Forcings and Feedbacks
From ClimateWiki
Researchers have identified other forcings and feedbacks about which little is currently known (or acknowledged by the IPCC), but which may ultimately prove to be important drivers of climate change. In this section we examine some of those phenomena that have been described in the peer-reviewed scientific literature.
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Stratospheric Water Vapor
Solomon et al. (2010) write, “the trend in global surface temperatures has been nearly flat since the late 1990s despite continuing increases in the forcing due to the sum of the well-mixed greenhouse gases (CO2, CH4, halocarbons, and N2O), raising questions regarding the understanding of forced climate change, its drivers, the parameters that define natural internal variability, and how fully these terms are represented in climate models.” In an effort to improve our understanding of climate forcing, they used observations of stratospheric water vapor concentration obtained over the period 1980–2008, together with detailed radiative transfer and modeling information, to calculate the global climatic impact of this important greenhouse gas and compare it with trends in mean global near-surface air temperature observed over the same time period.
According to the seven scientists, stratospheric water vapor concentrations decreased by about 10 percent after the year 2000, and their analysis indicates this decrease should have slowed the rate of increase in global near-surface air temperature between 2000 and 2009 by about 25 percent compared to what would have been expected on the basis of climate model calculations due to measured increases in carbon dioxide and other greenhouse gases over the same period. In addition, they found, “more limited data suggest that stratospheric water vapor probably increased between 1980 and 2000, which would have enhanced the decadal rate of surface warming during the 1990s by about 30% [above what it would have been without the stratospheric water vapor increase].”
In their concluding paragraph, Solomon et al. thus write it is “not clear whether the stratospheric water vapor changes represent a feedback to global average climate change or a source of decadal variability.” In either case, their findings elucidate a hugely important phenomenon not previously included in any prior analyses of global climate change. They also write that current climate models do not “completely represent the Quasi Biennial Oscillation [which has a significant impact on stratospheric water vapor content], deep convective transport [of water vapor] and its linkages to sea surface temperatures, or the impact of aerosol heating on water input to the stratosphere.” Consequently, in light of (1) Solomon et al.’s specific findings, (2) their listing of what current climate models do not do (which they should do), and (3) the questions they say are raised by the flat-lining of mean global near-surface air temperature since the late 1990s, it is premature to conclude that current state-of-the-art models know enough to correctly simulate the intricate workings of Earth’s climate regulatory system.
Volcanic and Seismic Activity
Tuffen (2010) writes, “there is growing evidence that past changes in the thickness of ice covering volcanoes have affected their eruptive activity.” He states, “the rate of volcanic activity in Iceland accelerated by a factor of 30–50 following the last deglaciation at approximately 12 ka (Maclennan et al., 2002)” and “analyses of local and global eruption databases have identified a statistically significant correlation between periods of climatic warming associated with recession of ice and an increase in the frequency of eruptions (Jellinek et al., 2004; Nowell et al., 2006; Huybers and Langmuir, 2009).” Thus he asks the next logical question: “Will the current ice recession provoke increased volcanic activity and lead to increased exposure to volcanic hazards?”
In response to his self-interrogation, Tuffen—a researcher at the Lancaster Environment Centre of Lancaster University in the United Kingdom—proceeds to “analyze our current knowledge of how ice thickness variations influence volcanism” and to “identify several unresolved issues that currently prevent quantitative assessment of whether activity is likely to accelerate in the coming century.”
At the conclusion of his review and analysis, Tuffen finds “ice unloading may encourage more explosive eruptions” but “melting of ice and snow may decrease the likelihood and magnitude of meltwater floods.” On the other hand, he writes, there is (1) “uncertainty about the time scale of volcanic responses to ice unloading,” (2) “poor constraint on how ice bodies on volcanoes will respond to twenty-first century climate change,” (3) “lack of data on how past changes in ice thickness have affected the style of volcanic eruptions and associated hazards,” and he notes (4) “the sensitivity of volcanoes to small changes in ice thickness or to recession of small glaciers on their flanks is unknown,” (5) “it is not known how localized ice withdrawal from stratovolcanoes [tall, conical volcanoes with many layers (strata) of hardened lava, tephra, and volcanic ash] will affect shallow crustal magma storage and eruption,” and (6) “broader feedbacks between volcanism and climate change remain poorly understood.”
