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kassy

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Re: Carbon Cycle
« Reply #600 on: November 02, 2020, 02:05:04 PM »
Warming of 2°C would release billions of tonnes of soil carbon

Global warming of 2°C would lead to about 230 billion tonnes of carbon being released from the world's soil, new research suggests.

Global soils contain two to three times more carbon than the atmosphere, and higher temperatures speed up decomposition - reducing the amount of time carbon spends in the soil (known as "soil carbon turnover").

The new international research study, led by the University of Exeter, reveals the sensitivity of soil carbon turnover to global warming and subsequently halves uncertainty about this in future climate change projections.

The estimated 230 billion tonnes of carbon released at 2°C warming (above pre-industrial levels) is more than four times the total emissions from China, and more than double the emissions from the USA, over the last 100 years.

"Our study rules out the most extreme projections - but nonetheless suggests substantial soil carbon losses due to climate change at only 2°C warming, and this doesn't even include losses of deeper permafrost carbon," said co-author Dr Sarah Chadburn, of the University of Exeter.

...

State-of-the-art models suggest an uncertainty of about 120 billion tonnes of carbon at 2°C global mean warming.

The study reduces this uncertainty to about 50 billion tonnes of carbon.

https://www.eurekalert.org/pub_releases/2020-11/uoe-wo2103020.php
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nanning

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Re: Carbon Cycle
« Reply #601 on: November 03, 2020, 05:24:59 AM »
^^
How much extra global heating would that produce?
How much extra soil carbon would be emitted by that extra global heating?
Etcetera...   Oh hey hellooo, look who's here to help out... Lord Methane! And he's brought his little friend Rev. Albedo.
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GeoffBeacon

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Re: Carbon Cycle
« Reply #602 on: November 03, 2020, 07:13:24 AM »
For 2°C:

Can 232 GtC (851 CO2) of soil carbon be used to update remaining carbon budgets in SR15, Ch 2, Table 2.2?

For 50% chance in Table 2.2, budget to keep below 2°C is 1500 GtCO2 (less Earth System Feedbacks less emissions since 1/1/2018).

Taking 851 from 1500 gives 650 GtCO2 (less Earth System Feedbacks less emissions since)

Earth system feedbacks include CO2 released by permafrost thawing or methane released by wetland. These in Table 2.2 given as 100 GtCO2 for  a 1.5°C rise, but will  be more for 2°C rise.
Guess 150GtCO2?

Emissions since date in SR15 (1/1/2018) about 100 GtCO2?

That gives remaining carbon budget of 650-150-100 = 400 Gt CO2.

That's a remaining budget of 53 tonnes CO2 per human for 2°C rise.

Crude but this it at all realistic?

How much does non-CO2 climate forcing reduce this?
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nanning

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Re: Carbon Cycle
« Reply #603 on: November 03, 2020, 07:54:01 AM »
Geoff, in my opinion the 'budget' is already empty.
I refer to the many tipping points, but also to interglacial paleoclimate records that show ca. +3°C for 410ppm CO2 GHG and that's without CH4 & N20  (and ca.20m SLR).

All of this FF anthropogenic CO2 is of course from outside the long-term carbon cycle.
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GeoffBeacon

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Re: Carbon Cycle
« Reply #604 on: November 03, 2020, 08:07:04 AM »
nanning

I agree but I'm searching for ways to test the 'official' view.

e.g. On this twitter thread.

https://twitter.com/richardabetts/status/1323333437068070912
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Re: Carbon Cycle
« Reply #605 on: November 03, 2020, 12:28:17 PM »
Geoff, in my opinion the 'budget' is already empty.
I refer to the many tipping points, but also to interglacial paleoclimate records that show ca. +3°C for 410ppm CO2 GHG and that's without CH4 & N20  (and ca.20m SLR).

All of this FF anthropogenic CO2 is of course from outside the long-term carbon cycle.
This is why you need to remember CO2e which, IIRC, is about 500 ppm right now.
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nanning

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Re: Carbon Cycle
« Reply #606 on: November 04, 2020, 08:54:33 AM »
Geoff, that twitter thread has made it to the Guardian:

https://www.theguardian.com/business/2020/nov/03/shells-climate-poll-on-twitter-backfires-spectacularly


Shell’s climate poll on Twitter backfires spectacularly

Oil giant accused of gaslighting after asking users: ‘What are you willing to change?’

