Chapter 2 Planetary Machinery : The Dynamics of the Earth System Prior to Significant Human Influence

1. Chapter 2 PlanetaryMachinery: The Dynamics ofthe Earth System Prior toSignificantHumanInfluence

2. 2.1 The natural dynamics of the Earth System © Springer-Velarg Berlin Heidelberg 2005 Fig 2.1. Chapter 2 focus: Earth System functioning prior to significant human influence Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 12.

3. 2.2 New Insights in Temporal Variability of the Earth System

4. 2.2.1 The long-term envelope of natural self regulation Fig. 2.2. Natural variability in Earth System functioning, from top to bottom: historic measurements of glacial ice accumulation rates, with insets focusing on the Younger Dryas cold interval and the very rapid termination of the last glaciation (adapted from Jacobson et al. 2000) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 13.

5. 2.2.2 Milennial scale oscillations and abrupt changes Box 2.1. The Ice Record ofAtmosphericGreenhouse Trace Gases: RellabilityandDating D. Raynaud – T. Blunier Air trapped in glaciers and ice sheets is unique as it provides a clear record of the changes in greenhouse trace gas (C02, CH4, N20) levels during the past. Not all glaciers and ice sheets provide an equally reliable record of greenhouse gas concentrations. Where melting occurs, gas content and gas composition may be altered by chemical reactions taking place in aquatic systems or by physical gas exchange between the gaseous and the aquatic sections. Under dry and cold conditions of polar areas, essentially in Antarctica and Greenland, the top layer of the ice sheets (the first 50 to 130 m) results from the compaction of the surface snow through sintering. In this porous firn layer air readily enters the open spaces and records essentially the same composition as the atmosphere. Below this zone the air in the firn is static and mixes only by molecular diffusion. An equilibrium between molecular diffusion and gravitational settling is reached for each gas component (Craig et al. 1988; Schwander 1989). As a consequence, the air, just before being trapped at the base of the firn column, dates back several decades due to the slow diffusion through the firn pores and has a composition that departs slightly from the atmosphere because of the gravitational fractionation. The magnitude of this fractionation is well known, allowing an accurately corrected ice core record to be constructed. Physi- or chemi-sorption of gases (especially CO2) at the surface of the snow and firn grains, and subsequent expulsion of the attached gas molecules after recrystallisation of the grains in the ventilated top layer of firn may induce uncertainty into ice records of trace gases. Selective fractionation of the atmospheric ratios may also occur during the last stage of the closing of channels leading to the bubble close-off (Bender 2002). However, this effect does not significantly affect the concentrations of major trace gases. Despite these possibilities, no significant modifications of greenhouse trace gas concentrations during the trapping phase have been identified. This is demonstrated by the consistency between trace gas concentrations measured in air from the firn and the gas record directly measured in the atmosphere (Battle et al. 1996; Etheridge et al. 1996) and the generally good match of atmospheric and ice core data (Fig. 2.3). Slow chemical reactions may alter CO2 concentrations after the gas has been trapped in ice. This has been observed in Greenland where high concentrations of impurities in the ice may lead to significant in situ CO2 production via acid-carbon­ate interactions and oxidation of organic material (Anklin et al. 1997; Delmas 1993; Haan and Raynaud 1998). Antarctic records provide the most reliable data of changes in global atmospheric CO2 (Raynaud et al.1993). Carbon dioxide measurements made several years apart on the same core show no significant changes. Antarctic results are consistent between sites to within a few parts per million by volume despite the coring sites having different ice accumulation rates, temperatures and concentrations of impurities. At depth, air bubbles progressively disappear and air hydrates form as the ice molecular structure encapsulates the air molecules in the so-called brittle zone (in which recovered ice commonly contains a high density of cracks and fractures). Results obtained from the brittle zone of a single ice core have to be considered with caution as the presence of air hydrates in the deeper parts of long ice cores may induce artifacts in the record. However, multi site data may be used with more confidence as the brittle zone usually does not have the same age in cores from different sites. Providing that appropriate extraction procedures are used, the agreement between records from different sites or measurements performed on the same core several years after the initial measurements confidently indicates that there are no significant artifacts linked with the air-hydrate occurrence in ice (Raynaud et al.1993). Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 14.

