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The Sequoia Burn
Giant Sequoias: A Climate Tipping Point
by Bruce Melton PE

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See the abridged version on August 9, 2022.

Summary: Up to 13,000 mature sequoias were killed by wildfire between 2015 and 2021, with a total known population of only about 75,500 mature trees. Sequoias are notoriously fireproof with their giant stature, fire resistant bark, and lack of flammable resin production. Normally, sequoias do not burn. This is why they live to be thousands of years old, in our old climate. With six new extreme fire behaviors caused by warming, and excess fuels accumulation for a century or more from fire suppression efforts, the National Park Service says a tipping point has been passed with this new sequoia mortality. We have entered an era where burned forests may not return unless we cool Earth to below the tipping point.

Cover Image: A giant sequoia in the KNP Complex Fire, California fires, 2021. Photo by Sue Cag. See for a tremendous firsthand look at the giant sequoia casualties.

References Below

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Giant sequoias are being killed by climate change in numbers that portend ecological disaster unless something is done to reverse impacts of climate change much faster than current climate policy suggests. Unburnable sequoias began to be widely destroyed by fire in 2015 and then in 2020 and 2021 California fires tripled in area covered. (1) The current best count of mature sequoias killed by increased fire intensity since 2015 is up to 13,000. (2) There are only about 75,500 mature sequoias in existence. (3)

There are 70 giant sequoia groves in existence and more than 85 percent burned between 2015 and 2021. In the preceding 100 years, only 25 percent of groves burned. (4) The National Park Service says, “Large sequoias typically died by falling or, occasionally, having extensive crown scorch from fire. Death while standing, unrelated to crown scorch, was almost never observed by scientists who had spent decades working in the Sierra Nevada. And while mature giant sequoias did die from fire impacts; those were relatively rare events and typically the result of many accumulated injuries over their long lives.” (5)

Some of these sequoias could have been 3,000 years old. They have achieved these great ages while battling fire time and time again as they have evolved to be nearly fire proof. Their spongy asbestos-like bark can be two to three feet thick. They don’t have flammable resin like almost all other conifers, and their great height, where their lowest branches can be 150 to 200 feet above the ground, allows them to tower over the other forest trees that when in flame are far below the needles of sequoias.

A giant sequoia saved by low intensity burn in the the 2017 Pier Fire in the Black Mountain Grove of Sequoia National Monument. Note the vehicle at the bottom of the shot

The National Park Service tells us, “The hotter drought of 2012-2016 appears to have been a tipping point for giant sequoias and other Sierra Nevada mixed-conifer forests. In hotter droughts, unusually high temperatures worsen the effects of low precipitation, resulting in greater water loss from trees and lower water availability. This is an emerging climate change threat to forests.” (6)

Across the American West warming has resulted in increased evaporation that has created what could be labelled perpetual drought, that has led to massive tree mortality from drying and drying induced attack from native bark beetles. In California 172 million trees have been killed by drought, disease and beetles since 2010 and one to two hundred million were killed in fires in 2021 alone. In Texas during their new Drought of Record between 2011 and 2013, 300 million trees were killed and their ongoing drought is now more severe than the last. Across the North American West, 100 million acres of forest have been significantly impacted or mostly killed by native bark beetles since 2017 and the attack is ongoing. (7, 8)

In 2022, New Mexico had its two largest wildfires ever recorded so far, in one year. In 2020, Colorado had its three largest wildfires ever recorded, in one year. The eight largest wildfires California has ever seen have happened since 2017. This doesn’t count the Santiago Canyon fire in 1889 that burned 300,000 acres at a time when there was very, very little firefighting ability in California. All but one of these new record fires in California were larger than 300,000 acres. The two largest fires ever recorded in California are one million acres each, in 2020 and 2021. (9)

The seven largest fires in California history burned since 2018. (10) As much area burned in 2020 as burned in pre-European times (11), only Cal Fire (California Department of Forestry and Fire Protection) spent $3.1 billion fighting fires in 2020, vs. zero spent in Pre-European times and this does not include local, US Forest Service and Bureau of Land Management firefighting expenditures. (12) The largest wildfires in California doubled in size from the 2000s to 2018, and doubled again in 2020 to one million acres per fire. (13)

The prevailing discussion about the cause of this threshold passing is that wildfire suppression for the last one hundred or two hundred years has allowed forest fuels to increase, which in combination with warming and increased drought from climate change have increased high-severity fire up to 800 percent since 1985. High-severity fires kill about 95 percent of forest species and drier conditions post-fire limit regeneration with an increased risk of conversion of forests to alternative vegetation types like shrub and grasslands. (14, 15)

Mesa Verde National Park where extreme wildfires at the turn of the century are not regenerating.