Sorry for off-topic
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kassy

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Re: Carbon Cycle
« Reply #607 on: December 07, 2020, 02:16:22 PM »
Krill could be vital in climate change battle, say British Antarctic Survey researchers

They could turn out to be a significant accomplice in the battle against climate change.

Vast swarms of krill in the Southern Ocean are now believed to remove double the amount of carbon from the atmosphere than previously assumed by global models.

Scientists have been aware that krill produce carbon-rich faecal pellets that sink in the water column and transfer carbon from the atmosphere to the deep ocean.

But now researchers at the British Antarctic Survey in Cambridge have found that the process of moulting, in which they shred their exoskeletons, performs a similar function.

Dr Clara Manno, a marine ecologist at BAS and lead author of the paper published in Nature Communications last Friday, says: “This is exciting news because it almost doubles the previous estimate of how much atmospheric carbon is transported into deep ocean layers by krill.

...

Antarctic krill (Euphausia superba) represent some of the highest concentrations of animal biomass in the world’s oceans – estimated to be more than 150 million tonnes. They are the main diet for whales, penguins and seals and also harvested for food by humans

...

Co-author and ecologist Prof Geraint Tarling said: “Krill are really unusual crustaceans in moulting so frequently. In fact, they renew their exoskeleton every 10 to 14 days, releasing their old ones to sink towards the seabed, and taking carbon with it.

https://www.cambridgeindependent.co.uk/news/krill-could-be-vital-in-climate-change-battle-say-british-antarctic-survey-researchers-9143897/

Open access:
Continuous moulting by Antarctic krill drives major pulses of carbon export in the north Scotia Sea, Southern Ocean

Abstract
Antarctic krill play an important role in biogeochemical cycles and can potentially generate high-particulate organic carbon (POC) fluxes to the deep ocean. They also have an unusual trait of moulting continuously throughout their life-cycle. We determine the krill seasonal contribution to POC flux in terms of faecal pellets (FP), exuviae and carcasses from sediment trap samples collected in the Southern Ocean. We found that krill moulting generated an exuviae flux of similar order to that of FP, together accounting for 87% of an annual POC flux (22.8 g m−2 y−1). Using an inverse modelling approach, we determined the krill population size necessary to generate this flux peaked at 261 g m−2. This study shows the important role of krill exuviae as a vector for POC flux. Since krill moulting cycle depends on temperature, our results highlight the sensitivity of POC flux to rapid regional environmental change.

https://www.nature.com/articles/s41467-020-19956-7
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vox_mundi

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Re: Carbon Cycle
« Reply #608 on: December 10, 2020, 10:12:46 PM »
The Greening of the Earth is Approaching Its Limit
https://phys.org/news/2020-12-greening-earth-approaching-limit.html

An international study published today in Science concludes that the fertilizing effect of CO2 is decreasing worldwide, and that the reduction has reached 50% progressively since 1982 due basically to two key factors: the availability of water and nutrients.

"There is no mystery about the formula, plants need CO2, water and nutrients in order to grow. However much the CO2 increases, if the nutrients and water do not increase in parallel, the plants will not be able to take advantage of the increase in this gas", explains Professor Josep Peñuelas. In fact, three years ago Prof. Peñuelas already warned in an article in Nature Ecology and Evolution that the fertilizing effect of CO2 would not last forever, that plants cannot grow indefinitely, because there are other factors that limit them.

... "These unprecedented results indicate that the absorption of carbon by vegetation is beginning to become saturated. This has very important climate implications that must be taken into account in possible climate change mitigation strategies and policies at the global level. ... If the fertilizing capacity of CO2 decreases, there will be strong consequences on the carbon cycle and therefore on the climate.

The team based it's conclusions on data obtained from hundreds of forests studied over the last 40 years. "This data show that concentrations of essential nutrients in the leaves, such as nitrogen and phosphorus, have also progressively decreased since 1990," explains researcher Songhan Wang, the first author of the article.

The team has also found that water availability and temporal changes in water supply play a significant role in this phenomenon. "We have found that plants slow down their growth, not only in times of drought, but also when there are changes in the seasonality of rainfall, which is increasingly happening with climate change," explains researcher Yongguan Zhang.





