Earth can’t warm suddenly - no temperature tipping point - radiates so much extra heat with each extra 1°C of warming - it can't trap or absorb it all - even with all possible feedbacks at their max

(virtually certain - IPCC AR6 / WG1 Chapter 7)

This is about temperature tipping point , the mistaken idea that a small temperature increase can lead to a large one of several degrees. The IPCC looked at this in 2021 AR6 / WG1 and showed it can’t happen, virtually certain. This has been much misunderstood by the popular press and infographic YouTube channels.

Tipping points more general are possible, see the end of this intro though often exaggerated in the press. You often hear people say, for instance, that as the ice in the Arctic melts the Earth will start to warm more and more with the extra warmth leading to more ice melting and more warmth and so on in a runaway effect. Sometimes you hear the same story for the permafrost melt. This is all junk science.

What these people don't take account of is that as the Earth warms it radiates away more heat - just like the way a hot radiator radiates more heat than a cold radiator.

Yes, more heat is trapped as the Earth warms but not nearly enough to compensate for the extra heat radiated away because it is warmer.

This explains how it works, notice how even though more heat is trapped or absorbed as the temperature rises, also a lot more heat is radiated away and when you add it all up you get more extra heat radiated away than extra heat trapped or absorbed which means you can’t have a tipping point of warming.

As the Earth warms it radiates away more heat

(just as a warm radiator radiates away more heat)

More heat is also trapped and more heat is absorbed but with each degree of warming far more heat is radiated away than absorbed or trapped.

IPCC AR6 / WG1 / Chapter 7 page 7–73:

“It is virtually certain that the net climate feedback is negative” i.e. no runaway warming
(Extra heat radiated away is counted as -ve feedback as it acts to prevent runaway)

For a runaway warming more extra heat must be trapped or absorbed than is radiated away with each 1°C

Trapped heat: 1.71 watts per square meter per °C

Absorbed heat: 0.35 watts per square meter per °C

Radiated heat: -3.22 watts per square meter per °C

With each 1°C of warming
3.22 watts extra radiated away
-1.71 watts trapped (per square meter)
-0.35 watts absorbed
__________________________
1.16 watts (range 0.51 to 1.81)
So more extra heat is radiated away
than is absorbed or trapped with each
degree of warming

Highlighed: It is virtually certain that the net climate feedback is negative, primarily due to the Planck temperature response, indicating that climate acts to stabilise in response to radiative forcing imposed to the system.

IPCC AR6 / WG1 / Ch 7.4.2.7 Synthesis page 7–73:

My comment: In non techy terms - Planck response is the way the Earth radiates more heat as it warms. They say as Earth warms due to radiative forcing from greenhouse gases, it also radiates more heat, and it is virtually certain the climate acts to stabilise in response, so there can’t be a global warming runaway effect.

Background photo Sun Over Earth (NASA, International Space Station, 07/21/03)

This means that as the planet warms, it radiates at least an extra 0.51 watts per square meter with every degree of warming

Tipping points are possible for ecosystems and for ice sheets. But the ice sheet tipping points unfold slowly over thousands of years and the ecosystem tipping points are often localized For tipping points more generally see:

. Most of the multiple climate tipping points unfold over thousands of years or are very localized - no risk of temperature tipping point

The only ecosystems at risk globally at 3 C are the coral reefs. We are headed for around 1.8 C with realistic pledges. A warmer world is more habitable for corals for slight warming but at 3 C the oceans get too acidic or them. At 2 C or below we are headed for a world more suited to corals than today after time to adapt though with a dip first as they adjust.

. Reason for hope for corals that many more survive at 2 C than previously thought - much quoted figure of 99% lost at 2 C based on study from 2016 - recent research suggests many corals may be more resilient

TECHY DETAILS - IF YOU ADD UP ALL THE WAYS HEAT CAN BE TRAPPED, ASSUME ALL ARE THE WORST THEY CAN BE, THEY AREN’T ENOUGH TO OVERCOME THE EXTRA HEAT THE WORLD RADIATES JUST BY BEING WARMER - SO THERE CAN’T BE A RUNAWAY

This has been very extensively studied. Chapter 7 of the IPCC AR6 / WR1 report is on this topic - and is summarizing a vast literature of papers written about it - lots of work done since 2018, I was amazed at how much more is known today.

In this next figure, I have simplified table 7-10 from the AR6 / WG1 latest IPCC report by removing a couple of columns (with results of previous reports) and one row - and added some extra notes to make it clearer. The arctic ice is included under "surface albedo".

For a runaway warming it has to lose less heat, or the same amount of heat, the warmer it gets

.

With each extra degree C of warming more extra heat is radiated away than is trapped.

So there is no runaway tipping point for global warming.

Once we stop emissions the temperature rise soon stops too.

You have to take account of the whole world there. There are some processes lead to more heat trapped and some lead to more heat radiated away.