Across the American West, a third of fires burning around the turn of the century are not regenerating. They are coming back as shrub or grasslands. Of those fires that do show some regeneration, half are only regenerating at half the twentieth century rate. (16) We have entered an era where prefire forests may not return. (17)

In addition to increased fuels, six climate change-caused fire enhancing behaviors are also increasing area burned and the severity of fires: record dry fuels from climate change drought, record low humidity, higher temperature creating easier ignition and more extreme burning, record wind storms, longer drying with earlier spring and later onset of fall conditions, and increased nighttime fire behavior. (18) Because of these six climate change-induced fire enhancing factors, CalFire says fires are now burning 400 degrees hotter. (19)

Scientists have warned for 30 years that tipping systems could activate if we delayed action on dealing with climate pollution. These tipping systems are the irreversible climate change impacts that were previously not supposed to happen until the end of the century with continued warming. Tipping systems are directly related to Earth systems like tropical forests, permafrost and sea level. When tipping systems collapse, their environmental services are degraded, eliminated or reversed. One of the most important of these environmental services is carbon dioxide sequestration.

In 2019, an article was published in the prestigious journal Nature, revealing tipping was now active in half of known tipping systems, when widespread consensus was that tipping was not supposed to activate until 5 C (9 F) warming at 2100 or later. (20)

These tipping systems are our basic Earth systems that have allowed our advanced civilization to develop and include: Arctic sea ice, Greenland ice sheet, boreal forests, permafrost, the Gulf Stream, the Amazon, coral, and the West Antarctic Ice Sheet. (21)

Tipping, or Earth systems collapses, happens when the evolutionary boundary conditions of those systems are exceeded. This is simple systems evolution where conditions become hostile to the species that have evolved in that system resulting in those species collapsing with new species tolerant of the changed condition evolving the system anew. (22)

Giant sequoias killed in the Castle Fire, November 2, 2020. Photo: Anthony Caprio, National Park Service

Today, there are three Earth systems that have been documented in collapse: The Amazon, because of drought mortality, fire and human degradation, is now emitting, not absorbing greenhouse gases to the tune of 1 gigaton (Gt) per year average from 2000 to 2018. Permafrost is now in thaw collapse with emission of 2.3 Gt per year average from 2003 to 2017. Canadian forests are now in collapse mostly from native bark beetle kill with emissions of 250 million tons greenhouse gases per year as of 2020. (23)

These numbers are misleading, at least the averages. If the Amazon and permafrost were stable and not emitting at the beginning of their averaging periods, with a steady increase in collapse at the end of their averaging periods they would be emitting twice the average amount, and it is unlikely that this trend is linear. What this means is that it is likely that just these studied systems are now emitting at least twice their total average emissions or up to seven Gt greenhouse gas per year. This is about the same as all of the transportation sectors emissions globally every year. (24)

Excess fuels from fire suppression is but one of the fire behaviors increasing the severity of wildfire. The six fire behavior enhancers from climate change are now likely creating fire conditions that would not have occurred with only increased fuels. In the past two decades these new megafires have been responsible for 97 percent of all area burned in California. (25). Findings published by the National Academy of Sciences tells us that policy and management focusing on fire suppression and fuels management (prescribed burns and etc.) are “inadequate to address a new era of western wildfires.” and that we must recognize “that fuels reduction cannot alter regional wildfire trends.” (26)

A climate change threshold has been crossed. We have warmed beyond the evolutionary boundaries of our Earth’s systems. As the National Park Service says, “Starting in 2015, higher-severity fires have killed large giant sequoias (those 4 feet or greater in diameter) in much greater numbers than has ever been recorded. We have reached a tipping point — lack of frequent fire for the past century in most groves, combined with the impacts of a warming climate — have made some wildfires much more deadly for sequoias.”