S. Wang el al., "Recent global decline of CO2 fertilization effects on vegetation photosynthesis," Science (2020)
https://science.sciencemag.org/content/370/6522/1295

... Our analyses showed a significant and spatially extensive decline in β, which implies a substantial reduction of the positive effects of increasing atmospheric CO2 on terrestrial carbon uptake.
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kassy

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Re: Carbon Cycle
« Reply #609 on: December 10, 2020, 10:57:41 PM »
Thanks! Another interesting puzzle piece.
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kassy

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Re: Carbon Cycle
« Reply #610 on: December 22, 2020, 05:40:42 PM »
Muddying the waters: Weathering might remove less atmospheric CO2 than thought

The weathering of rocks at the Earth's surface may remove less greenhouse gases from the atmosphere than previous estimates, says new research from the University of Cambridge.

The findings, published in PNAS, suggest Earth's natural mechanism for removing carbon dioxide (CO2) from the atmosphere via the weathering of rocks may in fact be weaker than scientists had thought -- calling into question the exact role of rocks in alleviating warming over millions of years.

The research also suggests there may be a previously unknown sink drawing CO2 from the atmosphere and impacting climate changes over long timescales, which researchers now hope to find.

Weathering is the process by which atmospheric carbon dioxide breaks down rocks and then gets trapped in sediment. It is a major part of our planet's carbon cycle, shuttling carbon dioxide between the land, sea and air, and influencing global temperatures.

"Weathering is like a planetary thermostat -- it's the reason why Earth is habitable. Scientists have long suggested this is why we don't have a runaway greenhouse effect like on Venus," said lead author Ed Tipper from Cambridge's Department of Earth Sciences. By locking carbon dioxide away in sediments, weathering removes it from the atmosphere over long timescales, reducing the greenhouse effect and lowering global temperatures.

The team's new calculations show that, across the globe, weathering fluxes have been overestimated by up to 28%, with the greatest impact on rivers in mountainous regions where rocks are broken down faster.

They also report that three of the largest river systems on Earth, including the neighbouring Yellow and Salween Rivers with their origins on the Tibetan Plateau and the Yukon River of North America, do not absorb carbon dioxide over long timescales -- as had been thought.

For decades the Tibetan plateau has been invoked as a long term sink for carbon and mediator of climate. Some 25% of the sediment in the world's oceans originate from the plateau.

"One of the best places to study the carbon cycle are rivers, they are the arteries of the continents. Rivers are the link between the solid Earth and oceans -- hauling sediments weathered from the land down to the oceans where their carbon is locked up in rocks," said Tipper.

"Scientists have been measuring the chemistry of river waters to estimate weathering rates for decades," said co-author Victoria Alcock "Dissolved sodium is one of the most commonly measured products of weathering -- but we've shown that it's not that simple, and in fact sodium often comes from elsewhere."

Sodium is released when silicate minerals, the basic building blocks of most of Earth's rocks, dissolve in carbonic acid -- a mix of carbon dioxide in the atmosphere and rainwater.

However, the team found not all sodium comes from this weathering process. "We've found an additional source of sodium in river waters across the globe," said co-author Emily Stevenson. "That extra sodium is not from weathered silicate rocks as other studies assume, but in fact from very old clays which are being eroded in river catchments."

Tipper and his research group studied eight of the largest river systems on Earth, a mission involving 16 field seasons and thousands of lab analyses in search of where that extra sodium was coming from.

They found the answer in a soupy 'gel' of clay and water -- known as the cation exchange pool -- which is carried along by muddy river sediment.

The exchange pool is a reactive hive of cations -- positively charged ions like sodium -- which are weakly bonded to clay particles. The cations can easily swap out of the gel for other elements like calcium in river water, a process that can take just a few hours.

Although it has been described in soils since the 1950s, the role the exchange pool plays in supplying sodium to rivers has been largely neglected.

"The chemical and isotopic makeup of the clays in the exchange pool tell us what they are made of and where they've come from," said co-author Alasdair Knight. "We know that many of the clays carried by these rivers come from ancient sediments, and we suggest that some of the sodium in the river must come from these clays."

The clays were originally formed from continental erosion millions of years ago. On their journey downstream they harvested cations from the surrounding water -- their exchange pool picking up sodium on reaching the sea. Today, after being uplifted from the seafloor, these ancient clays -- together with their sodium -- are now being eroded by modern rivers.

This old sodium, which can switch out of the clays in the exchange pool and into river water, has previously been mistaken as the dissolved remnants of modern weathering.