When you average them all out and add them up then with each extra degree C of warming

• + 0.35 watts per square meter is absorbed because of the albedo effect- this is the whole world not just the Arctic

If that was all there was it would be a runaway effect but then you have all the other effects and especially the way that the Earth radiates more heat away with each degree C of warming - an extra

• -3.22 watts radiated away for each degree of warming just because the Earth is warmer

• +1.3 watts is trapped because of water vapour in the atmosphere (taking account of compensation due to the lapse rate which means in a warmer world there is more efficient transport of heat - but not enough to compensate for the water vapour greenhouse)

• +0.42 watts is trapped by clouds

• -0.01 watts absorbed by biophysical processes

Once you take account of that - then it ends up being still negative which means that more heat is lost than is trapped with each extra degree C. The total is:

• -1.16 watts per square meter trapped. I.e.

• 1.16 watts per square meter lost

Since the number is negative that with each 1°C of warming, 1.16 more watts per square meter is radiated away than is trapped (range 0.51 to 1.81).

So we can’t get a runaway.

The ice albedo shouldn't be isolated away from the rest of what's going on. You need to take account of the whole thing. There isn't any runaway feedback as I explained in 2). If there was only the ice albedo change and not this increase in radiation from a warmer world then yes that would be true. But you need to take account of everything. A warmer Earth radiates away more heat than a cooler one and that has to be taken account of in your calculations.

ARCTIC SEA ICE HAS NO TIPPING POINT - BUT MELTS AT LEAST ONCE BY 2050 WITH ALL SCENARIOS - AND IS POTENTIALLY REVERSIBLE ON SCENARIOS WHERE THE EARTH COOLS AGAIN

"The annual Arctic sea ice area minimum will likely fall below 1 million km2 at least once before 2050 under all assessed SSP scenarios. This practically sea ice-free state will become the norm for late summer by the end of the 21st century in high CO2 emissions scenarios (high confidence).

[my comment: those high emissions scenarios where an almost ice free summer becomes the norm are bascially impossible now]

Arctic summer sea ice varies approximately linearly with global surface temperature, implying that there is no tipping point and observed/projected losses are potentially reversible (high confidence). ".

⁠From: TS.2.5 The Cryosphere

Page TS-43

ON LOW EMISSIONS - ALL UNCERTAINTIES IN EXTRA GLOBAL FEEDBACKS SUCH AS PERMAFROST EMISSIONS, CLATHRATES, EFFECTS OF FOREST LOSS ETC AMOUNT TO A FEW TENTHS OF A DEGREE

Text on graphic: At low emissions net zero, all these effects combined add at most 0.1 to 0.2°C extra non-CO₂ warming ±0.1°C geophysical uncertainties & Transient Climate Responses ±0.1°C for mitigation strategies in low-emission scenarios

On the 1.5 C path,

• all the permafrost greenhouse gases

• all extra global feedbacks of CO2, N20, everything, all non CO2 uncertainties

• all the short term climate responses

it all adds an extra warming of 0.1–0.2°C at the time of net zero

• with an uncertainty of ±0.1°C.

• additional uncertainty depending on what we choose to do to reduce the effects of the warming on these feedbacks of another ±0.1°C.

So the range then is -0.1°C to 0.4°C

Application of the SR1.5 method with AR6-calibrated emulators suggests a median additional non-CO2 warming contribution at the time global CO2 emissions reach net zero levels of about 0.1–0.2°C relative to 2010–2019..

Uncertainty surrounding this range due to geophysical uncertainties such as non-CO2 forcing uncertainties and TCR [Transient Climate Responses] is of the order of ±0.1°C. Differences in the choices of mitigation strategies considered in low-emission scenarios result in a potential additional variation around the central range of at least ±0.1°C. (spread across 55 scenarios, referred to as non-CO2 scenario uncertainty in Table 5.8).

IPCC / AR6 / WG1/ 5-94

All of the non CO2 feedbacks are taken account of when assessing the remaining climate budget, see 5.5.2.2.3

Details with more cites here:

. IPCC report on tipping points and CO2 feedbacks: permafrost adds tenths of a degree max & gas clathrates unlikely to have detectable effect - and on low emissions ALL non greenhouse forcers add 0.1°C to 0.2°C, uncertainty ±0.1°C mitigation ±0.1°C

NO EVIDENCE OF SUBSTANTIAL CHANGES IN CLIMATE FEEDBACKS - EXCEPT POSSIBLY AT 10 °C ABOVE PRESENT

See chapter 7. There is low confidence they exist at all:

7.4.3.1 State-dependence of feedbacks in models page 7-77

The possibility of more substantial changes in climate feedbacks, sometimes accompanied by hysteresis and/or irreversibility, has been suggested from some theoretical and modelling studies. It has been postulated that such changes could occur on a global scale and across relatively narrow temperature changes ….

However, the associated mechanisms are highly uncertain, and as such there is low confidence as to whether such behaviour exists at all, and in the temperature thresholds at which it might occur

If they do then evidence from past climate change suggest it’s not until 10°C

…

7.5.5 Combined assessment of ECS and TCR, 7-112

…

There is, however, no evidence for unforced instabilities of such magnitude occurring in the paleo record temperatures of the past 65 million years ..., possibly short of the PETM excursion ... that occurred at more than 10°C above present

TAKING ACCOUNT OF NON GREENHOUSE EFFECTS THERE IS ACTUALLY A COOLING ONCE WE REACH NET ZERO

• SSP1-1.9: Zero by 2050+, ~1.4°C by 2100, overshoot to 1.6°C by 2050.

