Climate change feedback

Last updated
Photo shows what appears to be permafrost thaw ponds in Hudson Bay, Canada, near Greenland. (2008) Global warming will increase permafrost and peatland thaw, which can result in collapse of plateau surfaces. Permafrost thaw ponds in Hudson Bay Canada near Greenland.jpg
Photo shows what appears to be permafrost thaw ponds in Hudson Bay, Canada, near Greenland. (2008) Global warming will increase permafrost and peatland thaw, which can result in collapse of plateau surfaces.

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 feedback amplifies the change in the first quantity while negative feedback reduces it. [2]

Global warming Current rise in Earths average temperature and its effects

Global warming is the long-term rise in the average temperature of the Earth's climate system. It is a major aspect of current climate change, and has been demonstrated by direct temperature measurements and by measurements of various effects of the warming. The term commonly refers to the mainly human-caused increase in global surface temperatures and its projected continuation. In this context, the terms global warming and climate change are often used interchangeably, but climate change includes both global warming and its effects, such as changes in precipitation and impacts that differ by region. There were prehistoric periods of global warming, but observed changes since the mid-20th century have been much greater than those seen in previous records covering decades to thousands of years.

Climate sensitivity is the globally averaged temperature change in response to changes in radiative forcing, which can occur, for instance, due to increased levels of carbon dioxide (CO
). Although the term climate sensitivity is usually used in the context of radiative forcing by CO2, it is thought of as a general property of the climate system: the change in surface air temperature following a unit change in radiative forcing, and the climate sensitivity parameter is therefore expressed in units of °C/(W/m2). The measure is approximately independent of the nature of the forcing (e.g. from greenhouse gases or solar variation). When climate sensitivity is expressed for a doubling of CO2, its units are degrees Celsius (°C).

Feedback process in which information about the past or the present influences the same phenomenon in the present or future;occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop

Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems:

Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole.


The term "forcing" means a change which may "push" the climate system in the direction of warming or cooling. [3] 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. [4]

Climate system Interactions that create Earths climate and may result in climate change

Earth's climate arises from the interaction of five major climate system components: the atmosphere (air), the hydrosphere (water), the cryosphere, the lithosphere and the biosphere. Climate is the average of weather, typically over a period of 30 years, and is determined by a combination of processes in the climate system, such as ocean currents and wind patterns. Circulation in the atmosphere and oceans is primarily driven by solar radiation and transports heat from the tropical regions to regions that receive less energy from the Sun. The water cycle also moves energy throughout the climate system. In addition, different chemical elements, necessary for life, are constantly recycled between the different components.

Greenhouse gas Gas in an atmosphere that absorbs and emits radiation within the thermal infrared range

A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). The atmospheres of Venus, Mars and Titan also contain greenhouse gases.

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. [5] 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. [6] Large positive feedbacks can lead to effects that are abrupt or irreversible, depending upon the rate and magnitude of the climate change. [7]

Stefan–Boltzmann law a physical law on the emissive power of blackbody

The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time is directly proportional to the fourth power of the black body's thermodynamic temperature T:

Tipping points in the climate system Thresholds that, when exceeded, can lead to large change in the earth system

A tipping point in the climate system is a threshold that, when exceeded, can lead to large changes in the state of the system. Potential tipping points have been identified in the physical climate system, in impacted ecosystems, and sometimes in both. For instance, feedback from the global carbon cycle is a driver for the transition between glacial and interglacial periods, with orbital forcing providing the initial trigger. Earth's geologic temperature record includes many more examples of geologically rapid transitions between different climate states.


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
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. [8] 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. [9] 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. [10] While models disagree on the strength of any terrestrial carbon cycle feedback, they each suggest any such feedback would accelerate global warming.

C4MIP (more fully, Coupled Climate Carbon Cycle Model Intercomparison Project) is a joint project between the International Geosphere-Biosphere Programme (IGBP)and the World Climate Research Programme (WCRP). It is a model intercomparison project along the lines of the Atmospheric Model Intercomparison Project, but for global climate models that include an interactive carbon cycle.

