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The Last Year Below 1.5 C – Remarkable Warming Acceleration In 2023 Surpasses the Dangerous Warming Threshold

Image: The “Flats” on the back side of Padre Island in South Texas. Just inches above sea level, these flats are mostly gone today from sea level rise.

The Last Year Below 1.5 C – Remarkable Warming Acceleration In 2023 Surpasses the Dangerous Warming Threshold

The Global 1.5 °C Climate Change Threshold Was Unexpectedly Exceeded in 2023, Generations Ahead of Schedule

by Bruce Melton PE
Abridged version published on January 27, 2024

(This Climate Discovery version includes 28 references with summaries and some really good photography of Earth systems that began collapsing at between 0.5 and 1.0 degrees C warming above normal, where once an Earth systems collapse begins, it will not self-restore unless the thing that caused the collapse to begin is removed.)

Summary: Our climate has crossed the “dangerous” 1.5 C warming threshold generations ahead of projections. This threshold crossing has been caused by a doubling of the warming rate over the last ten years, by the unmasking of cooling from the three-peat La Nina, a small amount by the new El Nino; by unmasking of warming from shipping and transportation regulations reducing emissions of global cooling sulfates, and by increased natural feedback emissions from collapsing Earth systems. This threshold crossing is permanent unless we restore our climate, and will now grow at greater than twice the warming rate of the past, with risks of even greater nonlinear increases and existential impacts that were formerly supposed to arrive at the end of the century. The cure is no longer driven by emissions eliminations because they only reduce further warming. The cure is now driven by atmospheric removal of greenhouse gases and emergency geoengineering cooling to lower the temperature from today, to eliminate the risk of irreversible tipping and existential futures.

Earth’s climate has crossed the “dangerous” 1.5°Celsius (2.7 degrees Fahrenheit) above normal warming threshold 50 years or more ahead of long-held projections. Of the four major Earth temperature evaluations released for 2023 so far, Berkeley Earth is at 1.54°C, the European Meteorological Service is at 1.48°C, the World Meteorological Service is at 1.45°C and NASA is at 1.44°C. Why choose Berkeley, the warmest temperature evaluation,  instead of one of the lower evaluations? Almost all climate change impacts are happening decades, generations and even a century ahead of projections. It would be a poor engineering decision with so much evidence of understatement in climate science, to choose a temperature that is not the most extreme. As recently as 2021, the Intergovernmental Panel on Climate Change (IPCC) said we would not cross the 1.5°C threshold until after 2032. The IPCC’s 1.5°C Report in 2018 said that a constant rate of warming from the mid 2020s would see us exceed 1.5°C warming in 2040.

Berkeley Earth says, in 2023, every month from June to December was warmer than the previous record warm month; something never before seen in the temperature record. Almost half of the days in 2023 were warmer than 1.5°C, more than doubling the previous record. Two days in November were above 2°C, a first ever occurrence.

What’s so important about a little warming? If the average warming on Earth today of 1.54°C is the land-ocean average, then warming over land is twice that over the cool oceans — on average, 3.08°C (5.4°F). Then consider that heat extremes are many times the average, and what seems like a paltry 1.5°C warming becomes a very large number with obviously dangerous implications.

This warming acceleration cannot be changed by elimination of emissions as it has been caused by current warming; by past emissions that have accumulated in our sky, from increasing natural warming feedbacks from collapsing Earth systems, and from cascading effects that amplify warming nonlinearly. In just two years in 2023 and 2024, warming could be as much as half of all warming we have experienced in the last 200 years.

The threshold to dangerous climate change has now been crossed in a very big way. Last  last fall, Berkeley Earth says that there was a 99 percent chance the 1.5 degree C warming target will be passed in 2023, but early in the year the chance was only in the low teen percentage (1). James Hansen, the now retired but still publishing 32 year director of the NASA Goddard Institute for Space Studies (the de facto US climate modeling agency) says it is quite likely that Earth’s temperature will not fall below 1.5 C again (until we restore our climate of course) (2). It is time to plan on climate change far more extreme than what we have endured so far, as end of century impacts are now advancing to our immediate future.

November’s warming was 0.38 degrees C (0.68 F) warmer than any previous November in the temperature record of the last 173 years, where the largest previous jump was 0.06 C (0.11 F) from 2019 to 2020. This new record is five times larger than the previous record. October’s warming was 0.26 C, three times larger than the previous record. September warming; 0.45 C, six times larger. August; 0.26 C, four times larger. July; 0.21 C, twice as large as the previous record. June; 0.14 C, twice as large. Prior to June, the warming rate was not substantially different than the trend of the previous 172 years (3).


The GISTEMP Seasonal Cycle since 1880 graphic above is from NASA’s Goddard Institute for Space Studies (GISS), showing the remarkable temperature jump since June in purple.

The Berkeley Earth global temperature evaluation shows 1.54 C warming above normal for the year 2023. Notice the baseline of 1850 – 1900. Baselines differ across institutions and create more than just a little confusion. The 1850 to 1900 baseline represents that vast majority of warming humans have caused since we began burning fossil fuels. 

Climate scientists warned us that if we did not reduce our greenhouse gas emissions, climate change would advance into a new and more acute mode, where solutions were different, impacts would increase nonlinearly, and some effects could be irreversible. They urged us to understand that actions to limit greenhouse gas emissions would likely eliminate this more acute warming mode, and that lesser than suggested actions could cause warming acceleration to arrive faster with more extreme impacts, and that this acute phase would include existential risks.

Remember, average global warming over land is double the global average because of the cooling influence of our oceans and ice sheets, or 3.56 degrees C in December (6.4 F). and the average over the arctic is four times the global average or 7.12 C (12.8 F). Importantly, the increase in extreme temperature is far greater than the average, and extreme weather increases nonlinearly because of the basics of heat and energy physics, where a little warming does not create a little more extremeness in the weather, it creates a lot more. Image: Lake Travis, Central Texas, ongoing drought where Travis is at 39 percent of capacity.

Over the last 30 years, the accumulated concentration of excess CO2 in our sky has doubled (4). Over the last ten years the warming rate has more than doubled (5). It is current warming however, that has amplified the warming rate. If we stopped emissions a decade or more ago, further warming in the pipeline from Earth’s energy imbalance would have still created this vault in the global temperature. Cessation of emissions does not halt warming (6). The cause can be related to five things other than the doubling of the warming rate over the last 10 years.

Another depiction showing December’s average global temperature at 1.78 degrees C above normal. Copernicus/ECMWF, European Weather Agency. the baseline for this evaluation is 1850 to 1900.

