CAPEX or OPEX but rather electricity from renewable sources. There is a whole lot of competition for that at the moment.

[Clive Elsworth]

I don’t see how DAC stands a snowball’s chance in hell of preventing what appears to be coming down the line, according to ‘Sam Carana’, NASA: https://arctic-news.blogspot.com/2023/12/double-blue-ocean-event-2024.html?fbclid=IwAR298XtOUsh08P7RzLQrstqhgidMa3svjjPtJl2S892lrgoGAIrVqC2q0HI

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[Dan Miller]

DAC won’t follow solar PV’s amazing run (99% drop in cost in 30 years) but it will have a learning curve that can drop the cost 80~90% at scale.  As for limits of renewable energy, most DAC systems use “Earth energy”, not manmade renewable electricity, to power most of the capture/release cycle and can use Earth energy for sequestration as well.  For example, the first commercial DAC system from Climeworks uses geothermal heat and cooling air for the capture/release cycle and basalt soil chemistry for the sequestration cycle. It does use geothermal electricity for fans, pumps, and balance of plant operations.

While Iceland has great geothermal resources, most places on Earth can provide the ~120ºC heat needed for DAC sorbent regeneration via geothermal wells. And many places have the basalt soils needed for that approach to sequestration. DAC can be situated anywhere on Earth where the appropriate energy sources (including wind and solar) and sequestration venues are available.  There is no need to compete with renewable energy powering cities, etc. And, as I mention below, there is no need to trade renewables vs. DAC. Instead we can trade DAC (which is needed for survival) against all the other things that are not need for survival.

It’s not that DAC will be cheap, it’s just that the cost of not doing it will be far more expensive.

DAC costs ~$500/ton at kiloton scale. At gigaton scale (1,000,000X) the cost should be in the $50/ton range.  AT $50/ton, 40 Gt/y costs $2 trillion/year, which is a bargain compared to having a 3ºC world.  We will need SRM in the interim to avoid devastating temperatures and tipping points, but in the medium to long term, we must remove the excess CO2 in the atmosphere.

For more on the practicality of DAC, listen to my interview with Klaus Lackner, one of the first scientists to explore direct air capture:

Dan

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[Kevin Wolf]

Dan,

Thanks for the thoughtful insights.  I do have issues with some of your statements

"Whatever temperature we are at when we finally stop emitting GHGs, that is the temperature we have for the next 1000 years..."

When CO2 PPM levels decrease to 350 and eventually to 300,  temperatures will go down.  Whatever sea level rise occurred in the meantime will likely stay there for a long time. But as I understand it, temperature correlates to GHG PPMs. 

For example, nature is good at removing CO2 and has a history of being so good at it that it has plunged the world into ice ages 10 times over the last million years.  Volcanic dust with iron and trace minerals preceded massive, multi-year phytoplankton blooms that caused PPM levels to plummet and result in ice ages.  We can replicate that on a scale that quickly brings CO2 levels  to 300 PPM, if we  use the help of Mother Nature and photosynthesis. 

The good news is that humans can increase  phytoplankton blooms, kelp forests,  mangrove forests and seagrass pastures, and in the process increase fisheries and help provide protein that otherwise is likely to be provided by GHG producing meat production.  In the process, no new renewable energy facilities have to be made to produce the energy to remove the CO2.

I appreciate that there are DAC technologies that won't compete for renewable energy sources but I know of none that won't require increasing the demand and thus prices for metals that will make renewable energy projects more costly which will result in fewer of them securing financing and being installed.   Could they scale to what is needed without forcing up the costs of metal and material for emission reduction strategies? Any idea how much metal and other material would be needed to remove a gigaton of CO2 per year?

Kevin Wolf, Co-chair

Ocean Iron Fertilization Alliance

kevin...@gmail.com

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/EC8F8C2E-5DBF-4371-942E-4D2DF5088EBE%40rodagroup.com.

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+1.530.758.4211

[Dan Miller]

While it is true that oceans, etc. will continue to take up CO2 after we stop emissions, it is also true that there is a large Earth Energy Imbalance (EEI) that will act to continue to warm the Earth after we stop emissions. If we are lucky, these two effects cancel each other out and temperatures stabilize after emissions stop. Another factor is that aerosols go away after emissions stop and that greatly adds to warming, but that too is hopefully offset by the dissipation of short-lived GHGs such as methane, which leads to cooling over a decade or so.

Hansen’s Pipeline paper shows that warming from GHGs is more than the IPCC says (ECS is 4.8ºC vs. IPCC’s 3ºC) and aerosol cooling is much higher than the IPCC says (warming from reduction of ship sulfur emissions is ~10X more than the IPCC predicts). So these two factors could screw up the “temperature stabilizes at zero emissions” hypothesis. Also, we will quite likely pass irreversible tipping points (e.g., AMOC shutdown) before we get to zero emissions and that is another reason for strong action on CDR and SRM.

Dan

On Dec 16, 2023, at 1:28 PM, Kevin Wolf <kevin...@gmail.com> wrote:

Dan,

Thanks for the thoughtful insights.  I do have issues with some of your statements

"Whatever temperature we are at when we finally stop emitting GHGs, that is the temperature we have for the next 1000 years..."

When CO2 PPM levels decrease to 350 and eventually to 300,  temperatures will go down.  Whatever sea level rise occurred in the meantime will likely stay there for a long time. But as I understand it, temperature correlates to GHG PPMs. 

