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The main attraction here are the paperlists but every once in a while I have also published some articles. Some of them are such that I have a need to dig them up occasionally. It’s getting increasingly difficult to find them from the backpages so I have gathered them all to one page. So, here it is, the article page. You can give feedback on the article page here.

Papers on permafrost thawing

This is a list of papers on permafrost thawing. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (April 5, 2012): Fedotov et al. (2012) added.

Permafrost thawing inferred from Arctic lake sediment of the Taimyr Peninsula, East Siberia, Russia – Fedotov et al. (2012) “The objective of this paper is to reconstruct permafrost thawing at 71°N of Arctic Siberia during the termination of the Little Ice Age and the subsequent Recent Warming. Sediment samples from Lake Dalgan of the Taimyr Peninsula were analysed by high-resolution X-ray fluorescence spectroscopy at 1 mm scan resolution, and Fourier-transform infrared techniques. Intense permafrost thawing was calculated from the level of terrigenous and leached matter supplied by meltwater into the lakes. We defined three episodes of increased permafrost thawing during the last 170 years. The first maximum of permafrost melting occurred from 1870 to 1880, the second episode was from 1900 to 1930 and the third began from 1960 and continues to date. During these periods, maxima of permafrost melting occurred with a specific time lag following temperature maxima.” A.P. Fedotova, M.A. Phedorin, A.S. Suvorov, M.S. Melgunov & T.V. Khodzher, International Journal of Environmental Studies, Volume 69, Issue 1, 2012, DOI:10.1080/00207233.2012.619879.

Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis – Lyon et al. (2009) “Permafrost thawing is likely to change the flow pathways taken by water as it moves through arctic and sub-arctic landscapes. The location and distribution of these pathways directly influence the carbon and other biogeochemical cycling in northern latitude catchments. While permafrost thawing due to climate change has been observed in the arctic and sub-arctic, direct observations of permafrost depth are difficult to perform at scales larger than a local scale. Using recession flow analysis, it may be possible to detect and estimate the rate of permafrost thawing based on a long-term streamflow record. We demonstrate the application of this approach to the sub-arctic Abiskojokken catchment in northern Sweden. Based on recession flow analysis, we estimate that permafrost in this catchment may be thawing at an average rate of about 0.9 cm/yr during the past 90 years. This estimated thawing rate is consistent with direct observations of permafrost thawing rates, ranging from 0.7 to 1.3 cm/yr over the past 30 years in the region.” S. W. Lyon, G. Destouni, R. Giesler, C. Humborg, M. Mörth, J. Seibert, J. Karlsson, and P. A. Troch, Hydrol. Earth Syst. Sci., 13, 595-604, 2009, doi:10.5194/hess-13-595-2009. [Full text]

Responses of permafrost to climate change and their environmental significance, Qinghai-Tibet Plateau – Cheng & Wu (2007) “In this paper we summarize recent research in geocryological studies carried out on the Qinghai-Tibet Plateau that show responses of permafrost to climate change and their environmental implications. Long-term temperature measurements indicate that the lower altitudinal limit of permafrost has moved up by 25 m in the north during the last 30 years and between 50 and 80 m in the south over the last 20 years. Furthermore, the thickness of the active layer has increased by 0.15 to 0.50 m and ground temperature at a depth of 6 m has risen by about 0.1° to 0.3°C between 1996 and 2001. Recent studies show that freeze-thaw cycles in the ground intensify the heat exchange between the atmosphere and the ground surface. The greater the moisture content in the soil, the greater is the influence of freeze-thaw cycling on heat exchange. The water and heat exchange between the atmosphere and the ground surface due to soil freezing and thawing has a significant influence on the climate in eastern Asia. A negative correlation exists between soil moisture and heat balance on the plateau and the amount of summer precipitation in most regions of China. A simple frozen soil parameterization scheme was developed to simulate the interaction between permafrost and climate change. This model, combined with the NCAR Community Climate Model 3.6, is suitable for the simulation of permafrost changes on the plateau. In addition, permafrost degradation is one of the main causes responsible for a dropping groundwater table at the source areas of the Yangtze River and Yellow River, which in turn results in lowering lake water levels, drying swamps and shrinking grasslands.” Cheng, G., and T. Wu (2007), J. Geophys. Res., 112, F02S03, doi:10.1029/2006JF000631. [Full text]

A projection of severe near-surface permafrost degradation during the 21st century – Lawrence & Slater (2005) “The current distribution and future projections of permafrost are examined in a fully coupled global climate model, the Community Climate System Model, version 3 (CCSM3) with explicit treatment of frozen soil processes. The spatial extent of simulated present-day permafrost in CCSM3 agrees well with observational estimates – an area, excluding ice sheets, of 10.5 million km2. By 2100, as little as 1.0 million km2 of near-surface permafrost remains. Freshwater discharge to the Arctic Ocean rises by 28% over the same period, largely due to increases in precipitation that outpace increases in evaporation, with about 15% of the rise directly attributable to melting ground ice. Such large changes in permafrost may provoke feedbacks such as activation of the soil carbon pool and a northward expansion of shrubs and forests.” Lawrence, D. M., and A. G. Slater (2005), Geophys. Res. Lett., 32, L24401, doi:10.1029/2005GL025080. [Full text]

Permafrost Thaw Accelerates in Boreal Peatlands During Late-20th Century Climate Warming – Camill (2005) “Permafrost covers 25% of the land surface in the northern hemisphere, where mean annual ground temperature is less than 0°C. A 1.4–5.8 °C warming by 2100 will likely change the sign of mean annual air and ground temperatures over much of the zones of sporadic and discontinuous permafrost in the northern hemisphere, causing widespread permafrost thaw. In this study, I examined rates of discontinuous permafrost thaw in the boreal peatlands of northern Manitoba, Canada, using a combination of tree-ring analyses to document thaw rates from 1941–1991 and direct measurements of permanent benchmarks established in 1995 and resurveyed in 2002. I used instrumented records of mean annual and seasonal air temperatures, mean winter snow depth, and duration of continuous snow pack from climate stations across northern Manitoba to analyze temporal and spatial trends in these variables and their potential impacts on thaw. Permafrost thaw in central Canadian peatlands has accelerated significantly since 1950, concurrent with a significant, late-20th-century average climate warming of +1.32 °C in this region. There were strong seasonal differences in warming in northern Manitoba, with highest rates of warming during winter (+1.39 °C to +1.66 °C) and spring (+0.56 °C to +0.78 °C) at southern climate stations where permafrost thaw was most rapid. Projecting current warming trends to year 2100, I show that trends for north-central Canada are in good agreement with general circulation models, which suggest a 4–8 °C warming at high latitudes. This magnitude of warming will begin to eliminate most of the present range of sporadic and discontinuous permafrost in central Canada by 2100.” Philip Camill, Climatic Change, Volume 68, Numbers 1-2, 135-152, DOI: 10.1007/s10584-005-4785-y.