First there is the rebound from the just passed triple-dip La Nina, a very long La Nina. This three year cooling in the equatorial surface Pacific Ocean masked warming that would have otherwise occurred.  Then there is the flip to El Nino, which is a warming of the equatorial Pacific. The year 2023 was initially projected to be no big deal on the warming scale because of the lag of La Nina’s cooling that did not end until spring 2023. It takes a half a year or thereabouts for Earth’s temperature to warm back up to normal after a La Nina passes. El Nino too, has a lag in causing Earth’s temperature to warm. Normal El Ninos begin to manifest in the spring and summer, but significant changes to Earth’s temperature do not occur until late fall and winter. (7)  El Nino’s warming impact, while present, was likely low. Now that November’s average global temperatures have arrived, El Nino is probably beginning to play a significant role. But these two things alone do not explain the enormity of the temperature jump.

The magnitude of the 2023 jump in temperature is unmistakable, but look at the amount. This evaluation compares the average temperature between 1991 and 2020 to the 2023 temperature and see where the zero line is. This shows how much of the warming has occurred recently.

The Tonga eruption in January 2022 could counterintuitively be playing a warming role, but conflicting findings say maybe not (8). Volcanic eruptions normally cool our climate. Tonga was an undersea eruption that injected so much water into the stratosphere that it overwhelmed the normal cooling caused by sulfur oxide aerosols from the volcanic plume (that rotten egg smell ever-present near active volcanoes and geothermal features). Sulfur oxides cause cooling by reflecting light from the sun back into space before it can strike an object and be changed to heat energy that can be trapped by the greenhouse effect. They also aid in the formation of brighter and longer-lived clouds, that also reflect the sun’s light harmlessly back into space. Warming from sulfur oxide reduction regulations has been largely unanticipated in the mainstream but has likely played a major role (9).

The International Maritime Organization’s (IMO) has implemented new fuel regulations limiting sulfur content. Sulfur oxide air pollution from fossil fuels have historically been identified as one of the causes of 6.7 to 8.4 million deaths per year globally. Strict sulfur emissions limits from burning fossil fuels have been in force for generations in the US and Europe, with the exception of ship fuels.  In 2010 and 2015 the IMO imposed modest sulfur regulations on fuels in critical near-shore areas. In 2020, full-force reductions of about 85 percent went into to effect globally (10). Like with the Tonga eruption, sulfur emissions from ship fuels are global cooling emissions, where all global cooling emissions (mostly sulfur oxides) have masked a third of warming that should have taken place to date (11).

Image: Ship’s trails from sulfur oxide emissions, NASA, North Pacific, 2009.

With ship fuel sulfur there is an additional global cooling feedback where ship exhausts create cloud trails similar to jet trails or condensation trails, except a ship’s engine exhaust creates condensation trails that hover just hundreds of feet above the water. Because the sulfur oxide emissions from ship fuel enhances cloud brightness, ship trails with lower sulfur fuels now reflect less sunlight harmlessly back into space. The way this is extra-important to climate warming is that our oceans are extremely efficient at changing sunlight into heat energy. Ninety percent of sunlight striking a significant water body is absorbed and changed to heat where the whitest clouds reflect 90 percent of sunlight back into space. The worst place to limit sulfur emissions then, is over the oceans.

The last place to look for increased warming is a topic that is becoming more familiar in the popular press; climate tipping. There is a lot of controversy over tipping that revolves around when it will begin and what it means. The controversy arises in the definition of tipping: tipping is the process of collapse of an Earth system that is irreversible and results (generally) in feedback emissions of greenhouse gases in quantities that can dwarf humankind’s. The problem with this definition is that it does not consider the reversible phase of tipping, or the tipping activation phase.

Most tipping systems can be reversed; they are not irreversible. To reverse them, the thing that caused the Earth systems tipping collapse to begin (warming), must be removed before the point of no return. This “point of no return” is that point in time where even if the thing that caused the collapse to begin is removed, the inertia or momentum of the collapse continues and the collapse becomes irreversible with those feedback emissions dwarfing humankind’s (12). It is those feedback emissions that are beginning to happen now that complete our pentad of the causes of this sudden warming acceleration.

This is yet another way to look at both how much stronger recent warming is, and how much greater the 2023 temperature jump is than recent warming. The pink forms representing individual years are a statistical representation of the uncertainty in the global temperature evaluations for each year. 

A textbook example of emerging feedback emissions is from our global forests. Earth’s climate’s temperature has now warmed beyond the evolutionary boundaries of her systems. This means their collapses are now activated so they can re-evolve with species that are tolerant of the new conditions. The Amazon is now emitting, not sequestering any longer, 1 Gigaton (Gt) CO2eq (all climate pollution equivalents evaluated as CO2) with only 25 percent of these emissions from deforestation (13, 14). Permafrost collapse emissions are 2.3 Gt CO2eq annually including drowned forests. Canadian forests are emitting 250 megatons CO2eq annually, almost all from beetle kill with fires increasing. The Amazon and permafrost were averages where at the beginning of the averaging period the ecologies were sequestering and not emitting so the actual emissions today are at least double the average. This means that it is likely that their emissions are 7 Gigatons per year. And, similar ecologies globally are likely behaving similarly.

McDowell 2015 tells us forest mortality across the western US and Canada has doubled to quadrupled between about the 1980 and 2010 (15). Rosenblad 2023 says forest mortality increased eight times in Western US from 2010 to 2018 (16).  Liu 2023 says Canadian forest mortality has more than doubled 1970 to 2020 (17). Bauman 2023 says Australian tropical forests mortality has doubled between 1984 and 2019 and have flipped from sequestration to emissions (18).  A personal communication with Bauman confirmed what appears obvious. He said he believes it likely that tropical forests globally are behaving similarly to Australian tropical forests because of similar water stress. The crux is that when forest mortality doubles, both forest age and corresponding carbon storage are halved. By extension, on average globally forests are now emitting and not sequestering.

What does this sudden temperature jump mean?

For starters, plan on extremes that are much more extreme than what we have been enduring and there is risk that “much more extreme” may be a big understatement because of nonlinearity. Warming from El Nino and any from the Tonga eruption will go away, but the increased warming rate from feedbacks will only increase further and warming from reduction of ship fuel sulfur is permanent unless the regulations are reversed. Conspicuously, the sudden jump in temperature increases risk of tipping cascades (19, 20) and passing irreversible tipping points (21, 22, 23, 24, 25, 26). We do not want to deal with tipping cascades or irreversible Earth systems tipping collapse responses.

The final meaning is that, now that this abrupt warming threshold has been crossed, emissions reductions or even complete emissions elimination can no longer change our future, in time frames that matter. Tipping collapses mostly do not self-restore once activated, unless the thing that caused the collapse to begin is removed before the point of no return. The cure now is to restore our climate back to within the evolutionary boundaries of our Earth systems –before the point of no return– so their collapses stabilize. To do this we must ramp up atmospheric carbon dioxide removal and begin implementing emergency geoengineering cooling. (Emissions reductions help a little, but they do not cool; they only reduce future warming. It is current warming that must be cooled.) The reason emergency cooling is needed is the great risks from tipping collapses that create feedback emissions far greater than humankind’s, and the poor scientific understanding of the time we have left before the point of no return. This is not like the carbon budget. That is no longer a thing once tipping collapses have started.