"Generating just one data point took a huge amount of work in the lab and we also had to do a lot of maths," said Stevenson. "It's like unmixing a cake, using a forensic approach to isolate key ingredients in the sediments, leaving behind the exchange pool and the clays. People have used the same methods for a really long time -- and they work -- but we've been able to find an extra ingredient that provides the sodium and we need to account for this."

"It's thanks to the hard work of many collaborators and students over many years that our samples had the scope to get to grips with this complex chemical process at a global scale," said Tipper.

Scientists are now left to puzzle over what else could be absorbing Earth's carbon dioxide over geological time. There are no certain candidates -- but one controversial possibility is that life is removing carbon from the atmosphere. Another theory is that silicate dissolution on the ocean floor or volcanic arcs may be important. "People have spent decades looking on the continents for weathering -- so maybe we now need to start expanding where we look," said Tipper.

https://www.sciencedaily.com/releases/2020/12/201221160459.htm

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Tor Bejnar

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Re: Carbon Cycle
« Reply #611 on: December 22, 2020, 07:23:39 PM »
Thanks, Kassy.

Eroded uplifted sedimentary rocks (not just "clays" - e.g., ever heard of salt domes?) is an obvious source of cations in river water, and I presumed this source was already in the calculations demonstrating that weathering was a significant long-term device for removing CO2 from the atmosphere.  I guess what is special about eroding clay minerals is that carbon is released when clay minerals 'dissolve' in river water (or if not dissolved, not taking into account some cations 'in the water' have been in a long-term relationship with carbon), whereas there is functionally no carbon in mafic igneous rocks.

Quote
one controversial possibility is that life is removing carbon from the atmosphere
This one floors me!  Where do they think peat, oil, coal, odiferous shales and submerged log furniture come from?

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kassy

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Re: Carbon Cycle
« Reply #612 on: January 23, 2021, 10:29:16 PM »
Climate and carbon cycle trends of the past 50 million years reconciled

Predictions of future climate change require a clear and nuanced understanding of Earth's past climate. In a study published today in Science Advances, University of Hawai'i (UH) at Mānoa oceanographers fully reconciled climate and carbon cycle trends of the past 50 million years--solving a controversy debated in the scientific literature for decades.

Throughout Earth's history, global climate and the global carbon cycle have undergone significant changes, some of which challenge the current understanding of carbon cycle dynamics.

Less carbon dioxide in the atmosphere cools Earth and decreases weathering of rocks and minerals on land over long time scales. Less weathering should lead to a shallower calcite compensation depth (CCD), which is the depth in the ocean where the rate of carbonate material raining down equals the rate of carbonate dissolution (also called "snow line"). The depth of the CCD can be traced over the geologic past by inspecting the calcium carbonate content of seafloor sediment cores.

...

Contrary to expectations, the deep-sea carbonate records indicate that as atmospheric carbon dioxide (CO2) decreased over the past 50 million years, the global CCD deepened (not shoaled), creating a carbon cycle conundrum.

"The variable position of the paleo-CCD over time carries a signal of the combined carbon cycle dynamics of the past," said Komar, lead author of the study. "Tracing the CCD evolution across the Cenozoic and identifying mechanisms responsible for its fluctuations are therefore important in deconvolving past changes in atmospheric CO2, weathering, and deep-sea carbonate burial. As CO2 and temperature dropped over the Cenozoic, the CCD should have shoaled but the records show that it actually deepened."

Komar and Zeebe's computer model allowed them to investigate possible mechanisms responsible for the observed long-term trends and provide a mechanism to reconcile all the observations.

"Surprisingly, we showed that the CCD response was decoupled from changes in silicate and carbonate weathering rates, challenging the long-standing uplift hypothesis, which attributes the CCD response to an increase in weathering rates due to the formation of the Himalayas and is contrary to our findings," said Komar.

