REFERENCES
These references come in two parts: The Amazon, and General Forest Regeneration Failure.
THE AMAZON
Commentary – The Amazon has been influenced by droughts of increasing extremeness beyond the 100-year event in 2005, 2010 and 2016 and likely the drought ongoing in the early 2020s. In 2005 and 2010, drought mortality (and other human degradation) caused the Amazon to flip from carbon sequestration to emissions. The rapid cycling of organic material in tropical forests likely reversed this flip before the next drought pulse arrived. Warnings after the 2010 drought, that repeated droughts such as these could flip the Amazon permanently, have now almost certainly occurred with the Super El Nino drought of 2016 and subsequent drying from continued warming. Current findings (Qin 2021, and Gatti 2021) show the Amazon is emitting between 1 Gt and 2.45 Gt CO2eq annually, based on averages from 2010 through 2018 and 2010 through 2019. Deforestation is responsible for about a quarter of these emissions, forest degradation from climate change-caused fire and water stress mortality is responsible for the remaining 75 percent. It is also important to note these quantities of emissions are averages and the degradation is very likely increasing in extremeness, making the 1 Gt and 2.45 Gt CO2eq quantities understated.
September 30, 2024 – Drought in 2024 is worse than in 2023 – CNN, “In many regions of the Amazon “the drought is already more intense today than it was at the worst point last year,” said Romulo Batista, a biologist and spokesperson for Greenpeace Brazil.” … “An intense El Niño, a natural climate pattern, brought warmer and drier weather to the region last year and into 2024. El Niño has now ended but heat and drought are being influenced by an unusually hot Atlantic Ocean, said Cemaden’s Cuartas. (Cemaden is the Brazil’s natural disaster monitoring center.)
Paddison and Mezzofiore, Stark before-and-after pictures reveal dramatic shrinking of major Amazon rivers, CNN, September 30, 2024.
https://www.cnn.com/2024/09/30/climate/amazon-rivers-drought-satellite-pictures/index.html
January 24, 2024 – Fifth 100-year drought in the Amazon since 2005… The fifth 100-year drought since 2005 has struck the Amazon, this one more extreme than any of the previous events. Each drought except one were more extreme than the previous. The others were 2010, 2015/2016, a smaller one in 2020, and the current in 2023-2024. As another possible sign of worsening climate change conditions, this one started in the pre-rainy season, where the others started in the rainy season. From the World Meteorological Attribution Network evaluation, “In datasets based on weather records the drought is exceptional, even in today’s climate, characterised as a 1 in 100 year event for the meteorological drought… The strong drying trend was almost entirely due to increased global temperatures, so the severity of the drought currently being experienced is largely driven by climate change… We find that the likelihood of the meteorological drought occurring has increased by a factor of 10, while the agricultural drought has become about 30 times more likely… Using the US drought monitoring classification system, based on agricultural drought, this means that what is now classified an exceptional drought (D4), would have only been a ‘severe drought’ (D2) without the effects of climate change, caused by burning fossil fuels and deforestation…. These results highlight that despite ‘low confidence’ in IPCC projections for drought in the region, increasing water stress driven by human-induced climate change as well as other systemic factors continues to be a major threat for the population and requires urgent efforts for more effective water management strategies, interdisciplinary humanitarian response, and regional cooperation that includes farmers and other stakeholders in the planning.”
Worst 100-year Amazon Drought in 2023…
Costa and Morengo, Statement on the 2023 Amazon Drought and Its Unforeseen Consequences, United Nations Sustainable Solutions Network, December 7, 2023.
https://www.theamazonwewant.org/wp-content/uploads/2023/12/231207-AMAZON-DROUGHT-STATEMENT_ENGLISH.pdf
Summary of 2023 drought in the Amazon… World Weather Attribution, January 24, 2024.
https://www.worldweatherattribution.org/climate-change-not-el-nino-main-driver-of-exceptional-drought-in-highly-vulnerable-amazon-river-basin/
Clarke 2024 – page 28, “In a statement by the United Nations Sustainable Development Solutions Network, the 2023 Amazon drought is described as both unprecedented and unforeseen (2023). While the current drought is the most extreme on the historical record and unique due to its timing (commencing during the pre-rainy season), it is not an isolated case in relation to the exposure and vulnerability pathways highlighted by previous (severe) droughts in the Amazon – including in 2005, 2010, 2015/2016, and 2020.”
(Full) Clarke et al., Climate change, not El Niño, main driver of exceptional drought in highly vulnerable Amazon River Basin, World Weather Attribution network, Imperial College of London, January 24, 2024.
https://www.worldweatherattribution.org/climate-change-not-el-nino-main-driver-of-exceptional-drought-in-highly-vulnerable-amazon-river-basin/
Espinoza 2023 – Introduction, page 8, “In a statement by the United Nations Sustainable Development Solutions Network, the 2023 Amazon drought is described as both unprecedented and unforeseen (2023). While the current drought is the most extreme on the historical record and unique due to its timing (commencing during the pre-rainy season), it is not an isolated case in relation to the exposure and vulnerability pathways highlighted by previous (severe) droughts in the Amazon – including in 2005, 2010, 2015/2016, and 2020.” … “Moreover, droughts in the northwestern Amazon such as this can be especially devastating to the forest and potentially accelerate a tipping point because the forest there is less resilient to rainfall variability than that in the eastern Amazon, which experiences more variability.”