Sequoia National Park entry monument after the 2021 fire season. Photo: Sue Cag. See her for a tremendous firsthand look at the giant sequoia casualties.

Once activated, tipping collapses do not self-restore unless the perturbation, the warming, is removed. (27) What this means is that current warming of 1.2 degrees C (2.2 F) above “normal” of the late nineteenth century is too warm. To stabilize tipping and allow our Earth systems to self-restore, we must cool Earth to below the tipping threshold.

This small amount of warming doesn’t seem like much, but it has caused the activation of collapse of global Earth systems. Because tipping collapse began with at most 1 degree C (1.8 F) warming, to stabilize these systems we must cool Earth to below the tipping point, or below 1 degree C warming, and herein lies great meaning.

Our current climate culture warming target is 1.5 degrees C above normal and this is almost completely accepted by all consensus climate science publications and policy setting entities. But 1.5 C is warmer than the tipping point of no more than 1 C. Because collapsing tipping systems do not self-restore unless the perturbation is removed, a 1.5 C warming target allows tipping to complete and become irreversible. Irreversible Earth systems collapses carry with them existential scenarios.

Fundamentally then, a new warming target is needed of less than 1 degree C above normal. This is a temperature that James Hansen, former 32-year director of the NASA Goddard Institute for Space Studies the defacto US climate modeling agency, has been suggesting since he first realized in 2008 that the maximum safe carbon dioxide concentration of Earth’s atmosphere was 350 ppm CO2. This limit was necessary to preserve the natural evolution of our Earth systems and to prevent them from collapsing with the elimination or reversal of the environmental services they provided, with a special emphasis on sea level rise, as well as the ability of Earth systems to capture or sequester carbon. (28)

In 2017 Hansen finally had the confidence in advancing climate modeling to see what temperature would result with an atmospheric concentration of 350 ppm CO2. What he found was this temperature was less than 1 degrees C above the late nineteenth century normal. It was no accident that his initial reasoning was that Earth systems could only be stable at 350 ppm CO2 or less. (29)

What we need to do now is become motivated to reduce our climate culture’s warming target from 1.5 C, to less than 1 degree C to prevent these already activated climate tipping systems from become existentially irreversible.

Low severity burn in the Pier Fire, Black Mountain Grove, Sequoia National Monument, 2017. This is what fire in sequoia groves should be.

And, we cannot overlook the good news. Hansen told us in his work on 350 ppm CO2, “Realization that we must reduce the current CO2 amount 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.” (30)

Very few have so far realized that the mayhem going on all around us in ever increasing extremeness will not self-restore unless we restore our climate back to within the evolutionary boundaries of our Earth’s systems. Sierra Club is a shining example. In 2020 they adopted a new warming target of “less than 1 degree C above normal” that advanced their previous consensus target of 1.5 C. (31) This is a bold move than needs to be repeated across the globe if we are to see our Earth systems restored before their collapses become existentially irreversible.


1) Top 20 largest Wildfires in California… Compilation from:
Top 20 California Wildfires since 1932, Cal Fire, California Department of Forestry and Fire Protection
Wikipedia, California Wildfires, Includes the 1889 Santiago Fire

2) Up to 13,316 mature sequoias killed by fire since 2015… Compiled from two sources:
Wildfires Kill Unprecedented Numbers of Large Sequoia Trees, Six Fires in Six Years, Sequoia and Kings Canyon National Parks, February 25, 2022.
Stephenson and Brigham, Preliminary Estimates of Sequoia Mortality in the 2020 Castle Fire, Sequoia and Kinds Canyon National Parks, June 25, 2021, in press.

