Climate change feedback
Climate change feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of each climate forcing, and so play an important part in determining the climate sensitivity and future climate state. Feedback in general is the process in which changing one quantity changes a second quantity, and the change in the second quantity in turn changes the first. Positive (or reinforcing) feedback amplifies the change in the first quantity while negative (or balancing) feedback reduces it.
The term "forcing" means a change which may "push" the climate system in the direction of warming or cooling. An example of a climate forcing is increased atmospheric concentrations of greenhouse gases. By definition, forcings are external to the climate system while feedbacks are internal; in essence, feedbacks represent the internal processes of the system. Some feedbacks may act in relative isolation to the rest of the climate system; others may be tightly coupled; hence it may be difficult to tell just how much a particular process contributes. Forcing can also be driven by socioeconomic factors such as "demand for biofuels or demand for soy bean production." These drivers work as forcing mechanisms by the direct and indirect effects they cause from an individual to a global scale.
Forcings and feedbacks together determine how much and how fast the climate changes. The main positive feedback in global warming is the tendency of warming to increase the amount of water vapor in the atmosphere, which in turn leads to further warming. The main negative feedback comes from the Stefan–Boltzmann law, the amount of heat radiated from the Earth into space changes with the fourth power of the temperature of Earth's surface and atmosphere. Observations and modelling studies indicate that there is a net positive feedback to warming. Large positive feedbacks can lead to effects that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.
Carbon cycle feedbacks
There have been predictions, and some evidence, that global warming might cause loss of carbon from terrestrial ecosystems, leading to an increase of atmospheric CO
2 levels. Several climate models indicate that global warming through the 21st century could be accelerated by the response of the terrestrial carbon cycle to such warming. All 11 models in the C4MIP study found that a larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5 °C. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. The strongest feedbacks in these cases are due to increased respiration of carbon from soils throughout the high latitude boreal forests of the Northern Hemisphere. One model in particular (HadCM3) indicates a secondary carbon cycle feedback due to the loss of much of the Amazon Rainforest in response to significantly reduced precipitation over tropical South America. While models disagree on the strength of any terrestrial carbon cycle feedback, they each suggest any such feedback would accelerate global warming.
Observations show that soils in the U.K have been losing carbon at the rate of four million tonnes a year for the past 25 years according to a paper in Nature by Bellamy et al. in September 2005, who note that these results are unlikely to be explained by land use changes. Results such as this rely on a dense sampling network and thus are not available on a global scale. Extrapolating to all of the United Kingdom, they estimate annual losses of 13 million tons per year. This is as much as the annual reductions in carbon dioxide emissions achieved by the UK under the Kyoto Treaty (12.7 million tons of carbon per year).
It has also been suggested (by Chris Freeman) that the release of dissolved organic carbon (DOC) from peat bogs into water courses (from which it would in turn enter the atmosphere) constitutes a positive feedback for global warming. The carbon currently stored in peatlands (390–455 gigatonnes, one-third of the total land-based carbon store) is over half the amount of carbon already in the atmosphere. DOC levels in water courses are observably rising; Freeman's hypothesis is that, not elevated temperatures, but elevated levels of atmospheric CO2 are responsible, through stimulation of primary productivity.
Tree deaths are believed to be increasing as a result of climate change, which is a positive feedback effect.
Wetlands and freshwater ecosystems are predicted to be the largest potential contributor to a global methane climate feedback. Long-term warming changes the balance in the methane-related microbial community within freshwater ecosystems so they produce more methane while proportionately less is oxidised to carbon dioxide.
Arctic methane release
Warming is also the triggering variable for the release of carbon (potentially as methane) in the arctic. Methane released from thawing permafrost such as the frozen peat bogs in Siberia, and from methane clathrate on the sea floor, creates a positive feedback. In April 2019, Turetsky et al. reported permafrost was thawing quicker than predicted.
Thawing permafrost peat bogs
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Western Siberia is the world's largest peat bog, a one million square kilometer region of permafrost peat bog that was formed 11,000 years ago at the end of the last ice age. The melting of its permafrost is likely to lead to the release, over decades, of large quantities of methane. As much as 70,000 million tonnes of methane, an extremely effective greenhouse gas, might be released over the next few decades, creating an additional source of greenhouse gas emissions. Similar melting has been observed in eastern Siberia. Lawrence et al. (2008) suggest that a rapid melting of Arctic sea ice may start a feedback loop that rapidly melts Arctic permafrost, triggering further warming. May 31, 2010. NASA published that globally "Greenhouse gases are escaping the permafrost and entering the atmosphere at an increasing rate - up to 50 billion tons each year of methane, for example - due to a global thawing trend. This is particularly troublesome because methane heats the atmosphere with 25 times the efficiency of carbon dioxide" (the equivalent of 1250 billion tons of CO2 per year).
In 2019, a report called " Arctic report card " estimated the current greenhouse gas emissions from Arctic permafrost as almost equal to the emissions of Russia or Japan or less than 10% of the global emissions from fossil fuels.