Spatial and temporal variability in active layer thickness over the Russian Arctic drainage basin – Zhang et al. (2005) “Changes in active layer thickness (ALT) over northern high-latitude permafrost regions have important impacts on the surface energy balance, hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystems as a whole. This study examines the 20th century variations of ALT for the Ob, Yenisey, and Lena River basins. ALT is estimated from historical soil temperature measurements from 17 stations (1956–1990, Lena basin only), an annual thawing index based on both surface air temperature data (1901–2002) and numerical modeling (1980–2002). The latter two provide spatial fields. Based on the thawing index, the long-term average (1961–1990) ALT is about 1.87 m in the Ob, 1.67 in the Yenisey, and 1.69 m in the Lena basin. Over the past several decades, ALT over the three basins shows positive trends, but with different magnitudes. Based on the 17 stations, ALT increased about 0.32 m between 1956 and 1990 in the Lena. To the extent that results based on the soil temperatures represent ground “truth,” ALT obtained from both the thawing index and numerical modeling is underestimated. It is widely believed that ALT will increase with global warming. However, this hypothesis needs further refinement since ALT responds primarily to summer air temperature while observed warming has occurred mainly in winter and spring. It is also shown that ALT exhibits complex and inconsistent responses to variations in snow cover.” Zhang, T., et al. (2005), J. Geophys. Res., 110, D16101, doi:10.1029/2004JD005642.

Accelerated thawing of subarctic peatland permafrost over the last 50 years – Payette et al. (2004) “In this study we provide a quantification of the main patterns of change of a subarctic peatland caused by permafrost decay monitored between 1957 and 2003. Up-thrusting of the peatland surface due to permafrost aggradation during the Little Ice Age resulted in the formation of an extensive peat plateau that gradually fragmented into residual palsas from the 19th century to the present. Only about 18% of the original surface occupied by permafrost was thawed in 1957, whereas only 13% was still surviving in 2003. Rapid permafrost melting over the last 50 years caused the concurrent formation of thermokarst ponds and fen-bog vegetation with rapid peat accumulation through natural successional processes of terrestrialization. The main climatic driver for accelerated permafrost thawing was snow precipitation which increased from 1957 to present while annual and seasonal temperatures remained relatively stable until about the mid-1990s when annual temperature rose well above the mean. Contrary to current expectations, the melting of permafrost caused by recent climate change does not transform the peatland to a carbon-source ecosystem as rapid terrestrialization exacerbates carbon-sink conditions and tends to balance the local carbon budget.” Payette, S., A. Delwaide, M. Caccianiga, and M. Beauchemin (2004), Geophys. Res. Lett., 31, L18208, doi:10.1029/2004GL020358. [Full text]

Permafrost thaw and destabilization of Alpine rock walls in the hot summer of 2003 – Gruber et al. (2004) “Exceptional rockfall occurred throughout the Alps during the unusually hot summer of 2003. It is likely related to the fast thermal reaction of the subsurface of steep rock slopes and a corresponding destabilization of ice-filled discontinuities. This suggests that rockfall may be a direct and unexpectedly fast impact of climate change. Based upon our measurements in Alpine rock faces, we present model simulations illustrating the distribution and degradation of permafrost where the summer of 2003 has resulted in extreme thaw. We argue that hotter summers predicted by climate models for the coming decades will result in reduced stability of many alpine rock walls.” Gruber, S., M. Hoelzle, and W. Haeberli (2004), Geophys. Res. Lett., 31, L13504, doi:10.1029/2004GL020051. [Full text]

Thawing sub-arctic permafrost: Effects on vegetation and methane emissions – Christensen et al. (2004) “Ecosystems along the 0°C mean annual isotherm are arguably among the most sensitive to changing climate and mires in these regions emit significant amounts of the important greenhouse gas methane (CH₄) to the atmosphere. These CH₄ emissions are intimately related to temperature and hydrology, and alterations in permafrost coverage, which affect both of those, could have dramatic impacts on the emissions. Using a variety of data and information sources from the same region in subarctic Sweden we show that mire ecosystems are subject to dramatic recent changes in the distribution of permafrost and vegetation. These changes are most likely caused by a warming, which has been observed during recent decades. A detailed study of one mire show that the permafrost and vegetation changes have been associated with increases in landscape scale CH₄ emissions in the range of 22–66% over the period 1970 to 2000.” Christensen, T. R., T. Johansson, H. J. Åkerman, M. Mastepanov, N. Malmer, T. Friborg, P. Crill, and B. H. Svensson (2004), Geophys. Res. Lett., 31, L04501, doi:10.1029/2003GL018680.

Thermokarst ponds as indicators of the former distribution of palsas in Finnish Lapland – Luoto & Seppälä (2003) “Thermokarst ponds resulting from thawing of palsas were mapped in a 95 km-long transect area in northern Finland. The spatial distribution of thermokarst was related to palsa distribution and to geographical variables using GIS techniques and multivariate spatial modelling. In our 3370 km2 study area, the former distribution of palsas was about three times larger than the present one. This indicates that the formation and thawing of permafrost are not in balance; palsas are collapsing and melting more often than palsas are forming.” Miska Luoto, Matti Seppälä, Permafrost and Periglacial Processes, Volume 14, Issue 1, pages 19–27, January/March 2003, DOI: 10.1002/ppp.441.

Recent decay of a single palsa in relation to weather conditions between 1996 and 2000 in Laivadalen, northern Sweden – Zuidhoff (2002) “This study presents the decay of a small palsa complex between 1996 and 2000 in Sweden’s southernmost major palsa bog. The outline of the palsa was mapped during three summers in 1996, 1999 and 2000 and an automatic weather station measured air temperature, precipitation, snow depth, wind speed and wind direction between 1997 and 2000. The decay of the palsa was enormous in the dome–shaped part of the palsa complex: the height decreased during the observation period from 2.3 m to 0.5 m. In 2000, the palsa dome had almost totally disappeared: only some peat blocks in a palsa pond were left. The decay of the palsa was complex with a number of degradational processes, of which the main processes were block erosion, thermokarst and wind erosion. Thermal melting has occurred along the edges of the palsa and possibly below the frozen core of the palsa since 1998/99. Wind erosion was observed during summer and the maximum estimated deflation was 80 cm. The decay of the palsa dome was especially large between 1999 and 2000, probably due to a high mean annual temperature, high summer precipitation and the warming influence of the large pond surrounding the palsa. The present climate in the palsa bog with a mean annual temperature of −0.8°C is not favourable for palsa development and maintenance, despite a strong wind regime which can provide suitable conditions for snowdrift.” Frieda Sjoukje Zuidhoff, Geografiska Annaler: Series A, Physical Geography, Volume 84, Issue 2, pages 103–111, August 2002, DOI: 10.1111/1468-0459.00164.

Permafrost Degradation and Ecological Changes Associated with a WarmingClimate in Central Alaska – Jorgenson et al. (2001) “Studies from 1994–1998 on the TananaFlats in central Alaska reveal that permafrostdegradation is widespread and rapid, causing largeshifts in ecosystems from birch forests to fens andbogs. Fine-grained soils under the birch forest areice-rich and thaw settlement typically is 1–2.5 mafter the permafrost thaws. The collapsed areas arerapidly colonized by aquatic herbaceous plants,leading to the development of a thick, floatingorganic mat. Based on field sampling of soils,permafrost and vegetation, and the construction of aGIS database, we estimate that 17% of the study area(263,964 ha) is unfrozen with no previous permafrost,48% has stable permafrost, 31% is partiallydegraded, and 4% has totally degraded. For thatportion that currently has, or recently had,permafrost (83% of area), 42% has been affected bythermokarst development. Based on airphoto analysis,birch forests have decreased 35% and fens haveincreased 29% from 1949 to 1995. Overall, the areawith totally degraded permafrost (collapse-scar fensand bogs) has increased from 39 to 47% in 46 y. Based on rates of change from airphoto analysis andradiocarbon dating, we estimate 83% of thedegradation occurred before 1949. Evidence indicatesthis permafrost degradation began in the mid-1700s andis associated with periods of relatively warm climateduring the mid-late 1700s and 1900s. If currentconditions persist, the remaining lowland birchforests will be eliminated by the end of the nextcentury.” M.Torre Jorgenson, Charles H. Racine, James C. Walters and Thomas E. Osterkamp, Climatic Change, Volume 48, Number 4, 551-579, DOI: 10.1023/A:1005667424292. [Full text]