Espinoza et al., The new record of drought and warmth in the Amazon in 2023 related to regional and global climatic features, Nature Scientific Reports, April 6, 2024.
https://www.nature.com/articles/s41598-024-58782-5
December 2023 – Conflict over Amazon tipping point… Tao 2023, questions Boulton 2022’s pronounced loss of forest resilience over Amazonia since 2003 because of the vegetation optical depth (VOD) they used in their analysis and contamination from soil moisture and sensor discontinuity over Amazonia. Tao 2023 uses an independent radar dataset to show that the decreasing trend in forest resilience is at best limited, and has been partly reversed in recent years, thus challenging the conclusion that Amazonian rainforests are approaching a tipping point.
Boulton 2023 response –
Flooding: “Changes occurred after the anomalies had already started to develop… At first glance, there are indeed strong positive VOD anomalies close to 2009 and 2012 (Fig. 1a). However, the VOD anomaly is high already a year before the flood onset in 2009, and the flood of 2012 ends before the corresponding VOD anomaly. Moreover, large floods in the Amazon basin also occurred in the years 1999 and 2014, which do not appear in the VOD time series.”
Sensor discontinuity: Boulton 2023 Reply to Tao 2023 included a single sensor evaluation for July 2002–June 2011 (to obtain complete months and years), using a five-year moving window as before. Due to the overall shorter time span of AMSR-E, we also show results using a three-year window; this does not qualitatively change the results.”
Boulton 2022 – “We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.”
Boulton 2022 – Boulton, Lenton and Boers, Pronounced loss of Amazon rainforest resilience since the early 2000s, Nature Climate Change, March 7, 2022.
https://www.nature.com/articles/s41558-022-01287-8
Tao et al., Little evidence that Amazonian rainforests are approaching a tipping point, November 9, 2023.
Researchgate free account required)
Boulton 2023 Reply to Tao 2023 – Boulton, Lenton and Boers, Reply to: Little evidence that Amazonian rainforests are approaching a tipping point, Nature Climate Change, November 9, 2023.
(Paywall)
(Publisher preview) Reply to: Little evidence that Amazonian rainforests are approaching a tipping point, Nature Climate Change, November 9, 2023.
https://www.researchgate.net/publication/375523505_Reply_to_Little_evidence_that_Amazonian_rainforests_are_approaching_a_tipping_point
September 30, 2024 – Drought in the Amazon in 2024 is worse than in 2023 – CNN, “In many regions of the Amazon “the drought is already more intense today than it was at the worst point last year,” said Romulo Batista, a biologist and spokesperson for Greenpeace Brazil.” … “An intense El Niño, a natural climate pattern, brought warmer and drier weather to the region last year and into 2024. El Niño has now ended but heat and drought are being influenced by an unusually hot Atlantic Ocean, said Cemaden’s Cuartas. (Cemaden is the Brazil’s natural disaster monitoring center.)
Paddison and Mezzofiore, Stark before-and-after pictures reveal dramatic shrinking of major Amazon rivers, CNN, September 30, 2024.
https://www.cnn.com/2024/09/30/climate/amazon-rivers-drought-satellite-pictures/index.html
January 24, 2024 – Fifth 100-year drought in the Amazon since 2005… The fifth 100-year drought since 2005 has struck the Amazon, this one more extreme than any of the previous events. Each drought except one were more extreme than the previous. The others were 2010, 2015/2016, a smaller one in 2020, and the current in 2023-2024. As another possible sign of worsening climate change conditions, this one started in the pre-rainy season, where the others started in the rainy season. From the World Meteorological Attribution Network evaluation, “In datasets based on weather records the drought is exceptional, even in today’s climate, characterised as a 1 in 100 year event for the meteorological drought… The strong drying trend was almost entirely due to increased global temperatures, so the severity of the drought currently being experienced is largely driven by climate change… We find that the likelihood of the meteorological drought occurring has increased by a factor of 10, while the agricultural drought has become about 30 times more likely… Using the US drought monitoring classification system, based on agricultural drought, this means that what is now classified an exceptional drought (D4), would have only been a ‘severe drought’ (D2) without the effects of climate change, caused by burning fossil fuels and deforestation…. These results highlight that despite ‘low confidence’ in IPCC projections for drought in the region, increasing water stress driven by human-induced climate change as well as other systemic factors continues to be a major threat for the population and requires urgent efforts for more effective water management strategies, interdisciplinary humanitarian response, and regional cooperation that includes farmers and other stakeholders in the planning.”