Methane clathrate, also called methane hydrate, is a form of water ice that contains a large amount of methane within its crystal structure. Extremely large deposits of methane clathrate have been found under sediments on the sea and ocean floors of Earth. The sudden release of large amounts of natural gas from methane clathrate deposits, in a runaway global warming event, has been hypothesized as a cause of past and possibly future climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; it is thought that this might increase the global temperature by an additional 5° in itself, as methane is much more powerful as a greenhouse gas than carbon dioxide. The theory also predicts this will greatly affect available oxygen content of the atmosphere. This theory has been proposed to explain the most severe mass extinction event on earth known as the Permian–Triassic extinction event, and also the Paleocene-Eocene Thermal Maximum climate change event. In 2008, a research expedition for the American Geophysical Union detected levels of methane up to 100 times above normal in the Siberian Arctic, likely being released by methane clathrates being released by holes in a frozen 'lid' of seabed permafrost, around the outfall of the Lena River and the area between the Laptev Sea and East Siberian Sea.
In 2020, the first leak of methane from the sea floor in Antarctica was discovered. The scientists are not sure what caused it. The area where it was found had not warmed yet significantly. It is on the side of a volcano, but it seems that it is not from there. The methane - eating microbes, eat the methane much fewer that was supposed, and the researchers think this should be included in climate models. They also claim that there is much more to discover about the issue in Antarctica Quart of the marine methane is found in the region of Antarctica
Abrupt increases in atmospheric methane
Literature assessments by the Intergovernmental Panel on Climate Change (IPCC) and the US Climate Change Science Program (CCSP) have considered the possibility of future projected climate change leading to a rapid increase in atmospheric methane. The IPCC Third Assessment Report, published in 2001, looked at possible rapid increases in methane due either to reductions in the atmospheric chemical sink or from the release of buried methane reservoirs. In both cases, it was judged that such a release would be "exceptionally unlikely" (less than a 1% chance, based on expert judgement). The CCSP assessment, published in 2008, concluded that an abrupt release of methane into the atmosphere appeared "very unlikely" (less than 10% probability, based on expert judgement). The CCSP assessment, however, noted that climate change would "very likely" (greater than 90% probability, based on expert judgement) accelerate the pace of persistent emissions from both hydrate sources and wetlands.
On 10 June 2019 Louise M. Farquharson and her team reported that their 12-year study into Canadian permafrost had "Observed maximum thaw depths at our sites are already exceeding those projected to occur by 2090. Between 1990 and 2016, an increase of up to 4 °C has been observed in terrestrial permafrost and this trend is expected to continue as Arctic mean annual air temperatures increase at a rate twice that of lower latitudes." Determining the extent of new thermokarst development is difficult, but there is little doubt the problem is widespread. Farquharson and her team guess that about 231,000 square miles (600,000 square kilometers) of permafrost, or about 5.5% of the zone that is permafrost year-round, is vulnerable to rapid surface thawing.
Organic matter stored in permafrost generates heat as it decomposes in response to the permafrost melting. As the tropics get wetter, as many climate models predict, soils are likely to experience greater rates of respiration and decomposition, limiting the carbon storage abilities of tropical soils.
Peat, occurring naturally in peat bogs, is a store of carbon significant on a global scale. When peat dries it decomposes, and may additionally burn. Water table adjustment due to global warming may cause significant excursions of carbon from peat bogs. This may be released as methane, which can exacerbate the feedback effect, due to its high global warming potential.
Rainforests, most notably tropical rainforests, are particularly vulnerable to global warming. There are a number of effects which may occur, but two are particularly concerning. Firstly, the drier vegetation may cause total collapse of the rainforest ecosystem. For example, the Amazon rainforest would tend to be replaced by caatinga ecosystems. Further, even tropical rainforests ecosystems which do not collapse entirely may lose significant proportions of their stored carbon as a result of drying, due to changes in vegetation.
The IPCC Fourth Assessment Report predicts that many mid-latitude regions, such as Mediterranean Europe, will experience decreased rainfall and an increased risk of drought, which in turn would allow forest fires to occur on larger scale, and more regularly. This releases more stored carbon into the atmosphere than the carbon cycle can naturally re-absorb, as well as reducing the overall forest area on the planet, creating a positive feedback loop. Part of that feedback loop is more rapid growth of replacement forests and a northward migration of forests as northern latitudes become more suitable climates for sustaining forests. There is a question of whether the burning of renewable fuels such as forests should be counted as contributing to global warming. Cook & Vizy also found that forest fires were likely in the Amazon Rainforest, eventually resulting in a transition to Caatinga vegetation in the Eastern Amazon region.
Desertification is a consequence of global warming in some environments. Desert soils contain little humus, and support little vegetation. As a result, transition to desert ecosystems is typically associated with excursions of carbon.
The global warming projections contained in the IPCC's Fourth Assessment Report (AR4) include carbon cycle feedbacks. Authors of AR4, however, noted that scientific understanding of carbon cycle feedbacks was poor. Projections in AR4 were based on a range of greenhouse gas emissions scenarios, and suggested warming between the late 20th and late 21st century of 1.1 to 6.4 °C. This is the "likely" range (greater than 66% probability), based on the expert judgement of the IPCC's authors. Authors noted that the lower end of the "likely" range appeared to be better constrained than the upper end of the "likely" range, in part due to carbon cycle feedbacks. The American Meteorological Society has commented that more research is needed to model the effects of carbon cycle feedbacks in climate change projections.