• SSP1-2.6: Zero by 2070+, ~1.8 °C by 2100 (was 2°C)

• SSP2-4.5 Low by 2100, ~2.7 °C by 2100 (was 3°C)

• SSP3-7.0 Double by 2100, ~3.6°C

• SSP4-8.5 Double by 2050, ~4.4°C

This shows the temperature predictions for the main scenarios

See: In-depth Q&A: The IPCC’s sixth assessment report on climate science - Carbon Brief

This is their longer term temperature prediction to 230

0

Figure 4.40 from page 4-190 of the report

WATER VAPOUR IS TREATED SEPARATELY AS A GREENHOUSE GAS AMPLIFYING THE EFFECT OF THE CO2 - BUT AMPLIFIES IT LESS IN THE TROPICS BECAUSE ALL THE MOIST AIR IN THE TROPICS HELPS TRANSPORT HEAT TO THE TOP OF THE ATMOSPHERE WHICH IS A COMPENSATING COOLING EFFECT

Water vapour isn't discussed in chapter 5 (except for clouds albedo) - it's treated separately as a greenhouse gas - but is central to all the modelling and well understood, likely increases by 1.2 to 1.4 watts per square meter per degree C. You need to look at chapters 7, 8 and 11.

QUOTE The combined water vapour plus lapse rate feedback is positive. The main physical processes that drive this feedback are well understood and supported by multiple lines of evidence including models, theory and observations. The combined water vapour plus lapse rate feedback parameter is assessed to be αLR+WV = 1.30 W m–2 °C–1, with a very likely range of 1.1 to 1.5 W m–2 °C–1 and a likely range of 1.2 to 1.4 W m–2 °C–1 13 with high confidence

7-63

There are many long sections in the report about water vapour. Another section is in 8.1.1.2 Overview of the global water cycle in the climate system page 8-11

Water vapour is a greenhouse gas, so in a warming world the increase in water vapour has a warming effect considered on its own, as a greenhouse gas.

However there is another effect goes the other way. When there is more water vapour in the tropics, this helps to move heat from the Earth’s surface to the top of the atmosphere faster.

So that’s an extra negative feedback. In a warmer world the tropics can cool down more than in a cooler world.

But the combination of those two processes is still positive.

This shows the idea of a lapse rate feedback. In a warmer world then the moister air conveys heat upwards more efficiently and this leads to the negative feedback - the upper layer of the troposphere is warmer - and so radiates away more heat - so it cools the world down more than in a cooler world.

In this diagram then when the top of the tropopause is cooler this means more heat is trapped, less is radiated away. So - if more heat gets moved up to the top of the tropopause as happens in the tropics, this warms the top of the tropopause and so cools the Earth

.

Lapse rate feedback is additional to the greenhouse effect due to water vapour.

-ve in tropics, +ve elsewhere, net effect -ve or cooling

Tropics: heat travels more easily upwards in a warmer world - cooling

Mid-high latitudes: Heat gets trapped near the surface - warming

Diagram from:

http://www.climate.be/textbook/chapter4_node7.html

QUOTE In the tropics, the vertical temperature profile is mainly driven by moist convection and is close to a moist adiabat. The warming is larger in the upper troposphere than in the lower troposphere, leading to a larger radiative emission to space and therefore a negative feedback. ,

7-62.

QUOTE the combined water vapour plus lapse rate feedback is positive. The main physical processes that drive this feedback are well understood and supported by multiple lines of evidence including models, theory and observations. The combined water vapour plus lapse rate feedback parameter is assessed to be αLR+WV = 1.30 W m–2 °C–1, with a very likely range of 1.1 to 1.5 W m–2 °C–1 and a likely range of 1.2 to 1.4 W m–2 °C–1 13 with high confidence.

7-63.

Summary in chapter 11.

QUOTE Temperature extremes = An increase in the concentration of greenhouse gases in the atmosphere leads to the warming of tropospheric air and the Earth’s surface. This direct thermodynamic effect leads to warmer temperatures everywhere with an increase in the frequency and intensity of warm extremes and a decrease in the frequency and intensity of cold extremes. The initial increase in temperature in turn leads to other thermodynamic responses and feedbacks affecting both the atmosphere and the surface. These include an increase in the water vapour content of the atmosphere and a change in the vertical profile of temperature.

While the water vapour feedback always amplifies the initial temperature increases (positive feedback), the lapse rate feedback amplifies near-surface temperature increases (positive feedback) in mid- and high latitudes but reduces temperature increases (negative feedback) in tropical regions.

11-15

COMITTED WARMING OF THE OCEAN IS COMPENSATED FOR ALMOST EXACTLY BY THE RAPID ABSORPTION OF CO2 AT NET ZERO

CO2 absorbed by land (low emissions)

CO2 absorbed by oceans (low emisisons)

Low emissions with overshoot - ocean briefly source in 22nd century.