The U.K. researcher concludes, “in order to resolve these problems, both new data and improved models are required.” In the data area, he states, “existing databases of known volcanic eruptions need to be augmented by numerous detailed case studies of the Quaternary eruptive history of ice-covered volcanoes.” Regarding models, he writes, “improved physical models are required to test how magma generation, storage and eruption at stratovolcanoes are affected by stress perturbations related to the waxing and waning of small-volume ice bodies on what is commonly steep topography.” Last, he suggests “feedbacks between the mass balance of ice sheets and glaciers and volcanic activity need to be incorporated into future earth-system models.” Hence, it is clear that much is known about the subject, but it is equally clear that much is still to be learned.
O. Molchanov (2010) of the Russian Academy of Sciences’ Institute of the Physics of the Earth, headquartered in Moscow, Russia, makes a case for the hypothesis that, at least partially, global climate changes and corresponding activity indices such as the ENSO phenomenon are induced by similar variations in seismicity. Molchanov (1) calculates the cumulative annual seismic energy released by large earthquake events originating from depths of 0 to 38 km, based on data archived by the U.S. Geological Survey for the 35-year time interval of 1973–2008 for various earthquake activity zones spread across the tropical and western Pacific—including the Chilean subduction zone; the Tonga-Kermadec zone; the Sunda, Philippine, and Solomon Sea zones; and the Mariana, Japan, and Kuril-Kamchatka zones—and (2) compares the then-evident periodicity of seismic energy production with that of sea surface temperature oscillations that occurred over the same 35-year period within the Niño zones 1+2 (0–10°S, 90–80°W), 3 (5°N–5°S, 150–90°W), and 4 (5°N–5°S, 160°E–150°W).
It was first determined that the “climate indices show expected ENSO variation” and “amazingly,” as Molchanov describes it, the earthquake indices demonstrate “similar quasi-ENSO variations.” So the next question was obviously: which is the action and which is the reaction? From a number of other factors, the Russian researcher concludes it is “more probable” that earthquake activity is “forcing the ENSO variation in the climate” than vice versa.
In concluding his paper, Molchanov states, “trends in the climate and seismic variations are similar to each other” and “it is rather probable that the climate ENSO effect is at least partially induced by seismicity with a time lag of about 1.5 years,” leaving it up to others to further study and debate the issue.
Carbon Sequestration
Lin et al. (2010) observe that “most models predict that climate warming will increase the release of carbon dioxide from the terrestrial biosphere into the atmosphere, thus triggering positive climate-terrestrial carbon feedback which leads to a warmer climate.” However, they state the “stimulation of biomass accumulation and net primary productivity of terrestrial ecosystems under rising temperature (Rustad et al., 2001; Melillo et al., 2002; Luo et al., 2009) may enhance carbon sequestration and attenuate the positive feedback between climate warming and the terrestrial biosphere.”
In an effort to find out which view is correct, Lin et al. conducted a meta-analysis of pertinent data from 127 individual studies published before June 2009, in order to determine whether the overall impact of a substantial increase in the air’s CO2 concentration on terrestrial biomass production would likely be positive or negative.
The three scientists report that for the totality of terrestrial plants included in their analysis, “warming significantly increased biomass by 12.3%” and there was a “significantly greater stimulation of woody (+26.7%) than herbaceous species (+5.2%).” They also found the warming effects on plant biomass production “did not change with mean annual precipitation or experimental duration” and “other treatments, including CO2 enrichment, nitrogen addition, drought, and water addition, did not alter warming responses of plant biomass.” Given such findings, the Chinese researchers conclude, “results in this and previous meta-analyses (Arft et al., 1999; Rustad et al., 2001; Dormann and Woodin, 2002; Walker et al., 2006) have revealed that warming generally increases terrestrial plant biomass, indicating enhanced terrestrial carbon uptake via plant growth and net primary productivity.” Thus, we can logically expect that (1) the ongoing rise in the air’s CO2 content will soften its own tendency to increase global temperatures, while simultaneously (2) enhancing Earth’s terrestrial vegetation with greater growth rates and biomass production, both in the agricultural arena and throughout the planet’s many natural ecosystems.
In another study, Geibert et al. (2010) write, “the Southern Ocean (SO) plays a key role in modulating atmospheric CO2 via physical and biological processes,” but “over much of the SO, biological activity is iron-limited,” which restricts the SO’s ability to do its job in this regard. However, they note “new in situ data from the Antarctic zone south of Africa in a region centered at ~20°E–25°E reveal a previously overlooked region of high primary production.” They sought to learn the cause of this anomalous production, which is an integral part of the globe’s deep-ocean carbon transferal system, whereby massive quantities of CO2-carbon recently absorbed from the atmosphere are photosynthetically incorporated into phytoplanktonic biomass, which either directly or indirectly—via marine food chains—is transported to the bottom layers of the sea, where it experiences long-term separation from the atmosphere.