For example, nature is good at removing CO2 and has a history of being so good at it that it has plunged the world into ice ages 10 times over the last million years.  Volcanic dust with iron and trace minerals preceded massive, multi-year phytoplankton blooms that caused PPM levels to plummet and result in ice ages.  We can replicate that on a scale that quickly brings CO2 levels  to 300 PPM, if we  use the help of Mother Nature and photosynthesis. 

The good news is that humans can increase  phytoplankton blooms, kelp forests,  mangrove forests and seagrass pastures, and in the process increase fisheries and help provide protein that otherwise is likely to be provided by GHG producing meat production.  In the process, no new renewable energy facilities have to be made to produce the energy to remove the CO2.

I appreciate that there are DAC technologies that won't compete for renewable energy sources but I know of none that won't require increasing the demand and thus prices for metals that will make renewable energy projects more costly which will result in fewer of them securing financing and being installed.   Could they scale to what is needed without forcing up the costs of metal and material for emission reduction strategies? Any idea how much metal and other material would be needed to remove a gigaton of CO2 per year?

Kevin Wolf, Co-chair

Ocean Iron Fertilization Alliance

kevin...@gmail.com

On Sat, Dec 16, 2023 at 12:18 PM Dan Miller <d...@rodagroup.com> wrote:

DAC won’t follow solar PV’s amazing run (99% drop in cost in 30 years) but it will have a learning curve that can drop the cost 80~90% at scale.  As for limits of renewable energy, most DAC systems use “Earth energy”, not manmade renewable electricity, to power most of the capture/release cycle and can use Earth energy for sequestration as well.  For example, the first commercial DAC system from Climeworks uses geothermal heat and cooling air for the capture/release cycle and basalt soil chemistry for the sequestration cycle. It does use geothermal electricity for fans, pumps, and balance of plant operations.

While Iceland has great geothermal resources, most places on Earth can provide the ~120ºC heat needed for DAC sorbent regeneration via geothermal wells. And many places have the basalt soils needed for that approach to sequestration. DAC can be situated anywhere on Earth where the appropriate energy sources (including wind and solar) and sequestration venues are available.  There is no need to compete with renewable energy powering cities, etc. And, as I mention below, there is no need to trade renewables vs. DAC. Instead we can trade DAC (which is needed for survival) against all the other things that are not need for survival.

It’s not that DAC will be cheap, it’s just that the cost of not doing it will be far more expensive.

DAC costs ~$500/ton at kiloton scale. At gigaton scale (1,000,000X) the cost should be in the $50/ton range.  AT $50/ton, 40 Gt/y costs $2 trillion/year, which is a bargain compared to having a 3ºC world.  We will need SRM in the interim to avoid devastating temperatures and tipping points, but in the medium to long term, we must remove the excess CO2 in the atmosphere.

For more on the practicality of DAC, listen to my interview with Klaus Lackner, one of the first scientists to explore direct air capture:

--

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[Dan Miller]

I’m interviewing Jim Hansen on my Climate Chat podcast on Sunday, December 17 at 10am Pacific.

Here is the link to the YouTube Live stream: 

https://youtube.com/live/8Ag3UVSrlhE 

If there is a problem with the live stream, go to the Climate Chat home page and see if there is an alternative stream: https://www.youtube.com/channel/UC3BXcpYFCzTndJ9Fisi32qg 

Regards,

Dan

[Anton Alferness]

Kevin - 

The heat energy in the system (stored in the oceans) will contribute to temperature levels in ways that lower PPM's of GHG may not be able to attenuate. I think this is obviously uncharted territory for anyone alive today. So while we might get down to 300ppm, we may still have a temperature problem. 

-Anton 

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/B15516A3-6049-4573-8A51-AF17FBEBD6AC%40rodagroup.com.

[Kevin Wolf]

Anton,

Reducing CO2 levels to 300 PPM or less (it was at 280 when the industrial revolution started) will certainly reduce the amount of heat that is retained as the intensity of the 'greenhouse" lessens.  You may be right that the expected drop in temperature may lag or may not correlate exactly to lower PPM levels as anticipated but we know that lower CO2 and methane levels will reduce the amount of heat that is retained each day, which will eventually result in lower temperatures.

Kevin Wolf - Co-chairf

Ocean Iron Fertilization Alliance

kevin...@gmail.com

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[robert...@gmail.com]

Kevin

The time lag is critical.  The longer the climate response time, the greater the danger of cascading tipping events being triggered.  If they are, all that CDR effort becomes somewhat futile.  Hansen et al's recent paper puts the e-folding time at closer to 100 years in contrast to earlier assumptions that it is 10 to 20 years.  That issue needs to be bottomed out because however great it might be to see the cavalry arrive, they need to arrive in good time.  'Eventually' isn't very helpful!

All discussions about CDR must be address not just their scaling but also the speed at which they can be scaled.  For the avoidance of doubt 'can' here means in the real world with all its messy constraints, not in some idealised theoretical world constructed on a spreadsheet.

Regards

Robert

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[Tom Goreau]

100 years is a good guess at e-folding time for the surface ocean, but for the deep sea it is 1500 years, so the more heat gets into the deep sea, the longer it will take to equilibrate, which buys time..

 

From: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> on behalf of robert...@gmail.com <robert...@gmail.com>
Date: Monday, December 18, 2023 at 8:58 AM
To: Kevin Wolf <kevin...@gmail.com>, Anton Alferness <an...@paradigmclimate.com>
Cc: Dan Miller <d...@rodagroup.com>, Albert Bates <alb...@thefarm.org>, Carbon Dioxide Removal <carbondiox...@googlegroups.com>
Subject: Re: [CDR] Dissing DAC

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/62bf9e6b-897f-4d0b-9026-a1ab53c22ab6%40gmail.com.