Isaken et al. (2010) considered how future methane release from the Arctic might contribute to global warming. Their study suggested that if global methane emissions were to increase by a factor of 2.5 to 5.2 above (then) current emissions, the indirect contribution to radiative forcing would be about 250% and 400% respectively, of the forcing that can be directly attributed to methane. This amplification of methane warming is due to projected changes in atmospheric chemistry.
Schaefer et al. (2011) considered how carbon released from permafrost might contribute to global warming. Their study projected changes in permafrost based on a medium greenhouse gas emissions scenario (SRES A1B). According to the study, by 2200, the permafrost feedback might contribute 190 (+/- 64) gigatons of carbon cumulatively to the atmosphere. Schaefer et al. (2011) commented that this estimate may be low.
Implications for climate policy
Uncertainty over climate change feedbacks has implications for climate policy. For instance, uncertainty over carbon cycle feedbacks may affect targets for reducing greenhouse gas emissions. Emissions targets are often based on a target stabilization level of atmospheric greenhouse gas concentrations, or on a target for limiting global warming to a particular magnitude. Both of these targets (concentrations or temperatures) require an understanding of future changes in the carbon cycle. If models incorrectly project future changes in the carbon cycle, then concentration or temperature targets could be missed. For example, if models underestimate the amount of carbon released into the atmosphere due to positive feedbacks (e.g., due to melting permafrost), then they may also underestimate the extent of emissions reductions necessary to meet a concentration or temperature target.
Warming is expected to change the distribution and type of clouds. Seen from below, clouds emit infrared radiation back to the surface, and so exert a warming effect; seen from above, clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling effect. Whether the net effect is warming or cooling depends on details such as the type and altitude of the cloud. Low clouds tend to trap more heat at the surface and therefore have a positive feedback, while high clouds normally reflect more sunlight from the top so they have a negative feedback. These details were poorly observed before the advent of satellite data and are difficult to represent in climate models. Global climate models were showing a near-zero to moderately strong positive net cloud feedback, but the effective climate sensitivity has increased substantially in the latest generation of global climate models. Differences in the physical representation of clouds in models drive this enhanced climate sensitivity relative to the previous generation of models.
A 2019 simulation predicts that if greenhouse gases reach three times the current level of atmospheric carbon dioxide that stratocumulus clouds could abruptly disperse, contributing to additional global warming.
Release of gases of biological origin may be affected by global warming, but research into such effects is at an early stage. Some of these gases, such as nitrous oxide released from peat or thawing permafrost, directly affect climate. Others, such as dimethyl sulfide released from oceans, have indirect effects.
When ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and this cycle continues. During times of global cooling, additional ice increases the reflectivity which reduces the absorption of solar radiation which results in more cooling in a continuing cycle. Considered a faster feedback mechanism.
Albedo change is also the main reason why IPCC predict polar temperatures in the northern hemisphere to rise up to twice as much as those of the rest of the world, in a process known as polar amplification. In September 2007, the Arctic sea ice area reached about half the size of the average summer minimum area between 1979 and 2000. Also in September 2007, Arctic sea ice retreated far enough for the Northwest Passage to become navigable to shipping for the first time in recorded history. The record losses of 2007 and 2008 may, however, be temporary. Mark Serreze of the US National Snow and Ice Data Center views 2030 as a "reasonable estimate" for when the summertime Arctic ice cap might be ice-free. The polar amplification of global warming is not predicted to occur in the southern hemisphere. The Antarctic sea ice reached its greatest extent on record since the beginning of observation in 1979, but the gain in ice in the south is exceeded by the loss in the north. The trend for global sea ice, northern hemisphere and southern hemisphere combined is clearly a decline.
Ice loss may have internal feedback processes, as melting of ice over land can cause eustatic sea level rise, potentially causing instability of ice shelves and inundating coastal ice masses, such as glacier tongues. Further, a potential feedback cycle exists due to earthquakes caused by isostatic rebound further destabilising ice shelves, glaciers and ice caps.
The ice-albedo in some sub-arctic forests is also changing, as stands of larch (which shed their needles in winter, allowing sunlight to reflect off the snow in spring and fall) are being replaced by spruce trees (which retain their dark needles all year).
Water vapor feedback
If the atmospheres are warmed, the saturation vapor pressure increases, and the amount of water vapor in the atmosphere will tend to increase. Since water vapor is a greenhouse gas, the increase in water vapor content makes the atmosphere warm further; this warming causes the atmosphere to hold still more water vapor (a positive feedback), and so on until other processes stop the feedback loop. The result is a much larger greenhouse effect than that due to CO2 alone. Although this feedback process causes an increase in the absolute moisture content of the air, the relative humidity stays nearly constant or even decreases slightly because the air is warmer. Climate models incorporate this feedback. Water vapor feedback is strongly positive, with most evidence supporting a magnitude of 1.5 to 2.0 W/m2/K, sufficient to roughly double the warming that would otherwise occur. Water vapor feedback is considered a faster feedback mechanism.
As the temperature of a black body increases, the emission of infrared radiation back into space increases with the fourth power of its absolute temperature according to Stefan–Boltzmann law. This increases the amount of outgoing radiation as the Earth warms. The impact of this negative feedback effect is included in global climate models summarized by the IPCC. This is also called the Planck feedback.
