Consequences of global climate change

[Spathi]

TL;DR Summary

Not only the concentration of CO2 is important, but also the rate of its change (with the current rate, the ecosystems do not have time to react), and also that positive feedback can work now (the ocean, heating up, releases steam, which is also a greenhouse gas). But I would like to see these points explained in more detail.

It is known, that due to global warming, the average temperature on Earth over the past 100 years has increased by 1.2 degrees. At the same time, I heard that earlier the temperature of the Earth was 7 degrees higher than the current one.
I do not deny the danger of global warming, because I have seen the information that not only the concentration of CO2 is important, but also the rate of its change (with the current rate, the ecosystems do not have time to react), and also that positive feedback can work now (the ocean, heating up, releases steam, which is also a greenhouse gas). But I would like to see these points explained in more detail.

How probable is this scenario considered?

https://www.pnas.org/doi/full/10.1073/pnas.1910114117

Specifically, 3.5 billion people will be exposed to MAT ≥29.0 °C, a situation found in the present climate only in 0.8% of the global land surface, mostly concentrated in the Sahara, but in 2070 projected to cover 19% of the global land

And what here means “business-as-usual climate scenario” in this article?
I also heard that 500 million years ago the concentration of CO2 was 6000 ppm, and with this concentration, a man suffocates. Is it true?

 

[Baluncore]

I also heard that 500 million years ago the concentration of CO2 was 6000 ppm, and with this concentration, a man suffocates. Is it true?

Then plants covered the land and converted CO₂ into coal and O₂. Meanwhile, the CO₂ in seawater precipitated out as limestone. That lowered the CO₂, and raised the O₂, to the point where animals could breathe the air. Then those animals evolved to mine the coal and make cement.

6000 ppm CO₂ would cause your blood to become too acidic. You suffocate when there is insufficient oxygen in the air you breathe.

 

[Bandersnatch]

And what here means “business-as-usual climate scenario” in this article?

It's a scenario where concentrations of greenhouse gases keep growing throughout the century as if no mitigating action were taken. It's a sort of the worst case scenario.
Specifically, the paper means the RCP 8.5 scenario, as explained here:
https://en.wikipedia.org/wiki/Representative_Concentration_Pathway

 

[jim mcnamara]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380556/
To be clear on carbon dioxide- hypoxia and toxicant effects, per some comments in posts above:

Discussion of hypoxia and toxic effects of carbon dioxide poisoning, either or both of which can kill humans.
Symptoms are often not sufficient to correctly diagnose carbon dioxide victims. Article mentions that rescue workers should be well trained for carbon dioxide events for their own safety and a correct response by the ER team. Apparently symptoms vary widely.

Recent example where it took a long time to conclude that massive amounts of carbon dioxide were a cause of a major disaster ---
https://en.wikipedia.org/wiki/Lake_Nyos_disaster
A large overturn there led to a mass effervescent loss of carbon dioxide from the lower levels of the lake in 1986.

Also see: https://en.wikipedia.org/wiki/Lake_Monoun

The Nyos article mentions several possible reasons for the out-gassing. On a human scale, think of what happens when you shake a bottle of soda pop. Lake Monoun has been shown to have experienced a limnic eruption (shaking) in 1984, resulting in CO₂ out-gassing.

And yes it can happen again:
A. in Lake Nyos or Lake Monoun
B. in other lakes world wide situated over volcanic out-gassing events.

 

[BillTre]

Lake Nyos is a very deep lake. For some interesting reasons I not going to discuss, the lake has a high concentration of dissolved CO₂in deep regions of the lake. Large amounts of CO₂in can be dissolved in water. Besides actually dissolving in the water as CO₂in, it can also chemically react with water molecules to make carbonic acid.
H⁺ + HCO₃^–.
This forms a chemical buffer for the dissolved CO₂ in solution. It can be released quickly.

The deep and more shallow waters do not normally mix, the lake is stratified.
Physical disturbances (like the earth quake or maybe some underwater landslides) can cause mixing to start to happen.
As the deeper water moves up to lower pressure depths, the pressure drops and the CO₂ comes out of solution.
This causes bubble in the local volume of water which lowers its density, causing it to rise in the water column. This is basically an uncontained airlift (like in a home aquarium), except it can be driven across great differences in pressure since the lake is so deep.
Once a strong airlift condition is established, much of the volume of the lower regions of the lake will turn over, releasing large amounts of CO₂ in a short period of time.
This happened in a valley in low wind conditions and killed a lot of people.
Due to ongoing geological things at the bottom of the lake, the gas is expected to build up again.