Long-Term Monitoring of Permafrost Change in a Palsa Peatland in Northern Quebec, Canada: 1983-1993 – Laberge & Payette (1995) “Changes in the spatial distribution of permafrost in the Ouiatchouane palsa peatland (northern Quebec) were monitored from 1957 to present, using aerial photographs taken in 1957 (starting date) and three field surveys in 1973, 1983, and 1993, respectively. Between 1983 and 1993, palsa degradation occurred at about the same rate as between 1957 and 1983, although minor differences in rate of permafrost decay during the three periods (1957-1973, 1973-1983, 1983-1993) may be attributed in part to misidentification of marginal permafrost landforms. Permafrost degradation appeared to be influenced by height of individual palsas and their location within the peatland. Since 1983, thermokarst ponds have been progressively invaded by sedges and Sphagnum, a situation promoting successional peatland development and palsa formation as suggested by the presence of a small incipient palsa. Although the main geomorphic process at work is palsa degradation, permafrost aggradation is possible under present climatic conditions.” Marie-Josée Laberge and Serge Payette, Arctic and Alpine Research, Vol. 27, No. 2 (May, 1995), pp. 167-171. [Full text]

Effects of Changes in Groundwater Level on Palsas in Central Iceland – Thórhallsdóttir (1994) “In the central highland of Iceland, the creation of a small lake partly flooded a dried-up palsa bog. The palsas upshore experienced raised summer soilwater levels and inundation during winter. The effects of these changed hydrological conditions on 5 palsas were monitored over a period of 5 years. All the palsas increased in height, from 14 to 43 cm, with a mean of 27 cm. A core through one palsa showed that while it was formed by segregation ice, the observed height increases were caused by the addition of a layer of pure ice.” Thóra Ellen Thórhallsdóttir, Geografiska Annaler. Series A, Physical Geography, Vol. 76, No. 3 (1994), pp. 161-167.

Distribution and thawing of permafrost in the southern part of the discontinuous permafrost zone in Manitoba – Thie (1974) “This study was carried out to evaluate the environmental factors which influence the distribution and collapse of perennially frozen peats in the southern part of the discontinuous permafrost zone in Manitoba. The changes in permafrost bodies were measurebdy means of aerial photography carried out over a period of 20 years. About 25 per cent of the once occurring permafrost is still present. Melting appears to have exceeded aggradation of permafrost since about 150 years B.P. Two types of collapse were noticed: peripheral collapse around very small permafrost bodies; and a central collapse for the larger bodies. The amount of collapse has varied from 0 to 30 metres horizontally in a 20 year period.” Thie, J., Arctic, 27, 189– 200. [Full text]

Papers on Rossby wave breaking

This is a list of papers on the effect of Rossby wave breaking and its effect to climate and weather. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Links between Rossby Wave Breaking and the North Atlantic Oscillation–Arctic Oscillation in Present-Day and Last Glacial Maximum Climate Simulations – Rivière et al. (2010) “Upper-tropospheric Rossby wave–breaking processes are examined in coupled ocean–atmosphere simulations of the Last Glacial Maximum (LGM) and of the modern era. LGM statistics of the Northern Hemisphere in winter, computed from the Paleoclimate Modeling Intercomparison Project Phase II (PMIP2) dataset, are compared with those from preindustrial simulations and from the 40-yr ECMWF Re-Analysis (ERA-40). Particular attention is given to the role of wave-breaking events in the North Atlantic Oscillation (NAO) for each simulation. Anticyclonic (AWB) and cyclonic (CWB) wave-breaking events during LGM are shown to be less and more frequent, respectively, than in the preindustrial climate, especially in the Pacific. This is consistent with the slight equatorward shift of the eddy-driven jets in the LGM runs. The most remarkable feature of the simulated LGM climate is that it presents much weaker latitudinal fluctuations of the eddy-driven jets. This is accompanied by less dispersion in the wave-breaking events. A physical interpretation is provided in terms of the fluctuations of the low-level baroclinicity at the entrance of the storm tracks. The NAO in the preindustrial simulations and in ERA-40 is characterized by strong latitudinal fluctuations of the Atlantic eddy-driven jet as well as by significant changes in the nature of the wave breaking. During the positive phase, the eddy-driven jet moves to the north with more AWB events than usual and is well separated from the subtropical African jet. The negative phase exhibits a more equatorward Atlantic jet and more CWB events. In contrast, the LGM NAO is less well marked by the latitudinal vacillation of the Atlantic jet and for some models this property disappears entirely. The LGM NAO corresponds more to acceleration–deceleration or extension–retraction of the Atlantic jet. The hemispheric point of view of the Arctic Oscillation exhibits similar changes.” Rivière, Gwendal, Alexandre Laîné, Guillaume Lapeyre, David Salas-Mélia, Masa Kageyama, 2010, J. Climate, 23, 2987-3008, doi: 10.1175/2010JCLI3372.1.

On the upper tropospheric formation and occurrence of high and thin cirrus clouds during anticyclonic poleward Rossby wave breaking events – Eixmann et al. (2010) “Ground-based lidar measurements and balloon soundings were employed to examine the dynamical link between anticyclonic Rossby wave breaking and cirrus clouds from 13 to 15 February 2006. For this event, an air mass with low Ertel’s potential vorticity appeared over Central Europe. In the tropopause region, this air mass was accompanied with both an area of extreme cold temperatures placed northeastward, and an area of high specific humidity, located southwestward. ECMWF analyses reveal a strong adiabatic northeastward and upward transport of water vapour within the warm conveyor belt on the western side of the ridge over Mecklenburg, Northern Germany. The backscatter lidar at Kühlungsborn (54.1°N, 11.8°E) clearly identified cirrus clouds at between 9 and 11.4 km height. In the tropopause region high-vertical resolution radiosoundings showed layers of subsaturated water vapour over ice but with a relative humidity over ice >80%. Over Northern Germany radiosondes indicated anticyclonically rotating winds in agreement with backward trajectories of ECMWF analyses in the upper troposphere, which were accompanied by a relatively strong increase of the tropopause height on 14 February. Based on ECMWF data the strong link between the large-scale structure, updraft and ice water content was shown.” RONALD EIXMANN, DIETER H.W. PETERS, CHRISTOPH ZÜLICKE, MICHAEL GERDING, ANDREAS DÖRNBRACK, Tellus A, Volume 62, Issue 3, pages 228–242, May 2010, DOI: 10.1111/j.1600-0870.2010.00437.x. [Full text]

The Role of Rossby Wave Breaking in Shaping the Equilibrium Atmospheric Circulation Response to North Atlantic Boundary Forcing – Strong & Magnusdottir (2010) “The role of Rossby wave breaking (RWB) is explored in the transient response of an atmospheric general circulation model to boundary forcing by sea ice anomalies related to the North Atlantic Oscillation (NAO). When the NCAR Community Climate Model, version 3, was forced by an exaggerated sea ice extent anomaly corresponding to one arising from a positive NAO, a localized baroclinic response developed and evolved into a larger-scale equivalent barotropic pattern resembling the negative polarity of the NAO. The initial baroclinic response shifted the phase speeds of the dominant eddies away from a critical value equal to the background zonal flow speed, resulting in significant changes in the spatial distribution of RWB. The forcing of the background zonal flow by the changes in RWB accounts for 88% of the temporal pattern of the response and 80% of the spatial pattern of the zonally averaged response. Although results here focus on one experiment, this “RWB critical line mechanism” appears to be relevant to understanding the equilibrium response in a broad class of boundary forcing experiments given increasingly clear connections among the northern annular mode, jet latitude shifts, and RWB.” Strong, Courtenay, Gudrun Magnusdottir, 2010, J. Climate, 23, 1269-1276. [Full text]