[Bruce Melton -- Austin, Texas]

Costs of DAC are currently $50/ton(+/-) for the lime-potash process (Keith 2018). This considers half of energy used being flame energy from natural gas to support oxidation, and the other half at $0.01 kWh renewables. AR6 shows DAC at $84 to $386 per ton and does not interpret Keith 2018 with renewable energy. Over 200, 1 million ton per year units are currently committed by 2035 under IRS 45Q. Of course there is a great risk that scaling DAC cannot happen fast enough to lower Earth's temperature sufficiently to stop irreversible tipping but without it we are faced with geoengineering for hundreds of years while emissions reductions work restores the energy imbalance.

B

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
(512)799-7998
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ClimateChangePhoto.org
MeltonEngineering.com
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[Seth Miller]

A mild push-back here. Oxy is current implementing the Keith process, but their costs are projected close to $500/ton once the first plants are at full capacity. And a plant like this won’t turn on at 24/7/365 utilization, so the cost will start considerably higher! Even once these plants are stabilized and fully operational, their projected costs are looking at best around $300/ton by 2030, and that is pretty optimistic.

Can we get to $50/ton in a world with nearly free, clean energy, and where the original capex has been fully depreciated? Maybe? We don’t live in that world, though.

Best,

Seth

-------

Seth Miller, Ph.D.

www.linkedin.com/in/sethmiller2

Check my blog at: perspicacity.xyz

On Dec 18, 2023, at 10:05 AM, Bruce Melton -- Austin, Texas <bme...@earthlink.net> wrote:

Costs of DAC are currently $50/ton(+/-) for the lime-potash process (Keith 2018). This considers half of energy used being flame energy from natural gas to support oxidation, and the other half at $0.01 kWh renewables. AR6 shows DAC at $84 to $386 per ton and does not interpret Keith 2018 with renewable energy. Over 200, 1 million ton per year units are currently committed by 2035 under IRS 45Q. Of course there is a great risk that scaling DAC cannot happen fast enough to lower Earth's temperature sufficiently to stop irreversible tipping but without it we are faced with geoengineering for hundreds of years while emissions reductions work restores the energy imbalance.

B

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
(512)799-7998
ClimateDiscovery.org
ClimateChangePhoto.org
MeltonEngineering.com
Face...@Bruce.Melton.395
Inst...@Bruce.C.Melton
The Band Climate Change
Twitter - BruceCMelton1

On 12/16/2023 2:17 PM, Dan Miller wrote:

DAC won’t follow solar PV’s amazing run (99% drop in cost in 30 years) but it will have a learning curve that can drop the cost 80~90% at scale.  As for limits of renewable energy, most DAC systems use “Earth energy”, not manmade renewable electricity, to power most of the capture/release cycle and can use Earth energy for sequestration as well.  For example, the first commercial DAC system from Climeworks uses geothermal heat and cooling air for the capture/release cycle and basalt soil chemistry for the sequestration cycle. It does use geothermal electricity for fans, pumps, and balance of plant operations.

While Iceland has great geothermal resources, most places on Earth can provide the ~120ºC heat needed for DAC sorbent regeneration via geothermal wells. And many places have the basalt soils needed for that approach to sequestration. DAC can be situated anywhere on Earth where the appropriate energy sources (including wind and solar) and sequestration venues are available.  There is no need to compete with renewable energy powering cities, etc. And, as I mention below, there is no need to trade renewables vs. DAC. Instead we can trade DAC (which is needed for survival) against all the other things that are not need for survival.

It’s not that DAC will be cheap, it’s just that the cost of not doing it will be far more expensive.

DAC costs ~$500/ton at kiloton scale. At gigaton scale (1,000,000X) the cost should be in the $50/ton range.  AT $50/ton, 40 Gt/y costs $2 trillion/year, which is a bargain compared to having a 3ºC world.  We will need SRM in the interim to avoid devastating temperatures and tipping points, but in the medium to long term, we must remove the excess CO2 in the atmosphere.

For more on the practicality of DAC, listen to my interview with Klaus Lackner, one of the first scientists to explore direct air capture:

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/c548774b-87f7-4bf7-ad61-8cc35f92872b%40earthlink.net.

[Dan Miller]

Let’s put things in perspective. We are currently at kiloton scale with DAC and for it to make an impact, it must grow to gigaton scale, 1,000,000X more.

There will be lots of innovation and cost reduction on the way to gigaton scale. $50/ton is certainly possible at gigaton scale in this world. And keep in mind, whatever the eventual cost is of DAC, the cost of not removing our emissions is far higher.

Getting to gigaton scale will be a challenge unless there are policies in place to make people pay for current emissions (e.g., an honest carbon fee) and a way to pay for removing past emissions. DAC is waste removal and it’s not going to happen at scale as long as it’s free to pollute the atmosphere.

Dan

[Kevin Wolf]

Can you imagine what kind of progress we'd be making on Blue Carbon and ocean restoration if the U.S had investing 10% of the money spent on DAC into research and experimentation for CDR in the ocean?  The challenge is how to have some reasonable percentage of federal and other funds that invest in DAC into Blue Carbon.

Kevin

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[Bruce Melton -- Austin, Texas]

Thanks Seth - citation please ~ ~ ~ It seems like you are referencing Socolow 2011 and House 2011 which used poor process assumptions and calculated enthalpy backwards.

The following is my interpretation of Keith 2018.