Taiga the worlds largest land biome, characterized by coniferous forests

Taiga, generally referred to in North America as boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, and larches.

HadCM3 is a coupled atmosphere-ocean general circulation model (AOGCM) developed at the Hadley Centre in the United Kingdom. It was one of the major models used in the IPCC Third Assessment Report in 2001.

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 [11] 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). [12]

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. [13] 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. [14] [15]

Professor Chris Freeman is a British environmental scientist at the University of Wales, Bangor. Freeman is Professor of Aquatic Biogeochemistry in the College of Natural Sciences in Bangor. Freeman's research focuses on carbon cycling, with an emphasis on peatland carbon storage and dissolved organic carbon dynamics. His work is best known for its description of a mechanism known as the "peatland enzymic latch" and observation of a rising trend in aquatic dissolved organic carbon concentrations. His work has been recognised with awards from the American Society for Limnology and Oceanography and the Royal Society.

Dissolved organic carbon (DOC) is the fraction of total organic carbon operationally defined as that which can pass through a filter size that typically ranges in size from 0.22 and 0.7 micrometers. The fraction remaining on the filter is called particulate organic carbon (POC).

Peat Accumulation of partially decayed vegetation

Peat, also known as turf, is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem is the most efficient carbon sink on the planet, because peatland plants capture CO2 naturally released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m [4.9 to 7.5 ft], which is the average depth of the boreal [northern] peatlands". Sphagnum moss, also called peat moss, is one of the most common components in peat, although many other plants can contribute. The biological features of Sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed 'habitat manipulation'. Soils consisting primarily of peat are known as histosols. Peat forms in wetland conditions, where flooding or stagnant water obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition.

Tree deaths are believed to be increasing as a result of climate change, which is a positive feedback effect. [16]

Methane climate feedbacks in natural ecosystems. The methane climate feedback loop for natural ecosystems.jpg
Methane climate feedbacks in natural ecosystems.

Wetlands and freshwater ecosystems are predicted to be the largest potential contributor to a global methane climate feedback. [17]

Arctic methane release

Warming is also the triggering variable for the release of carbon (potentially as methane) in the arctic. [18] 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. [19] [20] [21] In April 2019, Turetsky et al. reported permafrost was thawing quicker than predicted. [22] [21]

Methane release from thawing permafrost peat bogs

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. [23] Similar melting has been observed in eastern Siberia. [24] 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. [25] [26]

Methane release from hydrates

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. [27] [28] [29]

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" [30] (less than a 1% chance, based on expert judgement). [31] The CCSP assessment, published in 2008, concluded that an abrupt release of methane into the atmosphere appeared "very unlikely" [32] (less than 10% probability, based on expert judgement). [33] 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. [32]


Organic matter stored in permafrost generates heat as it decomposes in response to the permafrost melting. [34]

Peat decomposition

Peat, occurring naturally in peat bogs, is a store of carbon significant on a global scale. [35] When peat dries it decomposes, and may additionally burn. [36] Water table adjustment due to global warming may cause significant excursions of carbon from peat bogs. [37] This may be released as methane, which can exacerbate the feedback effect, due to its high global warming potential.

Rainforest drying

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. [38] [39] 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. [40] [41]

Forest fires

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. [42] [43] [44] 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.[ citation needed ]


Desertification is a consequence of global warming in some environments. [45] Desert soils contain little humus, and support little vegetation. As a result, transition to desert ecosystems is typically associated with excursions of carbon.

Modelling results

The global warming projections contained in the IPCC's Fourth Assessment Report (AR4) include carbon cycle feedbacks. [46] Authors of AR4, however, noted that scientific understanding of carbon cycle feedbacks was poor. [47] 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. [46] 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. [46] The American Meteorological Society has commented that more research is needed to model the effects of carbon cycle feedbacks in climate change projections. [48]

Isaken et al. (2010) [49] 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) [50] 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. [51] 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.