6. 2.2.2 Milennial scale oscillations and abrupt changes Bacterial activity has the potential to alter trace gas composition and its isotopic signature. In polar regions the bacterial concentration is low and bacterially induced alteration of the trace gas composition has yet to be confirmed. However, polar ice cores sporadically show high N2O values that may originate from in situ bacterial production (Fluckiger et al. 1999; Sowers 2001) but the significance of any resultant bacterial alteration of the record has yet to be demonstrated. Dating ice-core records presents challenges. As a consequence of the air trapping process, the air bubbles found at the bottom of the firn column were closed off at different times. Consequently a given ice sample does not have an exact age reflecting its last contact with the atmosphere, but rather an age distribution. The width of the age distribution is as low as seven years at high accumulation/high temperature sites but can be several centuries for Antarctic low accumulation/low temperature sites (Schwander and Stauffer 1984). Furthermore, because the enclosure process occurs 50 to 130 m below surface, the gas is younger than the surrounding ice and the difference in age between ice and gas depends on the temperature and accumulation rate at the site. It can vary between a few hundred to a few thousand years under present day conditions and becomes larger under ice age conditions. A critical question in global change science is the establishment of the extent to which anthropogenic atmospheric changes over the last few centuries have been unprecedented over the last 400000 years. The record of atmospheric gas composition is smoothed during the air trapping process. Since in the case of the Vostok record this smoothing averages over centuries, it may be questioned whether an anthropogenic signal can be observed in the Vostok data. A simulation to obtain a smoothed Vostok-like record of the present anthropogenic CO2 increase (Raynaud et al. 2003) shows that such an increase would be imprinted in the record through a CO2 peak reaching concentrations higher than 315 ppmv with a very slow return toward the pre-industrial level. Such a CO2 signal is not visible in the Vostok record (Fig. 2.4), although the time resolution of the record does not exclude a pulse-like atmospheric CO2 signal of a few decades duration with concentrations as high as today. However, this would require both a large carbon release within a few decades (of the order of 200 Gt C) and an equally large and rapid uptake. Such an oscillation is not compatible with the present understand­ing of the global carbon cycle. An important question is whether the time resolution of the ice record is precise enough to resolve the leads or lags between greenhouse gases and climate signals. The main uncertainties in this respect arise in connection with the age differences between enclosed air and the surrounding ice. In regard to the onsets of the last two glacial-inter­glacial transitions, the best-resolved records indicate an uncertainty of about hundred to a few hundred years and an Antarctic warming leading the CO2 increase by a few hundred years (Monnin et al. 2001; Caillon et al. 2003). In the case of rapid signals like those of the Dansgaard/Oeschger events (cf. Sect. 2.2.2), the uncertainty in age difference is reduced to 10-20 years (Leuenberger et al.1999; Severinghaus et al. 1998). Despite the uncertainties and caveats discussed above, ice­core data provide an excellent record of past changes; the record can be used with confidence and provides the most direct and accurate evidence for past atmospheric change yet obtained. The atmospheric greenhouse gas record meas­ured in ice cores is a smoothed temporal record whose accuracy is currently of the order of ±5 ppmv for CO2 and ±10 ppbv for CH4. Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 14 - 15.

7. 2.2.2 Milennial scale oscillations and abrupt changes Fig. 2.3. Greenhouse trace gas records since AD 1700 (adapted from Raynaud et al. 2003). The ice core measurements overlap with direct atmospheric measurements in the contemporary period (solid lines) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 14.

8. 2.2.2 Milennial scale oscillations and abrupt changes Fig. 2.4. Simulation of the minimum smoothed Vostok-like CO2, record (in grey) that would result from the hypothetical incorporation of the present anthropogenic CO2, increase (in black) in an ice core record (Raynaud et al. 2003) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 15.

9. 2.2.2 Milennial scale oscillations and abrupt changes Fig. 2.5. Ice accumulation and oxygen isotope (interpreted as temperature) records from the GISP2 (central Greenland) ice core for the period between the present and 18000 years ago (Alley et al. 1993; Alverson and Oldfield 2000), showing the abrupt climate shift at the termination of the Younger Dryas cold event some 11600 years ago. In this record the event is manifested as a warming estimated to be as much as 15°C, accompanied by a doubling in annual precipitation volume, that occurred in less than a decade © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 15.