Their research suggests that the disconnect developed partially because of the increasing proportion of carbonate buried in the open ocean relative to the continental shelf due to the drop in sea level as Earth cooled and continental ice sheets formed. In addition, ocean conditions caused the proliferation of open-ocean carbonate-producing organisms during that period of time.

https://www.eurekalert.org/pub_releases/2021-01/uoha-cac012121.php
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Bruce Steele

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Re: Carbon Cycle
« Reply #613 on: February 01, 2021, 06:00:00 PM »
Kassy, The Komar/ Zeebe paper is open access.

https://advances.sciencemag.org/content/7/4/eabd4876

Thanks for the news article, now for some deep reading.

kassy

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Re: Carbon Cycle
« Reply #614 on: February 20, 2021, 07:26:33 PM »
Fishes contribute roughly 1.65 billion tons of carbon in feces and other matter annually
Study estimates fishes contribute about 16 percent of the sinking carbon in upper ocean waters

Scientists have little understanding of the role fishes play in the global carbon cycle linked to climate change, but a Rutgers-led study found that carbon in feces, respiration and other excretions from fishes - roughly 1.65 billion tons annually - make up about 16 percent of the total carbon that sinks below the ocean's upper layers.

https://www.eurekalert.org/pub_releases/2021-02/ru-fcr021721.php

Paper:
Toward a better understanding of fish‐based contribution to ocean carbon flux
https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.11709

This article explains the research , good start if it is new to you:
Why Scientists Just Ran Numbers on All The Fish Poop in The World's Oceans
https://www.sciencealert.com/scientists-calculated-all-the-fish-poo-in-the-ocean-for-climate-research
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kassy

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Re: Carbon Cycle
« Reply #615 on: February 24, 2021, 07:07:13 PM »
Effects of past ice ages more widespread than previously thought

A new study suggests that cold temperatures in unglaciated North America during the last ice age shaped past and modern landscape as far south as Texas and Arkansas.

...

The findings help shape understanding of the earth's "Critical Zone," the relatively thin layer of the planet that extends from where vegetation meets the atmosphere to the lowermost extent of weathered bedrock. "Climate and ecosystems determine how quickly bedrock weathers, how soil is produced, how sediment moves on land and in rivers and other factors that shape the landscape," the authors wrote.

In cold lands, such as Alaska today, frost can crack or weather rock that is at or near the surface of the earth -- making it more porous and turning solid rock into sediment. By applying a frost-weathering model to North America paleoclimate simulations tracking temperatures during the Last Glacial Maximum approximately 21,000 years ago, Marshall and her team determined that a large swath of North America, from Oregon to Georgia and as far south as Texas and Arkansas, were likely affected by such periglacial processes.

While permafrost landscapes like the modern Arctic experience frozen ground for two years or more, periglacial landscapes, though not permanently frozen, experience below-freezing temperature for much of the year. Though the evidence of past periglacial processes is easily hidden by vegetation and/or erased by subsequent geological processes, the teams' results suggest that frost weathering (and by extent other periglacial processes) covered an area about 3.5 times larger than the mapped extent of permafrost during the Last Glacial Maximum. This predicted influence of past cold climates on below ground weathering may significantly influence modern landscape attributes that we depend on such as soil thickness and water storage.

...

https://www.sciencedaily.com/releases/2021/02/210222192830.htm
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Re: Carbon Cycle
« Reply #616 on: February 25, 2021, 10:35:12 PM »
Forests' Long-Term Capacity to Store Carbon is Dropping In Regions With Extreme Annual Fires
https://phys.org/news/2021-02-forests-long-term-capacity-carbon-regions.html

Researchers have analyzed decades' worth of data on the impact of repeated fires on ecosystems across the world. Their results, published today in the journal Nature Ecology and Evolution, show that repeated fires are driving long-term changes to tree communities and reducing their population sizes.

Savannah ecosystems, and regions with extreme wet or dry seasons were found to be the most sensitive to changes in fire frequency. Trees in regions with moderate climate are more resistant. Repeated fires also cause less damage to tree species with protective traits like thicker bark.

These effects only emerge over the course of several decades: the effect of a single fire is very different from repeated burning over time. The study found that after 50 years, regions with the most extreme annual fires had 72% lower wood area—a surrogate for biomass—with 63% fewer individual trees than in regions that never burned. Such changes to the tree community can reduce the forest's long-term ability to store carbon, but may buffer the effect of future fires.

... Past studies have found that frequent fires reduce levels of nutrients—including nitrogen—in the soil. The new study demonstrates that this can favor slower-growing tree species that have adaptations to help them survive with less nutrients. But these tree species also slow down nutrient cycling in the soil—they hold onto what they have. This can limit the recovery of the forest as a whole by reducing the nutrients available for plant growth after an intense fire.

In the past, the majority of carbon released by wildfires was recaptured as ecosystems regenerated. But the more frequent fires of recent years, driven by changes in climate and land use, don't always allow time for this.