Castle Fire 2020, 170,648 acres, lightning
9,281 killed

Rough Fire 2015, 151,547 acres, lightning
101 sequoias killed

Railroad Fire 2017, 12 407 acres, lightning
92 killed

Pier Fire 2017, 36,556 acres, stolen car (author’s local knowledge)
205 killed

KNP Complex, 2021 lightning, 88,307 acres
Up to 2,380 over 4 feet dia killed

Windy, 2021, lightning, 97,528 acres
1,257 over 4 feet dia killed

TOTAL up to 13,316 mature sequoias over 4 feet diameter
2015 to 2019: 398
2020 and 2021: 12,918

3) There are an estimated 75,580 sequoias over 3.5 feet diameter in the Sierra Nevada… Based on Sequoia Kings Canyon (SEKI) data.
Stephenson and Brigham, Preliminary Estimates of Sequoia Mortality in the 2020 Castle Fire, Sequoia and Kings Canyon National Parks, June 25, 2021, in press.

4) 70 giant Sequoia Groves, 85 percent burned 2015 to 2021, 25 percent burned in preceding 100 years…
Wildfires Kill Unprecedented Numbers of Large Sequoia Trees, Six Fires in Six Years, Sequoia and Kings Canyon National Parks, February 25, 2022.

5) Large sequoias typically died by falling or occasionally, extensive crown scorch…
Giant Sequoias Face New Threats, Sequoia and Kings Canyon National Parks, 2020.

6) An emerging climate change threat to forests…
Giant Sequoias Face New Threats, Sequoia and Kings Canyon National Parks, 2020.

7) Trees Killed in California and Texas…
In California, 172 million trees killed from beetles, disease and drought since 2010. In 2021 a few hundred million trees may have been killed by fire…
Texas Forest Service 301 million trees killed in the 2011 drought…

8) 100 million acres of forest attack from native beetles across North America…
Base document:  Katz, Small Pests, Big Problems: The Global Spread of Bark Beetles, Yale Environment 360, September 21, 2017.
U.S. 2017: 85,000 square miles (54.4 million acres) in the western U.S.
Canada 2012: 65,000 square miles (41.6 million acres) in Canada. An area the size of New England, New York and New Jersey combined.
Richards, Beetles Warm BC Forests, The Scientist, November 2012.

9) Largest wildfires in California… Compilation from:
Top 20 California Wildfires since 1932, Cal Fire, California Department of Forestry and Fire Protection
Wikipedia, California Wildfires, Includes the 1889 Santiago Fire

10) ibid.

11) Area burned in California in pre-European times… In 2020 California met its pre-European area burned area average of 4 million acres, doubling their previous contemporary record set in 2018 of 1.975 million acres, which doubled the previous record set in 2003 of 1.02 million acres.
Stephens et al., Prehistoric fire area and emissions from California’s forests, woodlands, Forest Ecology and Management, June 6, 2007.

12) Cal Fire alone spent $3.1 billion in fire suppression costs in 2020… As of October 19, 2020, the California Legislative Analyst’s Office projected the 2020 fire season’s fire suppression costs to be $3.1 billion. This does not count local, Bureau of land management or National Forest Service expenditures.
State Wildfire Response Costs Estimated to Be Higher Than Budgeted, California Legislative Analyst’s Office, October 19, 2020.

13) Largest fires in California have doubled in size twice since the 2000s… Compilation from:
Top 20 California Wildfires since 1932, Cal Fire, California Department of Forestry and Fire Protection
Wikipedia, California Wildfires, Includes the 1889 Santiago Fire

14) Increase in high-severity fire of 800 percent…  “Significant increases in annual area burned at high severity (AABhs) were observed across most ecoregions, with an overall eightfold increase in AABhs across western US forests. The relationships we identified between the annual fire severity metrics and climate, as well as the observed and projected trend toward warmer and drier fire seasons, suggest that climate change will contribute to increased fire severity in future decades where fuels remain abundant. The growing prevalence of high‐severity fire in western US forests has important implications to forest ecosystems, including an increased probability of fire‐catalyzed conversions from forest to alternative vegetation types.”
Parks and Abatzoglou, Warmer and Drier Fire Seasons Contribute to Increases in Area Burned at High Severity in Western US Forests From 1985 to 2017, Geophysical Research Letters, October 22, 2020.

15) Mortality of 95 percent or greater in high-severity fire…
Stevens et al., Changing spatial patterns of stand-replacing fire in California conifer forests, Forest and Ecology Management, June 23, 2017.