10. 2.2.2 Milennial scale oscillations and abrupt changes Fig. 2.6. Low latitude expression of millennia scale climate oscillations taken from GISP2 oxygen isotopes, Santa Barbara basin (Site 893) bioturbation index and high-frequency variations in the CaC03 record of 70KL (Behl and Kennett 1996). Comparison of site 893 bioturbation index and benthic foraminiferal 6180 records with 6180 ice time series from GISP2, showing the excellent correlation of site 893 anoxia (lamination) events to 16 of 17 of the warm interstadials of GISP2. Bioturbation index is presented as a 49 cm (ca. 300-400 years) running average to dampen high-frequency variation and to match the resolution of the GISP2 record. Chronologies for GISP2 and site 893 were independ­ently derived. Radiocarbon age control points (+) and SPECMAP data used for the site 893 age model are shown to the right. Numbers in 0 refer to standard data of the SPECMAP stratigraphy. The base of each core interval in Hole 893A is indicated by arrows to the left © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 16.

11. 2.2.3 Climate Variability in Interglacial Periods Fig. 2.7. Inter-hemispheric phasing of the Antarctic Cold Reversal and the Younger Dryas and the timing of the Antarctic Cold Reversal and the atmospheric CO2 increase with respect to the Younger Dryas event, as deduced from the CH4 synchronisation, the isotopic records of the GRIP, Byrd and Vostok ice cores, together with the CO2 record from Byrd (Blunier et al. 1998) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 17.

12. 2.2.3 Climate Variability in Interglacial Periods • Fig. 2.8. • The end of the Younger Dryas in the GISP2 ice core from central Greenland (Alley 2000). Shown are selected curves illustrating the possible flickering behaviour near the transition: snow accumulation in mice yr-1(orange); electrical conductivity, ECM current in microamps (red); insoluble­particulate concentration in number ml-1(green); soluble­calcium concentration in ppb (blue). The main step at the end of the Younger Dryas falls between 1677 and 1678 m depth, between the two probable flickers indicated by the vertical lines at 1676.9 and 1678.2 m depth © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 17.

13. 2.2.3 Climate Variability in Interglacial Periods Fig. 2.9. Snow accumulation and iso­topically inferred temperature records in the Greenland GISP2 ice core and a temperature record derived from oxygen isotope measurements of fossil shells in the sediments of Lake Ammersee, southern Germany (Von Grafenstein et al. 1998), showing a major climatic instability event that occurred around 8200 years ago, during the Holocene. The event was large both in magnitude, as reflected by a temperature signal in Greenland of order 5°C, and in its geographical extent, as indicated by the close correlation of the signal in these two locations. The dramatic event is also seen in the methane record from Greenland, indicating possible major shifts in hydrology and land cover in lower latitudes © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 18.

14. 2.2.3 Climate Variability in Interglacial Periods Fig.2.10. Changes in lake level over the past 15 000 years in an east to west transect of lakes in the northern monsoon domain of Africa (Gasse 2000), showing lake level variations as much as 100 metres, an indication of large changes in the regional hydrological balance © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 19.

15. 2.2.3 Climate Variability in Interglacial Periods © Springer-Velarg Berlin Heidelberg 2005 Fig.2.11. Multiyear drought recon­structed from tree rings: a a severe drought through much of the central USA centred around 1820, surpass­ing in extent and severity the so-called Dust Bowl of the 1930S; b Palmer Drought Severity Index grid derived from optimally interpolated tree ring chronologies; and c time series of drought as recorded in tree rings for the period 1200-1994, with a correlation with instrumental data of 0.77 on an annual basis and 0.86 on a smoothed, inter-decadal basis over the period 1895-1994 (Cook et al. 1998; NOAA NESDIS drought variability data: http://www.ngdc.noaa.gov/paleo/drought.html) Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 20.