The CO2 in the atmosphere is added so fast that given that the half life is 40 years there is just no way for the ocean and land to absorb more than half of the CO2 we added in 2021 until 2061 - so if we reach net zero by 2050 then there will be a lot of the CO2 even from 2021 still in the atmosphere and out of equilibrium in the sense that the ocean and land haven't had time to absorb it yet and of course lots of CO2 from the other years from now to 2050.

The diagram shows the result of feeding details of the sinks and how they behave into their models

Black text added: Atmospheric CO2 falls fast at zero emissions because atmosphere is out of balance with the sinks

Energy imbalances lead to committed warming but the CO2 reductions almost exactly compensate

Blue Text added: CO2 falls fast after zero emissions - falls by 100 ppm in a century.

World temperature stays stable after zero emissions slightly falling.

Not including effects of excess methane, aerosols etc - leads to faster fall in temperature after a fraction of a degree overshoot if all stop at once.

Figure 4–39 from IPCC AR6 / WG1 P 4–189

MORE DETAIL ABOUT WHY OCEAN HEATING IS COMPENSATED FOR BY CO2 ABSORBED BECAUSE CO2 IN ATMOSPHERE IS OUT OF EQUILIBRIUM

1. Ocean heating is compensated for almost exactly by the CO2 absorbed from the atmosphere at zero emissions.

Once all CO2 emissions stop there is continuing warming of the ocean - but the land and ocean also take up a lot of CO2. Right now the system is way out of equilibrium in two ways.

There is a lot more CO2 in the atmosphere than the land and ocean has had time to absorb. So, once we reach zero emissions the CO2 will fall very rapidly at first then gradually slow down as the system gets into equilibrium.

Also at zero emissions the warming of the ocean continues, as the energy flows are out of balance leading to the Earth warming, again rapidly at first then slowly.

At zero emissions, by chance, those two effects almost exactly compensate for each other. As the CO2 is absorbed, the extra warming effect on the ocean also falls.

This leads to an unnatural looking flat line curve - it's not due to everything suddenly stopping, it's due to these two effects almost exactly counteracting each other. Warms due to the energy flow imbalances but cools because of the CO2 absorption. There are other effects on top of this as we’ll see in a moment but if we only had the CO2 and the ocean warming to take account of, this is what would happen

:

The red line shows constant concentrations - this means that we keep emitting exactly enough CO2 to keep the atmosphere at the same CO2 level as it was when we reached net zero.

The blue is a more realistic net zero scenario.

Matthews and Weaver found that, in a constant concentration scenario, the world would continue to warm by around 0.3C by 2200 – with some additional warming in centuries to come as the deep oceans continued to slowly warm.

Given that the world has already warmed by around 1.3C, this means that the 1.5C limit would be breached, if current CO2 concentrations are held steady due to some continued emissions.

By contrast, they suggested that temperatures would stabilise in a world of net-zero emissions, remaining roughly at the level they were when emissions ceased.

Zeke Hausfather explains that this is due to the two effects almost exactly cancelling out

The Earth is currently out of thermal equilibrium, meaning more energy from the sun is being trapped by the greenhouse gases in the atmosphere than is escaping back to space. Over 90% of this extra heat is going into warming the oceans. However, as the oceans continue to warm, they will take up less heat from the atmosphere and global average surface temperatures will rise further.

At the same time, the land and ocean are absorbing about half of the CO2 that humans emit each year. If emissions go to zero, these “carbon sinks” continue to take up some of the extra CO2 that was emitted in the past – quickly at first and then more slowly over time as they move toward a new equilibrium. This reduces the levels of CO2 in the atmosphere and, thus, the warming it causes.

By chance, these two factors cancel each other out. The additional surface warming from the oceans continuing to heat up is balanced by the cooling from falling atmospheric CO2.

Both of these factors are also expected to have similar patterns over time, being larger in the first few years after net-zero emissions and gradually tailing off over time.

This graphic combines it with the previous graphic

Text on graphic: Constant CO₂ (artificial models thing) - continues to warm.

Zero emissions (falling CO₂)

- steady temperature

Some other effects will lead to cooling after zero emissions (HFCs and control of methane emissions).

CO2 falls fast after zero emissions - falls by 100 ppm in a century.

World temperature stays stable after zero emissions slightly falling.

Not including effects of excess methane, aerosols etc - leads to faster fall in temperature after a fraction of a degree overshoot if all stop at once.

Constant CO₂ (artificial models thing) - continues to warm.

Zero emissions (falling CO₂)

- steady temperature

Some other effects will lead to cooling after zero emissions (HFCs and control of methane emissions).

CO2 falls fast after zero emissions - falls by 100 ppm in a century.

World temperature stays stable after zero emissions slightly falling.

Not including effects of excess methane, aerosols etc - leads to faster fall in temperature after a fraction of a degree overshoot if all stop at once.