Worst 100-year Amazon Drought in 2023…
Costa and Morengo, Statement on the 2023 Amazon Drought and Its Unforeseen Consequences, United Nations Sustainable Solutions Network, December 7, 2023.
https://www.theamazonwewant.org/wp-content/uploads/2023/12/231207-AMAZON-DROUGHT-STATEMENT_ENGLISH.pdf
Summary of 2023 drought in the Amazon… World Weather Attribution, January 24, 2024.
https://www.worldweatherattribution.org/climate-change-not-el-nino-main-driver-of-exceptional-drought-in-highly-vulnerable-amazon-river-basin/
Clarke 2024 – page 28, “In a statement by the United Nations Sustainable Development Solutions Network, the 2023 Amazon drought is described as both unprecedented and unforeseen (2023). While the current drought is the most extreme on the historical record and unique due to its timing (commencing during the pre-rainy season), it is not an isolated case in relation to the exposure and vulnerability pathways highlighted by previous (severe) droughts in the Amazon – including in 2005, 2010, 2015/2016, and 2020.”
(Full) Clarke et al., Climate change, not El Niño, main driver of exceptional drought in highly vulnerable Amazon River Basin, World Weather Attribution network, Imperial College of London, January 24, 2024.
https://www.worldweatherattribution.org/climate-change-not-el-nino-main-driver-of-exceptional-drought-in-highly-vulnerable-amazon-river-basin/
Espinoza 2023 – The 2023 Amazon drought is described as both unprecedented and unforeseen… Introduction, page 8, “In a statement by the United Nations Sustainable Development Solutions Network, the 2023 Amazon drought is described as both unprecedented and unforeseen (2023). While the current drought is the most extreme on the historical record and unique due to its timing (commencing during the pre-rainy season), it is not an isolated case in relation to the exposure and vulnerability pathways highlighted by previous (severe) droughts in the Amazon – including in 2005, 2010, 2015/2016, and 2020.” … “Moreover, droughts in the northwestern Amazon such as this can be especially devastating to the forest and potentially accelerate a tipping point because the forest there is less resilient to rainfall variability than that in the eastern Amazon, which experiences more variability.”
Espinoza et al., The new record of drought and warmth in the Amazon in 2023 related to regional and global climatic features, Nature Scientific Reports, April 6, 2024.
https://www.nature.com/articles/s41598-024-58782-5
December 2023 – Conflict over Amazon tipping point with Tao 2023… Tao 2023, questions Boulton 2022’s pronounced loss of forest resilience over Amazonia since 2003 because of the vegetation optical depth (VOD) they used in their analysis and contamination from soil moisture and sensor discontinuity over Amazonia. Tao 2023 uses an independent radar dataset to show that the decreasing trend in forest resilience is at best limited, and has been partly reversed in recent years, thus challenging the conclusion that Amazonian rainforests are approaching a tipping point.
Boulton 2023 response –
Flooding: “Changes occurred after the anomalies had already started to develop… At first glance, there are indeed strong positive VOD anomalies close to 2009 and 2012 (Fig. 1a). However, the VOD anomaly is high already a year before the flood onset in 2009, and the flood of 2012 ends before the corresponding VOD anomaly. Moreover, large floods in the Amazon basin also occurred in the years 1999 and 2014, which do not appear in the VOD time series.”
Sensor discontinuity: Boulton2023 Reply to Tao 2023 included a single sensor evaluation for July 2002–June 2011 (to obtain complete months and years), using a five-year moving window as before. Due to the overall shorter time span of AMSR-E, we also show results using a three-year window; this does not qualitatively change the results.”
Boulton 2022 – “We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.”
Boulton 2022 – Boulton, Lenton and Boers, Pronounced loss of Amazon rainforest resilience since the early 2000s, Nature Climate Change, March 7, 2022.
https://www.nature.com/articles/s41558-022-01287-8
Tao et al., Little evidence that Amazonian rainforests are approaching a tipping point, November 9, 2023…
(Researchgate free account required) https://www.researchgate.net/profile/Jean_Pierre_Wigneron/publication/375523532_Little_evidence_that_Amazonian_rainforests_are_approaching_a_tipping_point/links/654f812b3fa26f66f4f466cd/Little-evidence-that-Amazonian-rainforests-are-approaching-a-tipping-point.pdf?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6InB1YmxpY2F0aW9uIiwicGFnZSI6InB1YmxpY2F0aW9uRG93bmxvYWQiLCJwcmV2aW91c1BhZ2UiOiJwdWJsaWNhdGlvbiJ9fQ
Boulton 2023 Reply to Tao 2023 – Boulton, Lenton and Boers, Reply to: Little evidence that Amazonian rainforests are approaching a tipping point, Nature Climate Change, November 9, 2023.
(Paywall)
(Publisher preview) Reply to: Little evidence that Amazonian rainforests are approaching a tipping point, Nature Climate Change, November 9, 2023.https://www.researchgate.net/publication/375523505_Reply_to_Little_evidence…”
South American Monsoon Tipping activated… (needs read and high-graded) Abstract, “The Amazon rainforest is threatened by land-use change and increasing drought and fire frequency. Studies suggest an abrupt dieback of large parts of the rainforest after partial forest loss, but the critical threshold, underlying mechanisms, and possible impacts of forest degradation on the monsoon circulation remaining certain. Here, we use a nonlinear dynamical model of the moisture transport and recycling across the Amazon to identify several precursor signals for a critical transition in the coupled atmosphere-vegetation dynamics. Guided by our simulations, we reveal both statistical and physical precursor signals of an approaching critical transitioning re-analysis and observational data. In accordance with our model results, we attribute these characteristic precursor signals to the nearing of a critical transition of the coupled Amazon atmosphere-vegetation system induced by forest loss due to deforestation, droughts, and fires. The transition would lead to substantially drier conditions, under which the rainforest could likely not be maintained.”