Cheers,

B

•    Keith's 2018 is based on scaling their 1Kt annual Squamish British Columbia demonstration to 1 Mt using existing industrial components with known scaling factors.
•    The $94 to $232 per ton range reflects the low and high energy costs of the cheapest fracked gas at the time of $0.03 kWh to $0.06 kWh.
•    87 percent of process costs are energy.
•    Costs include upstream emissions and the carbon penalty to remove the carbon emitted from burning the natural gas to create the energy to run the process.
•    Latest wind and solar costs at utility scale are now at $0.01 kWh.
•    Keith allows that 40 percent of process costs can be as electricity. With $0.01 kWh renewable site-built energy, this reduces total costs $81 ton.
•    Process refinements reduce costs further.
•    Scaling beyond 1 Mt per year reduces costs further dependent upon the amount of scaling.
Keith et al., A Process for Capturing CO2 from the Atmosphere, Joule, August 15, 2018.
https://www.sciencedirect.com/science/article/pii/S2542435118302253

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
(512)799-7998
ClimateDiscovery.org
ClimateChangePhoto.org
MeltonEngineering.com
Face...@Bruce.Melton.395
Inst...@Bruce.C.Melton
The Band Climate Change
Twitter - BruceCMelton1

[Anton Alferness]

I'll bet you a chicken sandwich the US gov will put money into other CDR methodologies including mCDR of most kinds, hopefully including nutrient fertilization. 

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[Seth Miller]

Let’s also keep in mind that cost-downs are human-led processes, not laws of nature. The construction industry is surely at some equivalent of giga-scale, but we barely had any improvement in construction efficiency since the 1960s. Cost-downs can happen under specific circumstances, but they can also not happen, and it’s important to be able to recognize which is which.

In the case of Keith’s technology, most of the cost of DAC is in plant construction! To answer Bruce’s question on citing sources, I built my own technoeconomic model to reproduce Keith’s paper. One finding was that Keith used a 30 year depreciation period for his investments, which is long by conventional standards for a new technology. He also assumed a pretty low interest rate on his lowball estimate. Most importantly, he was wildly short on his capex requirements; right now, Oxy plans to invest $1.3 billion for a 500 kT/yr capacity plant. (See the link below for that figure - it won’t embed. Note that this number keeps going up as they get closer to the goal.)

https://www.reuters.com/sustainability/climate-energy/blackrock-invest-550-mln-occidentals-carbon-capture-project-2023-11-07/#:~:text=Occidental%20on%20Tuesday%20increased%20project,for%202025%2C%20from%202024%20previously.

If you are making bets on how fast a technology will cost reduce, one of the important considerations is whether the owners of the technology have control over their major input costs. Oxy does not have control over the cost of construction workers, or concrete, or renewable power. Building more DAC plants doesn’t change the cost of these inputs, and therefore we will not expect them to scale with experience. 

The problem that Oxy in particular has is that these are their main drivers of cost. Oxy is an integrator, not an inventor! This is good for them, because it means they are ahead of everyone else in the world. But it should limit our expectations for scaling. Climeworks, by contrast, as amine sorbents as its main cost. If it can make progress on those sorbents, costs will decline. The downside for Climeworks is that their technical risk level is quite high, whereas Oxy’s is quite low. Choose your investment path based on your risk preference.

None of this means that energy won’t get cheaper as well, of course! It will just do so at a pace that is unrelated to DAC. Maybe this is good for DAC, maybe it is bad, but it surely is different from what I’m seeing people predict here.

Best,

Seth

-------

Seth Miller, Ph.D.

www.linkedin.com/in/sethmiller2

Check my blog at: perspicacity.xyz

[Dan Miller]

There is no question if we pursue DAC like we pursued nuclear in the past — each unit a new building project — then costs will not go down much. But if we modularize DAC so we build 1 or 2 ton-per-day (TPD) units in standard shipping containers, then learning curves kick in and costs come down.

If each container is 1 TPD, then we would need 110M for 40 Gt/y, which is 11M/year built over 10 years. That might sound like a lot but we currently build 90M cars/year, so it is doable.

Dan

[Seth Miller]

This is a decent take. But Carbon Engineering is not this technology. Carbon Engineering scales up, but doesn’t number up.

There are other technologies that might fit better with your sort of implementation path. And it’s fine for the world to start building DAC using Carbon Engineering technology, even if it doesn’t fit this model. Someone has to prove out the market mechanics with whatever can be built quickest. There is lots of value in derisking the market, even if the cost reduction path taps out.

We should be clear on what we are building, though!  The most successful technology long-term may not be the first one we scale. It also may not hit our $50/ton dreams. Or even $100/ton, for that matter. There is no requirement that DAC is a good idea, after all, only that it is reasonable enough to try, given our climate emergency. 

Let’s try all of the above, but not get trapped into a given set of expectations. Reality has a way of spoiling our plans, and we should stay sensitive to that.

Seth

-------

Seth Miller, Ph.D.

www.linkedin.com/in/sethmiller2

Check my blog at: perspicacity.xyz

[Daniel Nepstad]

Let’s not forget the Earth system we have today as we discuss the potential of DAC. Nature continues year after year to remove an amount of carbon from the atmosphere equivalent to 55% of anthropogenic emissions (figure from Global Carbon Budget 2023). This means that atmospheric CO2 concentrations will start to fall if we cut emissions in half. 

There is no guarantee that the terrestrial and oceanic sinks will continue indefinitely, of course. But they aren’t going to disappear in the next few decades either. At the very least, nature is buying us precious time to take other forms of CDR to scale.  