16) Fire regeneration, regrowth, forest recovery – One third of burned forests are not regenerating at all… “Significantly less tree regeneration is occurring after wildfires in the start of 21st century compared to the end of the 20th century, and key drivers of this change were warmer and drier mean climatic conditions. Our findings demonstrate the increased vulnerability of both dry and moist forests to climate-induced regeneration failures following wildfires. The lack of regeneration indicates either substantially longer periods of forest recovery to pre-fire tree densities, or potential shifts to lower density forests or non-forest cover types after 21st-century wildfires… Our results suggest that predicted shifts from forest to non-forested vegetation may be underway, expedited by fire disturbances [and] that short post-fire periods of wetter climate that have favoured tree regeneration in the past may not occur frequently enough to facilitate tree regeneration in the future, across a broad region and multiple forest types in the Rocky Mountains… Our results suggest a high likelihood that future wildfires will facilitate shifts to lower density forest or non-forested states under a warming climate.”
Data, “For sites burned at the end of the 20th century vs. the first decade of the 21st century, the proportion of sites meeting or exceeding pre-fire tree densities (e.g. recruitment threshold of 100%) decreased by nearly half (from 70 to 46%) and the percentage of sites experiencing no post-fire tree regeneration nearly doubled (from 19 to 32%)… This negative relationship demonstrates the potential increased vulnerability and lack of resilience on hotter and drier sites, or of dry forest species, to climate warming… Tree seedlings may establish in response to short-term anomalous wetter periods in the future, but our results highlight that such conditions have become significantly less common since 2000, and they are expected to be less likely in the future…  Further, persistent or long-lasting vegetation changes following wildfires have been observed worldwide.”
Stevens-Rumann et al., Evidence for declining forest resilience to wildfires under climate, Ecology Letters, December 12, 2017. (paywall)
Press Release, University of Montana –

17) An era when prefire forests may not return… “Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest type or nonforest vegetation. Conversion implies major, extensive, and enduring changes in dominant species, life forms, or functions, with impacts on ecosystem services. In the present article, we synthesize a growing body of evidence of fire-driven conversion and our understanding of its causes across western North America. We assess our capacity to predict conversion and highlight important uncertainties. Increasing forest vulnerability to changing fire activity and climate compels shifts in management approaches, and we propose key themes for applied research coproduced by scientists and managers to support decision-making in an era when the prefire forest may not return.”
Coop et al., Wildfire Driven Forest Conversion in Western North American Landscapes, BioScience, July 1, 2020.

18) California fire behavior response and excess fuels accumulation… In our old climate, excess fuels accumulation from fire suppression have caused an increase in fire behavior, but six climate change-caused warming related fire behavior drivers have now greatly enhanced this increased fuels response with drier fuels, lower humidity, easier ignition, bigger wind storms, delayed onset of fall precipitation, and increased nighttime fire activity. The result is that Cal Fire says fires are now burning 400 degrees hotter.
Williams 2019, Williams et al., Observed Impacts of Anthropogenic Climate Change on Wildfire in California …  Abstract “Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful. Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California’s diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.”
Williams et al., Observed Impacts of Anthropogenic Climate Change on Wildfire in California, Earth’s Future, August 4, 2019.
Westerling – large California Wildfires are increasing nonlinearly with drying and earlier onset of spring… “Increases in large wildfires associated with earlier spring snowmelt scale exponentially with changes in moisture deficit, and moisture deficit changes can explain most of the spatial variability in forest wildfire regime response to the timing of spring.”
Westerling, Increasing western US forest wildfire activity, sensitivity to changes in the timing of spring, Philosophical Transactions of the Royal Society B, May 23, 2016, abstract.
A paper in the Journal Fire describing increased fire behavior criteria… Summary and Conclusions: “most acute fire weather in over two decades… longest duration Santa Ana wind event in the 70-year record… the most extreme drought on record… lowest fuel moisture on record… driest March through December since 1895.”
Nauslar et al., The 2017 North Bay and Southern California Fires, A Case Study, Fire, June 9, 2018.