Bochow and Boers, The South American monsoon approaches a critical transition in response to deforestation, Science Advances, October 4, 2023.
https://www.science.org/doi/epdf/10.1126/sciadv.add9973
NASA 2020 – Second most extreme drought ever in the amazon in 2020… “Large parts of South America are in the grip of a serious drought. Signs of the drought began to appear in satellite gravimetry observations of southeastern Brazil in mid-2018, and had spread into parts of Paraguay, Bolivia, and northern Argentina by 2020.” … “This is the second most intense drought in South America since 2002,” said Matthew Rodell, a hydrologist based at NASA’s Goddard Space Flight Center. “The calculation is based on the extent, duration, and volume of water lost during the drought as measured by the GRACE and GRACE-FO satellites.” A drought in eastern Brazil and Venezuela in 2015-16 is the only more intense drought on the record.
Severe Drought in South America, NASA Earth Observatory, October 26, 2020.
https://earthobservatory.nasa.gov/images/147480/severe-drought-in-southamerica
The Amazon has flipped from carbon sink to emissions 80 years ahead of projections… The Amazon was not supposed to flip until over 4 degrees C of warming, that under most worst-case business as usual scenarios would not occur until beyond the end of the 21 century. Lovejoy and Nobre 2019 now tell us that , “The increasing frequency of unprecedented droughts in 2005, 2010, and 2015/16 is signaling that the tipping point is at hand.”
Lovejoy and Nobre, Amazon Tipping Point, Science advances, February 21, 2018.
https://advances.sciencemag.org/content/advances/4/2/eaat2340.full.pdf
Amazon emissions of 0.67 Pg C (2.45 Gt CO2eq) from 2010 to 2019 based on satellite canopy density, with forest degradation 3X the loss of 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 – https://www.researchgate.net/publication/361323731_Carbon_loss_from_forest_degradation_exceeds_that_from_deforestation_in_the_Brazilian_Amazon
Paywall – https://www.nature.com/articles/s41558-021-01026-5
Amazon emitting, not absorbing, 1 Gt CO2 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, vander Werf etal.24 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.
https://pure.rug.nl/ws/files/176729920/s41586_021_03629_6.pdf
https://www.nature.com/articles/s41586-021-03629-6.epdf?sharing_token=lsfPlVRsW05dUMB_VD-zItRgN0jAjWel9jnR3ZoTv0NILaci0q8CXtVe4JKM-xF0Z0ZQpmJpnpSclAjJeIV-vCjviXK_Mb9hvvU5C3CiJVgu82-RGuHR01gFiQZAVMzDCCxiRyvlh0MBQxTvGN2oHmf2jIOC7MEEGXrOPGIblsh57v9qXkkZbM7U0OH8zbdQ4jnVO1zD9R1jeDcUVBS22YVLkjWEvC5vrNMdQ416fmEBL9kIHYs2ptVibFKXLxEuh-TQ08w-QGSFzN6221KgguYTe0Q9FoZ1J-Wksf4tWXrjv-xu34UpgYqxQWwLTTbTgHYTuglT_tSVd4WaweL9fg%3D%3D&tracking_referrer=www.theguardian.com
Guardian article above based on Gatti 2021… “The study found fires produced about 1.5bn tonnes of CO2 a year, with forest growth removing 0.5bn tonnes. The 1bn tonnes left in the atmosphere is equivalent to the annual emissions of Japan.”
Carrington, Amazon rainforest now emitting more CO2 than it absorbs, Guardian, July 14, 2021.
https://www.theguardian.com/environment/2021/jul/14/amazon-rainforest-now-emitting-more-co2-than-it-absorbs
Last change for action, Lovejoy and Nobre… “We are scientists who have been studying the Amazon and all its wondrous assets for many decades. Today, we stand exactly in a moment of destiny: The tipping point is here, it is now. The peoples and leaders of the Amazon countries together have the power, the science, and the tools to avoid a continental-scale, indeed, a global environmental disaster. Together, we need the will and imagination to tip the direction of change in favor of a sustainable Amazon.”