The point of no return is something that is very difficult to disentangle from low resolution prehistoric evidence. But just the risk of cascading tipping systems and out of control feedback loops requires we cool immediately, because the risk of existential outcomes is so meaningful.

We don’t have a choice. Carbon dioxide removal and geoengineering are now required in addition to decarbonization. Eliminating emissions only limits further warming. This abrupt threshold crossing has been caused by current warming. To stop irreversible feedback emissions and eliminate the risks from extremes that are an unknown amount more extreme than what we have been enduring so far, we have to cool, not allow further warming.

Carbon dioxide removal (CDR) however is slow and decarbonization is very slow. Later is too late. Tipping collapses will likely become irreversible with no further warming above 1.5 °C. We must buy time with geoengineering so that carbon dioxide removal and decarbonization have time to become effective. This is the critical path.

Emissions reductions or elimination, decarbonization, net zero or whatever it is called; it is very slow. It will take centuries to cool Earth back to the evolutionary boundaries of our Earth system at less than 1 C warming above normal. We need to by time with CDR and geoengineering so that decarbonization can be effective. 

Carbon dioxide removal (CDR) is not new, expensive, or risky. We have been removing carbon dioxide from the air for a century in processes that are widespread in Industry and their components are even more widespread. The three mature CDR processes were developed to keep our sailors safe in submarines from carbon dioxide poisoning, to liberate the summer beer brewing industry in Bavaria in the late 19th century, and in the discovery of vitamins also in the late 19th century (27). Carbon dioxide removal however, is also slow. It is not near as slow as decarbonization though. If we could find the same motivation as we had to save our advanced civilization in World War II, we could build an infrastructure to remove CO2 and other greenhouse gases from our sky that have accumulated over the last 200 years, in just a couple of decades or less. But this time frame too, is too long. To ensure we do not cross irreversible tipping thresholds with existential implications, geoengineering is now the critical path.

The vast increase in the number of days with warming that is 1.5 C or greater than normal in 2023 is astonishing. And the rate that days above 1.5 C are accumulating too, is astonishing. We have crossed a warming acceleration threshold and unfortunately, the increase in the warming rate will increase nonlinearly from here; like an avalanche. This is the beginning of runaway warming. We must do everything in our power to stop it absolutely as soon as possible or warming could far exceed the worst-case scenarios that do not consider tipping collapses and runaway feedbacks. Given the time frames we have of just decades, geoengineering is at the top of the critical path.

Geoengineering may sound risky with much concern in popular press and academic publishing over adverse side effects, termination shock, and other scary sounding effects. The concern is not only because of the perceived risks, but because of the perception that geoengineering will give climate polluters license to continue polluting. There is one geoengineering strategy however, that does not follow these “rules.” This is the inadvertent geoengineering we have been implementing in our climate system for 150 years, caused by burning fossil fuels with sulfur that creates global cooling sulfates.

The new sulfur pollution regulations in China and Europe are, plain and simple, a cessation of ongoing inadvertent geoengineering. This purposeful geoengineering strategy when applied over our oceans is called marine cloud brightening (28) or MCB, and it is not new. It has been happening across Earth for 150 years inadvertently as we burn fossil fuels with their ubiquitous sulfur content. The new sulfur pollution regulations are now diminishing the cooling effects of this all too familiar inadvertent geoengineering we have been practicing since the horse and buggy were commonplace.

By temporarily rescinding these new rules (29) we can restore this inadvertent geoengineering for a while and cool some of this temperature jump to help us buy time to eliminate the risk of tipping passing the point of no return while we ramp up carbon dioxide removal and decarbonization. We absolutely understand the risks of reversing this ban on inadvertent geoengineering with fossil fuel sulfur. We know how many respiratory disease deaths are caused every year by the long-term emissions of these sulfur oxides. We know how this strategy affects ozone, and we know how this specific type of geoengineering affects global weather patterns because we have been doing it for generation upon generation.

There is another great advantage to temporarily rescinding these new air pollution regulations. The emission of global cooling sulfur oxides from fossil fuels is actually a very large-scale global inadvertent geoengineering experiment. Now that we have a relatively abrupt cessation of this inadvertent experiment, it can provide evidence on how geoengineering works and give clues as to the response of other geoengineering strategies and importantly, on a very large scale, the scale of the entire Earth. This evidence will be much increased as reverse the cessation of this inadvertent fossil fuel sulfur geoengineering.  This is the single most important thing about geoengineering: we don’t have a good idea of what all the side effects are of the various geoengineering strategies. By reversing these new sulfur rules, we get a glimpse into what this very real, but inadvertent fossil fuel sulfur geoengineering actually is; how it behaves and confirmation of side effects. The knowledge we will gain from this grand inadvertent global cooling cessation experiment and by hopefully reversing it, will help us understand how better to implement further emergency cooling in the future if (when) it is needed.


(1) Berkeley – 99 percent chance of 2023 exceeding 1.5 C… “We now consider there to be a 99% chance that 2023 has an annual-average temperature anomaly more than 1.5 °C (2.7 °F) above the 1850-1900 average. Prior to the start of 2023, the likelihood of a 1.5 °C annual average this year was estimated at ~1%. The fact that this forecast has shifted so greatly serves to underscore the extraordinarily progression of 2023, whose warmth has far exceeded expectations.”
Rohde, November 2023 Temperature Update, Berkeley Earth, December 19, 2023.

(2) Hansen – last year at below 1.5 C 2023 or 2024… “The September global temperature anomaly leaped to more than +1.7°C relative to the 1880-1920 mean (Fig. 1). Public discussion has focused on the remarkable magnitude of this monthly anomaly, which exceeds the prior warmest September in the period of instrumental data by about +0.5°C; we will comment on this extreme September anomaly below. However, the average anomaly of the
past 4 months (+0.44°C relative to the same months in 2015, the origin year of the 2015-16 El Nino) is probably more important. If this relative anomaly is maintained through this El Nino (through Northern Hemisphere 2024 spring) the peak 12-month mean global warming will reach +1.6-1.7°C relative to 1880-1920. Decline of global temperature following an El Nino peak is 0.2- 0.3°C. Thus, if this El Nino peak is as high as we project it will be, global temperature will oscillate about the yellow region in Fig. 2. The 1.5°C global warming level will have been reached, for all practical purposes. There will be no need to ruminate for 20 years about whether the 1.5°C level has been reached, as IPCC proposes. On the contrary, Earth’s enormous energy imbalance (references 8, 13, 14 below) assures that global temperature will be rising still higher for the foreseeable future.”
Hansen, Sato, Ruedy and Simons, El Nino Fizzles. Planet Earth Sizzles. Why?, Communication, Columbia University, October 13, 2023. 