These situations where a conditions combine to have big effects on gas solubility are an interesting aspect of aquacultural engineering. Thus some aquacultural engineers came up with a nice solution.
They made a small airlift in a pipe (controllable with valves) that once started, will use the airlift power of the CO₂ bubbles to continuously move some of the increasingly CO₂ loaded water to the surface where the CO₂ is released in small harmless amounts.

 

[Spathi]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380556/
To be clear on carbon dioxide- hypoxia and toxicant effects, per some comments in posts above:

This article is not fully clear for me, since the CO2 concentrations in in are described in other units than ppm. And again, one more question. In Jurassic era, the concentraion of CO2 was 900 ppm. Can such concentration be dangerous for a human?

 

[Baluncore]

https://en.wikipedia.org/wiki/Carbon_dioxide#Toxicity

 

[256bits]

This article is not fully clear for me, since the CO2 concentrations in in are described in other units than ppm. And again, one more question. In Jurassic era, the concentraion of CO2 was 900 ppm. Can such concentration be dangerous for a human?

900ppm could be the upper concentration in an indoor setting reasonably ventilated.
above 1000 the air can feel stuffy and make you feel a little bit sleepy, if you are just sitting around.
workplace limits are 5000ppm, which could be expressed as an averaged exposure limit over 8 hours ( or other time limits if applicable )
You do not want to be in a 40,000 ppm atmosphere for very long as that is the toxicity leading to death, or at the very least organ damage.

 

[Spathi]

I'm sorry, but can't anyone on this forum answer my basic questions (about the positive feedback and the probability of the scenario in article cited above)?

 

[Baluncore]

I'm sorry, but can't anyone on this forum answer my basic questions (about the positive feedback and the probability of the scenario in article cited above)?

Please restate your questions that have not been answered.

It should not be necessary to read and understand the paper, to extract a scenario from the paper. You need to specify clearly what the scenario is that you are seeing in the paper.

 

[Spathi]

Please restate your questions that have not been answered.

1) I want to get more specific information about the positive feedback and the idea, that if the ocean is heating, it will release the steam and this will lead to further heating. What models/calculations for this have been made?
2) In this article in PNAS, it is stated that in case of buisness-as-usuall scenario, the territories where now live 3.5 billion people (half of Africa, half of Arabian Peninsula, most of India, most of Southeast Asia, a part of Australia and a half os South America) will be uninhabited. What is the probability of this scenario (if there will be not enough significant actions from the states)?

 

[Baluncore]

1) I want to get more specific information about the positive feedback and the idea, that if the ocean is heating, it will release the steam and this will lead to further heating. What models/calculations for this have been made?

That is correct, and it will happen, in many different ways. All realistic climate models are very much more complex than your example of a simple feedback cycle. The important thing to understand is the presence and position of a "tipping point" or a "game changer", where negative feedback that stabilised the system response in the past, is replaced by positive feedback that then runs away, kicking the system into a new stable state, from which recovery to the previous state is certainly economically impossible.

2) In this article in PNAS, it is stated that in case of buisness-as-usuall scenario, the territories where now live 3.5 billion people (half of Africa, half of Arabian Peninsula, most of India, most of Southeast Asia, a part of Australia and a half os South America) will be uninhabited. What is the probability of this scenario (if there will be not enough significant actions from the states)?

Nation states capture and control resources, while taxing the economy. In the shortest term, economy is critical to their survival. In the longer term, survival involves building defences against the threats from the physical world, or moving dynamically to reposition into more survivable environments. We build cities, invest in concrete and transport infrastructure that makes it possible for the economy to survive for now. If the climate changes are too big, parts of the built environment will become inefficient, as migration of people, corporations, and the economy occurs, the investment in infrastructure must be selectively abandoned.

People have always migrated, but climate is changing faster now. Those who cannot move will become less efficient. While the older generation tries to hold on where they are, the younger generation will leave their childhood home to seek their fortune. That is the way of life. Geographically better positioned populations will grow in place over the next generation, so the distribution of population will move on the map, even if the majority of the individuals do not.