Pellegrini, A.F.A. et al: 'Decadal changes in fire frequencies shift tree communities and functional traits.' Nature Ecology & Evolution, February 2021
https://www.nature.com/articles/s41559-021-01401-7
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gerontocrat

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Re: Carbon Cycle
« Reply #617 on: March 24, 2021, 10:58:32 PM »
Yet another possibility for AGW to accelerate.

https://www.theguardian.com/environment/2021/mar/24/soils-ability-to-absorb-carbon-emissions-may-be-overestimated-study
One of Earth’s giant carbon sinks may have been overestimated - study

The potential of soils to slow climate change by soaking up carbon may be less than previously thought

Quote
The storage potential of one of the Earth’s biggest carbon sinks – soils – may have been overestimated, research shows. This could mean ecosystems on land soaking up less of humanity’s emissions than expected, and more rapid global heating.

Soils and the plants that grow in them absorb about a third of the carbon emissions that drive the climate crisis, partly limiting the impact of fossil-fuel burning. Rising carbon dioxide levels in the atmosphere can increase plant growth and, until now, it was assumed carbon storage in soils would increase too.

But the study, based on over 100 experiments, found the opposite. When plant growth increases, soil carbon does not. The finding is significant because the amount of organic carbon stored in soils is about three times that in living plants and double that in the atmosphere. Soils can also store carbon for centuries, whereas plants and trees rot quickly after they die.

It is not yet known how big the effect of lower carbon storage in soils might be on the speed of climate change, and experts cautioned that other impacts of the climate emergency such as drought would also affect how well plants and soils store carbon.

“We found that when rising CO2 increases plant growth, there is a decrease in soil carbon storage. That’s a very important conclusion,” said César Terrer, who led the research while at Stanford University in the US. He said that if soils do absorb less in future, “the speed of global warming could be higher”.

Terrier said soils, plants and trees were important for carbon levels, but that ending the burning of fossil fuels remains essential. “If we really want to stop global warming, we need to stop emissions, because ecosystems only take up a fraction of all the CO2 emissions,” he said.

The study, published in the journal Nature, analysed more than 100 experiments from across the world in which soils, plants and trees were exposed to higher CO2 levels than in today’s atmosphere. The biomass growing in forests rose by 23% in experiments where the CO2 level used was double pre-industrial atmospheric levels. It is 50% higher today. But the forest soils did not store any more organic carbon at all.

It was thought that biomass and soil carbon would increase in tandem, as more plant biomass falls to the ground and turns into organic matter. But increased plant and tree growth requires more nutrients from the soil, which may explain the new finding, the scientists said. Extracting the extra nutrients requires the plants to increase the symbiotic microbial activity in their roots, which then releases CO2 to the atmosphere that might otherwise have remained locked in the soil.

The researchers found that in grasslands, elevated CO2 led to 9% plant growth – less than forests – but soil carbon rose by 8%. Terrier said there has been a lot of discussion about tree planting as a way to tackle the climate crisis. “What I found very concerning in that debate is that people were suggesting planting trees in natural grasslands, savannah, and tundra,” he said. “I think that would be a terrible mistake because, as our results imply, there is a very large potential to increase soil carbon storage in grasslands.”

Open access article - cannot download pdf
https://www.nature.com/articles/s41586-021-03306-8.epdf?sharing_token=TmGNRC-Kphbf-zH7cCY8_9RgN0jAjWel9jnR3ZoTv0N2nuYqS5Si1oM85m9uPVbHtSoElmnSOceF_iSQhP1hfFAkwk2zkiuCDFYLMQUcWZ449oya-b_b0UwO-hnx_pjFJ9gmuFo7O9lrCLLifZ20c-ZUT3DZBSpOHb0b5Fqvp24p_KRkyABFbdQ1hqI_6thGftvWq4mOuSbtzwO5bbFqfwUKqJGWN8vrTjBiiyPdetYtiWWVN-8L521MmwBg1eZXB1F1oO9dbULOJm_v6RHa_mHW0Dy9Ace4IWWVVTMYb8nzBuZcqt3iekOpS8b8vFrA6QMXj942FKewZV_veXZJTXtsTgOmMoyOaaZPmKZAl1E%3D&tracking_referrer=www.theguardian.com
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kassy

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Re: Carbon Cycle
« Reply #618 on: March 25, 2021, 03:08:19 PM »
Here we synthesized data from 108 eCO2 experiments and found that the effect of eCO2 on SOC stocks is best explained by a negative relationship with plant biomass: when plant biomass is strongly stimulated by eCO2, SOC storage declines; conversely, when biomass is weakly stimulated, SOC storage increases. This trade-off appears to be related to plant nutrient acquisition, in which plants increase their biomass by mining the soil for nutrients, which decreases SOC storage. We found that, overall, SOC stocks increase with eCO2 in grasslands (8±2 per cent) but not in forests (0±2 per cent), even though plant biomass in grasslands increase less (9±3 per cent) than in forests (23±2 per cent). Ecosystem models do not reproduce this trade-off, which implies that projections of SOC may need to be revised.