(3) NOAA Climate at a Glance, November back through June – NOAA’s monthly temperature anomalies and previous records… The astonishing thing about these remarkable record smashing temperatures is that previous to 2023, the largest record smashing only increased the previous records by 0.02 to 0.03 degrees C for almost all records except a very few that were only slightly larger.
Climate at a Glance – Global Time Series, National Oceanic and Atmospheric Administration (NOAA), National Centers for Environmental Information, December 2023.

(4) Mauna Loa CO2 – Atmospheric concentration of CO2 doubled in the last 30 years… The Mauna Loa Atmospheric Observatory shows our current CO2 concentration of about 420 ppm CO2 is double the approximate 350 ppm CO2 concentration in 1990, where the preindustrial CO2 concentration from the mid- and late-19th century was about 280 ppm CO2.
Mauna Loa Atmospheric Observatory.

(5) Hansen, December 14, 2023 – warming rate more than doubled the last ten years… From 2015 to 2023, the “warming rate of 0.49°C/decade, more than double the 1970-2010 rate of 0.18°C/decade.”
Hansen, Sako and Reudy, Global Warming Acceleration: El Nino Measuring Stick Looks Good, communication, Columbia University, December 14, 2023.

(6) Hansen 2023 – Global Warming In the Pipeline… Recent findings telling us that if we stop emissions that warming will cease are not valid. Hansen and his team wrote this paper to show this concept was inaccurate. How they did this was to look at warming in the past when our Earth systems were in balance. The previous recent findings that show no further warming if emissions cease are modelled findings, where modeling has a long history of understatement because of a poor understanding of feedbacks. By looking at direct evidence from the past, Hansen et al eliminate the need to understand feedbacks. The great imbalance of greenhouse gases in our sky will truly be responsible for more warming, or warming in the pipeline, as our cool oceans and ice sheets come into balance with the excess greenhouse gases in our sky. In 100 years, Hansen et al suggest 4.8 degrees C (8.6 F) warming from our current energy imbalance, without further emissions.
Hansen et al., Global warming in the pipeline, Oxford Open Climate Change, November 2, 2023.

(7) El Nino – La Nina lag… “Historically Speaking, El Niño and La Niña events tend to develop during the period Apr-Jun and they tend to reach their maximum strength during October – February.”
ENSO Forecast, January 2023 Quick Look, January 19, 2023.

(8) Tonga Eruption – The jury is still out on Tonga as there have been projections of both significant warming and slight cooling, Whatever the answer, the warming/cooling will abate in five to ten years…

Tonga’s January 2022 eruption’s reverse climate impact… So much sea water was injected into the stratosphere that Tonga will create warming from the excess water vapor, not the normal volcanic cooling from sulfate aerosols. This is quite concerning. Millan 2022 states that, “Preliminary climate model simulations (see Supporting Information S1 for details) suggest an effective radiative forcing (e.g., Forster et al., 2001; Myhre et al., 2013; Smith et al., 2020; Wang et al., 2017) at the tropopause of +0.15 Wm−2 due to the stratospheric H2O enhancement (Figure S3b in Supporting Information S1). For comparison, the radiative forcing increase due to the CO2 growth from 1996 to 2005 was about +0.26 Wm−2 (Solomon et al., 2010).” In other words, the Tonga eruption may increase warming over the next five to ten years by more than half of warming we experienced from human emissions from 1996 to 2005. Warming from 1996 to 2005 as per NASA GISS was 0.275 C and 57% of this means additional warming of 0.16 C, or an additional 14 percent on top of our current 1.1 C above normal.Tonga Volcano Eruption Blasted Unprecedented Amounts of Water Vapor into the Atmosphere, NASA, August 2, 2022.
Millan et al., The Hunga Tonga-Hunga Haapai Hydration of the Stratosphere, Geophysical Research Letters, July 1, 2022.
Tonga – Slight Cooling, not warming… (abstract) “On 15 January 2022, the Hunga Tonga-Hunga Ha’apai (HT) eruption injected SO2 and water into the middle stratosphere. The SO2 is rapidly converted to sulfate aerosols. The aerosol and water vapor anomalies have persisted in the Southern Hemisphere throughout 2022. The water vapor anomaly increases the net downward IR radiative flux whereas the aerosol layer reduces the direct solar forcing. The direct solar flux reduction is larger than the increased IR flux. Thus, the net tropospheric forcing will be negative. The changes in radiative forcing peak in July and August and diminish thereafter. Scaling to the observed cooling after the 1991 Pinatubo eruption, HT would cool the 2022 Southern Hemisphere’s average surface temperatures by less than 0.037°C.”
Schoeberl et al., Estimated Climate Impact of the Hunga Tonga‐Hunga Ha apai Eruption, Geophysical Research Letters, September 26, 2023.

(9) Hansen on unexpected warming from ship fuel regulations – The Great Inadvertent Aerosol Experiment… Reduction of ship fuel sulfur from 23.5 percent to 0.5 percent in 2020 has likely resulted in decreased reflection of sunlight back into space via the reflection of bright aerosols, and decreased whitening of clouds that also reflects sunlight back into space. “Changes of IMO emission regulations provide a great opportunity for insight into aerosol climate forcing. Sulfur content of fuels was limited to 1% in 2010 near the coasts of North America and in the North Sea, Baltic Sea and English Channel, and further restricted there to 0.1% in 2015. In 2020 a limit of 0.5% was imposed worldwide. The 1% limit did not have a noticeable effect on ship-tracks, but a striking reduction of ship-tracks was found after the 2015 IMO regulations, especially in the regions near land where emissions were specifically limited. Following the additional 2020 regulations, global ship-tracks were reduced more than 50%.”
Hansen et al., Global Warming in the Pipeline, Oxford Open Climate Change, November 2, 2023.

(10) IMO Sulfur regulations for ship fuel… In 2010 and 2015, the reduced the allowable sulfur content in ship fuel by about 15 percent but only in critical near-shore areas. In 2020 the final phase of IMO’s sulfur regulations went into effect reducing global ship fuels sulfur content by about 85% to 0.5 % from 3.5 percent prior to 2010.
Reduced limit on sulfur in marine fuel oil implemented smoothly through 2020, International Maritime Organization, Downloaded December 2023.,The%20upper%20limit%20of%20the%20sulphur%20content%20of%20ships’%20fuel,sulphur%20oxide%20emanating%20from%20ships.