In the meantime, we need to do what we can to secure these sinks and strengthen them where possible. Brazil’s success last year in slowing Amazon deforestation kept nearly 0.4 GtCO2 out the atmosphere and in Amazon trees. With even a partial reversal of deforestation, the Amazon forest could go from its current role absorbing 2-3% of global CO2 emissions to 4% or more, avoiding one of the major climate tipping points in the process. In this scenario, Amazon deforestation emissions would decline from 2% of global emissions to zero. Such a reversal is well within reach if we grow demand in the carbon market for forest carbon credits from jurisdictional programs.  Our teams are currently helping seven Amazon states and regional governments sell these high-integrity credits. Reversing deforestation is possible by 2030.

We should be doing everything we can to secure and strengthen the terrestrial and oceanic carbon sinks–this is the Earth system context for DAC and CDR more generally.

We should be doing everything we can to support efforts to slow deforestation by Brazil, Indonesia, DRC and the 40+ other countries whose main emissions are tropical deforestation.  

This is not a zero sum game.  

Dan

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/9F89B924-FF34-4E01-B5F3-579208EB07AF%40gmail.com.

[Clive Elsworth]

Dan

 

Firstly, thanks for your great interview with Jam Hansen, which covered a great deal of useful material in accessible form: https://www.youtube.com/watch?v=8Ag3UVSrlhE&t=193s

 

Re: costs coming down with scale, I fear that you don’t question where the energy comes from to produce at low cost the processed materials needed for high volumes of solar PV and wind turbines. Could it be China burning more coal?

 

Clive

 

From: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> On Behalf Of Dan Miller
Sent: Tuesday, December 19, 2023 12:09 AM
To: Seth Miller <setha...@gmail.com>
Cc: Bruce Melton -- Austin, Texas <bme...@earthlink.net>; Albert Bates <alb...@thefarm.org>; Carbon Dioxide Removal <CarbonDiox...@googlegroups.com>
Subject: Re: [CDR] Dissing DAC

 

There is no question if we pursue DAC like we pursued nuclear in the past — each unit a new building project — then costs will not go down much. But if we modularize DAC so we build 1 or 2 ton-per-day (TPD) units in standard shipping containers, then learning curves kick in and costs come down.

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/DCD6CAF9-F03F-46F9-AE9A-6A3654EC8C5B%40rodagroup.com.

[Michael MacCracken]

Dear Dan--I would very much like to hear from other scientists on this, but I don't think that carbon removal fluxes will continue at the quantitative levels they are at as emissions go down to zero even though the removal of 55% of current emissions may continue. It is important to understand what is driving these fluxes and their time scales.

So, there are three components to the fast response component of the carbon system--the atmosphere, the upper (~100+ meter) ocean, and the most active component of the terrestrial biosphere. When fossil fuel emissions are emitted to the atmosphere, the fluxes spread the new excess carbon out among these three reservoirs. The exchange between the atmosphere and upper ocean is quite rapid--wind stirs the upper ocean and there are large amounts of CO2 going into and out of the upper ocean seeking to achieve chemical equilibrium,. The small net flux that has to occur to re-establish equilibrium given the fossil fuel CO2 that has been emitted, will occur quite rapidly (years, not decades). And the same sort of thing happens between the atmosphere and the living biosphere (indeed. FACE field experiments show that even a doubling of the CO2 concentration pretty much leads to a new equilibrium with the most active part of the terrestrial biosphere within years and not decades. It is these two exchanges that largely lead to the airborne fraction being just under one-half (the complement to the 55% removal you mention). Model simulations of even large pulse injections show the airborne fraction is arrived at mostly within a decade and pretty much completely in two decades.

As emissions come down, the net fluxes needed to get to near global equilibrium (and it is a bit of a dynamic one given the seasons and that cold water holds more CO2 than cold) will become smaller and smaller and so the actual quantities of carbon removed are going to drop and drop. It is simply not the case that the atmospheric concentration is going to be falling by amounts anything like the rate of fall based on the current rate of transfer of carbon out of the atmosphere.

So, what will the rate of fall be as emissions get to zero. Well, the larger carbon system is also pushing toward a new equilibrium. Thus, the upper ocean is also connected to the deep ocean by the circulation of the ocean and by a biological pump--both of which are dependent largely on the ocean overturning circulation (downwelling colder waters taking more carbon down than is brought up in slightly warmer waters that were exposed to a slightly lower atmospheric CO2 concentration, but also super-saturated through dissolution of sinking carbon from the biological pump, which itself depends on the upwelling waters bringing nutrients into the upper ocean. These processes in the ocean will quite gradually pull down the mixed layer concentration. The lower amount in the mixed layer will then be seeking equilibrium with the other components of the active carbon cycle, pulling a bit out of the atmosphere which in turn will want to pull a bit back from the active part of the terrestrial biosphere, so even if the flux from the upper ocean to the deep ocean remains at its current amount, only 45% of the quantitative flux would count as a reduction in the atmospheric content. [Changes in the very slow transfer of deep ocean carbon to the sediments is far too slow to matter for any of us]

And there is a similar longer term carbon reservoir [actually reservoirs} for the terrestrial biosphere and again one only gets to count 45% of that flux as a decrease in the atmospheric loading. Fertilization of the ocean is intended to augment this rate, but as far as the natural process is concerned, it is pretty slow and will get slower as emissions drop.

For the deep ocean adjustment, the time scale is of order a thousand years, and similarly for the longer-term terrestrial biospheric components. Great to grow more trees--they make the rapid cycling part of the terrestrial biosphere a bit larger, and they benefit from the CO2 concentration being higher--and as the CO2 concentration drops, so will the CO2 fertilization. The natural transfer to a longer term carbon reservoir will continue, but is very slow and will slowly drop as the atmospheric CO2 concentration drops (biochar being a way to add to this flux).