19) 400 Degrees Hotter…  Wildfires are burning 400 degrees F hotter because of drier fuels. “The infernos bellowed by those winds once reached a maximum temperature of 1,700 degrees Fahrenheit, Cal Fire’s Angie Lottes says; now they reach 2,100 degrees, hot enough to turn the silica in the soil into glass.”
Wallace-Wells, Los Angeles Fire Season Is Beginning Again. And It Will Never End. A bulletin from our climate future,  New York Magazine, May 12, 2019.

20) More than half of known tipping points are now active up to 100 years ahead of projections…  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.
Lenton et al., Climate tipping points-too risky to bet against, Nature, November 27, 2019
University of Exeter Press –

21) ibid.

22) Earth systems tipping collapse when environmental boundaries area exceeded…
Alternative Stable States… “Ecologists are interested in observing and understanding their study systems so as to be able to predict what they might do in the future. The problem with ASS is that if we do not know that they are possible, they present surprises. Thus, our ecological frameworks need to include them, where they may occur, to predict when and why a sudden change might happen.”
Beisner, Alternative Stable States, Department of Biological Sciences, University of Quebec at Montreal, Nature, 2012. Environmental community thresholds and collapse… “Unusual environmental events can quickly push the communities past a critical threshold leading to a collapse (Matusick et al., 2013; Valenzuela et al., 2019). Unusual or extreme environmental events are sudden and of great magnitude. They can be pulse events or step events. We can describe pulse events as a sudden and significant change of system parameters for a short period, for example, bolide events, volcanic eruptions, sudden, temporary cooling or warming, fires. During step events, the system parameters also change suddenly, but these changes last much longer. Step events are typically related to climate changes when the temperature rises or drops considerably and stays high or low for an extended time.”
Palinkas and Hufnagel, Distinctive patterns and signals at major environmental events and collapse zone boundaries, Environmental montiroing and Assessment, September 2021.
Abrupt Loss of Environmental Services… “Regime shifts can abruptly affect hydrological, climatic and terrestrial systems, leading to degraded ecosystems and impoverished societies.” Earth systems collapses or climate tipping points could happen in a matter of years or decades, not according to ecological evolutionary time scales of hundreds of years or longer.
Cooper et al., Regime shifts occur disproportionately faster in larger ecosystems, Nature Communications, March 2020.
The In-System Tipping Feedback… “Regime shifts have been documented in a variety of natural and social systems. These abrupt transitions produce dramatic shifts in the composition and functioning of socioecological systems. Existing theory on ecosystem resilience has only considered regime shifts to be caused by changes in external conditions beyond a tipping point and therefore lacks an evolutionary perspective. In this study, we show how a change in external conditions has little ecological effect and does not push the system beyond a tipping point. The change therefore does not cause an immediate regime shift but instead triggers an evolutionary process that drives a phenotypic trait beyond a tipping point, thereby resulting (after a substantial delay) in a selection-induced regime shift.”
Chaparro-Pedraza and de Roos, Ecological changes with minor effect initiate evolution to delayed regime shifts, Nature Ecology and Evolution, March 2020.
A documentation of a twelve large or sub-continental scale ecosystems collapses caused or enhanced by climate change… “The word “collapse” is challenging to apply because in many cases we do not know (i.e., it is too early to tell) whether a given ecosystem may recover through time. In other cases, however, the ecosystem’s prognosis is poor and the chance of recovery to its initial state appears unlikely, particularly so in the face of the continuing intensification of climate change… [In some cases global ecosystem changes have] triggered the question as to whether we were seeing predicted future climate impacts now with the rapid transformation and loss of ecosystems as we know them… In other cases, however, the ecosystem’s prognosis is poor and the chance of recovery to its initial state appears unlikely, particularly so in the face of the continuing intensification of climate change… One goal of this book is to raise awareness of the transitions that are already occurring through climate change today, and particularly those transitions associated with abrupt dynamics in response to one of the most important manifestations of climate change: the increasing intensity and sometimes frequency of climate variability and extremes. Some of the transitions might be critical, in so far that they may be irreversible or signal the beginning of a new level of abrupt changes that will ultimately lead to an irreversible outcome.” … “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… for those collapse in which anthropogenic climate change is a dominant driver, the long-term prognosis is more likely of a permanent transition. The reason is because global warming is likely to intensify for decades, then stabilize at best in the strongest mitigation scenarios, but not revert to prior levels during this century (Collins et al. 2013)… defining ecosystem collapse as a transition beyond a bounded threshold in one or more variables that define the identity of the ecosystem; collapse as a transformation of identity, loss of defining features, and replacement by a novel ecosystem. (Lindenmayer et al. 2016) call for three key conditions to be met, with changes being: (1) irreversible or time- and energy-consuming to reverse, (2) widespread, and (3) undesirable in terms of impairing ecosystem services or major losses of biodiversity… For most case studies in this book, however, the collapse dynamics are too recent or still emerging to have observations available long enough to determine whether the changes are irreversible and, therefore, the likelihood of transitioning into an alternate or permanent state, degraded or novel.
Canadell and Jackson, Ecosystem Collapse and Climate Change, Springer Nature Switzerland, 364 pages, 2021.