(11) IPCC, Masked warming from aerosols – Aerosols, mostly sulfates, have masked 30% of warming that should have already occurred… Total aerosol masking, including negative radiative forcing (RF) from sulfates and positive RF from black carbon, is -0.9 W/m-2. Total RF from all greenhouse gases is 3.0 Wm-2. The net masking, or cooling effect from all aerosols is 0.9/3.0 = 30 percent.
The RF from emissions of well-mixed greenhouse gases (CO2, CH4, N2O, and Halocarbons) for 2011 relative to 1750 is 3.00 [2.22 to 3.78] W m–2 (see Figure SPM.5). The RF from changes in concentrations in these gases is 2.83 [2.26 to 3.40] W m–2. {8.5}
The RF of the total aerosol effect in the atmosphere, which includes cloud adjustments due to aerosols, is –0.9 [–1.9 to −0.1] W m−2 (medium confidence), and results from a negative forcing from most aerosols and a positive contribution from black carbon absorption of solar radiation. There is high confidence that aerosols and their interactions with clouds have offset a substantial portion of global mean forcing from well-mixed greenhouse gases. They continue to contribute the largest uncertainty to the total RF estimate.
Volcanic Masking: Several small eruptions 2008 to 2011 created 0.11 W/m-2 negative RF, or cooling of 4% of total forcing from all well-mixed greenhouse gases. This forcing was twice the forcing from 1999 to 2002.Intergovernmental Panel on Climate Change (IPCC), Scientific Basis, Summary For Policymakers, 2013. 

(12) Tipping (Earth systems collapse) and the “point of no return…   Evolutionary boundaries of our Earth systems in the Holocene, Tipping and The Point of No Return… (First use of “point of no return.”) We define: (1) the tipping level, the global climate forcing that, if long maintained, gives rise to a specific consequence, and (2) the point of no return, a climate state beyond which the consequence is inevitable, even if climate forcings are reduced. A point of no return can be avoided, even if the tipping level is temporarily exceeded. Ocean and ice sheet inertia permit overshoot, provided the climate forcing is returned below the tipping level before initiating irreversible dynamic change… Points of no return are inherently difficult to define, because the dynamical problems are nonlinear. Existing models are more lethargic than the real world for phenomena now unfolding, including changes of sea ice [65], ice streams [66], ice shelves [36], and expansion of the subtropics [67, 68]… Paleoclimate evidence and ongoing global changes imply that today’s CO2, about 385 ppm, is already too high to maintain the climate to which humanity, wildlife, and the rest of the biosphere are adapted. Realization that we must reduce the current CO2 amount [in the atmosphere] has a bright side: effects that had begun to seem inevitable, including impacts of ocean acidification, loss of fresh water supplies, and shifting of climatic zones, may be averted by the necessity of finding an energy course beyond fossil fuels sooner than would otherwise have occurred.”
Hansen et. al., Target Atmospheric CO2 Where should humanity aim, Open Atmospheric Science Journal August 2008.

(13) Gatti 2021 – Amazon emitting 1 Gt CO2eq annually on average from 2010 to 2018… based on atmospheric measurements over time…  “Considering the upwind areas of each site, we combine fluxes from all sites to calculate a total Amazonia carbon balance for our nine-year study period (see Methods) of 0.29±0.40 Pg Cyr−1 (FCTotal=0.11±0.15gCm−2d−1), where fire emissions represent 0.41±0.05PgCyr−1 (FCFire=0.15±0.02gCm−2d−1), with NBE removing −0.12±0.40PgCyr−1 (31% of fire emissions) from the atmosphere (FCNBE=−0.05±0.15gCm−d−1). The east (region 1 in Extended Data Fig.6), which represents 24% of Amazonia (of which 27% has been deforested), is responsible for 72% of total Amazonian carbon emissions, where 62% is from fires. One recent study showed cumulative gross emissions of carbon of about 126.1MgCO2 ha−1 for 30yr after a fire event, where cumulative CO2 uptake from forest regrowth offsets only 35% of the emissions. Another recent study13 reported that fire emissions from Amazonia are about 0.21±0.23PgCyr−1. Recently, van der Werf et al.  estimated for the period 1997–2009 that globally, fires were responsible for an annual mean carbon emission of 2.0PgCyr−1, where about 8% appears to have been associated with South American forest fires, according to estimates from the Global Fire Emission Data set (GFED V.3). The Amazon Forest Inventory Network (RAINFOR) project showed a decline in sink capacity of mature forests due to an increase in mortality1–3. Adjusting the three RAINFOR studies to a consistent area (7.25×106km2) and taking their mean yields a basin-wide sink for intact forests of about −0.57, −0.41 and −0.23PgCyr−1 for 1990–1999, 2000–2009 and 2010–2019, respectively. The NBE from this study is consistent with the RAINFOR results for the last decade, because NBE represents the uptake from forest but also all non-fire emissions, such as decomposition, degradation and other anthropogenic emissions (see Supplementary Table 3).”
Gatti et al., Amazonia as a carbon source linked to deforestation and climate change, Nature, July 14, 2021.

(14) Qin 2021 – Amazon emissions are 75 percent from warming and 25 percent from deforestation… “During 2010-2019, the Brazilian Amazon had a cumulative gross loss of 4.45 Pg C against a gross gain of 3.78 Pg C, resulting in net AGB loss of 0.67 Pg C. Forest  degradation (73%) contributed three times more to the gross AGB loss than deforestation (27%), given that the areal extent of degradation exceeds deforestation. This indicates that forest degradation has become the largest process driving carbon loss and should become a higher policy priority.”
Qin et al., Carbon loss from forest degradation exceeds that from deforestation in the Brazilian Amazon, Nature Climate Change, April 29, 2021.
preprint –
Paywall –

(15) McDowell 2015 tells us forest mortality across the western US and Canada has doubled to quadrupled between about the 1980s and the about 2010… It is also pertinent that warming since the mid-2000s has just about doubled as of 2022, and that much of the western US forest mortality from bark beetles was not captured in these evaluations.
— Sierra Nevada mortality has about doubled from 0.75 to 1.5 percent
— Western Canada mortality has quadrupled from 0.6 percent to 2.5 percent
— Eastern Canada has nearly doubled from 0.8 to 1.45 percent
— Western US interior forests have more than doubled from 0.3 percent to 0.65 percent.
— Pacific Northwest has tripled from 0.45 to 1.25 percent
McDowell et al., Multi-scale predictions of massive conifer mortality due to chronic temperature rise, Los Alamos National lab, nature Climate Change, December 21, 2015.

(16) Rosenblad 2023, Thermophilization – Mortality increased eight times in Western US Forests 2010 to 2018 … Simply put, thermophilization is forest evolution due to warming. It is driven in Western US forests by two factors, recruitment of new heat and drought tolerant species and mortality of less heat and drought tolerant species. Mortality is winning by 2:1. Rosenblad reveals a 20 percent mortality rate in 10 years – four to eight times normal. A doubling of mortality rate halves carbon storage… “”Here, we analyze 10-y changes in tree community composition across 44,992 forest subplots in the western United States… The dataset comprised 316,519 trees that survived between censuses (mean = 5.6 per subplot), 64,024 that died (1.1 per subplot), and 35,836 that recruited (0.63 per subplot).”
Thermophilization… Rosenblad et al., Climate change, tree demography, and thermophilization in western US forests, PNAS, April 24, 2023.