Cloud feedback

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. High clouds tend to trap more heat and therefore have a positive feedback, low clouds normally reflect more sunlight 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. [52]

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. [53]

Gas release

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. [54] [55] Others, such as dimethyl sulfide released from oceans, have indirect effects. [56]

Ice-albedo feedback

Aerial photograph showing a section of sea ice. The lighter blue areas are melt ponds and the darkest areas are open water, both have a lower albedo than the white sea ice. The melting ice contributes to ice-albedo feedback. Sea Ice MeltPonds.png
Aerial photograph showing a section of sea ice. The lighter blue areas are melt ponds and the darkest areas are open water, both have a lower albedo than the white sea ice. The melting ice contributes to ice-albedo feedback.

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. [57] 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. [58] Considered a faster feedback mechanism. [59]

1870-2009 Northern hemisphere sea ice extent in million square kilometers. Blue shading indicates the pre-satellite era; data then is less reliable. In particular, the near-constant level extent in Autumn up to 1940 reflects lack of data rather than a real lack of variation. Seaice-1870-part-2009.png
1870–2009 Northern hemisphere sea ice extent in million square kilometers. Blue shading indicates the pre-satellite era; data then is less reliable. In particular, the near-constant level extent in Autumn up to 1940 reflects lack of data rather than a real lack of variation.

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. [60] [61] 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. [62] The record losses of 2007 and 2008 may, however, be temporary. [63] 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. [64] The polar amplification of global warming is not predicted to occur in the southern hemisphere. [65] The Antarctic sea ice reached its greatest extent on record since the beginning of observation in 1979, [66] 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. [67]

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). [68]

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. [52] 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. [69] Water vapor feedback is considered a faster feedback mechanism. [59]


Blackbody radiation

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. [70] 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.

Carbon cycle

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". [71] 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

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. [72] 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. [73] The complete conversion of CO2 to limestone takes thousands to hundreds of thousands of years. [74]

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. [75]

Lapse rate

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. [76] [77]

Impacts on humans

Feedback loops from the book Al Gore (2006). An inconvenient truth. Gore inconvenient truth loops.png
Feedback loops from the book Al Gore (2006). An inconvenient truth.

The graphic at right suggests that the overall effect of climate change upon human numbers and development will be negative. [78] 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.