23) Amazon, Permafrost, Canadian Forests Flip from sequestration to emissions…
Amazon flip from sequestration to emissions… Amazon collapse of 1 Gt annual CO2eq emissions 2010 to 2018… The Amazon is now emitting 1 Gt CO2eq annually based on a nine year average. All sources are included: drought mortality, drying soils, drought-caused fire, subsistence fire and logging. The current emissions are likely greater because this 1 Gt is an average 2010 through 2018. It is also likely the situation has worsened since.  Tropical forests in Africa are a bit behind the Amazon, and tropical forests in Asia and the rest of the Americas are likely not far behind the Amazon, especially as four years of warming have elapses since the Amazon flip.
Gatti et al., Amazonia as a carbon source linked to deforestation and climate change, Nature, July 14, 2021.
Permafrost Flip from sequestration to emissions…
Northern Hemisphere Permafrost emissions of 2.3 Gt CO2eq…
Across the Northern Hemisphere, permafrost melt emitted 630 TgC, or 2.3 Gt CO2eq (including methane). “We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October–April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (−1,032 TgC per year).” Emission are average per year from 2003 – 2017. With permafrost melt increasing rapidly today, this means emission in 2017 were much more than in 2003, therefore much more than the 2.3 Gt per year estimated on average… “The dataset represents more than 100 high-latitude sites and comprises more than 1,000 aggregated monthly fluxes. We examined patterns and processes driving winter CO2 emissions and scaled fluxes to the permafrost domain using a boosted regression tree (BRT) machine learning model based on hypothesized drivers of winter CO2 flux. Environmental and ecological drivers (for example, vegetation type and productivity, soil moisture and soil temperature) obtained from satellite remote sensing and reanalysis data were used to estimate regional winter CO2 emissions for contemporary (2003–2017) climatic conditions.”
Natali et al., Large loss of CO2 in winter observed across the northern permafrost region, Nature Climate Change, October 21, 2019.
University of the Arctic Press Release… “Today winter CO2 emissions are ~30% more than the CO2 assimilated by these regions during summer-The North is a net emitter of CO2-C adding to a rising CO2 concentration in the atmosphere-a critical feed-forward process associated with warmer winters.”
Canada’s forests flipped from sequestration to emissions, mostly because of native beetle kill… Canadian public forests have been net emitters of greenhouse gases since the early 2000s when the native bark beetle attack advanced off the charts. The total is now 250 million tons per year and 93 percent of all of Canada’s forests are publicly owned. From Seamus O’Regan, Minister of Natural Resources introductory letter to The State of Canada’s Forests, 2020, “Scientists predict that increasing temperatures and changes in weather patterns associated with climate change will drastically affect Canada’s forests in the near future… with the rate of projected climate change expected to be 10 to 100 times faster than the ability of forests to adapt naturally… Traditionally, foresters have used local tree seed for planting seedlings, as local populations were generally thought to be best adapted to the climate conditions of the site. However, with a rapidly changing climate, these local populations may not be able to adapt quickly enough, and while well-established adult trees can often withstand increased stress, seedlings are highly vulnerable.”
Seamus O’Regan, Minister of Natural Resources, Introductory Letter.
The State of Canadas Forests, Canadas Forests, Adapting to Change, Canadian Forest Service, 2020.