(17) Canada’s boreal forest mortality about doubled 1970 to 2020 and  lost (net) 3.5 Gt carbon as CO2, about 90 percent since 2002… “From 1970 to 2020. We show that the average annual tree mortality rate is approximately 2.7%. Approximately 43% of Canada’s boreal forests have experienced significantly increasing tree mortality trends (71% of which are located in the western region of the country), and these trends have accelerated since 2002. This increase in tree mortality has resulted in significant biomass carbon losses at an  approximate rate of 1.51 ± 0.29 MgC ha−1 year−1 (95% confidence interval) with an approximate total loss of 0.46 ± 0.09 PgC year−1 (95% confidence interval). Under the drought condition increases predicted for this century, the capacity of Canada’s boreal forests to act as a carbon sink will be further reduced, potentially leading to a significant positive climate feedback effect… The boreal ecosystem accounts for about a third of the Earth’s extant forests, containing an estimated one-third of the stored terrestrial C stocks (Bradshaw & Warkentin, 2015; Pan et al., 2011). The land area of Canada’s boreal forests (including other wooded land types) covers 309 Mha (Brandt et al., 2013), nearly 30% of the global boreal forested area (Brandt, 2009)… The overall increase in the biomass loss rate led to a significant reduction in biomass over the study period. From 1970 to 2020, the reduction in biomass was estimated at 3.01 ± 0.58 Mg ha−1 year−1 (95% confidence interval) with a total biomass loss throughout the entire boreal forested area of Canada (310 Mha) of approximately 0.93 ± 0.18 Pg, [3.4 Gt CO2eq] of which 83% was aboveground biomass and 17% was belowground biomass.” Mortality increase from Figure 1b.
Liu et al., Drought-induced increase in tree mortality and corresponding decrease in the carbon sink capacity of Canada’s boreal forests from 1970 to 2020, Global Change Biology, January 3, 2023.

(18) Bauman 2023 – Australian tropical forest mortality doubled in the last 35 years, mostly recently. A personal communication with Bauman says global tropical forests are likely behaving similarly because of the same water stress… Bauman 2022 analyzed a 49-year record across 24 old-growth tropical forests in Australia and found mortality has doubled because of water stress across all plots in the last 35 years indicating a halving of life expectancy and carbon residence time and suggesting that Australian tropical forests have now flipped from a CO2 sink to a source of CO2 emissions. Further, they suggest Southeast Asian tropical forests are behaving similarly. When I asked Bauman to confirm that Australian tropical forests are analog to Southeast Asian tropical forests,  he suggested what he believed now was that the same water stress is likely affecting all tropical forests globally in a similar way.
Bauman et al., Tropical tree mortality has increased with rising atmospheric water stress, Nature, May 17, 2022.
(Researchgate, free account required)

(19) Kemp 2023 – The risk of tipping cascades… “There are feedbacks in the carbon cycle and potential tipping points that could generate high GHG concentrations that are often missing from models. Examples include Arctic permafrost thawing that releases methane and CO2, carbon loss due to intense droughts and fires in the Amazon, and the apparent slowing of dampening feedbacks such as natural carbon sink capacity. These are likely to not be proportional to warming, as is sometimes assumed. Instead, abrupt and/or irreversible changes may be triggered at a temperature threshold. Such changes are evident in Earth’s geological record, and their impacts cascaded across the coupled climate–ecological–social system. Particularly worrying is a “tipping cascade” in which multiple tipping elements interact in such a way that tipping one threshold increases the likelihood of tipping another… The potential for tipping points and higher concentrations despite lower anthropogenic emissions is evident in existing models… There are even more uncertain feedbacks, which, in a very worst case, might amplify to an irreversible transition into a “Hothouse Earth” state (although there may be negative feedbacks that help buffer the Earth system). In particular, poorly understood cloud feedbacks might trigger sudden and irreversible global warming. Such effects remain underexplored and largely speculative “unknown unknowns” that are still being discovered. For instance, recent simulations suggest that stratocumulus cloud decks might abruptly be lost at CO2 concentrations that could be approached by the end of the century, causing an additional ∼8 °C global warming . Large uncertainties about dangerous surprises are reasons to prioritize rather than neglect them.”
Kemp et al., Climate Endgame, Exploring catastrophic climate change scenarios. PNAS, August 1, 2022.

(20) Willcock 2023 – Compound and cascading tipping drivers… “A major concern for the world’s ecosystems is the possibility of collapse, where landscapes and the societies they support change abruptly. Accelerating stress levels, increasing frequencies of extreme events and strengthening intersystem connections suggest that conventional modelling approaches based on incremental changes in a single stress may provide poor estimates of the impact of climate and human activities on ecosystems. We conduct experiments on four models that simulate abrupt changes in the Chilika lagoon fishery, the Easter Island community, forest dieback and lake water quality—representing ecosystems with a range of anthropogenic interactions. Collapses occur sooner under increasing levels of primary stress but additional stresses and/or the inclusion of noise in all four models bring the collapses substantially closer to today by ~38–81%.”
Willcock et al., Earlier collapse of Anthropocene ecosystems driven by multiple faster and noisier drivers, Nature Sustainability, June 22, 2023.

(21) Ritchie 2023 – Rate Dependent Tipping can create a point of no return faster than steady state forcing… This work describes an accelerated forcing rate that is faster than the classic steady-state forcing, that can create irreversible tipping response before the classic tipping projection time. It works in both biologic, natural and mechanical systems. Biologic and most natural systems are dynamic and self-restoring, as long as their collapses have not passed the point of no return. If the activation phase of tipping collapse is particularly abrupt, this can literally kill a system before the steady state forcing kills it.Example: beetle attack that kills enough of the trees in a forest to break the forest-cloud machine response. If there are no longer enough trees in the forest to create the clouds and precip that made the forest possible, this fast rate collapse results in completion of irreversible tipping before the steady rate increase state is encountered and the system does not self-restore. This is compared to the slow or steady state rate of change that most modeling uses, where tipping is suggested to occur at some point after collapse initiation – Hansen’s point of no return. With mechanical systems an electrical grid is considered with the UK grid collapse in 2007 where grid operators scheduled increased generation after the conclusion of a the 2007 semi-final soccer match. The match went into overtime with penalties and its abrupt conclusion gave grid operators too little time to react and the grid went down.
Ritchie et al., Rate-induced tipping in natural and human systems, Earth Systems Dynamics, June 14, 2023.