Details here:

. Explainer: Will global warming ‘stop’ as soon as net-zero emissions are reached? - Carbon Brief

TOTAL EFFECT FROM ALL NON GREENHOUSE FORCINGS

Short summary - it dependson how we reduce non greenhouse emissions. But there are many "win win" situations where you can reduce a harmful pollutant and at the same time counteract global warming. If we do this carefully we can get a decrease in temperature to help offset some of the warming.

If only CO2 emissions went to zero, average temperatures remain approximately steady neither rising nor falling (because the ocean continues to warm for a while, almost exactly compensating for the temperature reduction from falling CO2 levels).

However on low emissions net zero, we can also achieve:

1. up to -0.2 C feasible by controlling methane emissions

2. -0.2 to -0.4 C by phasing out HFCs which we are already doing to protect the ozone layer by the Kigali amendment to the Kyoto protocol on ozone depleting gases.

3. + 0.1 C from removing aerosols (SO2 is cooling, and black carbon is warming, removing both is a slight net warming)

For the source quotes and page numbers see this comment - and more details in next section.

For these reasons, on low emissions net zero by 2050, we end the century -0.3 to -0.5 C cooler than the peak, not far from present day temperatures - and it continues to fall after 2100. Those figures are from chapter 6 of the IPCC's AR6 / WG1 on aerosols.

This is the Carbon Brief graphic, the curve Zero GHGs + Aerosols is where we reduce everything to the max feasible.

See also Explainer: Will global warming ‘stop’ as soon as net-zero emissions are reached? - Carbon Brief

DETAILS ABOUT THE AEROSOLS, DEPENDS ON HOW IT IS DONE, + 0.1 C IF TRANSITION TO ALL RENEWABLES

This summarizes some of Chapter 6.

For the source quotes and page numbers see this comment

If we rapidly transition from fossil fuels to renewables with zero aerosols and without an overshoot of the final temperature - then the increase is about 0.1 C - that is just from the reduction of the aerosols from the fossil fuels, no offsetting or reduction of anything else.

That 0.1 C increase can be more than counteracted by other things such as methane reduction.

This is what the AR6 physical science report says - it is so much more detailed now.

It says some aerosols like SO2 are cooling, others like soot are warming, and the climate response to the aerosols has a strong regional pattern and is different from greenhouse gas driven warming.

The aerosols do affect global warming but it's complicated. You still get regional effects e.g. some of the warming we are already seeing in the Arctic is due to the clean air in Europe / North America as a result of the clean air acts.

The same warming hasn't happened further south because of other factors.

They also go on to say that the aerosols are expected to increase on the path to zero emissions not decrease because the path involves reforestation

Forests emit BVOCs ( biogenic volatile organic compounds) which oxidise in the atmosphere to similar compounds to the ones you get from coal and biomass burning.

Wildfires may increase emissions similar to coal burning, which is probably cooling in its effect - the more wildfires the cooler the climate. But if we control them well they may even decrease relative to current wildfires, which then would be a warming.

[Sorry I can’t find this in the report now - there is a section on wildfires but it is very technical and rather hard to read - but this covers why wildfires are expected to be cooling in a non-technical way:

https://www.sciencenewsforstudents.org/article/wildfires-australia-siberia-california-cool-climate-aerosols

But then reforestation is also a factor. In a world with fewer wildfires and more reforestation, adding more forests leads to the forests emitting those volatiles that oxidise to similar reflecting chemicals to the smoke from wildfires, and so has a cooling effect.

Our SO2 levels have already fallen very fast almost everywhere except India where it's still increasing [this is due to clean air acts]. Over historical periods to date the aerosols have acted to cool the climate, with high confidence but in an asymmetrical way with the result that the Arctic warms more than the rest of the world because as a result of the clean air acts most of the remaining cooling has been in the southern hemisphere and the tropics

LARGE INCREASE IF WE ONLY REMOVE SO2 OF 0.67 C - BUT IF WE ALSO REMOVE SOOT IT IS 0.1 C

If you only remove the SO2 this can lead to a large increase of 0.67 C.

However if instead we transition from fossil fuels to renewables - very ambitious but plausible with no overshoot - eliminate burning fossil fuels altogether rather than just clean the emissions of SO2, then this leads to an increase of about 0.1 C. That’s because reducing soot is a cooling effect. The IPCC report says:

6-72 QUOTE Recent studies show that very ambitious but plausible gradual phasing out of fossil-fuels in 1.5°C compatible pathways with little or no overshoot, lead to a near-term future warming of less than 0.1°C, when considering associated emission reduction of both warming and cooling species. This suggests that there may not be a strong conflict, at least at the global scale, between climate and air-quality benefits in the case of a worldwide transition to clean energy. However, at the regional scale, the changes in spatially variable emission and abundance changes might result in different responses including implications for precipitation, monsoon, etc. (Chapter 8), especially over South Asia.

