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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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Tom_Mazanec

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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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