(22) Rockstrom 2023 – Safe and just Earth systems boundaries identified where seven of eight quantified boundaries in over half of global land area are now exceeded… We identify safe ESBs (Earth systems boundaries) for warming based on minimizing likelihoods of triggering climate tipping elements; maintaining biosphere and cryosphere functions; and accounting for Holocene (<0.5–1.0 °C) and previous interglacial (<1.5–2 °C) climate variability… Some climate tipping points, such as circulation collapse or Amazon dieback, have high uncertainty or low confidence in their dynamics and potential warming thresholds16, but the complementary palaeoclimate and biosphere analyses independently support the safe climate ESB assessment. Cryosphere function includes maintaining permafrost in the northern high latitudes, permanent polar  ice sheets and mountain glaciers and minimizing sea ice loss. We find that global warming beyond 1.0 °C above pre-industrial levels, which has already been exceeded9, carries a moderate likelihood of triggering tipping elements, such as the collapse of the Greenland ice sheet or localized abrupt thawing of the boreal permafrost16. One-degree Celsius global warming is consistent with the safe limit proposed in 1990 of 350 ppm CO2. Above 1.5 °C or 2.0 °C warming, the likelihood of triggering tipping points increases to high or very high, respectively (high confidence in Extended Data Table 1). Biosphere damage and the risk of global carbon sinks becoming carbon sources, potentially triggering further climate feedbacks, increase substantially.”
Seven ESB’s beyond their safe zone: Biosphere – natural ecosystem area, Biosphere – functional integrity, Water – surface flows, Water – groundwater flows,  Green water – soil moisture, Nutrient cycles – nitrogen, Nutrient cycles – phosphorus, Atmospheric loading – aerosols.
Rockstrom et al., Safe and just Earth system boundaries Nature, May 31, 2023.
Supplementary Materials – boundaries and discussion of climate tipping points begins on page 4.

(23) Ripple 2023 – Twenty physical and 21 biological tipping feedback loops threatened… “Many feedback loops significantly increase warming due to greenhouse gas emissions. However, not all of these feedbacks are fully accounted for in climate models. Thus, associated mitigation pathways could fail to sufficiently limit temperatures. A targeted expansion of research and an accelerated reduction of emissions are needed to minimize risks…  We suggest that further small increases in short-term warming are a big risk, considering the suffering that we are already experiencing from climate disasters of ‘‘unprecedented’’ wildfires, intense storms, coastal flooding, permafrost thaw, and extreme  weather that have occurred with just 1.1C to 1.2C global average warming. Second, as part of a longer timeline, positive feedback loops and tipping points may pose a major threat. Given the potential for catastrophic climate change and the lack of complete scientific understanding to date, policymakers should strongly consider the potentially dangerous effects of feedback loops, tipping points, and climate cascades, even if all desired scientific data are not available at this time… if the worst-case risks posed by feedback loops and tipping points have been underestimated, the future of a hospitable planet Earth may be at stake.”
Ripple et al., Many risky feedback loops amplify the need for climate action, One Earth, February 17, 2023.
(Paywall),fail%20to%20sufficiently%20limit%20temperatures. Summary –

(24) McKay 2022 – Exceeding 1.5 C global warming could trigger multiple climate tipping points with self-perpetuating change… (Note: some  of these tipping points have already been identified as being crossed by others: Permafrost, the Amazon, West Antarctic Ice Sheet, Greenland Ice Sheet, and the Gulf Stream.) “We show that even the Paris Agreement goal of limiting warming to well below 2°C and preferably 1.5°C is not safe as 1.5°C and above risks crossing multiple tipping points. Crossing these CTPs can generate positive feedbacks that increase the likelihood of crossing other CTPs. Currently the world is heading toward ~2 to 3°C of global warming; at best, if all net zero pledges and nationally determined contributions are implemented it could reach just below 2°C. This would lower tipping point risks somewhat but would still be dangerous as it could trigger multiple climate tipping points.” Tipping likely with a threshold of 1.5 C to less than 2 C: Greenland Ice Sheet, West Antarctic ice Sheet, Labrador Sea/Subpolar Gyre, low-latitude corals, Barents Sea ice, widespread permafrost thaw. At 2 to 4C: Amazon Rainforest dieback, East Antarctic Ice Sheet, Sahel/West African Monsoon, Mountain Glaciers. At +4 C: Atlantic Meridonal Overturning (Gulf Stream) Boreal Forest, Arctic Winter Sea Ice… Self-perpetuation mechanisms are critical to the existence of a tipping point in a system, beyond which they propel qualitative change such that even if forcing of the system ceases the qualitative change usually continues to unfold regardless.”
McKay, Lenton et al., Exceeding 1.5 C global warming could trigger multiple climate tipping points, Science, September 9, 2022.
Press Release  – University of Exeter

(25) Canadell and Jackson 2021 – In-depth description of a dozen global ecologies currently in collapse (13 papers)… Here are descriptions of regional or sub-continental scale ecological collapses that are ongoing. ” Ecosystem collapse is associated with the crossing of critical thresholds not only as a result of gradual climate changes, but more often due to abrupt climate extremes or compounded effects of multiple disturbances occurring at greater than historical frequencies… In each case of ecosystem collapse documented here, the authors believe that climate change is playing a dominant or contributing role to the ecosystem’s apparent demise, often interacting with other pressures. The book covers three latitudinal regions: (1) polar and boreal ecosystems, such as the impacts of water stress with a novel pathogen on alpine vegetation mosaics in Antarctic Macquarie Island, forest transitions to shrublands and grasslands due to interactions between temperature and fire in Southern Siberia and North America, and rapid changes in vegetation and ecosystem functions in the permafrost region as thawing is rapidly taking place; (2) temperate and semi-arid ecosystems, including the impacts of fire on a paleo-endemic alpine ecosystem in Tasmania, and the interactions between drought and heatwaves in forests in the Mediterranean, Western USA, and elsewhere; (3) tropical and temperate coastal ecosystems, including the impacts of marine heatwaves on coral reefs of the Great Barrier Reef and Mediterranean Sea, and kelp forests and seagrass meadows in Western Australia. One goal of this book is to raise awareness of the abrupt transitions already occurring today.”
Canadell and Jackson, Ecosystem Collapse and Climate Change, Springer Nature Switzerland, 364 pages, 2021.