Planetary Wave Breaking and Tropospheric Forcing as Seen in the Stratospheric Sudden Warming of 2006 – Coy et al. (2009) “The major stratospheric sudden warming (SSW) of January 2006 is examined using meteorological fields from Goddard Earth Observing System version 4 (GEOS-4) analyses and forecast fields from the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics, High Altitude (NOGAPS-ALPHA). The study focuses on the upper tropospheric forcing that led to the major SSW and the vertical structure of the subtropic wave breaking near 10 hPa that moved low tropical values of potential vorticity (PV) to the pole. Results show that an eastward-propagating upper tropospheric ridge over the North Atlantic with its associated cold temperature perturbations (as manifested by high 360-K potential temperature surface perturbations) and large positive local values of meridional heat flux directly forced a change in the stratospheric polar vortex, leading to the stratospheric subtropical wave breaking and warming. Results also show that the anticyclonic development, initiated by the subtropical wave breaking and associated with the poleward advection of the low PV values, occurred over a limited altitude range of approximately 6–10 km. The authors also show that the poleward advection of this localized low-PV anomaly was associated with changes in the Eliassen–Palm (EP) flux from equatorward to poleward, suggesting an important role for Rossby wave reflection in the SSW of January 2006. Similar upper tropospheric forcing and subtropical wave breaking were found to occur prior to the major SSW of January 2003.” Coy, Lawrence, Stephen Eckermann, Karl Hoppel, 2009, J. Atmos. Sci., 66, 495-507. [Full text]

The Role of Tropospheric Rossby Wave Breaking in the Pacific Decadal Oscillation – Strong & Magnusdottir (2009) “The leading pattern of extratropical Pacific sea surface temperature variability [the Pacific decadal oscillation (PDO)] is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic (cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. The RWB patterns that are relevant to the PDO are closely tied to El Niño–Southern Oscillation, the Pacific–North American pattern, and the northern annular mode. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Niño anomalies emerge in summer and modify circulation patterns that act over several months to force sea surface temperature anomalies in the extratropical Pacific during late winter or early spring. Leading patterns of RWB account for a significant fraction of PDO interannual variability for any month of the year. A multilinear model is developed in which the January mean PDO index for 1958–2006 is regressed upon the leading principal components of cyclonic and anticyclonic RWB from the immediately preceding winter and summer months (four indexes in all), accounting for more than two-thirds of the variance.” Strong, Courtenay, Gudrun Magnusdottir, 2009, J. Climate, 22, 1819-1833. [Full text]

Role of Rossby wave breaking in the west Pacific teleconnection – Rivière (2009) “The dynamical link between the west Pacific (WP) teleconnection and Rossby wave breaking (RWB) events is analyzed during winter months using ERA40 reanalysis data from 1957 to 2002. The WP pattern which is characterized by latitudinal fluctuations of the Pacific jet is closely linked to variations in the nature of RWB, similarly to the North Atlantic Oscillation. More anticyclonic (cyclonic) RWBs than usual occur in the Central Pacific during the positive (negative) WP phase when the Pacific jet is more to the north (south) than usual. Time lag daily composites show that before the occurrence of an anticyclonic RWB event, WP anomalies close to the positive phase preexist that are then reinforced during the breaking leading to an increase of the WP index even few days after the peak of the event. Cyclonic RWB events have similar but opposite effects on the WP pattern since they trigger and maintain the negative phase. Finally, a comparison with the RWB anomalies of the Pacific-North American (PNA) teleconnection is provided.” Rivière, G. (2010), Geophys. Res. Lett., 37, L11802, doi:10.1029/2010GL043309.

Modulation of tropical convection by breaking Rossby waves – Allen et al. (2009) “This work discusses observations of both the convective-inhibiting and convective-promoting properties associated with Rossby waves that break in the extratropics and extend into the tropics. Two tropical drought periods—times of reduced tropical cloudiness and rainfall—were observed during mid to late November 2005 over a wide area of north-west Australia, with an observed eruption of a nearby synoptic tropical cloud band in between times. Both convective inhibition and promotion appear to be linked to the descent of dry upper tropospheric air within a series of tropopause folds; convective inhibition was observed within the dry pool itself, whilst convective promotion was observed on the high moisture gradient at the leading edge of an advancing dry slot. A range of satellite images, surface rain gauges, radiosonde and ozonesonde data are used in conjunction with back trajectories and European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields to investigate the origins and dynamics associated with these convective events, showing each to be ultimately linked to breaking Rossby wave activity on the southern subtropical jet. Together, these observations support a growing number of studies linking midlatitude tropopause-level dynamics with the modulation of tropical deep convection, an influence that is poorly characterized when considering the climatology of tropical cloudiness and rainfall.” G. Allen, G. Vaughan, D. Brunner, P. T. May, W. Heyes, P. Minnis, J. K. Ayers, Quarterly Journal of the Royal Meteorological Society, Volume 135, Issue 638, pages 125–137, January 2009 Part A, DOI: 10.1002/qj.349.

Tropospheric Rossby Wave Breaking and the NAO/NAM – Strong & Magnusdottir (2008) “Objective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby waves is performed for the Northern Hemisphere (NH) winters of 1958–2006. A winter climatology of both anticyclonic and cyclonic Rossby wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective wave-breaking analysis method are provided in the appendix.” Strong, Courtenay, Gudrun Magnusdottir, 2008, J. Atmos. Sci., 65, 2861-2876, doi: 10.1175/2008JAS2632.1. [Full text]

How Rossby wave breaking over the Pacific forces the North Atlantic Oscillation – Strong & Magnusdottir (2008) “Anticyclonic Rossby wave breaking (RWB) over a well-defined, limited-area region of the east Pacific leads to the positive polarity of the North Atlantic Oscillation (NAO) by locally piling up wave activity where it may be advected downstream, resulting in increased wave activity flux and anticyclonic RWB over the subtropical Atlantic. A composite time series shows that Pacific RWB occurs several days prior to the Atlantic RWB and the peak of the NAO index. Following Pacific RWB, a channel of increased pseudomomentum flux extends from the Pacific wave breaking region, northeastward toward midlatitudes of eastern North America where pseudomomentum density accumulates for several days prior to moving eastward and leading to anticyclonic RWB over the Atlantic.” Strong, C., and G. Magnusdottir (2008), Geophys. Res. Lett., 35, L10706, doi:10.1029/2008GL033578. [Full text]

A New Rossby Wave–Breaking Interpretation of the North Atlantic Oscillation – Woollings et al. (2008) “This paper proposes the hypothesis that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wave–breaking events over the North Atlantic. These events lead to synoptic situations similar to midlatitude blocking that are referred to as high-latitude blocking episodes. A positive NAO is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic, unblocked situation. A negative NAO is a description of periods in which episodes occur frequently. A similar, but weaker, relationship exists between wave breaking over the Pacific and the west Pacific pattern. Evidence is given to support this hypothesis by using a two-dimensional potential-vorticity-based index to identify wave breaking at various latitudes. This is applied to Northern Hemisphere winter data from the 40-yr ECMWF Re-Analysis (ERA-40), and the events identified are then related to the NAO. Certain dynamical precursors are identified that appear to increase the likelihood of wave breaking. These suggest mechanisms by which variability in the tropical Pacific, and in the stratosphere, could affect the NAO.” Woollings, Tim, Brian Hoskins, Mike Blackburn, Paul Berrisford, 2008, J. Atmos. Sci., 65, 609-626. [Full text]