The Carbon Brief graphic seems to show a slightly different scenario where removing SO2 + soot leads to a larger rise looks more like 0.2 C from their diagram and then increasing further with increasing methane emissions (removing SO2 can only have a short term increase). I am not sure how to interpret the text.

https://www.carbonbrief.org/explainer-will-global-warming-stop-as-soon-as-net-zero-emissions-are-reached/

CONTROL OF HFC GASES FOR THE OZONE LAYER SUBTRACTS 0.2 TO 0.4 C BY 2100

The Kigali amendment which added additional gases to control to protect the ozone layer just happened to also control some very strong greenhouse gases. If this is implemented it will subtract 0.05°–0.07°C by 2050 and 0.2–0.4°C in 2100

Without Kigali, surface temperature warming from HFCs might have been as high as 0.3°–0.5°C by 2100. With Kigali it is projected to be about 0.06°C by 2100.

https://www.fluorocarbons.org/environment/climate-change/kigali-amendment/

IPCC AR6 / WG1 / 6-71
QUOTE Efficient implementation of the Kigali Amendment and national and regional regulations has been projected to reduce global average warming in 2050 by 0.05°–0.07°C and by 0.2–0.4°C in 2100 compared with the baseline

MAXIMUM METHANE REDUCTION TECHNICALLY POSSIBLE REDUCES TEMPERATURE 0.2 C

Reducing methane by 50% (the maximum technically possible) reduces the temperature by 0.2 C and is also beneficial for air quality (because there is more reactive oxygen available to clean the air)

It's possible to get much larger reductions locally, for instance, a global policy to remove 80% of black carbon and the maximum technical reduction for methane would reduce temperatures in the Arctic by 0.2 to 0.6 C.

There is much more., The whole of chapter 6 is devoted to this. It is very long and detailed. By comparison in 2018 there were only a few paragraphs and sections on the topic. Really interesting stuff.

You can download the report here: Sixth Assessment Report

For the source quotes and page numbers see this comment

Their FAQ says that mitigation of these short lived climate forcers [SLCFs] is often viewed as a win-win policy because it reduces warming while at the same time improving air quality :

QUOTE Although policies to limit climate change and discussions of the so-called remaining carbon budget primarily focus on carbon dioxide, SLCFs [Short Lived Climate Forcers, e.g. aerosols] can significantly affect temperature changes. It is therefore important to understand how SLCFs work and to quantify their effects. Because reducing some of the SLCF emissions, such as methane, can simultaneously reduce warming effects and adverse effects on air quality as well as help attaining Sustainable Development Goals, mitigation of SLCFs is often viewed as a favourable ‘win-win’ policy option.

6-90.

IN PRACTICE WE MAY BE ABLE TO REDUCE THE CO2 FAR MORE THAN THIS WITH THE TECHNOLOGY OF THE SECOND HALF OF THE CENTURY - AND BY VARIOUS OPTIONS WE ALREADY HAVE FOR CLIMATE RESTORATION E.G. SOIL IMPROVEMENT

This is not taking account of ways to achieve net negative CO2 emissions - which can include e.g. a major program to enrich soils with carbon globally, giant kelp seaweed farming, making and reinforcing concrete from atmospheric CO2 and various other options for climate restoration.

See my: Dare to Hope - Climate Restoration - Three ways to get CO2 levels back to pre-industrial 300 ppm by 2050 - They potentially pay for themselves

Also, this will be with technology 30 years ahead of what we have now,

Look back to the 1990s and how much we've moved forward since then technologically and you can get an idea of how much more we can likely do by 2050. IMHO the most important thing is to be on track for low emissions by the 2030s and to have a feasible way to reach zero emissions by 2050 already.

The details of the actual way we achieve net zero by 2050 are pretty certain to be radically different involving technology we don't have yet. But we shouldn't rely on that technology but be sure we can do it already with present day technology.

So if we go rapidly to zero emissions, which is still possible, on the 1.5 C path we end the century below 1.5C and can be substanatially below. With current optimistic targets - then we end the century likely still above 1.5 C but with more ambition even if we overshoot we may end up below 1.5 C.

See:

. Already down to 1.8 C with the pledges to COP26 so far according to the IEA assessment - from 2.7 C earlier this year (COP26, 2021), nearly a degree reduction

SSP1–2.6 GIVES A ROUGH IDEA OF WHAT TO EXPECT ON THE 1.8 C PATH - AR6 / WG1 PROJECTS TO BEYOND 2100 TO 2300

Here the AR6 / WG1 IPCC report doesn’t model the current optimistic targets but their SSP1–2.6 isn’t far off it, so gives a rough idea of what to expect if we kept to current targets with no improvements.

Text on graphic:
All countries abandon all climate policies [SSP3-7.0]

Burn 6.5 times as much coal per year by 2100 (in reality coal burning already peaked) - coal burning maximises CO2 emissions - also exceeds current estimates of technically extractable coal reserves[SSP5-8.5]

All countries abandon all climate policies [SSP3–7.0]

If countries fulfilll their NDC pledges [SSP1–2.6]

Zero emissions by 2050 [SSP1–1.9]

2018 IPCC example worst case abandon Paris agreement then too little too late just above this one [SSP2-4.5]

Above 4 °C even a fit young farmer can’t cool down with sweating to normal blood temperature and will have a slight fever during heat waves in hot damp areas of China and INdia, e.g. hottest paddy fields and great care needed to avoid heat stroke.