Le Chatelier's principle
Following Le Chatelier's principle, the chemical equilibrium of the Earth's carbon cycle will shift in response to anthropogenic CO2 emissions. The primary driver of this is the ocean, which absorbs anthropogenic CO2 via the so-called solubility pump. At present this accounts for only about one third of the current emissions, but ultimately most (~75%) of the CO2 emitted by human activities will dissolve in the ocean over a period of centuries: "A better approximation of the lifetime of fossil fuel CO2 for public discussion might be 300 years, plus 25% that lasts forever". However, the rate at which the ocean will take it up in the future is less certain, and will be affected by stratification induced by warming and, potentially, changes in the ocean's thermohaline circulation.
Chemical weathering over the geological long term acts to remove CO2 from the atmosphere. With current global warming, weathering is increasing, demonstrating significant feedbacks between climate and Earth surface. Biosequestration also captures and stores CO2 by biological processes. The formation of shells by organisms in the ocean, over a very long time, removes CO2 from the oceans. The complete conversion of CO2 to limestone takes thousands to hundreds of thousands of years.
Net primary productivity
Net primary productivity changes in response to increased CO2, as plants photosynthesis increased in response to increasing concentrations. However, this effect is swamped by other changes in the biosphere due to global warming.
The atmosphere's temperature decreases with height in the troposphere. Since emission of infrared radiation varies with temperature, longwave radiation escaping to space from the relatively cold upper atmosphere is less than that emitted toward the ground from the lower atmosphere. Thus, the strength of the greenhouse effect depends on the atmosphere's rate of temperature decrease with height. Both theory and climate models indicate that global warming will reduce the rate of temperature decrease with height, producing a negative lapse rate feedback that weakens the greenhouse effect. Measurements of the rate of temperature change with height are very sensitive to small errors in observations, making it difficult to establish whether the models agree with observations.
Impacts on humans
The graphic at right suggests that the overall effect of climate change upon human numbers and development will be negative. If this is so, then the century-scale prospects for climate change is that Earth's biosphere may adjust to a new, but radically different, equilibrium if large numbers of humans cannot survive future conditions.
- Climate change (modern)
- Climate change (general concept)
- Climate inertia
- Complex system
- Parametrization (climate)
- Tipping points in the climate system
- "The Causes of Climate Change". climate.nasa.gov. NASA. Archived from the original on December 21, 2019.
- "Climate Science Special Report / Fourth National Climate Assessment (NCA4), Volume I". science2017.globalchange.gov. U.S. Global Change Research Program. Archived from the original on December 14, 2019.
- "Summary for Policymakers" (PDF). ipcc.ch. Intergovernmental Panel on Climate Change. 2019. p. 6.
- "The Study of Earth as an Integrated System". nasa.gov. NASA. 2016. Archived from the original on November 2, 2016.
- "Climate feedback IPCC Third Assessment Report, Appendix I - Glossary". ipcc.ch.
- US NRC (2012), Climate Change: Evidence, Impacts, and Choices, US National Research Council (US NRC), p.9. Also available as PDF
- Lenton, Timothy M.; Rockström, Johan; Gaffney, Owen; Rahmstorf, Stefan; Richardson, Katherine; Steffen, Will; Schellnhuber, Hans Joachim (2019-11-27). "Climate tipping points — too risky to bet against". Nature. 575 (7784): 592–595. doi:10.1038/d41586-019-03595-0. PMID 31776487.
- Council, National Research (2 December 2003). Understanding Climate Change Feedbacks. nap.edu. doi:10.17226/10850. ISBN 9780309090728.
- "184.108.40.206 Water Vapour and Lapse Rate - AR4 WGI Chapter 8: Climate Models and their Evaluation". www.ipcc.ch. Archived from the original on 2010-04-09. Retrieved 2010-04-23.
- Stocker, Thomas F. (2013). IPCC AR5 WG1. Technical Summary (PDF).
- IPCC. "Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Pg 53" (PDF). Cite journal requires
- Cox, Peter M.; Richard A. Betts; Chris D. Jones; Steven A. Spall; Ian J. Totterdell (November 9, 2000). "Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model". Nature. 408 (6809): 184–7. Bibcode:2000Natur.408..184C. doi:10.1038/35041539. PMID 11089968. S2CID 2689847.
- Friedlingstein, P.; P. Cox; R. Betts; L. Bopp; W. von Bloh; V. Brovkin; P. Cadule; S. Doney; M. Eby; I. Fung; G. Bala; J. John; C. Jones; F. Joos; T. Kato; M. Kawamiya; W. Knorr; K. Lindsay; H.D. Matthews; T. Raddatz; P. Rayner; C. Reick; E. Roeckner; K.G. Schnitzler; R. Schnur; K. Strassmann; A.J. Weaver; C. Yoshikawa; N. Zeng (2006). "Climate–Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison". Journal of Climate. 19 (14): 3337–53. Bibcode:2006JCli...19.3337F. doi:10.1175/JCLI3800.1. hdl:1912/4178.
- "5.5C temperature rise in next century". The Guardian. 2003-05-29. Retrieved 2008-01-02.
- Tim Radford (2005-09-08). "Loss of soil carbon 'will speed global warming'". The Guardian. Retrieved 2008-01-02.