Long-term trends of synoptic-scale breaking Rossby waves in the Northern Hemisphere between 1958 and 2001 – Isotta et al. (2008) “Breaking synoptic-scale Rossby waves are frequent features of the upper troposphere and lower stratosphere (UTLS) which affect both global- and regional-scale dynamics. Furthermore, they directly influence ozone distribution through meridional transport of ozone-rich air towards the south and ozone-poor air towards the north. Here, trends in the frequency of these breaking waves are assessed by analysing a 44-year climatology (1958–2002) of potential vorticity (PV) streamers on isentropic surfaces from 310 to 350 K. These streamers are viewed as breaking Rossby waves, whereby stratospheric (tropospheric) streamers indicate southward (northward) breaking waves. Two complementary techniques are used to analyse the trends. First, linear trends are computed using the least-squares regression technique. Statistically significant linear trends are found to vary in location and magnitude between isentropic levels and the four seasons. In winter significant trends are detected in the eastern Pacific between 340 and 350 K. A positive trend of stratospheric streamers in the Tropics is related to an increase of total column ozone, whereas the positive trend of tropospheric streamers in the mid-latitudes is associated with a decrease of total ozone. Secondly, a nonlinear trend analysis is performed using the seasonal-trend decomposition procedure based on Loess (STL). With this technique, the low-frequency variability of the time series is analysed during the 44-year period. For instance, over the eastern Atlantic on 350 K, a phase of decreasing PV streamer frequencies in the 1950s and 1960s is followed by a positive streamer tendency after the 1970s. Additionally, trends of the zonal wind are investigated. One prominent outcome of this analysis is the observation that equatorial easterlies over the Atlantic are weakening. A dynamically meaningful link exists between the trends observed in both wind velocity and PV streamers. “ F. Isotta, O. Martius, M. Sprenger, C. Schwierz, International Journal of Climatology, Volume 28, Issue 12, pages 1551–1562, October 2008, DOI: 10.1002/joc.1647.

Linkage of atmospheric blocks and synoptic-scale Rossby waves: a climatological analysis – Altenhoff et al. (2008) “The link between atmospheric blocking and propagating and breaking synoptic-scale Rossby waves (termed PV streamers) are explored for the climatological period 1958–2002, using the ERA-40 re-analysis data. To this end, potential vorticity (PV) based climatologies of blocking and breaking waves are used, and features of the propagating waves is extracted from Hovmöller diagrams. The analyses cover the Northern Hemisphere during winter, and they are carried out for the Atlantic and Pacific basins separately. The results show statistically significant wave precursor signals, up to 5 d prior to the blocking onset. In the Atlantic, the precursor signal takes the form of a coherent wave train, emanating approximately 110° upstream of the blocking location. In the Pacific, a single long-lived (10 d) northerly velocity signal preludes the blocking onset. A spatial analysis is conducted of the location, frequency and form of breaking synoptic-scale Rossby waves, prior to the onset, during the lifetime and after the blocking decay. It reveals that cyclonic streamers are present to the southwest and anticyclonic streamers to the south and southeast, approximately 43% (36%) of the time in the Atlantic (Pacific) basin, and this is significantly above a climatological distribution.” ADRIAN M. ALTENHOFF, OLIVIA MARTIUS, MISCHA CROCI-MASPOLI, CORNELIA SCHWIERZ, HUW C. DAVIES, Tellus A, Volume 60, Issue 5, pages 1053–1063, October 2008, DOI: 10.1111/j.1600-0870.2008.00354.x.

Blocking and Rossby Wave Breaking on the Dynamical Tropopause in the Southern Hemisphere – Berrisford et al. (2007) “Rossby wave breaking on the dynamical tropopause in the Southern Hemisphere (the −2-PVU surface) is investigated using the ERA-40 dataset. The indication of wave breaking is based on reversal in the meridional gradient of potential temperature, and persistent large-scale wave breaking is taken as a strong indication that blocking may be present. Blocking in the midlatitudes is found to occur predominantly during wintertime in the Pacific and is most vigorous in the east Pacific, while during summertime, the frequency of blocking weakens and its extent becomes confined to the west Pacific. The interannual variability of blocking is found to be high. Wave breaking occurs most frequently on the poleward side of the polar jet and has some, but not all, of the signatures of blocking, so it is referred to as high-latitude blocking. In general, cyclonic wave breaking occurs on the poleward side of the polar jet, otherwise anticyclonic breaking occurs. However, at least in wintertime, wave breaking in the New Zealand/west to mid-Pacific sector between the polar and subtropical jets is a mixture between cyclonic and anticyclonic types. Together, episodes of wave breaking and enhanced westerly flow describe much of the variability in the seasonal Antarctic Oscillation (AnO) index and give a synoptic manifestation of it with a focus on the date line and Indian Ocean that is in agreement with the centers of action for the AnO. During summertime, anticyclonic wave breaking in the upper troposphere is also to be found near 30°S in both the Pacific and Atlantic, and appears to be associated with Rossby waves propagating into the subtropics from the New Zealand region.” Berrisford, P., B. J. Hoskins, E. Tyrlis, 2007, J. Atmos. Sci., 64, 2881-2898. [Full text]

A Seasonal Climatology of Rossby Wave Breaking in the 320–2000-K Layer – Hitchman & Huesmann (2007) “Differential advection in Rossby waves can lead to potential vorticity (PV; P) contours on isentropic surfaces folding over in latitude (P_y < 0) in a process called Rossby wave breaking (RWB). Exploring the properties of RWB may shed light on underlying dynamics and enable quantification of irreversible transport. A seasonal climatology of P_y and RWB statistics is presented for the 320–850-K layer using NCEP reanalysis data during 1979–2005 and for the 320–2000-K layer using the Met Office (UKMO) data during 1991–2003. A primary goal is to depict the spatial extent and seasonality of RWB maxima. This analysis shows seven distinct RWB regimes: poleward and equatorward of the subtropical westerly jets, poleward and equatorward of the stratospheric polar night jets, flanking the equator in the stratosphere and mesosphere, equatorward of subtropical monsoon anticyclones, and the summertime polar stratosphere. A striking PV gradient maximum exists at the equator throughout the layer 360–2000 K, flanked by subtropical RWB maxima, integral components of the Lagrangian cross-equatorial flow. Strong RWB occurs in the polar night vortex where β is small. Over the summer pole, strong poleward RWB associated with synoptic waves decays into small amplitude motions in the upper stratosphere, where heating gradients cause P_y < 0. The seven spatial regimes are linked to three different dynamical causes of reversals: wave breaking associated with westerly jets, a combined barotropic/inertial instability in cross-equatorial flow, and on the periphery of monsoon anticyclones." Hitchman, Matthew H., Amihan S. Huesmann, 2007, J. Atmos. Sci., 64, 1922-1940. [Full text]