Lovejoy and Nobre, Amazon tipping point, Last chance for action, Science Advances, December 20, 2019.
https://advances.sciencemag.org/content/advances/5/12/eaba2949.full.pdf
2005 Amazon drought continued to create carbon emissions through 2008 of 1.1 gigatons CO2 per year… “Amazon forests have experienced frequent and severe droughts in the past two decades. However, little is known about the large-scale legacy of droughts on carbon stocks and dynamics of forests. Using systematic sampling of forest structure measured by LiDAR waveforms from 2003 to 2008, here we show a significant loss of carbon over the entire Amazon basin at a rate of 0.3 ± 0.2 (95% CI) PgC yr−1 after the 2005 mega-drought, which continued persistently over the next 3 years (2005–2008). The changes in forest structure, captured by average LiDAR forest height and converted to above ground biomass carbon density, show an average loss of 2.35 ± 1.80 MgC ha−1 a year after (2006) in the epicenter of the drought. With more frequent droughts expected in future, forests of Amazon may lose their role as a robust sink of carbon, leading to a significant positive climate feedback and exacerbating warming trends.”
Yang et al., Post-drought decline of the Amazon carbon sink, Nature, August 9, 2018.
https://www.nature.com/articles/s41467-018-05668-6
The Amazon is flipping from carbon sink to source 70 years ahead of projections… The Amazon has flipped from carbon sink to carbon source three times 2005, 2010, 2016, with 100-year or more extreme drought, each increasing in severity from the previous event. Flipping three times is a fair enough interpretation. In 2010, the Amazon was near neutral with carbon emissions of 0.07 gigaton C (256 megatons CO2 equivalent.) The 2005 drought created emissions of 0.43 gigaton C (1.6 PgC reduction – 1.1 PgC) or 1.6 gigatons C. The 2016 drought was more severe than either, but the quantity of emissions has not yet been published.
2005 and 2010 Droughts… (Abstract) “Based on these ground data, live biomass in trees and corresponding estimates of live biomass in lianas and roots, we estimate that intact forests in Amazonia were carbon neutral in 2010 (-0.07 Pg C yr1 CI: -0.42, 0.23), consistent with results from an independent analysis of airborne estimates of land-atmospheric fluxes during 2010. Relative to the long-term mean, the 2010 drought resulted in a reduction in biomass carbon uptake of 1.1 Pg C, compared to 1.6 Pg C for the 2005 event.” Therefore, if the 2010 drought was carbon neutral, the 2005 drought resulted in carbon emissions.
Feldpausch et al., Amazon forest response to repeated droughts, Global Biogeochemical Cycles, July 1, 2016.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GB005133
Press Release – https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GB005133
2016 Amazon Drought – a drought of greater than 100-year frequency, following very closely behind two other 100-year droughts in 2005 and 2010… (Abstract) “Tropical and sub-tropical South America are highly susceptible to extreme droughts. Recent events include two droughts (2005 and 2010) exceeding the 100-year return value in the Amazon and recurrent extreme droughts in the Nordeste region, with profound eco-hydrological and socioeconomic impacts. In 2015–2016, both regions were hit by another drought. Here, we show that the severity of the 2015–2016 drought (“2016 drought” hereafter) is unprecedented based on multiple precipitation products (since 1900), satellite-derived data on terrestrial water storage (since 2002) and two vegetation indices (since 2004). The ecohydrological consequences from the 2016 drought are more severe and extensive than the 2005 and 2010 droughts. Empirical relationships between rainfall and sea surface temperatures (SSTs) over the tropical Pacific and Atlantic are used to assess the role of tropical oceanic variability in the observed precipitation anomalies. Our results indicate that warmer-than-usual SSTs in the Tropical Pacific (including El Niño events) and Atlantic were the main drivers of extreme droughts in South America, but are unable to explain the severity of the 2016 observed rainfall deficits for a substantial portion of the Amazonia and Nordeste regions. This strongly suggests potential contribution of nonoceanic factors (e.g., land cover change and CO2-induced warming) to the 2016 drought.”
Erfanian et al., Unprecedented drought over tropical South America in 2016 significantly under-predicted by tropical SST, Nature Scientific Reports, July 19, 2017.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5517600/
The Amazon has flipped from a carbon sink to a carbon source in 2011… A personal email correspondence with Lewis helped with the math… 2.2 and 1.6 Gt of Carbon (C) were killed in 2010 and 2005. It takes four years for half to decay and another 25 for the rest to decay resulting in 0.475 Gt emissions the first four years spread out non-linearly thereafter. The Amazon normally captures 0.4 Gt C in a non-drought year, so for the first +/- ten years after 2010 emissions will be greater than captured C.
Lewis et al., The 2010 Amazon Drought, Science, February, 2011.
Abstract only: http://www.sciencemag.org/content/331/6017/554
Press Release: https://www.eurekalert.org/news-releases/593178
Over 2 billion trees… Lewis 2011 is quoted in the Guardian “in the low billions of trees.”