- Schulze, E. Detlef; Annette Freibauer (September 8, 2005). "Environmental science: Carbon unlocked from soils". Nature. 437 (7056): 205–6. Bibcode:2005Natur.437..205S. doi:10.1038/437205a. PMID 16148922. S2CID 4345985.
- Freeman, Chris; Ostle, Nick; Kang, Hojeong (2001). "An enzymic 'latch' on a global carbon store". Nature. 409 (6817): 149. doi:10.1038/35051650. PMID 11196627. S2CID 3152551.
- Freeman, Chris; et al. (2004). "Export of dissolved organic carbon from peatlands under elevated carbon dioxide levels". Nature. 430 (6996): 195–8. Bibcode:2004Natur.430..195F. doi:10.1038/nature02707. PMID 15241411. S2CID 4308328.
- Connor, Steve (2004-07-08). "Peat bog gases 'accelerate global warming'". The Independent.
- "Science: Global warming is killing U.S. trees, a dangerous carbon-cycle feedback". climateprogress.org.
- Dean, Joshua F.; Middelburg, Jack J.; Röckmann, Thomas; Aerts, Rien; Blauw, Luke G.; Egger, Matthias; Jetten, Mike S. M.; de Jong, Anniek E. E.; Meisel, Ove H. (2018). "Methane Feedbacks to the Global Climate System in a Warmer World". Reviews of Geophysics. 56 (1): 207–250. doi:10.1002/2017RG000559. hdl:1874/366386.
- Zhu, Yizhu; Purdy, Kevin J.; Eyice, Özge; Shen, Lidong; Harpenslager, Sarah F.; Yvon-Durocher, Gabriel; Dumbrell, Alex J.; Trimmer, Mark (2020-06-29). "Disproportionate increase in freshwater methane emissions induced by experimental warming". Nature Climate Change. 10 (7): 685–690. doi:10.1038/s41558-020-0824-y. ISSN 1758-6798. S2CID 220261158.
- Larry D. Dyke, Wendy E. Sladen (2010). "Permafrost and Peatland Evolution in the Northern Hudson Bay Lowland, Manitoba". Arctic. 63 (4): 1018. doi:10.14430/arctic3332. Archived from the original on 2014-08-10. Retrieved 2014-08-02.CS1 maint: uses authors parameter (link)
- Kvenvolden, K. A. (1988). "Methane Hydrates and Global Climate". Global Biogeochemical Cycles. 2 (3): 221–229. Bibcode:1988GBioC...2..221K. doi:10.1029/GB002i003p00221.
- Zimov, A.; Schuur, A.; Chapin Fs, D. (Jun 2006). "Climate change. Permafrost and the global carbon budget". Science. 312 (5780): 1612–1613. doi:10.1126/science.1128908. ISSN 0036-8075. PMID 16778046. S2CID 129667039.
- Archer, D (2007). "Methane hydrate stability and anthropogenic climate change". Biogeosciences Discuss. 4 (2): 993–1057. CiteSeerX 10.1.1.391.1275. doi:10.5194/bgd-4-993-2007.
- Reuters (2019-06-18). "Scientists shocked by Arctic permafrost thawing 70 years sooner than predicted". The Guardian. ISSN 0261-3077. Retrieved 2019-07-02.
- Turetsky, Merritt R. (2019-04-30). "Permafrost collapse is accelerating carbon release". Nature. 569 (7754): 32–34. doi:10.1038/d41586-019-01313-4. PMID 31040419.
- Fred Pearce (2005-08-11). "Climate warning as Siberia melts". New Scientist. Retrieved 2007-12-30.
- Ian Sample (2005-08-11). "Warming Hits 'Tipping Point'". Guardian. Archived from the original on 2005-11-06. Retrieved 2007-12-30.
- "Permafrost Threatened by Rapid Retreat of Arctic Sea Ice, NCAR Study Finds" (Press release). UCAR. 10 June 2008. Archived from the original on 18 January 2010. Retrieved 2009-05-25.
- Lawrence, D. M.; Slater, A. G.; Tomas, R. A.; Holland, M. M.; Deser, C. (2008). "Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss" (PDF). Geophysical Research Letters. 35 (11): L11506. Bibcode:2008GeoRL..3511506L. doi:10.1029/2008GL033985. Archived from the original (PDF) on 2009-03-20.
- Cook-Anderson, Gretchen (2020-01-15). "Just 5 questions: What lies beneath". NASA Global Climate Change: Vital Signs of the Planet. Retrieved 2020-01-24.
- Freedman, Andrew (10 December 2019). "The Arctic may have crossed key threshold, emitting billions of tons of carbon into the air, in a long-dreaded climate feedback". The Whashington Post. Retrieved 20 December 2019.
- Connor, Steve (September 23, 2008). "Exclusive: The methane time bomb". The Independent. Retrieved 2008-10-03.
- Connor, Steve (September 25, 2008). "Hundreds of methane 'plumes' discovered". The Independent. Retrieved 2008-10-03.
- N. Shakhova; I. Semiletov; A. Salyuk; D. Kosmach; N. Bel’cheva (2007). "Methane release on the Arctic East Siberian shelf" (PDF). Geophysical Research Abstracts. 9: 01071.
- Carrington, Damian (22 July 2020). "First active leak of sea-bed methane discovered in Antarctica". The Guardian. Retrieved 24 July 2020.