Since the climate system and economy is multidimensional and complex, the analysis of individual feedback cycles (acting alone), is insufficient to understand the system as a whole. Realistic climate models have passed the point where one person can know or write the entire model. The best models are evolving with the science and hopefully will predict the tipping points.

Some nation states will survive economically by avoiding or adapting to the predicted changes in climate, others will fade into history, tied down by the investment in the infrastructure needed to make survival in one place possible.

 

[hutchphd]

That is the way of life. Geographically better positioned populations will grow in place over the next generation, so the distribution of population will move on the map, even if the majority of the individuals do not.

Of course there are no guarantees that there will be any suitable habitat for long term survival of the human species.

 

[Vanadium 50]

People have always migrated, but climate is changing faster now.

I actually don't think that's correct (although can probably be made correct), and I think the more accurate view of the situation is even worse. The last big migration was during the Little Ice Age, from c. 1400 to c. 1800. Much of the population decided where to live in a period when the Earth was unusually cold. Now regression to the mean on top of an overall warming trend both push in the same direction.

Essentially, our cities are located best for a colder planet than we have now.

As an aside, "global temperatures" are calculated quantities,, not measured, and probably not the most useful number. 90% of the world lives in the northern Hemisphere. The net warming is largely in winters and nights. If you average over too many variables to get a single number, you can lose perspective.

 

[Spathi]

The important thing to understand is the presence and position of a "tipping point" or a "game changer", where negative feedback that stabilised the system response in the past, is replaced by positive feedback that then runs away, kicking the system into a new stable state, from which recovery to the previous state is certainly economically impossible.

Ok, and can you write some more information, under what conditions the negative feedback is replaced by the positive one? Do you mean by the negative feedback the change of concentration of H2O in atmosphere? I understand that if there was only a positive feedback, the planet would either freeze or overheat without the influence of people.

 

[Baluncore]

... under what conditions the negative feedback is replaced by the positive one?

The presence of liquid water in the oceans stabilises the temperature over much of the surface. That is a robust system that makes a poor example of positive feedback.

Probably the best example of a positive feedback tipping point, soon to be reached, is the iron cycle in the Southern Ocean. The CO₂ dissolved in Southern Ocean seawater, is in equilibrium with atmospheric CO₂.

There is very little iron in seawater. Phytoplankton require two doses of iron in their seawater, about one week apart, in order to develop. The removal of CO₂ from the seawater, and it's replacement with O₂, is done by phytoplankton while assembling their biomass. The phytoplankton are eaten by krill, that moult their exoskeleton often, before the krill are eaten by whales, and the whales poop the iron back into the seawater, thereby supporting the initiation of the next generation of phytoplankton. The rate that CO₂ is being removed from the seawater, and dumped as carbon on the ocean floor, is directly proportional to the mass of circulating iron in the cycle.

As the CO₂ level in seawater rises, carbonic acid (H₂CO₃) is formed, which makes the seawater more acidic. Krill are unable to form their exoskeleton in more acidic seawater, so the iron cycle may be broken, and that would result in the CO₂ level running away in positive feedback.

Likewise, if we hunt krill or whales, we reduce the mass of circulating iron, and the biomass of phytoplankton in the cycle. That reduces the CO₂ removed by phytoplankton, which leads to more acidic seawater, the loss of the krill, and an end to the iron cycle.

Business as usual is now an impossibility. We must reduce our consumption of fossil fuels before we reach the acidic seawater tipping point. We must stop hunting whales, or using krill from the Southern Ocean as stock feed. We need many more whales than we have now.

We will begin to cross that ocean acidity tipping point over the next couple of decades. If we get it wrong, it will be the end of the world as we know it.

https://en.wikipedia.org/wiki/Ocean_acidification
https://en.wikipedia.org/wiki/Iron_cycle#Oceanic_ecosystem
https://en.wikipedia.org/wiki/Krill#Biogeochemical_cycles

 

[Spathi]

The presence of liquid water in the oceans stabilises the temperature over much of the surface. That is a robust system that makes a poor example of positive feedback.

You want to say that the idea I explained about the steam is fake? This means, that the heating of the ocean is compensated by the ocean cooling due to the steam release, and the greenhouse effect of the steam is relatevely small? So this idea about the greenhouse effect of steam is invented just to popularize the message about the danger?