The relationship is simple enough.

We take soils for granted which we should not do especially since we are degrading them.
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kassy

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Re: Carbon Cycle
« Reply #619 on: April 01, 2021, 05:50:12 PM »
Risk that the terrestrial carbon sink declines in the future

Climate consequences can in the future become even bigger than thought, because the capacity of the land vegetation to absorb carbon dioxide is likely to decline. This is the conclusion of a large international study with contribution by Umeå University. So far the vegetation has dampened climate change by taking up a significant fraction of carbon dioxide emissions, but it is uncertain if this effect will persist.

...

The land carbon sink has been around 11 billion tons carbon dioxide per year, compared to emissions of 35 billion tons. That's now, but to look into the future, to predict the carbon sink decades ahead, for our greatgrandchildren, the authors had to figure out the physiological mechanisms of the sink. That concerns what fraction of the carbon sink is due to carbon dioxide fertilization of photosynthesis, and if models of photosynthesis properly describe its increase. And finally one has to gauge if the current effects will persist over coming decades.

https://phys.org/news/2021-04-terrestrial-carbon-declines-future.html

Open source but very technical article:
https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.16866

From Conclusions:

Quote
Evidence for the CO2‐fertilization hypothesis suggests a highly valuable ecosystem service that is buying us time in the fight against climate change, although the size of this subsidy remains unclear. Based on diminishing theoretical GPP responses, probable increasing nutrient limitations, increasing mortality, and other negative temperature‐related effects (Peñuelas et al., 2017) it is highly likely that increases in terrestrial carbon storage as a result of iCO2 will decline into the future. A decline in this subsidy will result in accelerated climate change on the current trajectory of anthropogenic CO2 emissions.
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kassy

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Re: Carbon Cycle
« Reply #620 on: April 05, 2021, 05:58:30 PM »
Study Reveals Uncertainty In How Much Carbon The Ocean Absorbs Over Time

The ocean’s “biological pump” describes the many marine processes that work to take up carbon dioxide from the atmosphere and transport it deep into the ocean, where it can remain sequestered for centuries. This ocean pump is a powerful regulator of atmospheric carbon dioxide and an essential ingredient in any global climate forecast.

But a new MIT study points to a significant uncertainty in the way the biological pump is represented in climate models today. Researchers found that the “gold standard” equation used to calculate the pump’s strength has a larger margin of error than previously thought, and that predictions of how much atmospheric carbon the ocean will pump down to various depths could be off by 10 to 15 parts per million.

Given that the world is currently emitting carbon dioxide into the atmosphere at an annual rate of about 2.5 parts per million, the team estimates that the new uncertainty translates to about a five-year error in climate target projections.

“This larger error bar might be critical if we want to stay within 1.5 degrees of warming targeted by the Paris Agreement,” says Jonathan Lauderdale, a research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “If current models predict we have until 2040 to cut carbon emissions, we’re expanding the uncertainty around that, to say maybe we now have until 2035, which could be quite a big deal.”

...

In the new study, Lauderdale and Cael looked at how much difference it would make to estimates of carbon stored deep in the ocean if they changed the mathematical description of the biological pump.

*The martin curve was discovered in the 80ies but we do not know if this curve is correct and we can not really tell. There are 6 alernative equations see text for detail*

They started with the same six alternative equations, or remineralization curves, that Cael had previously studied. The team looked at how climate models’ predictions of atmospheric carbon dioxide would change if they were based on any of the six alternatives, versus the Martin curve’s power law.

https://scienceblog.com/522108/study-reveals-uncertainty-in-how-much-carbon-the-ocean-absorbs-over-time

Paper:
Reconciling the Size‐Dependence of Marine Particle Sinking Speed
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL091771

Even knowing what we do not know is quite a bit of work.  :)
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