16. 2.2.3 Climate Variability in Interglacial Periods Fig. 2.12. Changes over time in climate teleconnection patterns between the high latitudes and the tropics: records of sea surface temperature and precipitation, showing close correlation after 1900 but anti-correlation prior to 1900 (GWK Moore et al. 2001) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 21.

17. 2.2.3 Climate Variability in Interglacial Periods Fig. 2.13a. Evolutionary spectral analysis of sea surface temperature estimates as recorded in a coral from Mariana Atoll in the equatorial Pacific Ocean (Urban et al. 2000). Colours show how sea surface tem­peratures (related to EI Nino /La Nina conditions) have varied over time. In recent years this oscillation has been centred on a 4-year period but in the nineteenth century the oscillation occurred only once every 10 years; the shift from low to high frequencies took place early in the twentieth century © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.13b. Long-term ENSO variability during the Holocene (Moy et al. 2002). In this ENSO record in a laminated lake sediment sequence from Laguna Pallcacocha, south Ecuador, spanning the whole of the Holocene, ENSO events have been identified from the presence of light coloured, clastic laminae that, for the recent period, correspond with documented moderate to strong ENSO occurrences. The graph expresses the changing frequency of ENSO as events per overlapping hundred-year window. The horizontal line represents the level above which variance in the ENSO frequency band occurs. There is no record of variance within the ENSO band before 7000 calendar years before present, after which an irregular, pulsed increase occurs leading to peak ENSO activity some 1200 years ago Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 21.

18. 2.2.3 Climate Variability in Interglacial Periods Fig. 2.14. Examples of past temperature (Petit et al. 1999; Dansgaard et al. 1993) and hydrological (Gasse 2000; Verschuren et al. 2000; Urban et al. 2000) variability on different timescales as derived from palaeo-proxy measurements. Changes can occur over a few years, as in the case of ENSO events, or over millions of years, as in the case of evolution and Milankovitch cycles © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 22.

19. 2.2.4 Temporal Variability in the Biota Fig. 2.15. Long-term trend in biodiversity (Wilson 1992). The arrows indicate major extinction events. Biodiversity is represented here by families of marine organisms, not total number of species © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 23.

20. 2.2.4 Temporal Variability in the Biota © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.16. Lake Victoria sediment-core variations in a magnetic susceptibility (after Johnson et al.1996) and b lake water 180 (Beuning et al. 1998) to illustrate the early Holocene refilling and overflowing of the lake Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 24.

21. 2.3.1 Biogeophysical Processes Box 2.2. Biogeophysical Effects of Vegetation on Climate Richard Betts Vegetation can affect climate through its influence on the physical characteristics of the land surface. These characteristics determine the inputs and outputs of energy, water and momentum to/from the atmosphere at its lower boundary, and hence can exert major influences on both local and global climates. The fraction of solar radiation reflected away by the surface (the surface albedo) is strongly determined by the nature of the vegetation cover. A forested landscape generally absorbs a greater fraction of incident radiation than open land, partly due to darker tree foliage and partly because the complex canopy structure traps light through multiple reflections within the canopy. This effect is accentuated in snowy conditions - lying snow can entirely cover short vegetation and produce a bright, highly reflective surface, whereas snow falling on a forest may be shed from the canopy, leaving the dark foliage exposed. Even a snow-loaded canopy maintains a low albedo because of multiple internal reflections. Therefore, compared to unforested land, a forested surface will typically be warmed more by a given incident flux of solar radiation. Water falling as precipitation may be intercepted by a vegetation canopy and re-evaporated, or may reach the surface, infiltrate into the soil profile, be absorbed by plant roots and evaporated through leaves back to the atmosphere (transpiration). Evaporation and transpiration provide a recycling of water back to the atmosphere, and in some continental regions this can be a significant proportion of the supply of moisture for precipitation. Evaporation and transpiration also carry energy away from the surface in the form of latent heat, which would otherwise be available as sensible heat. The extent of this partitioning of the available energy affects temperature near the surface, with greater evaporation and transpiration providing a cooling influence. Moisture in the atmosphere also affects the radiation budget, either both directly through the action of water vapour as a greenhouse gas and indirectly through its influence on cloud formation. The rates of evaporation and transpiration are highly dependent on the nature of vegetation cover. On the whole, woody vegetation may provide a greater flux of moisture to the atmosphere by capturing more water on the canopy and by accessing soil moisture to a greater depth. In warm, moist regions, the cooling effect of enhanced evaporation and transpiration by forests generally exerts a greater influence on surface temperatures than the warming by decreased surface albedo. Tropical forests therefore cool their local climate and can enhance their local rainfall. As well as depending on vegetation type and climatic conditions, transpiration can be directly affected by the atmospheric CO2 concentration. Stomata, the microscopic pores in leaf surfaces which allow CO2 to diffuse in for photosynthesis, open less wide under elevated CO2 (Field et al.1995). This means that less water is lost by transpiration through the stomata, which may lead to a warmer surface climate and reduce moisture recycling. Vegetation type can also influence the frictional effect of the landscape on low-level air flow. A rougher land surface increases turbulence, which affects the fluxes of heat and moisture and also modifies windspeed. Large-scale changes in surface roughness can modify synoptic-scale atmospheric circulations and hence influence weather patterns. Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 25.