See also


  1. 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)
  2. "Climate feedback IPCC Third Assessment Report, Appendix I - Glossary".
  3. US NRC (2012), Climate Change: Evidence, Impacts, and Choices, US National Research Council (US NRC), p.9. Also available as PDF
  4. Council, National Research (2 December 2003). Understanding Climate Change Feedbacks. doi:10.17226/10850. ISBN   9780309090728.
  5. " Water Vapour and Lapse Rate - AR4 WGI Chapter 8: Climate Models and their Evaluation". Archived from the original on 2010-04-09. Retrieved 2010-04-23.
  6. Stocker, Thomas F. (2013). IPCC AR5 WG1. Technical Summary (PDF).
  7. 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 |journal= (help)
  8. 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" (abstract). Nature. 408 (6809): 184–7. Bibcode:2000Natur.408..184C. doi:10.1038/35041539. PMID   11089968 . Retrieved 2008-01-02.
  9. 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.
  10. "5.5C temperature rise in next century". The Guardian. 2003-05-29. Retrieved 2008-01-02.
  11. Tim Radford (2005-09-08). "Loss of soil carbon 'will speed global warming'". The Guardian. Retrieved 2008-01-02.
  12. 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 . Retrieved 2008-01-02.
  13. 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.
  14. 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.
  15. Connor, Steve (2004-07-08). "Peat bog gases 'accelerate global warming'". The Independent.
  16. "Science: Global warming is killing U.S. trees, a dangerous carbon-cycle feedback".
  17. 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.
  18. Kvenvolden, K. A. (1988). "Methane Hydrates and Global Climate" (PDF). Global Biogeochemical Cycles. 2 (3): 221–229. Bibcode:1988GBioC...2..221K. doi:10.1029/GB002i003p00221.
  19. 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.
  20. Archer, D (2007). "Methane hydrate stability and anthropogenic climate change". Biogeosciences Discuss. 4 (2): 993–1057. doi:10.5194/bgd-4-993-2007.
  21. 1 2 Reuters (2019-06-18). "Scientists shocked by Arctic permafrost thawing 70 years sooner than predicted". The Guardian. ISSN   0261-3077 . Retrieved 2019-07-02.
  22. Turetsky, Merritt R. (2019-04-30). "Permafrost collapse is accelerating carbon release". Nature.
  23. Fred Pearce (2005-08-11). "Climate warning as Siberia melts". New Scientist. Retrieved 2007-12-30.
  24. Ian Sample (2005-08-11). "Warming Hits 'Tipping Point'". Guardian. Archived from the original on 2005-11-06. Retrieved 2007-12-30.
  25. "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.
  26. 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.
  27. Connor, Steve (September 23, 2008). "Exclusive: The methane time bomb". The Independent . Retrieved 2008-10-03.
  28. Connor, Steve (September 25, 2008). "Hundreds of methane 'plumes' discovered". The Independent . Retrieved 2008-10-03.
  29. 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.
  30. 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. Retrieved 2011-05-18.
  31. 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.
  32. 1 2 Clark, P.U.; et al. (2008). "Executive Summary" (PDF). 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. Retrieved 2011-05-18.
  33. Clark, P.U.; et al. (2008). "Chapter 1: Introduction: Abrupt Changes in the Earth's Climate System" (PDF). 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. Retrieved 2011-05-18.
  34. 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 . Retrieved 2010-03-15.
  35. "Peatlands and climate change". IUCN. 2017-11-06. Retrieved 2019-08-23.
  36. 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. ISSN   1752-0894.
  37. 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.
  38. 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.
  39. Nobre, Carlos; Lovejoy, Thomas E. (2018-02-01). "Amazon Tipping Point". Science Advances. 4 (2): eaat2340. doi:10.1126/sciadv.aat2340. ISSN   2375-2548.
  40. 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.
  41. 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.
  42. "Climate Change and Fire". David Suzuki Foundation. Archived from the original on 2007-12-08. Retrieved 2007-12-02.
  43. "Global warming : Impacts : Forests". United States Environmental Protection Agency. 2000-01-07. Archived from the original on 2007-02-19. Retrieved 2007-12-02.
  44. "Feedback Cycles: linking forests, climate and landuse activities". Woods Hole Research Center. Archived from the original on 2007-10-25. Retrieved 2007-12-02.
  45. 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.
  46. 1 2 3 Meehl, G.A.; et al., "Ch 10: Global Climate Projections", Sec Synthesis of Projected Global Temperature at Year 2100, in IPCC AR4 WG1 2007
  47. Solomon; et al., "Technical Summary", TS.6.4.3 Global Projections: Key uncertainties , in IPCC AR4 WG1 2007.
  48. AMS Council (20 August 2012), 2012 American Meteorological Society (AMS) Information Statement on Climate Change, Boston, MA, USA: AMS
  49. 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..25B2002I. doi:10.1029/2010GB003845. hdl:1912/4553.
  50. 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.
  51. Meehl, G.A.; et al., "Ch 10: Global Climate Projections", Sec 10.4.1 Carbon Cycle/Vegetation Feedbacks, in IPCC AR4 WG1 2007
  52. 1 2 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
  53. Pressel, Kyle G.; Kaul, Colleen M.; Schneider, Tapio (March 2019). "Possible climate transitions from breakup of stratocumulus decks under greenhouse warming". Nature Geoscience. 12 (3): 163–167. doi:10.1038/s41561-019-0310-1. ISSN   1752-0908.[ verification needed ]
  54. 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.
  55. Caitlin McDermott-Murphy (2019). "No laughing matter". The Harvard Gazette. Retrieved 22 July 2019.Cite journal requires |journal= (help)
  56. 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.
  57. 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.
  58. 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.
  59. 1 2 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.
  60. "The cryosphere today". University of Illinois at Urbana-Champagne Polar Research Group. Retrieved 2008-01-02.
  61. "Arctic Sea Ice News Fall 2007". National Snow and Ice Data Center. Retrieved 2008-01-02..
  62. "Arctic ice levels at record low opening Northwest Passage". Wikinews. September 16, 2007.
  63. "Avoiding dangerous climate change" (PDF). The Met Office. 2008. p. 9. Retrieved August 29, 2008.
  64. Adam, D. (2007-09-05). "Ice-free Arctic could be here in 23 years". The Guardian. Retrieved 2008-01-02.
  65. Eric Steig; Gavin Schmidt. "Antarctic cooling, global warming?". RealClimate. Retrieved 2008-01-20.
  66. "Southern hemisphere sea ice area". Cryosphere Today. Archived from the original on 2008-01-13. Retrieved 2008-01-20.
  67. "Global sea ice area". Cryosphere Today. Archived from the original on 2008-01-10. Retrieved 2008-01-20.
  68. University of Virginia (March 25, 2011). "Russian boreal forests undergoing vegetation change, study shows". Retrieved March 9, 2018.
  69. "Science Magazine February 19, 2009" (PDF). Archived from the original (PDF) on 2010-07-14. Retrieved 2010-09-02.
  70. Yang, Zong-Liang. "Chapter 2: The global energy balance" (PDF). University of Texas. Retrieved 2010-02-15.
  71. Archer, David (2005). "Fate of fossil fuel CO2 in geologic time" (PDF). Journal of Geophysical Research . 110: C09S05. Bibcode:2005JGRC..11009S05A. doi:10.1029/2004JC002625.
  72. 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)
  73. "The Carbon Cycle - Earth Science - Visionlearning". Visionlearning.
  74. "Prologue: The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate by David Archer". Archived from the original on 2010-07-04. Retrieved 2010-08-09.
  75. 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.
  76. 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.
  77. 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. Archived from the original (PDF) on 2010-07-14. Retrieved 2010-09-02.
  78. 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.