Is the North Atlantic Oscillation a Breaking Wave? – Franzke et al. (2004) “Given the recent observational evidence that the positive (negative) phase of the North Atlantic Oscillation (NAO) is the remnant of anticyclonic (cyclonic) wave breaking, this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior. For this purpose, a hierarchy of different basic states (two- and three-dimensional) and initial perturbations are used. With the three-dimensional climatological flow as the basic state, it is found that initial perturbations located equatorward (poleward) and upstream of the climatological Atlantic jet lead to wave breaking similar to that of the positive (negative) NAO phase. Consistently, analysis of observational data indeed shows that the Pacific storm track is displaced equatorward (poleward) prior the onset of the positive (negative) NAO phase. This result suggests that the latitudinal position of the Pacific storm track plays an important role for determining the phase of the NAO. Sensitivity experiments show that individual life cycles resemble each other only within the NAO region, but have large case-to-case variability outside of the NAO region. Calculations with zonally symmetric basic states fail to produce wave breaking of the correct spatial and temporal scale, underscoring the dynamical significance of the three-dimensional climatological flow.” Franzke, Christian, Sukyoung Lee, Steven B. Feldstein, 2004, J. Atmos. Sci., 61, 145-160. [Full text]

Synoptic View of the North Atlantic Oscillation – Benedict et al. (2004) “This article investigates the synoptic characteristics of individual North Atlantic Oscillation (NAO) events by examining the daily evolution of the potential temperature field on the nominal tropopause (the 2-PVU surface). This quantity is obtained from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis dataset for the winter season. For both phases, the NAO is found to originate from synoptic-scale waves. As these waves evolve into the low-frequency NAO pattern, they break anticyclonically for the positive phase and cyclonically for the negative phase. The results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the NAO. Throughout the NAO events, for both phases, the NAO is maintained by the successive breaking of upstream synoptic-scale waves. When synoptic-scale disturbances are no longer present, mixing processes play an important role in the NAO decay. As in other recent studies of the NAO, it is found that these individual NAO events complete their life cycle in a time period of about two weeks. Additional differences between the wave breaking characteristics of the two NAO phases are found. For the positive NAO phase, anticyclonic wave breaking takes place in two regions: one over the North Atlantic and the other near the North American west coast. For the negative NAO phase, on the other hand, there is a single breaking wave confined to the North Atlantic. An explanation based on kinematics is given to account for this difference.” Benedict, James J., Sukyoung Lee, Steven B. Feldstein, 2004, J. Atmos. Sci., 61, 121-144. [Full text]

A New Perspective on Blocking – Pelly & Hoskins (2003) “It is argued that the essential aspect of atmospheric blocking may be seen in the wave breaking of potential temperature (θ) on a potential vorticity (PV) surface, which may be identified with the tropopause, and the consequent reversal of the usual meridional temperature gradient of θ. A new dynamical blocking index is constructed using a meridional θ difference on a PV surface. Unlike in previous studies, the central blocking latitude about which this difference is constructed is allowed to vary with longitude. At each longitude it is determined by the latitude at which the climatological high-pass transient eddy kinetic energy is a maximum. Based on the blocking index, at each longitude local instantaneous blocking, large-scale blocking, and blocking episodes are defined. For longitudinal sectors, sector blocking and sector blocking episodes are also defined. The 5-yr annual climatologies of the three longitudinally defined blocking event frequencies and the seasonal climatologies of blocking episode frequency are shown. The climatologies all pick out the eastern North Atlantic–Europe and eastern North Pacific–western North America regions. There is evidence that Pacific blocking shifts into the western central Pacific in the summer. Sector blocking episodes of 4 days or more are shown to exhibit different persistence characteristics to shorter events, showing that blocking is not just the long timescale tail end of a distribution. The PV–θ index results for the annual average location of Pacific blocking agree with synoptic studies but disagree with modern quantitative height field–based studies. It is considered that the index used here is to be preferred anyway because of its dynamical basis. However, the longitudinal discrepancy is found to be associated with the use in the height field index studies of a central blocking latitude that is independent of longitude. In particular, the use in the North Pacific of a latitude that is suitable for the eastern North Atlantic leads to spurious categorization of blocking there. Furthermore, the PV–θ index is better able to detect Ω blocking than conventional height field indices.” Pelly, J. L., B. J. Hoskins, 2003, J. Atmos. Sci., 60, 743-755. [Full text]

Papers on primary production and climate change

This is a list of papers on terrestrial net primary production and climate change. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009 – Zhao & Running (2010) “Terrestrial net primary production (NPP) quantifies the amount of atmospheric carbon fixed by plants and accumulated as biomass. Previous studies have shown that climate constraints were relaxing with increasing temperature and solar radiation, allowing an upward trend in NPP from 1982 through 1999. The past decade (2000 to 2009) has been the warmest since instrumental measurements began, which could imply continued increases in NPP; however, our estimates suggest a reduction in the global NPP of 0.55 petagrams of carbon. Large-scale droughts have reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased NPP in that area, counteracting the increased NPP over the Northern Hemisphere. A continued decline in NPP would not only weaken the terrestrial carbon sink, but it would also intensify future competition between food demand and proposed biofuel production.” Science 20 August 2010: Vol. 329. no. 5994, pp. 940 – 943, DOI: 10.1126/science.1192666.

Global potential net primary production predicted from vegetation class, precipitation, and temperature – Del Grosso et al. (2008) “Net primary production (NPP), the difference between CO2 fixed by photosynthesis and CO2 lost to autotrophic respiration, is one of the most important components of the carbon cycle. Our goal was to develop a simple regression model to estimate global NPP using climate and land cover data. Approximately 5600 global data points with observed mean annual NPP, land cover class, precipitation, and temperature were compiled. Precipitation was better correlated with NPP than temperature, and it explained much more of the variability in mean annual NPP for grass- or shrub-dominated systems (r² = 0.68) than for tree-dominated systems (r² = 0.39). For a given precipitation level, tree-dominated systems had significantly higher NPP (~100–150 g C·m^-2·yr^-1) than non-tree-dominated systems. Consequently, previous empirical models developed to predict NPP based on precipitation and temperature (e.g., the Miami model) tended to overestimate NPP for non-tree-dominated systems. Our new model developed at the National Center for Ecological Analysis and Synthesis (the NCEAS model) predicts NPP for tree-dominated systems based on precipitation and temperature; but for non-tree-dominated systems NPP is solely a function of precipitation because including a temperature function increased model error for these systems. Lower NPP in non-tree-dominated systems is likely related to decreased water and nutrient use efficiency and higher nutrient loss rates from more frequent fire disturbances. Late 20th century aboveground and total NPP for global potential native vegetation using the NCEAS model are estimated to be ~28 Pg and ~46 Pg C/yr, respectively. The NCEAS model estimated an ~13% increase in global total NPP for potential vegetation from 1901 to 2000 based on changing precipitation and temperature patterns.” Ecology, 89:2117—2126, doi:10.1890/07-0850.1. [Full text]

Europe-wide reduction in primary productivity caused by the heat and drought in 2003 – Ciais et al. (2005) “Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr^-1) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe’s primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.” Nature 437, 529-533 (22 September 2005) | doi:10.1038/nature03972. [Full text]

A Continuous Satellite-Derived Measure of Global Terrestrial Primary Production – Running et al. (2004) “Until recently, continuous monitoring of global vegetation productivity has not been possible because of technological limitations. This article introduces a new satellite-driven monitor of the global biosphere that regularly computes daily gross primary production (GPP) and annual net primary production (NPP) at 1-kilometer (km) resolution over 109,782,756 km² of vegetated land surface. We summarize the history of global NPP science, as well as the derivation of this calculation, and current data production activity. The first data on NPP from the EOS (Earth Observing System) MODIS (Moderate Resolution Imaging Spectroradiometer) sensor are presented with different types of validation. We offer examples of how this new type of data set can serve ecological science, land management, and environmental policy. To enhance the use of these data by nonspecialists, we are now producing monthly anomaly maps for GPP and annual NPP that compare the current value with an 18-year average value for each pixel, clearly identifying regions where vegetation growth is higher or lower than normal.” BioScience, June 2004, Vol. 54, No. 6, Pages 547–560, doi:10.1641/0006-3568(2004)054[0547:ACSMOG]2.0.CO;2. [Full text]

Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999 – Nemani et al. (2003) “Recent climatic changes have enhanced plant growth in northern mid-latitudes and high latitudes. However, a comprehensive analysis of the impact of global climatic changes on vegetation productivity has not before been expressed in the context of variable limiting factors to plant growth. We present a global investigation of vegetation responses to climatic changes by analyzing 18 years (1982 to 1999) of both climatic data and satellite observations of vegetation activity. Our results indicate that global changes in climate have eased several critical climatic constraints to plant growth, such that net primary production increased 6% (3.4 petagrams of carbon over 18 years) globally. The largest increase was in tropical ecosystems. Amazon rain forests accounted for 42% of the global increase in net primary production, owing mainly to decreased cloud cover and the resulting increase in solar radiation.” Science 6 June 2003: Vol. 300. no. 5625, pp. 1560 – 1563, DOI: 10.1126/science.1082750. [Full text]

Terrestrial net primary production estimates for 0.5° grid cells from field observations—a contribution to global biogeochemical modeling – Zhang et al. (2003) “Net Primary Production (NPP) is an important component of the carbon cycle and, among the pools and fluxes that make up the cycle, it is one of the steps that are most accessible to field measurement. While easier than some other steps to measure, direct measurement of NPP is tedious and not practical for large areas and so models are generally used to study the carbon cycle at a global scale. Nevertheless these models require field measurements of NPP for parameterization, calibration and validation. Most NPP data are for relatively small field plots that cannot represent the 0.5° × 0.5° grid cells that are commonly used in global scale models. Furthermore, technical difficulties generally restrict NPP measurements to aboveground parts and sometimes do not even include all components of aboveground NPP. Thus direct inter-comparison between field data obtained in different studies or comparison of these results with coarse resolution model outputs can be misleading. We summarize and present a series of methods that were used by original authors to estimate NPP and how and what we have done to prepare a consistent data set of NPP for 0.5 °grid cells for a range of biomes from these studies. The methods used for estimation of NPP include: (i) aggregation of fine-scale (plot or stand-level) vegetation inventory data to larger grid cells, (ii) mapping of grid cells and area weighting of field NPP observations in each mapped class, (iii) direct correlation of extensive data sets of ground measurements with remotely sensed spectral vegetation indices, (iv) local modeling of NPP using key independent variables, for which maps are available at the scale of the grid cell, and (v) regression analysis to link productivity with controlling environmental variables. For a few grid cells whose NPP were obtained for multiple years, temporal analysis was conducted. The grid cells are grouped to the biome level and are compared with existing compilations of field NPP and the results of the Miami potential NPP model. Mean NPP was similar to the well-known compilation of Whittaker and Likens, except for temperate evergreen needle-leaved forest, woodland, and shrubland. The grid cell datasets are a contribution to the International Geosphere-Biosphere Programme (IGBP) Data and Information System (DIS) Global Primary Production Data Initiative (GPPDI). The full dataset currently contains 3654 cells (including replicate measurements) developed from 15 studies representing NPP in croplands, sparse vegetation, shrub lands, grasslands, and forests worldwide. An edited subset consists of 2335 cells in which outliers were removed and all replicate measurements were averaged for each unique geographical location. Most of the data incorporated into GPPDI were wholly or partly developed by participants in the GPPDI, in addition to the present authors. These studies are gathered together here to provide a consistent account of the grid cell component of GPPDI and an analysis of the entire data set. The datasets have been deposited in an IGBP-DIS GPPDI database ( http://daacl.esd.ornl.gov/npq/GPPDI/Combined_GPPDI_des.html).” Global Change Biology, Volume 9, Number 1, January 2003 , pp. 46-64(19), DOI: 10.1046/j.1365-2486.2003.00534.x.

Terrestrial net primary productivity – A brief history and a new worldwide database – Scurlock & Olson (2002) “Consistent data on terrestrial net primary productivity (NPP) are urgently needed to constrain model estimates of carbon fluxes and hence to refine our understanding of ecosystem responses to climate change. The NPP data have been collected in a coordinated manner for the past 30 years, but comprehensive summaries are rare. We report on the development and availability of a global NPP database that is suitable for modeling of the terrestrial carbon cycle at global and regional scales, for validation of remote sensing data, and for other applications. These data were obtained from the literature on ecophysiological field work and from detailed consultation with the scientific community. Data on NPP, biomass, and associated environmental variables are now publicly available for 53 detailed study sites, of which more than half have data for belowground biomass or biomass dynamics. Aboveground NPP ranges from 35 to 2320 g m^–2a^–1 (dry matter) and total NPP from 182 to 3538 g m^–2a^–1. Well-known but previously unobtainable compilations of data, such as the “Osnabrück Data Set” and the International Biological Program (IBP) Woodlands Data Set, are also incorporated in this database. Preliminary exploration of relationships between NPP and mean annual precipitation and temperature suggests that the new 53-site data collection, as well as the Osnabrück and IBP data, are all consistent with the historic “Miami” statistical model. These data are available from the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC) for biogeochemical dynamics (see http://www.daac.ornl.gov/NPP/).” Environ. Rev. 10(2): 91–109 (2002), doi:10.1139/a02-002.

Net primary production in tropical forests: an evaluation and synthesis of existing field data – Clark et al. (2001) “Information on net primary production in tropical forests is needed for the development of realistic global carbon budgets, for projecting how these ecosystems will be affected by climatic and atmospheric changes, and for evaluating eddy covariance measurements of tropical forest carbon flux. However, a review of the database commonly used to address these issues shows that it has serious flaws. In this paper we synthesize the data in the primary literature on NPP in old-growth tropical forests to produce a consistent data set on NPP for these forests. Studies in this biome have addressed only a few NPP components, all aboveground. Given the limited scope of the direct field measurements, we sought relationships in the existing data that allow estimation of unmeasured aspects of production from those that are more easily assessed. We found a predictive relationship between annual litterfall and aboveground biomass increment. For 39 diverse tropical forest sites, we then developed consistent, documented estimates of the upper and lower bounds around total NPP to serve as benchmarks for calibrating and validating biogeochemical models with respect to this biome. We developed these estimates based on existing field measurements, current understanding of aboveground consumption and biogenic volatile organic carbon emissions, and our judgment that belowground production is bounded by the range 0.2–1.2 × ANPP (aboveground NPP). Across this broad spectrum of tropical forests (dry to wet, lowland to montane, nutrient-rich to nutrient-poor soils), our estimates of lower and upper bounds on total NPP range from 1.7 to 11.8 Mg C·ha^-1·yr^-1 (lower bounds) and from 3.1 to 21.7 Mg C·ha^-1·yr^-1 (upper bounds). We also showed that two relationships that have been used for estimating NPP (the Bray-Gorham relationship based on leaf litterfall and the Miami model based on temperature or precipitation) are not valid for the tropical forest biome.” Ecological Applications, 11:371—384, doi:10.1890/1051-0761(2001)011[0371:NPPITF]2.0.CO;2. [Full text]

Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components – Field et al. (1998) “Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.” Science 10 July 1998: Vol. 281. no. 5374, pp. 237 – 240, DOI: 10.1126/science.281.5374.237. [Full text]

Global Primary Production: A Remote Sensing Approach – Prince & Goward (1995) “A new model of global primary production (GLObal Production Efficiency Model, GLO-PEM), based on the production efficiency concept, is described. GLO-PEM is the first attempt to model both global net and gross primary production using the production efficiency approach and is unique in that it uses satellite data to measure both absorption of photosynthetically active radiation (APAR) and also the environmental variables that affect the utilization of APAR in primary production. The use of satellite measurements gives global, repetitive, spatially contiguous and time specific observations of the actual vegetation. GLO-PEM is based on physiological principles, in particular the amount of carbon fixed per unit absorbed photosynthetically active radiation ( epsilon ) is modelled rather than fitted using field observations. GLO-PEM is illustrated with the first available year (1987) of the 8 x 8 km resolution NOAA/NASA AVHRR land Pathfinder data set. The global net primary production, respiration and epsilon values obtained indicate that even the rather simple AVHRR provides a wealth of information relevant to biospheric monitoring. The algorithms and results presented indicate that there are significant possibilities of inferring biological and environmental variables using multispectral techniques that need to be explored if the new generation of satellite remote sensing systems is to be exploited productively.” Journal of Biogeography, Vol. 22, No. 4/5, Terrestrial Ecosystem Interactions with Global Change, Volume 2 (Jul. – Sep., 1995), pp. 815-835.