So, indeed, not only is there no guarantee that the current rates would continue when the emissions get to zero, they will be dropping along the path of getting to zero and so will not be continuing at their current magnitudes. Slowing/eliminating deforestation is helpful in storing more carbon, but this is not taking up more fossil carbon--just returning carbon that was there to that location so not doing anything significant with the fossil fuel carbon added to the atmosphere. This will make the overall problem a bit less as deforestation is now contributing something like 10-15% of the overall net CO2 emission--but with fossil fuel emissions still going up, it has been taking only a decade or so to be offset by the rising fossil fuel emissions. Every bit helps--but these natural DAC and CDR processes are aimed only at achieving equilibrium of carbon among reservoirs, not somehow returning fossil fuel C to long-term geological sequestration at a rate that will matter to the situation that we face.

Mike MacCracken

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/66B920AF-2BF7-4E36-B65F-5F83F1310297%40earthinnovation.org.

[Asbjørn Torvanger]

Dear all,

 

I am amazed over the large interest in DAC. How much more energy do you need to process 300 times more air to capture one tonne of CO2 compared to one tonne from exhaust gas from e.g. a waste incineration plant using biogenic fuel? In addition you need energy and money for transportation and geological sequestration of the CO2. The conditions for small amounts of DAC at Iceland is a rather rare phenomena. Ok, all CDR technologies have learning curves but you cannot beat physical laws.

 

 

Best regards

 

Asbjørn Torvanger

 

 

 

From: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> On Behalf Of Michael MacCracken
Sent: Tuesday, December 19, 2023 3:57 PM
To: Daniel Nepstad <dnep...@earthinnovation.org>; Seth Miller <setha...@gmail.com>
Cc: Dan Miller <d...@rodagroup.com>; Bruce Melton -- Austin, Texas <bme...@earthlink.net>; Albert Bates <alb...@thefarm.org>; Carbon Dioxide Removal <CarbonDiox...@googlegroups.com>
Subject: Re: [CDR] Dissing DAC

 

Dear Dan--I would very much like to hear from other scientists on this, but I don't think that carbon removal fluxes will continue at the quantitative levels they are at as emissions go down to zero even though the removal of 55% of current emissions may continue. It is important to understand what is driving these fluxes and their time scales.

So, there are three components to the fast response component of the carbon system--the atmosphere, the upper (~100+ meter) ocean, and the most active component of the terrestrial biosphere. When fossil fuel emissions are emitted to the atmosphere, the fluxes spread the new excess carbon out among these three reservoirs. The exchange between the atmosphere and upper ocean is quite rapid--wind stirs the upper ocean and there are large amounts of CO2 going into and out of the upper ocean seeking to achieve chemical equilibrium,. The small net flux that has to occur to re-establish equilibrium given the fossil fuel CO2 that has been emitted, will occur quite rapidly (years, not decades). And the same sort of thing happens between the atmosphere and the living biosphere (indeed. FACE field experiments show that even a doubling of the CO2 concentration pretty much leads to a new equilibrium with the most active part of the terrestrial biosphere within years and not decades. It is these two exchanges that largely lead to the airborne fraction being just under one-half (the complement to the 55% removal you mention). Model simulations of even large pulse injections show the airborne fraction is arrived at mostly within a decade and pretty much completely in two decades.

As emissions come down, the net fluxes needed to get to near global equilibrium (and it is a bit of a dynamic one given the seasons and that cold water holds more CO2 than cold) will become smaller and smaller and so the actual quantities of carbon removed are going to drop and drop. It is simply not the case that the atmospheric concentration is going to be falling by amounts anything like the rate of fall based on the current rate of transfer of carbon out of the atmosphere.

So, what will the rate of fall be as emissions get to zero. Well, the larger carbon system is also pushing toward a new equilibrium. Thus, the upper ocean is also connected to the deep ocean by the circulation of the ocean and by a biological pump--both of which are dependent largely on the ocean overturning circulation (downwelling colder waters taking more carbon down than is brought up in slightly warmer waters that were exposed to a slightly lower atmospheric CO2 concentration, but also super-saturated through dissolution of sinking carbon from the biological pump, which itself depends on the upwelling waters bringing nutrients into the upper ocean. These processes in the ocean will quite gradually pull down the mixed layer concentration. The lower amount in the mixed layer will then be seeking equilibrium with the other components of the active carbon cycle, pulling a bit out of the atmosphere which in turn will want to pull a bit back from the active part of the terrestrial biosphere, so even if the flux from the upper ocean to the deep ocean remains at its current amount, only 45% of the quantitative flux would count as a reduction in the atmospheric content. [Changes in the very slow transfer of deep ocean carbon to the sediments is far too slow to matter for any of us]

And there is a similar longer term carbon reservoir [actually reservoirs} for the terrestrial biosphere and again one only gets to count 45% of that flux as a decrease in the atmospheric loading. Fertilization of the ocean is intended to augment this rate, but as far as the natural process is concerned, it is pretty slow and will get slower as emissions drop.

For the deep ocean adjustment, the time scale is of order a thousand years, and similarly for the longer-term terrestrial biospheric components. Great to grow more trees--they make the rapid cycling part of the terrestrial biosphere a bit larger, and they benefit from the CO2 concentration being higher--and as the CO2 concentration drops, so will the CO2 fertilization. The natural transfer to a longer term carbon reservoir will continue, but is very slow and will slowly drop as the atmospheric CO2 concentration drops (biochar being a way to add to this flux).