22. 2.3 New Insights into the Role of Biology in Earth System Functioning

23. 2.3.1 Biogeophysical Processes A change in climate is determined by the forcing (the initial perturbation) and also any feedbacks present in the system. Biophysical effects of vegetation can feature in both of these components of climate change. Feedbacks on climate change forced by the enhanced greenhouse effect can occur from changes in the coverage and distribution of different vegetation types. For example, the onset of past ice ages may have been accelerated by shrinkage of the boreal forests providing a positive feedback on cooling by increasing the surface albedo (Gallimore and Kutzbach 1996). Precipitation reductions in tropical areas could be exacerbated by decreased evaporation and transpiration due to reduced forest cover. Vegetation may also be involved in direct anthropogenic forcings of climate change. Historical deforestation in the mid­latitudes exerted a direct cooling influence through increased surface albedo (Fig. 2.17), comparable with the climatic forcings exerted by anthropogenic aerosols and changes in greenhouse gases other than carbon dioxide and methane (IPCC 2001). Afforestation and reforestation activities intended to mitigate climate change through carbon sequestration may therefore also exert warming influences through decreased surface albedo (Betts 2000). A further forcing involving vegetation is the effect of CO2 on stomatal opening and transpiration. Since CO2 can warm surface temperatures directly through this mechanism, this means that increasing CO2 can actually exert two forcings on the climate system: (i) as a greenhouse gas, and (ii) as an influence on plant physiology (Sellers et al.1996). This may increase the difficulty of comparing the effects of CO2 with other greenhouse gases. © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.17. Simulated changes in near­surface air temperature (C) due to past deforestation (Betts 2001). Apparent changes over Antarctica are not statistically significant Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 25.

24. 2.3.1 Biogeophysical Processes © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.18. Differences in near-surface temperatures during northern hemisphere winter (December, January, February) between mid­Holocene climate and present-day climate simulated by Ganopolski et al. (1998). The authors used different model configurations: the atmosphere-only model (ATM), the atmosphere-ocean model (ATM + OCE), the atmosphere-vegetation model (ATM + VEG) and the fully coupled model (ATM + OCE + VEG). In ATM, ATM + OCE and ATM + VEG, present-day land-surface and ocean-surface conditions, depending on the model configuration, are used Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 26.

25. 2.3.2 Biogeochemical Processes © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.19. aElectronmicrograph of E. huxleyi (image: Helge Thomsen, Danish Fisheries Research Institute) and b coastal zone color scanner satellite image of a Coccolithophorid bloom (white area) in surface waters of the northern North Sea and Skagerrak (image: Thorkild Aarup, IOC) Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 28.

26. 2.3.2 Biogeochemical Processes Fig. 2.20. Initial paradigm for ecophysiological research in the Global Change and Terrestrial Ecosystems (GCTE) core project of the IGBP (Steffen et al. 1992) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 29.

27. 2.3.2 Biogeochemical Processes Table 2.1. Structure as a mediating factor in the ecosystem response to changes in production-related processes under a doubling of atmospheric CO2> showing the wide range of structural processes that can either attenuate or amplify the process response (Shugart 1997) Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 30.