Based on data obtained from expedition ANT XX/2 to the Weddell Gyre (WG) that took place from 24 November 2002 to 23 January 2003—carried out on the icebreaker RV Polarstern—Giebert et al. acquired “an in situ biogeochemical data set to complement indirect information from modeling and remote sensing techniques.” This dataset included multiple water samples for analyses of nutrients, oxygen, phytoplankton species identification and pigment and chlorophyll-a concentration, as well as for measurements of particulate matter, temperature, salinity, and the radionuclides 234Th and 238U.
The 11 researchers—from Germany, New Zealand, South Africa, and the United Kingdom—determined that “sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the WG,” where a sharp transition to warmer waters causes melting of ice that contains significant amounts of iron previously deposited upon it by aeolian transport of iron-rich dust. As the larger icebergs penetrate deeper into the sea, the researchers note, “they are exposed to warmer waters even during winter, when sea ice is present and growing,” which means the “continuous melting of icebergs in winter will lead to rising fresher and potentially iron-enriched waters from below, in the immediate vicinity of icebergs,” which meltwater “would spread under the sea ice as a thin lens of fresher water, where it can refreeze due to its comparatively low salinity, and it can undergo processes of sorption and biological uptake.” This hypothesis, in their words, “is consistent with maxima of iron concentrations in the lowermost parts of sea ice prior to the onset of spring melting (Lannuzel et al., 2007).” Thus, they conclude, “this melting hot spot causes an enhanced input of iron and salinity-driven stratification of the surface waters,” which are the ideal conditions for sustaining the “intense phytoplankton blooms” that characterize the waters they studied.
With respect to the significance of their work, Geibert et al. state their findings “imply that future changes in sea-ice cover and dynamics could have a significant effect on carbon sequestration in the SO.” If those changes included enhanced melting of Antarctic sea ice and icebergs, such as climate alarmists claim will occur, the planet’s deep-ocean carbon transferal system would shift into a higher gear and effectively sequester greater amounts of CO2-carbon from the atmosphere, reducing its rate of rise and thereby reducing the strength of the CO2 greenhouse effect.
Janssens et al. (2010) write that “atmospheric deposition of reactive nitrogen, originating mainly from fossil-fuel burning and artificial fertilizer applications, has increased three- to five-fold over the past century” and “in many areas of the globe, nitrogen deposition is expected to increase further.” This phenomenon stimulates plant growth and the uptake of carbon from the atmosphere, contributing to climate change mitigation. They state that Magnani et al. (2007) demonstrated nitrogen deposition to be “the dominant driver of carbon sequestration in forest ecosystems,” although there has been what they describe as “intense debate” about the magnitude and sustainability of the phenomenon and its underlying mechanisms.
In an effort designed to further explore the subject, Janssens et al. conducted “a meta-analysis of measurements in nitrogen-addition experiments, and a comparison of study sites exposed to elevated or background atmospheric nitrogen deposition.” The work of the 15 scientists revealed, in their words, that “nitrogen deposition impedes organic matter decomposition, and thus stimulates carbon sequestration, in temperate forest soils where nitrogen is not limiting microbial growth.” What is more, they find “the concomitant reduction in soil carbon emissions is substantial,” being “equivalent in magnitude to the amount of carbon taken up by trees owing to nitrogen fertilization.”
For those worried about the prospect of CO2-induced global warming, these findings should be good news, for in the concluding sentence of their paper, Janssens et al. state, “the size of the nitrogen-induced inhibition of below-ground respiration is of the same order of magnitude as the forest carbon sink.” And in the concluding sentence of their paper’s introduction, they state, “this effect has not been included in current carbon-cycle models,” suggesting that when it is included, it will contribute much to “climate change mitigation.”
In one final study of note, Blok et al. (2010) write of “fears” that if Earth’s permafrost thaws, “much of the carbon stored will be released to the atmosphere,” as will great quantities of the greenhouse gas methane (further exacerbating warming), as is claimed is already happening—and at an accelerating rate—by many climate alarmists, such as Al Gore in his 21 March 2007 testimony before the United States Senate’s Environment & Public Works Committee and Michael Mann and Lee Kump (2008) in their Dire Predictions book. Quite to the contrary, Blok et al. say “it has been demonstrated that increases in air temperature sometimes lead to vegetation changes that offset the effect of air warming on soil temperature,” citing the studies of Walker et al. (2003) and Yi et al. (2007) as specific examples of the phenomenon.