So, indeed, not only is there no guarantee that the current rates would continue when the emissions get to zero, they will be dropping along the path of getting to zero and so will not be continuing at their current magnitudes. Slowing/eliminating deforestation is helpful in storing more carbon, but this is not taking up more fossil carbon--just returning carbon that was there to that location so not doing anything significant with the fossil fuel carbon added to the atmosphere. This will make the overall problem a bit less as deforestation is now contributing something like 10-15% of the overall net CO2 emission--but with fossil fuel emissions still going up, it has been taking only a decade or so to be offset by the rising fossil fuel emissions. Every bit helps--but these natural DAC and CDR processes are aimed only at achieving equilibrium of carbon among reservoirs, not somehow returning fossil fuel C to long-term geological sequestration at a rate that will matter to the situation that we face.

Mike MacCracken

 

On 12/19/23 3:45 AM, Daniel Nepstad wrote:

Let’s not forget the Earth system we have today as we discuss the potential of DAC. Nature continues year after year to remove an amount of carbon from the atmosphere equivalent to 55% of anthropogenic emissions (figure from Global Carbon Budget 2023). This means that atmospheric CO2 concentrations will start to fall if we cut emissions in half. 

 

There is no guarantee that the terrestrial and oceanic sinks will continue indefinitely, of course. But they aren’t going to disappear in the next few decades either. At the very least, nature is buying us precious time to take other forms of CDR to scale.  

 

In the meantime, we need to do what we can to secure these sinks and strengthen them where possible. Brazil’s success last year in slowing Amazon deforestation kept nearly 0.4 GtCO2 out the atmosphere and in Amazon trees. With even a partial reversal of deforestation, the Amazon forest could go from its current role absorbing 2-3% of global CO2 emissions to 4% or more, avoiding one of the major climate tipping points in the process. In this scenario, Amazon deforestation emissions would decline from 2% of global emissions to zero. Such a reversal is well within reach if we grow demand in the carbon market for forest carbon credits from jurisdictional programs.  Our teams are currently helping seven Amazon states and regional governments sell these high-integrity credits. Reversing deforestation is possible by 2030.

 

We should be doing everything we can to secure and strengthen the terrestrial and oceanic carbon sinks–this is the Earth system context for DAC and CDR more generally.

 

We should be doing everything we can to support efforts to slow deforestation by Brazil, Indonesia, DRC and the 40+ other countries whose main emissions are tropical deforestation.  

 

This is not a zero sum game.  

 

Dan

 

 

 

 

 

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/6593dfd9-9949-4354-a511-1ee459bad226%40comcast.net.

[Dan Miller]

It will always be cheaper to not emit CO2 than to capture it using CCS or DAC.

It will always be cheaper to capture CO2 using CCS (point source) than DAC.

Emissions reduction and CCS cannot remove past emissions. There is already too much CO2 in the atmosphere. CDR is required for a safe climate.

Favorable DAC conditions are widespread. They are not limited to Iceland. Most of the energy for CO2 capture/release/sequestration can come from “Earth energy” rather than manmade renewable electricity. For example, a thermal-swing DAC can use low-grade ~120ºC geothermal heat available most places on land, air for cooling, and basalt soil chemistry for sequestration.  In addition, there are other CDR techniques besides “mechanical removal” that may prove to be effective.

Saying that DAC takes too much energy is like saying it takes too much energy to dry a pair of jeans in an electric or gas dryer and then I take the jeans outside and dry them on a clothesline.

Dan

 

 

 

<~WRD0003.jpg>

[Dan Miller]

For an almost immediate cessation of emissions (putting aside tipping points such as permafrost and clathrate melt) then the atmospheric “overpressure” of CO2 is almost identical to what it is now, so uptake rates will continue until (1) CO2 drops substantially and/or (2) uptake rates change due to environmental conditions (oceans warm, get stratified, AMOC collapse, etc.; plants stop taking up CO2 due to vapor pressure deficit, wildfire, etc.; soils start releasing gigatons of CO2 because of higher temps, etc.).

But current emissions add only about 2% per year to current cumulative emissions so stopping emissions won’t play a big role in near-term uptake rates. Note that those “environmental conditions” will occur if we continue our emissions as well.

For more on long-term carbon cycle, listen to my interview with David Archer:

Dan

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/6593dfd9-9949-4354-a511-1ee459bad226%40comcast.net.

[Bruce Melton -- Austin, Texas]

Aye, 10.4. --based on your independent modeling. Thanks. A couple of things to consider:

Air capture is not nuclear energy. The high CapEx of first generation simple processes is much more likely to come down than continue upwards like complex processes, especially with their 100, 1 ton per year unit commitment.

An energy concept that I have not seen in any scenarios is that for continued 100 percent use of natural gas energy at prices the operator is likely to pay. This is lucrative for oil and gas producers because their pockets are full of almost free natural gas, likely even much cheaper to them as producers than even the current best utility scale renewables at $0.01kWh. It is not logical they would use renewables then, unless mandated. Using natural gas has about a 10 percent carbon penalty, so scaling each unit 10 percent greater to adjust for the carbon penalty is little money.

The $85/ton IRS 45Q cash pay for enhanced oil recovery is worth looking at with Oxy's plans. Mined CO2 Oxy is currently using in the Permian for EOR is +/- $60 ton as per Carbon Engineering's chief engineer. The engineering margin for cost overruns in early units is certainly built in to Oxy's long term goals to create positive cash flow with 45Q's $85 a ton cash pay.

The rest of the story is as Dan alludes, trillions and trillions of $$$ in costs are a bargain compared to a world warmer than Earth systems tipping thresholds.