24) Global emissions from transportation sector… Global transportation CO2 emissions of about 7 GT CO2eq or 6.7 Gt CO2 annually.
IPCC 2013, Physical Science Basis, Chapter 8, Transport.

25) Extreme wildfires in California are responsible for 97 percent of the area burned in California in the last two decades… have increased significantly in the last two decades with the cause being climate warming related…
“Between 2000 and 2019, compared to 1920 to 1999, the proportion of extreme wildfires larger than 10,000 acres (40.47 km2 ) has increased significantly… The burned area of large wildfires accounted for 97.04 % of the total burned area (13,089.68 out of 13,488.19 thousand acres, that is 52,972.05 out of 54,584.77 km2 ) in the past two decades… The frequency and burned area growth of wildfires in the past two decades are much higher than that during the 80 years in history from 1920 to 1999… The frequency of large wildfires and the burned area of small wildfires in the recent 20 years even have decreased… From 2000 to 2019, the frequency of wildfires in July increased significantly and became much more considerable than in other months. Meanwhile, the start of the wildfire season has also advanced to May (from June) and the duration has increased each month… there has been a major increase in the natural wildfires in July in the past two decades.”
Summary: “We found that the frequency and total burned area of all wildfires have increased significantly. The start time and peak months of the wildfire season have been advanced, and the covered months have been lengthened. For large and small wildfires, the annual frequency of large wildfires has remained stable for the last 100 years, but the total burned area has increased rapidly in the past two decades… illustrat[ing] that the comprehensive environmental conditions, such as changes in climate and vegetation, have increased the coverage of potential wildfire ignitions… slope, temperature and maximum vapor pressure deficit have positive correlation with wildfire occurrence… natural factors, especially climate variables, have a greater impact on the density of wildfires.”
Li and Banerjee, Spatial and temporal pattern of wildfires in California from 2000 to 2019, Nature Scientific Reports, April 22, 2021.

26) Fire suppression and fuels management are inadequate to address a new era of western wildfire… “Policy and management have focused primarily on specified resilience approaches aimed at resistance to wildfire and restoration of areas burned by wildfire through fire suppression and fuels management. These strategies are inadequate to address a new era of western wildfires. In contrast, policies that promote adaptive resilience to wildfire, by which people and ecosystems adjust and reorganize in response to changing fire regimes to reduce future vulnerability, are needed. Key aspects of an adaptive resilience approach are (i) recognizing that fuels reduction cannot alter regional wildfire trends; (ii) targeting fuels reduction to increase adaptation by some ecosystems and residential communities to more frequent fire; (iii) actively managing more wild and prescribed fires with a range of severities; and (iv) incentivizing and planning residential development to withstand inevitable wildfire. These strategies represent a shift in policy and management from restoring ecosystems based on historical baselines to adapting to changing fire regimes and from unsustainable defense of the wildland–urban interface to developing fire-adapted communities. We propose an approach that accepts wildfire as an inevitable catalyst of change and that promotes adaptive responses by ecosystems and residential communities to more warming and wildfire.”
Schoennagel et al., Adapt to more wildfire in western North American forests as climate changes, PNAS, February 24, 2017.

27) Unless the perturbation is removed… See Reference 21 on tipping collapses.

28) James Hansen’s 2008, Target atmospheric CO2: Where should humanity aim?…
Hansen et al., Target Atmospheric CO2 Where Should Humanity Aim?, Open Atmospheric Science Journal, November 2008.

29) James Hansen 2017, Young people’s burden: requirement of negative CO2 emissions…
Hansen et al., Young people’s burden: requirement of negative CO2 emissions, Earth Systems Dynamics, July 18, 2017.

30) James Hansen’s 2008, Target atmospheric CO2: Where should humanity aim?…
Hansen et al., Target Atmospheric CO2 Where Should Humanity Aim?, Open Atmospheric Science Journal, November 2008.

31) Sierra Club’s New Warming Target of “less than 1 degree C above normal”… A first of its kind.