Thus, in an attempt to explore the subject within the context of real-world experimentation, Blok et al. conducted a study within the Kytalyk nature reserve in the Indigirka lowlands of northeastern Siberia (Russia), where they measured the thaw depth or active layer thickness (ALT) of the soil, the ground heat flux, and the net radiation in 10-meter-diameter plots either possessing or not possessing a natural cover of bog birch (Betula nana) shrubs, the latter of which set of plots had all B. nana shrubs removed from their native tundra vegetation in 2007.
The Dutch, Swiss, and Russian researchers report, “experimental B. nana removal had increased ALT significantly by an average of 9% at the end of the 2008 growing season, compared with the control plots,” which implies reduced warming in the shrub-dominated plots, and “in the undisturbed control plots with varying natural B. nana cover, ALT decreased with increasing B. nana cover,” also “showing a negative correlation between B. nana cover and ALT,” which again implies reduced warming in the more shrub-dominated plots.
Blok et al. say their results suggest “the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw” and the “increased shrub growth may thus partially offset further permafrost degradation by future temperature increases.” The six scientists write (1) permafrost temperature records “do not show a general warming trend during the last decade (Brown and Romanovsky, 2008), despite large increases in surface air temperature,” (2) during the decade before that, “data from several Siberian Arctic permafrost stations do not show a discernible trend between 1991 and 2000 (IPCC, 2007),” and (3) “a recent discovery of ancient permafrost that survived several warm geological periods suggests that vegetation cover may help protect permafrost from climate warming (Froese et al., 2008).” Last, they note this phenomenon “could feedback negatively to global warming, because the lower soil temperatures in summer would slow down soil decomposition and thus the amount of carbon released to the atmosphere.”
References
Arft, A.M., Walker, M.D., Gurevitch, J., Alatalo, J.M., Bret-Harte, M.S., Dale, M., Diemer, M., Gugerli, F., Henry, G.H.R., Jones, M.H., Hollister, R.D., Jonsdottir, I.S., Laine, K., Levesque, E., Marion, G.M., Molau, U., Molgaard, P., Nordenhall, U., Raszhivin, V., Robinson, C.H., Starr, G., Stenstrom, A., Stenstrom, M., Totland, O., Turner, P.L., Walker, L.J., Webber, P.J., Welker, J.M., and Wookey, P.A. 1999. Responses of tundra plants to experimental warming: meta-analysis of the international tundra experiment. Ecological Monographs 69: 491–511.
Blok, D., Heijmans, M.M.P.D., Schaepman-Strub, G., Kononov, A.V., Maximov, T.C., and Berendse, F. 2010. Shrub expansion may reduce summer permafrost thaw in Siberian tundra. Global Change Biology 16: 1296–1305.
Brown, J. and Romanovsky, V.E. 2008. Report from the International Permafrost Association: state of permafrost in the first decade of the 21st century. Permafrost and Periglacial Processes 19: 255¬–260.
Dormann, C.F. and Woodin, S.J. 2002. Climate change in the arctic: using plant functional types in a meta-analysis of field experiments. Functional Ecology 16: 4–17.
Froese, D.G., Westgate, J.A., Reyes, A.V., Enkin, R.J., and Preece, S.J. 2008. Ancient permafrost and a future, warmer Arctic. Science 321: 1648.
Geibert, W., Assmy, P., Bakker, D.C.E., Hanfland, C., Hoppema, M., Pichevin, L.E., Schroder, M., Schwarz, J.N., Stimac, I., Usbeck, R., and Webb, A. 2010. High productivity in an ice melting hot spot at the eastern boundary of the Weddell Gyre. Global Biogeochemical Cycles 24: 10.1029/2009GB003657.
Huybers, P. and Langmuir, C. 2009. Feedback between deglaciation, volcanism, and atmospheric CO2. Earth and Planetary Science Letters 286: 479–491.
IPCC. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, et al. Cambridge, UK: Cambridge University Press.
Jellinek, A.M., Manga, M., and Saar, M.O. 2004. Did melting glaciers cause volcanic eruptions in eastern California? Probing the mechanics of dike formation. Journal of Geophysical Research 109: 10.1029/2004JB002978.
Janssens, I.A., Dieleman, W., Luyssaert, S., Subke, J.-A., Reichstein, M., Ceulemans, R., Ciais, P., Dolman, A.J., Grace, J., Matteucci, G., Papale, D., Piao, S.L., Schulze, E.-D., Tang, J., and Law, B.E. 2010. Reduction of forest soil respiration in response to nitrogen deposition. Nature Geoscience 3: 315–322.