Carrington, Mass tree deaths prompt fears of Amazon ‘climate tipping point’, Guardian, February 3, 2011.
http://www.theguardian.com/environment/2011/feb/03/tree-deaths-amazon-climate
GENERAL FOREST REGENERATION FAILURE
A simple interpretation of findings reveals that except for our oceans, the most important Earth systems for sequestration are in collapse. McDowell 2020 says that on average in the US and Europe, forests have seen a doubling of mortality. A doubling of mortality halves a forest’s life and halves carbon storage, creating emissions instead of sequestration because forests are only modest sequestration resources when healthy. Work in the Amazon, western North American forests, from Canada and Australia, all show a doubling or greater of forest mortality. Work from the Amazon, permafrost lands that include forest drowning, and Canadian forests show net greenhouse gas emissions instead of sequestration. If these subcontinental-scale areas are seeing forest failure, similar forests globally are likely behaving similarly. When it is understood that even if the global temperature were stabilized tomorrow morning, not only would currently extreme chronic and acute weather events that have caused mortality to increase still occur, rarer and even more extreme weather events would still occur as time passed because of the distribution of different extremeness of weather events as a part of frequentist statistics. It is clear then that with our current global temperature, forest mortality rates will continue to worsen. This singular concept of, once a natural system collapse begins it does not stabilize unless the perturbation to the system that activated the collapse is removed, bodes poorly for continued sequestration of natural systems globally. The reality is that natural systems collapses generally create feedback emissions quite soon after collapse initiation. There is a high risk that if we use these systems to offset emissions or provide drawdown, the systems will not only fail at the task, but reverse the intention through feedback emissions. Below are numerous findings that show that it is plausible if not likely that globally, our natural systems are failing and likely even emitting greenhouse gases, not sequestering them as the standard body of the science climate change mitigation continues to suggest is reality.
One third of burned forests in the western US are not regenerating at all… Conclusion, “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 2017 found a significant decrease in tree regeneration in post fire landscapes in the last 15 years (since 2015) vs. the previous 15 years. For fires that burned in the early 21st century, regeneration tree density decreased by nearly half, and sites experiencing no post-fire regeneration nearly doubled, over fires that burned at the end of the 20th century.
From the abstract, “Forest resilience to climate change is a global concern given the potential effects of increased disturbance activity, warming temperatures and increased moisture stress on plants. We used a multi-regional dataset of 1485 sites across 52 wildfires from the US Rocky Mountains to ask if and how changing climate over the last several decades impacted post-fire tree regeneration, a key indicator of forest resilience. Results highlight significant decreases in tree regeneration in the 21st century. Annual moisture deficits were significantly greater from 2000 to 2015 as compared to 1985–1999, suggesting increasingly unfavourable post-fire growing conditions, corresponding to significantly lower seedling densities and increased regeneration failure. Dry forests that already occur at the edge of their climatic tolerance are most prone to conversion to non-forests after wildfires. Major climate-induced reduction in forest density and extent has important consequences for a myriad of ecosystem services now and in the future.”
Stevens-Rumann et al., Evidence for declining forest resilience to wildfires under climate, Ecology Letters, December 12, 2017.
(Paywall) https://onlinelibrary.wiley.com/doi/abs/10.1111/ele.12889
Full (Researchgate free account required)
https://www.researchgate.net/profile/Monica_Rother/publication/321753770_Evidence_for_declining_forest_resilience_to_wildfires_under_climate_change/links/5a315ae90f7e9b2a284cea8f/Evidence-for-declining-forest-resilience-to-wildfires-under-climate-change.pdf
Press Release, University of Montana –
https://www.eurekalert.org/pub_releases/2017-12/tuom-sfr121317.php
Case Study – Mesa Verde Forest Regeneration Failure
About 90 percent of Pinyon pine were killed by drought and bark beetles across 3 million acres of the four Corners Region of the US from 2000 to 2003… ” At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a pin˜ on) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Difference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 [3 million acres] or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous subcontinental drought of the 1950s. The limited, available observations suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species’ distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.
Breshears et al., Regional vegetation die-off in response to global-change-type drought, PNAS, October 18, 2005.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1250231/pdf/pnas-0505734102.pdf
Pinyon Juniper Woodlands in Mesa Verde are not regenerating after fire…
“Pinus edulis–Juniperus osteosperma (pi˜non-juniper) woodlands in the southwestern United States are of high conservation value and are threatened by changing climate and increasing frequency of large, severe fires. We followed vegetation development after three recent fires (1989, 1996, and 2000) in Mesa Verde National Park (MEVE). Two types of pinon-juniper vegetation are found in MEVE: sprouting woodlands (SPW), dominated by species that resprout after injury, and obligate seeding woodlands (OSW), dominated by non-sprouting species. SPW stands showed greater resilience than OSW in terms of recovery of pre-fire structure and species composition, and vulnerability to invasion by nonnative plant species. After all three fires, plant cover increased more rapidly in SPW stands; all major pre-fire species were present within 2 y, and fewer nonnative species became established. Plant cover developed more slowly in OSW stands; nonnative plant species proliferated, in places being more abundant than the newly germinating native species. No reestablishment of pinon or juniper trees has been observed. If current trends persist, some portions of the burned SPW may be converted to a persistent shrubland type, while much of the burned OSW may be converted to a persistent, novel herbaceous vegetation type with a large component of nonnative species. Similar changes after fire can be expected in pinon-juniper woodlands like those in MEVE, which are widely distributed throughout the region.”
Floyd et al., Effects of Recent Wildfires in Pinon-Juniper Woodlands of Mesa Verde, Bio One, February 2021.