From: Figure 4.40: "Simulated climate changes up to 2300 under the extended SSP scenarios" chapter 4 page 632 of IPCC AR6 / WG1

In draft report it is page 4-190, meant to be inserted on page 4-93 in the section "4.7.1.2 Change in Global Climate Indices Beyond 2100"

From IPCC AR6 / WG1, IPCC Sixth Assessment Report - the Physical basis

Surely we improve on current pledges in 2022, 2025 and 2030.

. 1st response to IPCC report: confirms predictions of previous reports, minor changes, able to be more exact.

RCP 8.5 - IMPOSSIBLE SCENARIO NOW - NEED TO BURN 6.5 TIMES AS MUCH COAL BY 2100 AND USE MORE THAN DOUBLE CURRENT EXTRACTABLE COAL RESERVES - PROBABLY MORE THAN THE AMOUNT TECHNICALLY EXTRACTABLE WITH 21ST CENTURY TECHNOLOGY - MEANWHILE IN REALITY COAL USE HAS ALREADY PEAKED

RCP 8.5 is mislabelled “business as usual” it was meant as a very high baseline - and many researchers say it is now impossible even if we were to try to acheve it

QUOTE According to the researchers who developed it, RCP8.5 was intended to be a “very high baseline emission scenario” representing the 90th percentile of no-policy baseline scenarios available at the time.

The creators of RCP8.5 had not intended it to represent the most likely “business as usual” outcome, emphasising that “no likelihood or preference is attached” to any of the specific scenarios.

One particular aspect of both the RCP8.5 and the new SSP 8.5 scenarios that has drawn quite a bit of criticism from energy researchers are their assumptions around future coal use. Reaching the CO2 emissions in these scenarios requires a large-scale increase in coal use – with 6.5 times more coal use in 2100 than today.

…

Overall, coal use is quite high in SSP3 and SSP5. In the SSP5 baseline marker scenario (REMIND), coal use between 2005 and 2100 is around 44,500 exajoules (EJ), considerably larger than current technologically and economically recoverable reserves of around 21,000EJ.

. Explainer: The high-emissions ‘RCP8.5’ global warming scenario

In reality coal use has already peaked.

. Fossil Fuels

SSP 7. HIGHLY IMPLAUSIBLE - IPCC WORST CASE SCENARIO WAS FOR COUNTRIES TO ABANDON PARIS AGREEMENT - BUT THEN ONCE WE NOTICE WHAT HAPPENS COUNTRIES REACT BUT TOO LITTLE TOO LATE AND END UP AT AROUND 3 C - DOING NOTHING ALL THE WAY TO 2100 IS NOT HUMANLY PLAUSIBLE

I go into that here, the IPCC in 2018 did an example of a worst-case scenario where by chance all the impacts are in remote places and few people are affected until 2030. That obviously hasn’t happened. In this scenario they also suppose that the Paris agreement didn’t get finalized - in reality it has been - and that countries abandon it - which hasn’t happened.

In that scenario they saw us reaching around 3 C by 2100. Details see my:

. The IPCC’s own worst case climate change example - a 3°C rise by 2100

WHY DO THE IPCC EVEN INCLUDE SUCH SCENARIOS - COMPATIBILITY WITH PREVIOUS REPORTS - AND ALSO BECAUSE EFFECTS ARE MORE OBVIOUS AND EASIER TO SEE AND STUDY IN MODELS WITH HIGH END SCENARIOS

You might wonder why the IPCC even include scenarios like this. Well the reason is for compatibility with previous reports, which explore high end scenarios - and because it is useful to have high end scenarios to model as the effects in the models are clearer to see and interpret e.g. if you are interested in the effects of clouds, for instance, you may see it more clearly in a model like SSP3–7.0 than SSP2–4.5.

For more detailed discussion see my

. 1st response to IPCC report: confirms predictions of previous reports, minor changes, able to be more exact.

CO2 LEVELS IN THE ATMOSPHERE WILL CONTINUE TO RISE UNTIL WE REACH ZERO EMISSIONS - AND CONTINUE TO RISE FASTER EACH YEAR UNTIL EMISSIONS PEAK AND START TO FALL - THIS IS EXPECTED AND HAPPENS ON ALL PATHS INCLUDING THE 1.5 C PATH

Every year in the spring we get stories about how the CO2 levels are the highest since before the ice ages.

This is expected. For as long as we have large CO2 emissions every year then the CO2 levels in the atmosphere will rise. It rises in this wavy fashion, because of the seasonal cycles as new plants take CO2 out of the atmosphere and then return it again in the northern hemisphere autumn (there is far more high latitude land mass in the northern than in the southern hemisphere).

If we can halve current CO2 emissions by 2030 it will rise by 1 ppm per year instead of the current 2 ppm per year. If we reach zero emissions in 2050 then it stops rising and starts to fall.

Each May the CO₂ level is the highest since the Pleistocene - becuase CO₂ rises by 2 ppm per year.

On low emissions it rises 1 ppm after 2030 then 0 ppm then starts to fall.

This is normal.