 

[hutchphd]

You want to say that the idea I explained about the steam is fake?

I am certain that had @Baluncore wished to say that he would have said that, and we can all read what he means.

Ok, and can you write some more information, under what conditions the negative feedback is replaced by the positive one?

As has been explained more than once this is a very complicated nonlinear system. No one knows exactly what the future holds. What is surprising to me is how prescient the early warnings have turned out to be. We can all thank Prof. Sagan for trying to tell us. But in the long run........

 

[Baluncore]

I want to get more specific information about the positive feedback and the idea, that if the ocean is heating, it will release the steam and this will lead to further heating.

You want to say that the idea I explained about the steam is fake? This means, that the heating of the ocean is compensated by the ocean cooling due to the steam release, and the greenhouse effect of the steam is relatevely small?

The steam is water vapour that must be dissolved in air at sea level. Wet air is less dense than dry air, so it rises, while the air pressure falls to where the air temperature equals the dew point, at the cloud base. The top of the cloud reflects solar energy back into space, which reduces the heating of, and evaporation from, the sea surface.
The percentage of cloud cover therefore regulates insolation, keeping the ocean surface temperature well below the point where steam condenses as it begins to rise from the surface.

 

[Spathi]

Probably the best example of a positive feedback tipping point, soon to be reached, is the iron cycle in the Southern Ocean. The CO₂ dissolved in Southern Ocean seawater, is in equilibrium with atmospheric CO₂.

There is very little iron in seawater. Phytoplankton require two doses of iron in their seawater, about one week apart, in order to develop. The removal of CO₂ from the seawater, and it's replacement with O₂, is done by phytoplankton while assembling their biomass. The phytoplankton are eaten by krill, that moult their exoskeleton often, before the krill are eaten by whales, and the whales poop the iron back into the seawater, thereby supporting the initiation of the next generation of phytoplankton. The rate that CO₂ is being removed from the seawater, and dumped as carbon on the ocean floor, is directly proportional to the mass of circulating iron in the cycle.

As the CO₂ level in seawater rises, carbonic acid (H₂CO₃) is formed, which makes the seawater more acidic. Krill are unable to form their exoskeleton in more acidic seawater, so the iron cycle may be broken, and that would result in the CO₂ level running away in positive feedback.

Likewise, if we hunt krill or whales, we reduce the mass of circulating iron, and the biomass of phytoplankton in the cycle. That reduces the CO₂ removed by phytoplankton, which leads to more acidic seawater, the loss of the krill, and an end to the iron cycle.

It is difficult for me to analyze your answer at once, please tell me whether the following is correct:

The higher the CO2 concentration (in the ocean) -> the more acidic the ocean -> the worse life for krill -> the less iron in the ocean -> the worse life for phytoplankton -> the less phytoplankton remove CO2 from the ocean, i.e. the higher the CO2 concentration (in the ocean), and so on.

And if so, it is not clear why this positive feedback did not exist earlier, before the emission of CO2 by humans?

 

[Baluncore]

And if so, it is not clear why this positive feedback did not exist earlier, before the emission of CO2 by humans?

Negative feedback returns a system to a stable value in an operating range.
Positive feedback causes an excursion towards more extreme positive, zero, or negative values.

The system was operating efficiently, with many whales. Then we killed lots of whales, and increased the CO2 from fossil fuel sources. Now we will see how the world's greatest CO2 absorbing system responds to the two perturbations we have applied.

Iron is being passed around a loop of chain. Break that circular chain, and the circulating iron will be lost from the system. It takes time to rebuild the processing capacity of the cycle.

 

[Vanadium 50]

Iron is more complicated. Increased temperature leads to increased desertification, which leads to increased erosion of iron-bearing minerals, some of which ends up in the oceans. So there's a negative feedback loop as well as the putative positive loop.

As a general rule, looking at one subsystem and drawing conclusions is a bad idea. Everything is interrelatd to everything else.

 

[Spathi]

Negative feedback returns a system to a stable value in an operating range.
Positive feedback causes an excursion towards more extreme positive, zero, or negative values.

I try to activate my mind as strongly as I can, sorry that I still don’t fully understand your answers. Two more questions:

1) With a big number of whales, the negative feedback works, but with a small number of whales, the feedback becomes positive?