Lannuzel, D., Schoemann, V., de Jong, J., Tison, J.L., and Chou, L. 2007. Distribution and biogeochemical behavior of iron in the East Antarctic sea ice. Marine Chemistry 106: 18–32.
Lin, D., Xia, J., and Wan, S. 2010. Climate warming and biomass accumulation of terrestrial plants: a meta-analysis. New Phytologist 188: 187–198.
Luo, Y.Q., Sherry, R., Zhou, X.H., and Wan, S.Q. 2009. Terrestrial carbon-cycle feedback to climate warming: experimental evidence on plant regulation and impacts of biofuel feedstock harvest. Global Change Biology Bioenergy 1: 62–74.
Maclennan, J., Jull, M., McKenzie, D.P., Slater, L., and Gronvold, K. 2002. The link between volcanism and deglaciation in Iceland. Geochemistry, Geophysics, Geosystems 3: 10.1029/2001GC000282.
Magnani, F., Mencuccini, M., Borghetti, M., Berbigier, P., Berninger, F., Delzon, S., Grelle, A., Hari, P., Jarvis, P.G., Kolari, P., Kowalski, A.S., Lankreijer, H., Law, B.E., Lindroth, A., Loustau, D., Manca, G., Moncrieff, J.B., Rayment, M., Tedeschi, V., Valentini, R., and Grace, J. 2007. The human footprint in the carbon cycle of temperate and boreal forests. Nature 447: 848–850.
Mann, M.E. and Kump, L.R. 2008. Dire Predictions: Understand Global Warming. New York, NY: DK Publishing Inc.
Melillo, J.M., Steudler, P.A., Aber, J.D., Newkirk, K., Lux, H., Bowles, F.P., Catricala, C., Magill, A., Ahrens, T., and Morrisseau, S. 2002. Soil warming and carbon-cycle feedbacks to the climate system. Science 298: 2173–2176.
Molchanov, O. 2010. About climate-seismicity coupling from correlation analysis. Natural Hazards and Earth System Sciences 10: 299–304.
Nowell, D., Jones, C., and Pyle, D. 2006. Episodic quaternary volcanism in France and Germany. Journal of Quaternary Science 21: 645–675.
Rustad, L.E., Campbell, J.L., Marion, G.M., Norby, R.J., Mitchell, M.J., Hartley, A.E., Cornelissen, J.H.C., Gurevitch, J., and GCTE-NEWS. 2001. A meta-analysis of the response of soil respiration, net nitrogen mineralization, and aboveground plant growth to experimental ecosystem warming. Oecologia 126: 543–562.
Solomon, S., Rosenlof, K., Portmann, R., Daniel, J., Davis, S., Sanford, T., and Plattner, G.-K. 2010. Contributions of stratospheric water vapor to decadal changes in the rate of global warming. Science 327: 1219-1223.
Tuffen H. 2010. How will melting of ice affect volcanic hazards in the twenty-first century? Philosophical Transactions of the Royal Society A 368: 2535–2558.
Walker, D.A., Jia, G.J., Epstein, H.E., Raynolds, M.K., Chapin III, F.S., Copass, C., Hinzman, L.D., Knudson, J.A., Maier, H.A., Michaelson, G.J., Nelson, F., Ping, C.L., Romanovsky, V.E., and Shiklomanov, N. 2003. Vegetation-soil-thaw-depth relationships along a low-arctic bioclimate gradient, Alaska: synthesis of information from the ATLAS studies. Permafrost and Periglacial Processes 14: 103–123.
Walker, M.D., Wahren, C.H., Hollister, R.D., Henry, G.H.R., Ahlquist, L.E., Alatalo, J.M., Bret-Harte, M.S., Calef, M.P., Callaghan, T.V., Carroll, A.B., Epstein, H.E., Jonsdottir, I.S., Klein, J.A., Magnusson, B., Molaug, U., Oberbauer, S.F., Rewan, S.P., Robinson, C.H., Shaver, G.R., Suding, K.N., Thompson, C.C., Tolvanen, A., Totland, O., Turner, P.L., Tweedie, C.E., Webber, P.J., and Wookey, P.A. 2006. Plant community responses to experimental warming across the tundra biome. Proceedings of the National Academy of Sciences USA 103: 1342–1346.
Yi, S., Woo, M., and Arain, M.A. 2007. Impacts of peat and vegetation on permafrost degradation under climate warming. Geophysical Research Letters 34: 10.1029/2007GL030550.