- Cockburn, Harry (23 July 2020). "Climate crisis: First active leaks of methane found on Antarctic seabed". The Independent. Retrieved 24 July 2020.
- IPCC (2001d). "4.14". In R.T. Watson; the Core Writing Team (eds.). Question 4. Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Print version: Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. This version: GRID-Arendal website. Archived from the original on 2011-06-04. Retrieved 2011-05-18.
- IPCC (2001d). "Box 2-1: Confidence and likelihood statements". In R.T. Watson; the Core Writing Team (eds.). Question 2. Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Print version: Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. This version: GRID-Arendal website. Archived from the original on 2011-06-04. Retrieved 2011-05-18.
- Clark, P.U.; et al. (2008). "Executive Summary". Abrupt Climate Change. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research (PDF). U.S. Geological Survey, Reston, VA. p. 2. Archived from the original (PDF) on 2011-07-21. Retrieved 2011-05-18.
- Clark, P.U.; et al. (2008). "Chapter 1: Introduction: Abrupt Changes in the Earth's Climate System". Abrupt Climate Change. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research (PDF). U.S. Geological Survey, Reston, VA. p. 12. Archived from the original (PDF) on 2011-07-21. Retrieved 2011-05-18.
- Farquharson, Louise M.; Romanovsky, Vladimir E.; Cable, William L.; Walker, Donald A.; Kokelj, Steven V.; Nicolsky, Dmitry (2019). "Climate Change Drives Widespread and Rapid Thermokarst Development in Very Cold Permafrost in the Canadian High Arctic". Geophysical Research Letters. 46 (12): 6681–6689. doi:10.1029/2019GL082187.
- Currin, Grant (June 14, 2019). "Arctic Permafrost Is Going Through a Rapid Meltdown — 70 Years Early". news.yahoo.com. Retrieved 2020-01-24.
- Heimann, Martin; Markus Reichstein (2008-01-17). "Terrestrial ecosystem carbon dynamics and climate feedbacks". Nature. 451 (7176): 289–292. Bibcode:2008Natur.451..289H. doi:10.1038/nature06591. PMID 18202646.
- Hays, Brooks (2020-05-06). "Wetter climate to trigger global warming feedback loop in the tropics". UPI. Retrieved 2020-05-11.
- "Peatlands and climate change". IUCN. 2017-11-06. Retrieved 2019-08-23.
- Turetsky, Merritt R.; Benscoter, Brian; Page, Susan; Rein, Guillermo; van der Werf, Guido R.; Watts, Adam (2014-12-23). "Global vulnerability of peatlands to fire and carbon loss". Nature Geoscience. 8 (1): 11–14. doi:10.1038/ngeo2325. hdl:10044/1/21250. ISSN 1752-0894.
- Ise, T.; Dunn, A. L.; Wofsy, S. C.; Moorcroft, P. R. (2008). "High sensitivity of peat decomposition to climate change through water-table feedback". Nature Geoscience. 1 (11): 763. Bibcode:2008NatGe...1..763I. doi:10.1038/ngeo331.
- Cook, K. H.; Vizy, E. K. (2008). "Effects of Twenty-First-Century Climate Change on the Amazon Rain Forest". Journal of Climate. 21 (3): 542–821. Bibcode:2008JCli...21..542C. doi:10.1175/2007JCLI1838.1.
- Nobre, Carlos; Lovejoy, Thomas E. (2018-02-01). "Amazon Tipping Point". Science Advances. 4 (2): eaat2340. doi:10.1126/sciadv.aat2340. ISSN 2375-2548. PMC 5821491. PMID 29492460.
- Enquist, B. J.; Enquist, C. A. F. (2011). "Long-term change within a Neotropical forest: assessing differential functional and floristic responses to disturbance and drought". Global Change Biology. 17 (3): 1408. Bibcode:2011GCBio..17.1408E. doi:10.1111/j.1365-2486.2010.02326.x.
- Rammig, Anja; Wang-Erlandsson, Lan; Staal, Arie; Sampaio, Gilvan; Montade, Vincent; Hirota, Marina; Barbosa, Henrique M. J.; Schleussner, Carl-Friedrich; Zemp, Delphine Clara (2017-03-13). "Self-amplified Amazon forest loss due to vegetation-atmosphere feedbacks". Nature Communications. 8: 14681. doi:10.1038/ncomms14681. ISSN 2041-1723. PMC 5355804. PMID 28287104.
- "Climate Change and Fire". David Suzuki Foundation. Archived from the original on 2007-12-08. Retrieved 2007-12-02.
- "Global warming : Impacts : Forests". United States Environmental Protection Agency. 2000-01-07. Archived from the original on 2007-02-19. Retrieved 2007-12-02.
- "Feedback Cycles: linking forests, climate and landuse activities". Woods Hole Research Center. Archived from the original on 2007-10-25. Retrieved 2007-12-02.
- Schlesinger, W. H.; Reynolds, J. F.; Cunningham, G. L.; Huenneke, L. F.; Jarrell, W. M.; Virginia, R. A.; Whitford, W. G. (1990). "Biological Feedbacks in Global Desertification". Science. 247 (4946): 1043–1048. Bibcode:1990Sci...247.1043S. doi:10.1126/science.247.4946.1043. PMID 17800060. S2CID 33033125.