Related Research Articles

Greenhouse effect atmosopheric phenomenon

The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.

Climate change Change in the statistical distribution of weather patterns for an extended period

Climate change occurs when changes in Earth's climate system result in new weather patterns that remain in place for an extended period of time. This length of time can be as short as a few decades to as long as millions of years. The climate system receives nearly all of its energy from the sun, with a relatively tiny amount from earth's interior. The climate system also gives off energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.

Permafrost soil frozen for a duration of at least two years

In geology, permafrost is ground, including rock or (cryotic) soil, with a temperature that remains at or below the freezing point of water 0 °C (32 °F) for two or more years. Most permafrost is located in high latitudes, but at lower latitudes alpine permafrost occurs at higher elevations. Ground ice is not always present, as may be in the case of non-porous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost accounts for 0.022% of total water on Earth and the permafrost region covers 24% of exposed land in the Northern Hemisphere. It also occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean, portions of which were exposed during the last glacial period.

Radiative forcing

Radiative forcing or climate forcing is the difference between insolation (sunlight) absorbed by the Earth and energy radiated back to space. The influences that cause changes to the Earth's climate system altering Earth's radiative equilibrium, forcing temperatures to rise or fall, are called climate forcings. Positive radiative forcing means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause warming. Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the sun, which produces cooling.

This glossary of climate change is a list of definitions of terms and concepts relevant to climate change, global warming, and related topics.