The wiggles are for the seasons - in high latitudes northern hemisphere fall, many leaves decay and CO₂ rises. it takes to May to reach Hawaii. As leaves grow, the CO₂ falls again.

See: Guest post: How the Keeling Curve will need to bend to limit global warming to 1.5C - Carbon Brief

We have increased pledges in 2022 then in 2025 then in 2030. We are already headed for 1.8 C with optimistic targets. For some reason many Western analysts ignore the zero emission pledges for China and India after 2030. IMHO we can count on the pledges from China and India more than we can from most countries as they tend to over promise and underdeliver.

So, CO2 emissions have stayed higher a bit longer than for the ideal 1.5 C path from 2015 but as you see in this graphic, 1.5 C is well within reach and even if it stays high to 2030 it is within reach with a rapid reduction. China and India are likely to overachieve and so bring us below that yellow line. The more it can be reduced by 2030 the easier.

With current pledges in yellow emissions stay high to 2030 but then fall fast.

Whether or not we reach 1.5 C, well below 2 C is certainly well within reach - and 1.5 C is as well with improving pledges - or indeed - with improving technlogy.

Solar panels and wind turbines will continue to go down in price making it easier to make more ambitious pledges in 2025 and 2030. It's certain they will fall in price, we don't know by how much yet, so countries can't count on this or build it into their pledges.

For more on all this see my:

. Already down to 1.8 C with the pledges to COP26 so far according to the IEA assessment - from 2.7 C earlier this year (COP26, 2021), nearly a degree reduction

SEE ALSO

. IPCC report on tipping points and CO2 feedbacks: permafrost adds tenths of a degree max & gas clathrates unlikely to have detectable effect - and on low emissions ALL non greenhouse forcers add 0.1°C to 0.2°C, uncertainty ±0.1°C mitigation ±0.1°C

. Small hot spots along coastlines briefly get so hot that you would feel like you have a fever if you stay in them for hours - like this since 1970s, it’s 4 C above preindustrial before it affects large areas

. Worst possible impacts of climate change? Using IPCC’s example worst case scenario from 2018 - NOT billions will die - NOT collapse of civilization - NOWHERE NEAR human extinction

. Humans do not go extinct on any climate scenario - you can ignore all the activists and doomists who use the IPCC report to get attention for their junk science - listen to the scientists themselves

. Not as scary as it seems: Planet at risk of heading towards “Hothouse Earth” state - it’s about thousands of years into the future and we avoid it on low emissions

MUCH POSITIVE GOING ON

It’s good to motivate yourself with positive framing. The psychologists say that a good ratio is three positive framings (positive stories about good things going on, about success, things working) with each negative framing.

Most activists have it the other way around or have only negative framing with no positive framing at all - that is why some of the things they say can be so dispiriting and discouraging for many. Has the opposite of the intended effect, only motivating activists to act.

Positive framing: Looking at the good things that are happening and that we are doing and can do.

. How to motivate your self, and others to act on climate change, biodiversity or anything else - tips from psychology - e.g. for maximum engagement present 3 positive or supporting framings for each climate threat

Here are some of my positive articles may help.

. Yes our generation’s children are headed for a world with nature and wonder in it

. Videos of good things that are happening in the world for climate change and biodiversity

. Simple lifestyle changes to help reduce global warming and biodiversity loss

. With statements of intent from US and China - “well below 2 C” gets more in reach, down to 2 C by 2100

. . With statements of intent from US and China - “well below 2 C” gets more in reach, down to 2 C by 2100

Also my

. Fact Check: IPCC's Transformative Change Maximises GOOD QUALITY OF LIFE With GROWTH In Everything We Value, Not COLLAPSE

Also my

. Seven tips for dealing with doomsday fears

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WHAT ABOUT JAMES HANSEN’S “RUNAWAY VENUS”? - THIS WAS SOON SHOWN TO BE IMPOSSIBLE

Some of you may have heard about James Hansen’s suggestion that Earth’s climate could enter a runaway to a Venus type climate.

It's not possible. Would need at least 3% CO2 in the atmosphere, 30,000 ppm.

It was just a passing remark in a book - without even a back of the envelope calculation to back it up.

He never shared a calculation and it wasn't peer reviewed.

His book is still on sale and it still says that we risk a runaway greenhouse even though it was almost immediately proved to be false.

We would need to burn ten times all the fossil fuels. It's not possible at present.

It may be possible 500 million years from now. One of the clear indications that it is not possible is the PETM. If we could trigger a runaway greenhouse today - then it should have happened back then.

As for Venus - then its continental plates got stuck and the best guess at present is a global overturning event which turned all its carbonate deposits into CO2. That's not possible for present-day Earth with our moving continents and the deep global ocean (which lubricates thek moving plates). You are talking about a superplume like the one under the Pacific rim of fire - but global and completely stuck until the whole thing overturns. That just can't happen to Earth. Not at present at least, talking about very far future, at least hundreds of millions of years, for continental drift to possibly stop on Earth.

See: Debunked: Global warming IS NOT a terrifying apocalyptic scenario - NO RISK OF ANYTHING LIKE VENUS - MISTAKEN story in the Independent