Cheers,

B

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
(512)799-7998
ClimateDiscovery.org
ClimateChangePhoto.org
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Inst...@Bruce.C.Melton
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Twitter - BruceCMelton1

[Daniel Nepstad]

Hi Michael,

The global carbon sink has been going strong for 70+ years, pulling more than half of humanity’s carbon pollution out of the atmosphere. This is good news and should be a source of hope. I found this simple fact to be surprisingly absent in dialogues in Dubai.  

I’m not saying that if we cut emissions in half we have solved the problem. What I did write was: 

There is no guarantee that the terrestrial and oceanic sinks will continue indefinitely, of course. But they aren’t going to disappear in the next few decades either. At the very least, nature is buying us precious time to take other forms of CDR to scale.  

A future weakening of the sinks is likely, but not because emissions are dropping. Many mature forest ecosystems are accumulating carbon (based on both field plots, eddy covariance and airborne sampling) because of CO2 fertilization. Extreme weather events can erase this effect on short time scales. In one of my Amazon forest experiments, imposed drought reduced living biomass by 30%. Eventually, a new equilibrium will be reached, as you point out, in recovering terrestrial ecosystems, mature ecosystems and soils.  

Dan

[Michael MacCracken]

Hi Dan N--I'll look at the interview Dan Miller recommended, but I don't agree that the CO2 overpressure for the rapidly exchanging fast reservoirs, which are mainly the ones that lead to the airborne fraction, is 420 ppm-280 ppm= 140 ppm; for the overall system over very long time scales, yes, but not for the fast exchanging reservoirs. Given the very large CO2 fluxes into and out of the ocean surface and the seasonal cycle of ocean mixed layer temperature, for example, the small departure from equilibrium created by one year's emissions are very largely reduced on time scales of one to a few years--so the overpressure is due to the most current emissions, and as emissions drop toward zero (it won't happen all at once), the overpressure created by each year's emissions and thus the net flux from atmosphere to the ocean will go down and down. Similarly, though not quite as tightly, for the active component of the terrestrial biosphere. As I indicated, field studies (known as FACE studies) show adjustment to a CO2 doubling in only several years--the overpressure is thus based on the last few year's emissions--not the overpressure based on all emissions since the start of the fossil fuel period. There are all sorts of studies and claims that the higher CO2 concentration has had effects on the biosphere already, and in this way reduced the notion that there has not been some amelioration of the overpressure--280 ppm is pretty clearly no longer the baseline. That adjustments are occurring and that the overpressure created by each year's emissions are pretty quickly moderated is the case is confirmed in my vie by how the airborne fraction has stayed so steady with the net flux growing with the amount of annual emissions, not the accumulated emissions.

And, of course, as you suggest, the net uptakes by the Arctic and the Amazon are diminishing and headed toward being sources rather than sinks of CO2, etc. The suggestion that the quantity of C uptake today will persist as the emissions go slowly down just does not seem plausible. I know there are some (leading) scientists have suggested this, but I've followed up with some and don't find their arguments credible, nor backed up by anything other than extrapolation--I don't know of independent verification situations that support the case, however. Pretty clearly at 280 ppm there was no net flux through the preindustrial Holocene, so there would need to be an explanation of why 280 ppm is the baseline for the overpressure calculation (i.e., why this is the level where equilibrium occurs).

Mike MacCracken

[Dan Miller]

Klaus Lackner estimated that that, if done correctly, the “embedded emissions” of a DAC system would be about 20 kg per ton of CO2 removed, so for each ton removed, the net removal would be 980 kg.

Dan

Dan

There will be lots of innovation and cost reduction on the way to gigaton scale. $50/ton is certainly possible at gigaton scale in this world. And keep in mind, whatever the eventual cost is of DAC, the cost of notremoving our emissions is far higher.

[Tom Goreau]

280 is the baseline because it is what ecosystems and people have adapted to over the last 10,000 years. If you go up in CO2, so will temperature. Below is what 66 million years of data shows (from Towards a history of Cenozoic CO2, Science, 2023, not models). It suggests we’re headed for at least 4 to 8 degrees of warming for today’s CO2 level if Net Zero were achieved tomorrow, and more if fossil fuels are not stopped.

 

 

From: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> on behalf of Michael MacCracken <mmac...@comcast.net>

Date: Tuesday, December 19, 2023 at 3:41 PM
To: Daniel Nepstad <dnep...@earthinnovation.org>

Cc: Seth Miller <setha...@gmail.com>, Dan Miller <d...@rodagroup.com>, Bruce Melton -- Austin, Texas <bme...@earthlink.net>, Albert Bates <alb...@thefarm.org>, Carbon Dioxide Removal <carbondiox...@googlegroups.com>
Subject: Re: [CDR] Dissing DAC

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/c619af14-b57a-4b6f-8500-c2d498460629%40comcast.net.

[Michael MacCracken]

Dear Thomas--Oh, I don't disagree why 280 ppm is called the baseline, and departures are relative to this. What I at least thought I was wondering is why 280 ppm happened to be the equilibrium value for the Holocene--and the answer is basically that is the amount that allowed an equilibrium to develop for a combination of flux flows for CO2 and energy, etc.

With all of the emissions that have occurred, the equilibrium will be different, and it is likely, I'm suggesting up near 420 ppm given enissions to date and not down a lot. I'm saying this because I think the fast C reservoirs are near equilibrium now and not lagged by some large amount, say back at 280 ppm, and that as emissions go to net zero, it is unlikely there will be a rapid and significant drop in the atmospheric concentration.

Best, Mike

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/BY3PR13MB499463F0AE45C29FDDB70FA3DD97A%40BY3PR13MB4994.namprd13.prod.outlook.com.