2) Can we skip talking about krill? Maybe we can unite the phytoplankton and krill together in one model for the explanation? So the explanation will use only the number of whales and the number of phytoplankton/krill.

These discussions are very important since in the world there are a lot of climate change deniers, and they need to be convinced. As far as I know, youtube bans videos with the climate denial, but that is terrible.

 

[berkeman]

These discussions are very important since in the world there are a lot of climate change deniers, and they need to be convinced. As far as I know, youtube bans videos with the climate denial, but that is terrible.

Please re-read the Climate Change Rules post that is stickied at the top of this forum. You are about to get your thread locked if you go down that path...

CC/GW threads in this forum are intended for discussion of the scientific content of well-researched models of weather, climatology, and global warming that have been published in peer-reviewed journals and well-established textbooks.

Threads such "Is global warming real" or "Are humans the cause of global warming" are too broad and are subject to being locked. We want to encourage questions about specific research, news and events involved with climate science.

 

[Baluncore]

2) Can we skip talking about krill?

Krill eat phytoplankton and moult every few days to a month, depending on their stage of growth. When they moult, the carbon in their exoskeleton falls to the ocean floor. That binds the carbon and removes it from availability in the surface water. The population of krill, and the availability of phytoplankton, decides the rate CO₂ is being removed from the surface waters in the Southern Ocean.

There are two elemental processes, locked together.

1. CO₂ flows from the atmosphere to the seawater, is converted by phytoplankton into O₂ and carbon biomass, that is then eaten by krill. The carbon containing exoskeleton is repeatedly moulted, falling to the ocean floor.

2. The iron cycle. Iron is a trace element in seawater. It is rare because it tends to precipitate. But, iron is held in the body of krill, until the krill are eaten by whales. The iron is then pooped out as bioavailable iron, that fertilises and supports the development of more phytoplankton, to be eaten by krill.

The rate that iron is recycled through the ocean biomass determines the rate CO₂ is removed from the ocean. Any reduction in the rate iron is circulated, reduces the rate CO₂ can be removed from the atmosphere via the ocean.

If the iron cycle krill link was broken by rising CO₂, a tipping point would occur where the iron cycle would be further reduced by the rising CO₂. That is a positive feedback that we must avoid.

There was a time when the residents of Hobart in Tasmania could not row their small boats across the river because of the danger of breaching whales. The residents were once kept awake at night by the sound of the whales calling. There are now half a dozen whales that visit the river each year. That suggests we have a capacity for many more whales to play their part in the iron cycle, indirectly removing proportionally more CO₂ from the atmosphere.

 

[Laroxe]

While climate generally is outside of my comfort zone, I do have an interest in the methods of science. As I read the PNAS article, I did become concerned about the quality and interpretation of what is known and the way in which data was used. If my concerns are misplaced I'd appreciate correction.

The first section which was appropriately entitled “significance” made a number of claims around an estimate of a mean global temperature around 13 C which it suggested might represent a human temperature niche. In this they raised the idea of the global climate as representing a niche and that this could be based on temperature. If people are happy that such a thing exists and can be represented by the mean temperature, I don't feel this automatically means it valid to talk about humans living in one. Humans live in local areas in which the temperatures are often seasonal and best described as having a range, the same thing is true of most animals and plants. The authors appear to think that the words temperature, climate and niche can be used interchangeably and that a global mean temperature is a valid metric of all of these things. They then state that humans have concentrated in a narrow subset of “climates” over the last 6000 years, which have serves us well and imply predicted future warming will be damaging. Considering that the article focusses on human migration over Africa and Eurasia during the Holocene. There are already numerous temperature reconstructions covering specific areas and periods that provide temperature ranges across human habitats provides much more reliable data that these claims are simply not true, in fact seemingly running counter to the evidence.