(Researchgate – Free subscription required) https://www.researchgate.net/publication/349013945_Effects_of_Recent_Wildfires_in_Pinon-Juniper_Woodlands_of_Mesa_Verde_National_Park_Colorado_USA
Mesa Verde Forest Age… “We believe that much of the piñon-juniper forest in MVNP has not been subjected to any major disturbance since the ancestral Puebloan people (who built the famous cliff dwellings) abandoned the area 700 years ago.”
Romme et al, Ancient Piñon-Juniper Forests of Mesa Verde and the West: A Cautionary Note for Forest Restoration Programs, USDA Forest Service Proceedings RMRS-P-29, 2003.
https://www.fs.usda.gov/rm/pubs/rmrs_p029/rmrs_p029_335_350.pdf
Oldest trees in the pinyon juniper woodland are about 1000 years old…
Mesa Verde Pinyon 1,000 years old, page 347 – Fire, Fuel Treatments, and Ecological Restoration, Conference Proceedings April 2002, Fort Collins CO, USDA.
https://www.fs.usda.gov/rm/pubs/rmrs_p029.pdf
Point of No Return…
The “point of no return” is that point in the collapse of a system where even if the perturbation to the system that caused the collapse is removed, the system collapse completes anyway as external forces from water stress and temperature are too great to allow seedling survival.
First Use – Hansen 2008… 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].
Hansen et. al., Target Atmospheric CO2 Where should humanity aim, Open Atmospheric Science Journal August 2008.
https://openatmosphericsciencejournal.com/contents/volumes/V2/TOASCJ-2-217/TOASCJ-2-217.pdf
FOREST REGENERATION FAILURE LITERATURE SUMMARY
Current warming is causing forest system collapse. Unless the warming (perturbation to the system) is removed before the point of no return, the system collapse completes. In the case of acute forest destruction like from fire or bark beetles, it is now too warm for most forests to regenerate.
Increased regeneration failure and wildfire risk from warming across the Sierra Nevada… Warming has created regeneration failure and a greater risk of wildfire across up to 19.5 percent of the Sierra Nevada. In this study that compared assumed stable forest conditions from 1915 to 1955, a mismatch in climate and forest regeneration of forest stability was found compared to the period 2000 to 2022. This mismatch is degrading or eliminating regeneration or the ability of sapling trees to survive because of water stress in the warmed environment at lower elevation areas along the western slope of the Sierras. Of most importance in this study, the comparison was made between the average conditions from 1915 to 1955 and 2000 to 2022. Because it is quite likely that the period 2000 to 2022 has seen more warming later rather than sooner during this period, the 19.5 percent mismatch is biased low or is understated.
Full – Hill et al., Low-elevation conifers in California’s Sierra Nevada are out of equilibrium with climate, PNAS, February 28, 2023.
https://academic.oup.com/pnasnexus/article-pdf/2/2/pgad004/49406200/pgad004.pdf
Press Release – Jordan, Stanford-led study reveals a fifth of California’s Sierra Nevada conifer forests are stranded in habitats that have grown too warm for them, Stanford, February 28, 2023.
https://news.stanford.edu/press-releases/2023/02/28/zombie-forests/
Seedling regeneration in unburned plots is reduced by 15 to 36 percent from 2000 to 2019 in Western forests… In burned plots, seedling regeneration is 89 percent greater than in unburned plots with regeneration reduced by 28 to 68 percent. This study is based on the average regeneration of 28 different tree species. It also includes a bias where recent warming is greater than earlier warming during the study period of 2000 to 2019, as well as not including the most warming during the period 2020 to present where wildfire burn area in California increased to Pre-European burned area in 2020.
Hill and Field, Forest fires and climate-induced tree range shifts in the western US, Nature Communications, November 15, 2022.
https://www.nature.com/articles/s41467-021-26838-z
Press Release – Jordan, Stanford researchers reveal how wildfire accelerates forest changes, Stanford, November 15, 2022.
https://news.stanford.edu/2021/11/15/trees-on-the-move/
Poor Ponderosa Regeneration because of climate warming and moisture limitation… “Regeneration density varied among fires but analysis of regeneration in aggregated edge and core plots showed that abundance of seed availability was not the sole factor that limited ponderosa pine regeneration, probably because of surviving tree refugia within high-severity burn patches. furthermore, our findings emphasize that ponderosa pine regeneration in our study area was significantly impacted by xeric topographic environments and vegetation competition. Continued warm and dry conditions and increased wildfire activity may delay the natural recovery of ponderosa pine forests, underscoring the importance of restoration efforts in large, high-severity burn patches.”