Clathrate gun hypothesis hypothesis that climate change can trigger a release of methane buried in seabeds which leads to runaway warming

The clathrate gun hypothesis refers to a proposed explanation for the periods of rapid warming during the Quaternary. The idea is that changes in fluxes in upper intermediate waters in the ocean caused temperature fluctuations that alternately accumulated and occasionally released methane clathrate on upper continental slopes, these events would have caused the Bond Cycles and individual interstadial events, such as the Dansgaard–Oeschger interstadials.

Climate change in the Arctic The effects of global warming in the Arctic

The effects of global warming in the Arctic, or climate change in the Arctic include rising air and water temperatures, loss of sea ice, and melting of the Greenland ice sheet with a related cold temperature anomaly, observed since the 1970s. Related impacts include ocean circulation changes, increased input of freshwater, and ocean acidification. Indirect effects through potential climate teleconnections to mid latitudes may result in a greater frequency of extreme weather events, ecological, biological and phenology changes, biological migrations and extinctions, natural resource stresses and as well as human health, displacement and security issues. Potential methane releases from the region, especially through the thawing of permafrost and methane clathrates, may occur. Presently, the Arctic is warming twice as fast compared to the rest of the world. The pronounced warming signal, the amplified response of the Arctic to global warming, is often seen as a leading indicator of global warming. The melting of Greenland's ice sheet is linked to polar amplification. According to a study published in 2016, about 0.5 °C (0.90 °F) of the warming in the Arctic has been attributed to reductions in sulfate aerosols in Europe since 1980.

This is a list of climate change topics.

Global warming in Russia describes the global warming related issues in Russia. This includes climate politics, contribution to global warming and the influence of global warming in Russia. In September 2019, Russia announced that it will implement the 2015 Paris Agreement to fight climate change.

Arctic methane emissions

Arctic methane release is the release of methane from seas and soils in permafrost regions of the Arctic. While it is a long-term natural process, methane release is exacerbated by global warming. This results in negative effects, as methane is itself a powerful greenhouse gas.

Arctic geoengineering

Temperatures in the Arctic region have tended to increase more rapidly than the global average. Projections of sea ice loss that are adjusted to take account of recent rapid Arctic shrinkage suggest that the Arctic will likely be free of summer sea ice sometime between 2059 and 2078. Various climate engineering schemes have been suggested to reduce the chance of significant and irreversible effects such as Arctic methane release.

Regional effects of global warming

Regional effects of global warming are long-term significant changes in the expected patterns of average weather of a specific region due to global warming. The world average temperature is rising due to the greenhouse effect caused by increasing levels of greenhouse gases, especially carbon dioxide. When the global temperature changes, the changes in climate are not expected to be uniform across the Earth. In particular, land areas change more quickly than oceans, and northern high latitudes change more quickly than the tropics, and the margins of biome regions change faster than do their cores.

Atmospheric methane

Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising.

Long-term effects of global warming

There are expected to be various long-term effects of global warming. Most discussion and research, including that by the Intergovernmental Panel on Climate Change (IPCC) reports, concentrates on the effects of global warming up to 2100, with only an outline of the effects beyond this.

This article is about the physical impacts of climate change; the change referred to may be due to natural causes but in the political context is more likely to be that due to the result of human activity, global warming. For some of these physical impacts, their effect on social and economic systems are also described.

The permafrost carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir that is seldom considered when determining global terrestrial carbon reservoirs. Recent and ongoing scientific research however, is changing this view.

Soil carbon feedback

The soil carbon feedback concerns the releases of carbon from soils in response to global warming. This response under climate change is a positive climate feedback. There is approximately two to three times more carbon in global soils than the Earth's atmosphere, which makes understanding this feedback crucial to understand future climate change. An increased rate of soil respiration is the main cause of this feedback, where measurements imply that 4 °C of warming increases annual soil respiration by up to 37%.