- Meehl, G.A.; et al., "Ch 10: Global Climate Projections", Sec 10.5.4.6 Synthesis of Projected Global Temperature at Year 2100, in IPCC AR4 WG1 2007
- Solomon; et al., "Technical Summary", TS.6.4.3 Global Projections: Key uncertainties, archived from the original on 2018-11-03, retrieved 2013-02-01, in IPCC AR4 WG1 2007.
- AMS Council (20 August 2012), 2012 American Meteorological Society (AMS) Information Statement on Climate Change, Boston, MA, USA: AMS
- Isaksen, Ivar S. A.; Michael Gauss; Gunnar Myhre; Katey M. Walter; Anthony and Carolyn Ruppel (20 April 2011). "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions" (PDF). Global Biogeochemical Cycles. 25 (2): n/a. Bibcode:2011GBioC..25.2002I. doi:10.1029/2010GB003845. hdl:1912/4553. Archived from the original (PDF) on 4 March 2016. Retrieved 1 February 2013.
- KEVIN SCHAEFER; TINGJUN ZHANG; LORI BRUHWILER; ANDREW P. BARRETT (2011). "Amount and timing of permafrost carbon release in response to climate warming". Tellus Series B. 63 (2): 165–180. Bibcode:2011TellB..63..165S. doi:10.1111/j.1600-0889.2011.00527.x.
- Meehl, G.A.; et al., "Ch 10: Global Climate Projections", Sec 10.4.1 Carbon Cycle/Vegetation Feedbacks, in IPCC AR4 WG1 2007
- Soden, B. J.; Held, I. M. (2006). "An Assessment of Climate Feedbacks in Coupled Ocean–Atmosphere Models". Journal of Climate. 19 (14): 3354. Bibcode:2006JCli...19.3354S. doi:10.1175/JCLI3799.1.
Interestingly, the true feedback is consistently weaker than the constant relative humidity value, implying a small but robust reduction in relative humidity in all models on average clouds appear to provide a positive feedback in all models
- Zelinka, Mark D.; Myers, Timothy A.; McCoy, Daniel T.; Po‐Chedley, Stephen; Caldwell, Peter M.; Ceppi, Paulo; Klein, Stephen A.; Taylor, Karl E. (2020). "Causes of Higher Climate Sensitivity in CMIP6 Models". Geophysical Research Letters. 47 (1): e2019GL085782. doi:10.1029/2019GL085782. ISSN 1944-8007.
- Watts, Jonathan (2020-06-13). "Climate worst-case scenarios may not go far enough, cloud data shows". The Guardian. ISSN 0261-3077. Retrieved 2020-06-19.
- Palmer, Tim (2020-05-26). "Short-term tests validate long-term estimates of climate change". Nature. 582 (7811): 185–186. doi:10.1038/d41586-020-01484-5. PMID 32457461.
- Pressel, Kyle G.; Kaul, Colleen M.; Schneider, Tapio (March 2019). "Possible climate transitions from breakup of stratocumulus decks under greenhouse warming" (PDF). Nature Geoscience. 12 (3): 163–167. doi:10.1038/s41561-019-0310-1. ISSN 1752-0908. S2CID 134307699.[verification needed]
- Repo, M. E.; Susiluoto, S.; Lind, S. E.; Jokinen, S.; Elsakov, V.; Biasi, C.; Virtanen, T.; Martikainen, P. J. (2009). "Large N2O emissions from cryoturbated peat soil in tundra". Nature Geoscience. 2 (3): 189. Bibcode:2009NatGe...2..189R. doi:10.1038/ngeo434.
- Caitlin McDermott-Murphy (2019). "No laughing matter". The Harvard Gazette. Retrieved 22 July 2019. Cite journal requires
- Simó, R.; Dachs, J. (2002). "Global ocean emission of dimethylsulfide predicted from biogeophysical data". Global Biogeochemical Cycles. 16 (4): 1018. Bibcode:2002GBioC..16d..26S. doi:10.1029/2001GB001829.
- Pistone, Kristina; Eisenman, Ian; Ramanathan, Veerabhadran (2019). "Radiative Heating of an Ice-Free Arctic Ocean". Geophysical Research Letters. 46 (13): 7474–7480. doi:10.1029/2019GL082914. ISSN 1944-8007.
- Stocker, T.F.; Clarke, G.K.C.; Le Treut, H.; Lindzen, R.S.; Meleshko, V.P.; Mugara, R.K.; Palmer, T.N.; Pierrehumbert, R.T.; Sellers, P.J.; Trenberth, K.E.; Willebrand, J. (2001). "Chapter 7: Physical Climate Processes and Feedbacks" (PDF). In Manabe, S.; Mason, P. (eds.). Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (Full free text). Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press. pp. 445–448. ISBN 978-0-521-01495-3.
- Hansen, J., "2008: Tipping point: Perspective of a climatologist." Archived 2011-10-22 at the Wayback Machine, Wildlife Conservation Society/Island Press, 2008. Retrieved 2010.
- "The cryosphere today". University of Illinois at Urbana-Champagne Polar Research Group. Retrieved 2008-01-02.
- "Arctic Sea Ice News Fall 2007". National Snow and Ice Data Center. Retrieved 2008-01-02..
- "Arctic ice levels at record low opening Northwest Passage". Wikinews. September 16, 2007.