The earth emerged from the last ice age into a cold dry period of the early Holocene, the climate then suddenly warmed and became wetter, the most extreme changes occurring in NW Europe, in which humans were starting to appear. This warming was also very sudden with temperatures increasing in Russia from a mean of 4 C to 12 C in a period of at most 50 years leading to massive changes in the local flora. The temperature gradient between summer and winter was greater and there were marked differences between the east and west of the region. By the mid Holocene the temperatures in Canada were around 4 C warmer than now, a period in history that is now called the climatic optimum as biological species had their hay-day. In fact over the whole of the Holocene, temperatures were highly variable with marked regional and seasonal differences, with even some of the more persistent changes that occurred over large areas happening quite quickly. These periods being characterised by rapid adaptations in both the fauna and flora with warmer temperatures increasing the biological “productivity”. For a useful measure of biological activity, we need to consider the range of species, that is the the set of locations where members of that species are found on Earth, a global mean temperature tells us nothing. In fact studies of changes in forestry cover have failed to identify any biological process that could causally be linked to mean annual temperature, even though its commonly used in species distribution models. (Korner et al 2016)

Animals can often introduce even more problems in making predictions, in that they interact with their environments in more active ways and can change these interactions based on environmental changes by alterations in their physiology or by making changes in their environment itself. Plants, animals and humans have evolved a variety of strategies to deal with challenging environments, in fact humans are so good at this there are few places in which humans can't survive. We have to consider that even local temperature ranges can be very poor indicators of what people have actually been exposed to.

As we talk about humans it introduces the issues of crops and livestock and how they provide an example of how quickly things can adapt to changing conditions, particularly with the help of selective breeding programs. As a result of the very varied requirements of populations there already exist many sub species that can tolerate a wide range of conditions. The evidence we have so far on food production is that we have steadily improved the productivity across the range of climatic conditions.

So I was left with the feeling that the only thing this provided evidence for other than the problems of trying to apply certain ideas to the understanding of complex biological systems. I didn't see any evidence for many of the claims made and even seemed to ignore evidence that is available. I do appreciate the problems in predicting the future and the way in which the most important are presented as tentative but they did seem to be writing about a history that is quite different to any I could find.

The links only provide some background info Really I'm interested in views about the quality of the paper.

https://www.britannica.com/science/Holocene-Epoch/Holocene-climatic-trends-and-chronology

https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.12574#jec12574-bib-0013

 

[Astronuc]

I happened to read an article describing the consequences for Alaska and Hawaii.
https://www.yahoo.com/news/finding-...hange-future-alaska-and-hawaii-100052363.html

More wildfires in some warmer/drier places, more flooding in some areas, and perhaps adverse affects in agriculture and food supply.

 

[johnbbahm]

TL;DR Summary: Not only the concentration of CO2 is important, but also the rate of its change (with the current rate, the ecosystems do not have time to react), and also that positive feedback can work now (the ocean, heating up, releases steam, which is also a greenhouse gas). But I would like to see these points explained in more detail.

It is known, that due to global warming, the average temperature on Earth over the past 100 years has increased by 1.2 degrees. At the same time, I heard that earlier the temperature of the Earth was 7 degrees higher than the current one.

I do not deny the danger of global warming, because I have seen the information that not only the concentration of CO2 is important, but also the rate of its change (with the current rate, the ecosystems do not have time to react), and also that positive feedback can work now (the ocean, heating up, releases steam, which is also a greenhouse gas). But I would like to see these points explained in more detail.

How probable is this scenario considered?

https://www.pnas.org/doi/full/10.1073/pnas.1910114117

And what here means “business-as-usual climate scenario” in this article?
I also heard that 500 million years ago the concentration of CO2 was 6000 ppm, and with this concentration, a man suffocates. Is it true?

Let's start with the probability RCP8.5, it means that by year 2100, they expect the CO2 level to be 1370 ppm.
Since the year 2000, the CO2 level has grown an average of 2.74 ppm per year.
to get from the current 418 ppm to 1370 ppm in 77 years, would require an average growth of,
1370 - 418 = 952 ppm / 77 years = 12.36 ppm per year. This is over four times the highest growth year every recorded, and highly unlikely(improbable).

The second assumption is likely one of the climate's sensitivity to added CO2.
They likely used ECS and a 2XCO2 sensitivity of 3°C.
Putting numbers to these assumptions would give 3°C/ln(2) =4.33 so 4.33 X ln(1370/280)= 6.88°C.
When they combine an unrealistic emission scenario, with a high climate sensitivity, they get a high result.

A more likely scenario is RCP4.5, which would have CO2 levels at 650 ppm, or growth of ~3 ppm per year, combined with sensitivity that matches observations, Past warming trend constrains future warming in CMIP6 models TCR 2XCO2 =1.6°C. This combination would produce warming by 2100 of 1.94°C.

 

[russ_watters]

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