(26) Lenton et al., Climate tipping points-too risky to bet against, 2019, Identifies nine tipping systems activated within the last ten years with warming above 0.5 C… Nine Earth systems collapses have been identified by scientists as active: Arctic sea ice, Greenland ice sheet, boreal forests, permafrost, the Gulf Stream, the Amazon, coral, the West Antarctic Ice Sheet and parts of the East Antarctic Ice Sheet. Until 2018, the Intergovernmental Panel on Climate Change (IPCC) has assumed that tipping would not occur before 5 C of warming above preindustrial times, something that the worst-case scenario put well into the 22nd century. In 2018 however, IPCC lowered this limit to between 1 and  2 C above preindustrial times in both the 1.5 C Report and the Cryosphere Report.  Lenton tells us, “The Intergovernmental Panel on Climate Change (IPCC) introduced the idea of tipping points two decades ago. At that time, these ‘large-scale discontinuities’ in the climate system were considered likely only if global warming exceeded 5 °C above pre-industrial levels. Information summarized in the two most recent IPCC Special Reports (published in 2018 and in September this year) suggests that tipping points could be exceeded even between 1 and 2 °C of warming.”  Climate tipping is now active greater than 100 years ahead of projections.      Press release selected quotes from the Exeter press release: “More than half of the climate tipping points identified a decade ago are now “active”, a group of leading scientists have warned. This “cascade” of changes sparked by global warming could threaten the existence of human civilization, Evidence is mounting that these events are more likely and more interconnected than was previously thought, leading to a possible domino effect. It is not only human pressures on Earth that continue rising to unprecedented levels. It is also that as science advances, we must admit that we have underestimated the risks of unleashing irreversible changes, where the planet self-amplifies global warming. This is what we now start seeing, already at 1°C global warming. No amount of economic cost–benefit analysis is going to help us. We need to change our approach to the climate problem.”
Selected quotes from the paper, “The Intergovernmental Panel on Climate Change (IPCC) introduced the idea of tipping points two decades ago. At that time, these ‘large-scale discontinuities’ in the climate system were considered likely only if global warming exceeded 5 °C above pre-industrial levels. Information summarized in the two most recent IPCC Special Reports (published in 2018 and in September this year) suggests that tipping points could be exceeded even between 1 and 2 °C of warming.”
Perhaps the most salient part of this work is that tipping points seem to be interrelated. The authors make strong links that 45 percent of tipping points create positive feedbacks that increase the reaction of other tipping points through dynamic global effects.
Lenton et al., Climate tipping points-too risky to bet against, Nature, November 27, 2019.
University of Exeter Press Release must read More than half of identified tipping points are active.

27) Early 20th Century air capture of CO2: lime-potash, cryoseparation, amines… In 1904 the recyclable lime-potash process was discovered to separate CO2 from air as a simple chemical reaction using extremely common potash and lime. In 1930 the first patent was issued for an ammonia-based process that used amines to remove CO2 from air. Notable applications were in submarines in World War II to keep our sailors safe form carbon dioxide poisoning. Also in World War II, the Habor-Bosch Process was developed to synthesize ammonia from hydrocarbons in Germany, mostly for explosives, as the Allies had cut off the German supplies of guano needed to generate the ammonia. This process became an extremely important process globally in synthesizing fertilizers. An important part of this process is removing CO2 to allow the formation of ammonia. This CO2 removal process advanced the state of amine technology for removal of CO2 from air. These three processes are mature today and represent some of the most important industrial processes known to humankind. Their components are widespread in industry making their implementation into a scaled atmospheric CO2 removal infrastructure a challenge of motivation and money, not technology.

Cryoseparation of air… Carl von Linde was the first to remove carbon dioxide from air. His technology was developed from his refrigeration discovery that itself was first used in the 1870s to help the brewing industry in Bavaria overcome limitations on summer season brewing and beer storage that was plagued by bacterial contamination that soured the beer, where from 1553 to 1850 summer brewing was literally banned between April 23 and September 29. After 1850, brewers learned to brew over produce in march and April and store their beer in caves where they had stockpiled winter ice. By 1890 Linde had sold 747 of his “ice machines” and summer brewing was flourishing. In 1892 Guinness contracted with Linde to build a CO2 liquefaction plant to sell excess CO2 from fermentation as an industrial chemical. This set in motion the ultra-cold refrigeration technology that Linde used in cryoseparation to distill the components of air into usable products that included not only carbon dioxide but, oxygen, nitrogen, and argon. The cryoseparation technology first supercools air to a liquid, then evaporates the liquid in a tall column where the temperature rises upwards in the column, condensing individual components at different temperatures, much like water vapor condenses in clouds to make rain. Linde’s work was the foundation of the Nobel Prize in Physics in 1913 awarded to Heike Kamerlingh Onnes.

Potash/Potassium Carbonate… A US patent granted in 1904, described a process for absorbing CO2 in a hot solution of potassium carbonate and then stripping the solution by pressure reduction without additional heating (Behrens, 1904).

Potash/ Lye… Giammarco was the first to patent an activated potash solution in 1955, and there are now a number of such processes – Kohl and Riesenfeld mentions some – they are still widely applied.

Haber-Bosch process… This was an extremely important process developed just before WWI that allowed nitrogen production for use in explosives and fertilizers, with a key part of the process being the CO2 removal. It was a German invention because the Allies controlled all the guano deposits that were the nitrogen source. CO2 is a byproduct of the process and development of removal processes played an important role in advanced amine processes today.

WWII – Lime/Potash and Amines: Keeping our sailors safe from CO2 Poisoning… The history of CO2 removal in submarines begins in World War II… “Air monitoring was by colorimetric tubes, soda lime was used to remove carbon dioxide and oxygen candles provide a source of oxygen replenishment.” With the advent of long submerse times with nuclear submarines , amines were used to scrub CO2 from submarine air.

Mazurek, Key developments in submarine air monitoring and purification, SAMAP Proceedings, October 2015.

Mention of soda ash and amines…

Amines… In 1930, Robert Bottoms was awarded a patent for removing CO2 from air with amines. The discovery of amines was first published in 1911 by Kazimierz Funk. Funk was inspired by Christiaan Eijkman work that showed eating brown rice reduced vulnerability to beri-beri, compared to those who at normal milled rice. (Beri-beri is a vitamin B deficiency that causes nerve and heart inflammation.) He was able to isolate the substance and because it contained an amine group he called it “vitamine”. It was later to be known as vitamin B3 (niacin), though he thought that it would be thiamine (vitamin B1) and described it as “anti-beri-beri-factor”. Amines have gone on to become one of the most important chemical groups in all of industry with processes that include: dyes, nylon, medicines, cooling systems, surfactants, cosmetics, agrochemicals, corrosion inhibitor, machining fluids, powder coatings, polyurethane, and epoxy coatings. Amines are a $32 billion industry in 2023.

(Thanks to Richard Darton, Emeritus Professor, University of Oxford, for information on the importance of potash in the early development of CO2 processes in industry.)

1903, Separation of CO2 from air –
Linde, Patent, Process of producing low temperatures, the liquefaction of gases, and the separation of the constituents of gaseous mixtures

Carl von Linde,  Carl von Linde’s Breakthrough in the Refrigeration Process, SciHi blog, June 11, 2018,1913%20Nobel%20Prize%20in%20Physics.
Nobel Prize 1913 –
125 Years of Linde

1904, Potash/Lye –
Behrens 1904, Patent, Process for manufacturing carbonic acid…

1930, Amines –
Bottoms, Patent, Process for separating acidic gases (amines), 1930…

1955 Activated Potash (Arsenic) –
Giammarco, 1955, Patent Process for the separation and recovery of carbonic acid from gas mixtures…

28) Marine Cloud Brightening, Duke University. 

29) Baiman et al., An Open Letter to the IMO Supporting the Utilization of Ship Fuels that Cool the Atmosphere While Preserving Air Quality Benefits, Healthy Planet Action Coalition paper, December 7, 2023.