- "Avoiding dangerous climate change" (PDF). The Met Office. 2008. p. 9. Retrieved August 29, 2008.
- Adam, D. (2007-09-05). "Ice-free Arctic could be here in 23 years". The Guardian. Retrieved 2008-01-02.
- Eric Steig; Gavin Schmidt. "Antarctic cooling, global warming?". RealClimate. Retrieved 2008-01-20.
- "Southern hemisphere sea ice area". Cryosphere Today. Archived from the original on 2008-01-13. Retrieved 2008-01-20.
- "Global sea ice area". Cryosphere Today. Archived from the original on 2008-01-10. Retrieved 2008-01-20.
- University of Virginia (March 25, 2011). "Russian boreal forests undergoing vegetation change, study shows". ScienceDaily.com. Retrieved March 9, 2018.
- "Science Magazine February 19, 2009" (PDF). Archived from the original (PDF) on 2010-07-14. Retrieved 2010-09-02.
- Yang, Zong-Liang. "Chapter 2: The global energy balance" (PDF). University of Texas. Retrieved 2010-02-15.
- Archer, David (2005). "Fate of fossil fuel CO2 in geologic time" (PDF). Journal of Geophysical Research. 110 (C9): C09S05. Bibcode:2005JGRC..110.9S05A. CiteSeerX 10.1.1.364.2117. doi:10.1029/2004JC002625.
- Sigurdur R. Gislason, Eric H. Oelkers, Eydis S. Eiriksdottir, Marin I. Kardjilov, Gudrun Gisladottir, Bergur Sigfusson, Arni Snorrason, Sverrir Elefsen, Jorunn Hardardottir, Peter Torssander, Niels Oskarsson (2009). "Direct evidence of the feedback between climate and weathering". Earth and Planetary Science Letters. 277 (1–2): 213–222. Bibcode:2009E&PSL.277..213G. doi:10.1016/j.epsl.2008.10.018.CS1 maint: uses authors parameter (link)
- "The Carbon Cycle - Earth Science - Visionlearning". Visionlearning.
- "Prologue: The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate by David Archer". princeton.edu. Archived from the original on 2010-07-04. Retrieved 2010-08-09.
- Cramer, W.; Bondeau, A.; Woodward, F. I.; Prentice, I. C.; Betts, R. A.; Brovkin, V.; Cox, P. M.; Fisher, V.; Foley, J. A.; Friend, A. D.; Kucharik, C.; Lomas, M. R.; Ramankutty, N.; Sitch, S.; Smith, B.; White, A.; Young-Molling, C. (2001). "Global response of terrestrial ecosystem structure and function to CO2and climate change: results from six dynamic global vegetation models". Global Change Biology. 7 (4): 357. Bibcode:2001GCBio...7..357C. doi:10.1046/j.1365-2486.2001.00383.x.
- National Research Council Panel on Climate Change Feedbacks (2003). Understanding climate change feedbacks (Limited preview). Washington D.C., United States: National Academies Press. ISBN 978-0-309-09072-8.
- A.E. Dessler; S.C. Sherwood (20 February 2009). "A matter of humidity" (PDF). Science. 323 (5917): 1020–1021. doi:10.1126/science.1171264. PMID 19229026. S2CID 10362192. Archived from the original (PDF) on 2010-07-14. Retrieved 2010-09-02.
- Gore, Al (2006). An inconvenient truth: the planetary emergency of global warming and what we can do about it. Emmaus, Pa., Melcher Media and Rodale Press.
- IPCC AR4 WG1 (2007), Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K.B.; Tignor, M.; Miller, H.L. (eds.), Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, ISBN 978-0-521-88009-1 (pb: 978-0-521-70596-7)
- Amplification of Global Warming by Carbon-Cycle Feedback Significantly Less Than Thought ScienceDaily, Jan. 28, 2010
- Arctic permafrost leaking methane at record levels guardian.co.uk, Thursday 14 January 2010
- Chapter 7. Physical Climate Processes and Feedbacks IPCC Third Assessment Report
- CO2: The Thermostat that Controls Earth's Temperature by NASA, Goddard Institute for Space Studies, October, 2010
- Deniers delight — a negative climate feedback! from Climate Progress, July 28, 2008
- "Global warming 20 years later: tipping points near" (2008) PDF, address to National Press Club, and House Select Committee on Energy Independence & Global warming, Washington DC [44 pages]:
- Global Warming: Climate Feedback
- More Climate Feedback Loops Past Peak, November 27, 2007
- Tipping point: Perspective of a climatologist. In State of the Wild 2008–2009: A Global Portrait of Wildlife, Wildlands, and Oceans. W. Woods, Ed. Wildlife Conservation Society/Island Press, pp. 6–15.
- What are ‘climate feedbacks’? Big Picture TV video February 20, 2007, David Wasdell, Director of the Meridian Programme
- How does climate change happen? (Part 1) Big Picture TV video February 20, 2007, David Wasdell, Director of the Meridian Programme
- How does climate change happen? (Part 2) Big Picture TV video February 20, 2007, David Wasdell, Director of the Meridian Programme
- Understanding Climate Change Feedbacks by Board on Atmospheric Sciences and Climate 2003 online text book
- 'Tipping point' risk for Arctic hotspot" BBC Jan 24, 2019