28. 2.3.2 Biogeochemical Processes Fig. 2.21. Results of three model experiments based on the averaged output of six dynamic global vegetation models driven by dynamic CO2 and climate scenarios from 1861 to 2099 with a loa-year stabilisation period (no further changes in CO2 and climate) beyond 2099 (Cramer et al. 2001): a simulated vegetation distribution at the end of the twentieth and the twenty-first centuries and after 100 additional years of stabilised CO2 and climate; and b model average net ecosystem productivity (NEP) at 2000,2100 and the end of the stabilisation period (2100 + 100) from the three model experiments (mean of last 10 years in each century). The final column shows the sum of NEP from the climate-only and CO2,only experiments © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 31.

29. 2.3.2 Biogeochemical Processes © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.22. Estimation of the amount of carbon emitted to the atmosphere from forest fires in Canada compared to fossil fuel emissions over the last 40 years (adapted from Amiro et al. 2003) Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 32.

30. 2.3.2 Biogeochemical Processes Fig. 2.23. Variability in annual CO2 growth rate, estimated globally and measured at two observing stations, and global fossil fuel emissions. Also shown is the Southern Oscillation Index (SOl), an indicator of ENSO events (R. J. Francey, pers. camm.) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 33.

31. 2.3.3 The Role of Biodiversity © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.24. Responses of a total or (b and c) aboveground plant biomass to experimental manipulations of (a and b) plant species richness or c functional group richness in grasslands: a in Minnesota (Tilman 2001); b across Europe (Hector et al. 1999) and c in California (Hooper and Vitousek 1997) (Loreau et al. 2001). Points for a and b are data for individual plots. In b different regression slopes are shown for eight sites to focus on between-location differences rather than the general log-linear relationship. Filled squares and line 1, Germany; filled circles and line 2, Portugal; filled triangles and line 3, Switzerland; filled diamonds and line 4, Greece; open squares and line 5, Ireland; open circles and line 6, Sweden; open diamonds and line 7, Sheffield (UK); open diamonds and line 8, Silwood Park (UK). Symbols in c correspond to functional groups and their combinations: B, bare ground; E, early-season annuals; L, late­season annuals; P, perennial bunchgrasses; N, nitrogen fixers Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 34.

32. 2.3.3 The Role of Biodiversity Fig. 2.25. Observed decreases in variability of ecosystem processes as species richness increases (Loreau et al. 2001): a adjusted coefficient of temporal variation (CV) of annual total plant biomass (g m-z) over 11 years for plots differing in number of species in experimental and natural grasslands in Minnesota (Tilman 1999) (the correlation of variation in soil nitrogen with species richness in these plots precludes the interpretation of increased stability as a pure diversity effect (Huston 1997), although the diversity effect remained significant even after controlling for potential confounding vari­ables (Tilman et al. 1996)); b standard deviation (SD) of COzflux (in microlitres per 18 hours) from microbial microcosms (McGrady­Steed et al. 1997) (in these data temporal variability in response to diversity is confounded with between-replicate variability) © Springer-Velarg Berlin Heidelberg 2005 Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 35.

33. 2.3.3 The Role of Biodiversity © Springer-Velarg Berlin Heidelberg 2005 Fig. 2.26. a Hypothesised relationship between diversity-productivity patterns driven by environmental conditions across sites; and b the local effect of species diversity on productivity (Loreau et al. 2001). In a comparative data often indicate a unimodal relationship between diversity and productivity driven by changes in environmental conditions. That is, the environment drives changes in the productivity of terrestrial ecosystems, which in turn affects the biological diversity of the system. In b experimental variation of species richness under three specific sets of environmental conditions (thin lines) show increasing productivity with increasing diversity for all environmental conditions. The experiments also produce a pattern of decreasing between-replicate variance and increasing mean response with increasing diversity, as indicated by the shaded areas (scatter of responses) around the thin, curved regression lines Source: Steffen at al., 2004. Global Change and the Earth System. A planet under preassure. IGBP Book Series. Springer Verlag Chapter 2: Planetary Machinery: The dynamics of the earth system prior to significant human influence pg. 35.