Singleton, Moisture and vegetation cover limit ponderosa pine regeneration in high-severity burn patches in the southwestern US, Fire Ecology, May 7, 2021.
https://fireecology.springeropen.com/articles/10.1186/s42408-021-00095-3
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.
https://doi.org/10.1093/biosci/biaa061<
Old trees just don’t die, they are killed by something and old forests are a part of a stable ecology…
“Large, majestic trees are iconic symbols of great age among living organisms. Published evidence suggests that trees do not die because of genetically programmed senescence in their meristems, but rather are killed by an external agent or a disturbance event. Long tree lifespans are therefore allowed by specific combinations of life history traits within realized niches that support resistance to, or avoidance of, extrinsic mortality. Another requirement for trees to achieve their maximum longevity is either sustained growth over extended periods of time or at least the capacity to increase their growth rates when conditions allow it. The growth plasticity and modularity of trees can then be viewed as an evolutionary advantage that allows them to survive and reproduce for centuries and millennia. As more and more scientific information is systematically collected on tree ages under various ecological settings, it is becoming clear that tree longevity is a key trait for global syntheses of life history strategies, especially in connection with disturbance regimes and their possible future modifications.”
Piovesan and Biondi, On tree longevity, New Phytologist, November 25, 2020.
https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.17148
Davis 2019 — Forests Exceed Climate Change Regeneration Threshold Leading to Non-forested States
The take-away, “In areas that have crossed climatic thresholds for regeneration, stand-replacing fires may result in abrupt ecosystem transitions to nonforest states.” The authors “examine[d] the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States… [They] demonstrate[d] that … forests of the western United States have crossed a critical climate threshold for postfire tree regeneration. [They] found abrupt declines in modeled annual recruitment probability in the 1990s for both species and across all regions. Annual rates of tree regeneration exhibited strongly nonlinear relationships with annual climate conditions, with distinct threshold responses to summer VPD [humidity], soil moisture, and maximum surface temperatures. Across the study region, seasonal to annual climate conditions from the early 1990s through 2015 have crossed these climate thresholds at the majority of sites. [Their] findings suggest that many low elevation mixed conifer forests in the western United States have already crossed climatic thresholds beyond which the climate is unsuitable for regeneration. The nonlinear relationships between annual climate and regeneration observed in this study are likely not unique to these two species.”
Davis et al., Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration, PNAS, March 26, 2019.
https://www.pnas.org/content/116/13/6193
“Ecological Drought,” collapsing ecosystems, regeneration failure – New Climate Change Drought Category…
“Ecological drought has recently been proposed as a fifth drought metric classification. In contrast to other drought classifications, ecological drought metrics attempt to describe abnormal departures from moisture conditions when accounting for local ecosystems without a human-specific viewpoint of drought effects. Ecological drought metrics identify droughts on longer time and larger spatial scales that have the potential to shift ecosystems—as well as human systems—past their adaptive capacity (Crausbay et al. 2017). Addressing the prevalence of ecologically significant droughts in the twentieth and twenty-first centuries requires a metric suited to addressing long-term ecosystem trends.”
Crockett and Westerling, Greater Temperature and Precipitation Extremes Intensify Western US Drought, Wildfire Severity, and Sierra Nevada Tree Mortality, Journal of Climate, January 2018.
https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0254.1
Anticipated transition from forested to shrubland ecosystems from regeneration failure of forests after fire and other mortality events…
“Droughts of the 21st century are characterized by hotter temperatures, longer duration and greater spatial extent, and are increasingly exacerbated by human demands for water. This situation increases the vulnerability of ecosystems to drought, including a rise in drought-driven tree mortality globally (Allen et al. 2015) and anticipated ecosystem transformations from one state to another, e.g., forest to a shrubland (Jiang et al. 2013).”
Crausbay et al., Defining ecological drought for the 21 st century, BAMS, July 27, 2017.
https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-16-0292.1
An eightfold increase (800 percent) in high-severity fire (95% or greater mortality, Stevens 2017) burned area from 1985 to 2017, implicates increased probability of conversion of forests to alternative vegetation types…
“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.
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL089858
Zombie Forests – Lack of regeneration creates an unsustainably old forest with no young trees… current warming regeneration failure can also result in a forest with only old trees that have yet to be killed by fire, insects or disease. This happens when it becomes too warm and dry for the forests seedlings to survive. Warming has created regeneration failure and a greater risk of wildfire across up to 19.5 percent of the Sierra Nevada. In this study that compared assumed stable forest conditions from 1915 to 1955, a mismatch in climate and forest regeneration of forest stability was found compared to the period 2000 to 2022. This mismatch is degrading or eliminating regeneration or the ability of sapling trees to survive because of water stress in the warmed environment at lower elevation areas along the western slope of the Sierras. Of most importance in this study, the comparison was made between the average conditions from 1915 to 1955 and 2000 to 2022. Because it is quite likely that the period 2000 to 2022 has seen more warming later rather than sooner during this period, the 19.5 percent mismatch is biased low or is understated.
Full – Hill et al., Low-elevation conifers in California’s Sierra Nevada are out of equilibrium with climate, PNAS, February 28, 2023.
https://academic.oup.com/pnasnexus/article-pdf/2/2/pgad004/49406200/pgad004.pdf
Press Release – Jordan, Stanford-led study reveals a fifth of California’s Sierra Nevada conifer forests are stranded in habitats that have grown too warm for them, Stanford, February 28, 2023.
https://news.stanford.edu/press-releases/2023/02/28/zombie-forests/