Terrestrial biogeochemical cycles: Global estimates with remote sensing – Schimel (1995) “The carbon and nitrogen cycles are crucial for understanding the changing Earth system, influencing atmospheric concentrations of greenhouse gases, primary productivity of the biosphere, and biogenic emissions of reactive trace species. The carbon budget of the terrestrial biosphere has attracted special attention because of its role in atmospheric changes in carbon dioxide. The terrestrial biosphere influences atmospheric CO₂ through three main modes: First, large, nearly balanced fluxes of CO₂ in photosynthesis and respiration exhibit a degree of interannual variability which can influence atmospheric CO₂, at least on annual to decadal time scales. Second, land use changes release C0₂ to the atmosphere. Third, poorly understood processes are likely resulting in enhanced uptake of CO₂ in certain ecosystems, acting as a sink in the global carbon cycle. This sink may result from forest demographics, atmospheric N deposition, or direct CO₂ fertilization, or some synergistic combination of those processes. Global estimates of terrestrial carbon cycle components requires the use of remote observations; however, the appropriate remote sensing strategies are quite different for the various components.” Remote Sensing of Environment, Volume 51, Issue 1, January 1995, Pages 49-56, doi:10.1016/0034-4257(94)00064-T.

Global net primary production: Combining ecology and remote sensing – Field et al. (1995) “Terrestrial net primary production (NPP) is sensitive to a number of controls, including aspects of climate, topography, soils, plant and microbial characteristics, disturbance, and anthropogenic impacts. Yet, at least at the global scale, models based on very different types and numbers of parameters yield similar results. Part of the reason for this is that the major NPP controls influence each other, resulting, under current conditions, in broad correlations among controls. NPP models that include richer suites of controlling parameters should be more sensitive to conditions that disrupt the broad correlations, but the current paucity of global data limits the power of complex models. Improved data sets will facilitate applications of complex models, but many of the critical data are very difficult to produce, especially for applications dealing with the past or future. It may be possible to overcome some of the challenges of data availability through increased understanding and modeling of ecological processes that adjust plant physiology and architecture in relation to resources. The CASA (Carnegie, Stanford, Ames Approach) model introduced by Potter et al. (1993) and expanded here uses a combination of ecological principles, satellite data, and surface data to predict terrestrial NPP on a monthly time step. CASA calculates NPP as a product of absorbed photosynthetically active radiation, APAR, and an efficiency of radiation use, ε. The underlying postulate is that some of the limitations on NPP appear in each. CASA estimates annual terrestrial NPP to be 48 Pg and the maximum efficiency of PAR utilization (ε*) to be 0.39 g C MJ⁻¹ PAR. Spatial and temporal variation in APAR is more than fivefold greater than variation in ε.” Remote Sensing of Environment, Volume 51, Issue 1, January 1995, Pages 74-88,doi:10.1016/0034-4257(94)00066-V.

Global climate change and terrestrial net primary production – Melillo et al. (1993) “A process-based model was used to estimate global patterns of net primary production and soil nitrogen cycling for contemporary climate conditions and current atmospheric C0₂ concentration. Over half of the global annual net primary production was estimated to occur in the tropics, with most of the production attributable to tropical evergreen forest. The effects of C0₂ doubling and associated climate changes were also explored. The responses in tropical and dry temperate ecosystems were dominated by C0₂, but those in northern and moist temperate ecosystems reflected the effects of temperature on nitrogen availability.” Nature 363, 234 – 240 (20 May 1993); doi:10.1038/363234a0. [Full text]

Potential Net Primary Productivity in South America: Application of a Global Model – Raich et al. (1991) “We use a mechanistically based ecosystem simulation model to describe and analyze the spatial and temporal patterns of terrestrial net primary productivity (NPP) in South America. The Terrestrial Ecosystem Model (TEM) is designed to predict major carbon and nitrogen fluxes and pool sizes in terrestrial ecosystems at continental to global scales. Information from intensively studies field sites is used in combination with continental—scale information on climate, soils, and vegetation to estimate NPP in each of 5888 non—wetland, 0.5° latitude °0.5° longitude grid cells in South America, at monthly time steps. Preliminary analyses are presented for the scenario of natural vegetation throughout the continent, as a prelude to evaluating human impacts on terrestrial NPP. The potential annual NPP of South America is estimated to be 12.5 Pg/yr of carbon (26.3 Pg/yr of organic matter) in a non—wetland area of 17.0 x 10⁶ km². More than 50% of this production occurs in the tropical and subtropical evergreen forest region. Six independent model runs, each based on an independently derived set of model parameters, generated mean annual NPP estimates for the tropical evergreen forest region ranging from 900 to 1510 g m^-2 yr^-1 of carbon, with an overall mean of 1170 g m^-2 yr^-1. Coefficients of variation in estimated annual NPP averaged 20% for any specific location in the evergreen forests, which is probably within the confidence limits of extant NPP measurements. Predicted rates of mean annual NPP in other types of vegetation ranged from 95 g m^-2 yr^-1 in arid shrublands to 930 g m^-2 yr^-1 in savannas, and were within the ranges measured in empirical studies. The spatial distribution of predicted NPP was directly compared with estimates made using the Miami mode of Lieth (1975). Overall, TEM predictions were ~10% lower than those of the Miami model, but the two models agreed closely on the spatial patterns of NPP in south America. Unlike previous models, however, TEM estimates NPP monthly, allowing for the evaluation of seasonal phenomena. This is an important step toward integration of ecosystem models with remotely sensed information, global climate models, and atmospheric transport models, all of which are evaluated at comparable spatial and temporal scales. Seasonal patterns of NPP in South America are correlated with moisture availability in most vegetation types, but are strongly influenced by seasonal differences in cloudiness in the tropical evergreen forests. On an annual basis, moisture availability was the factor that was correlated most strongly with annual NPP in South America, but differences were again observed among vegetation types. These results allow for the investigation and analysis of climatic controls over NPP at continental scales, within and among vegetation types, and within years. Further model validation is needed. Nevertheless, the ability to investigate NPP—environment interactions with a high spatial and temporal resolution at continental scales should prove useful if not essential for rigorous analysis of the potential effects of global climate changes on terrestrial ecosystems.” Ecological Applications. 1:399—429, doi:10.2307/1941899. [Full text]

Mapping Regional Forest Evapotranspiration and Photosynthesis by Coupling Satellite Data with Ecosystem Simulation – Running et al. (1989) “Annual evapotranspiration (ET) and net photosynthesis (PSN) were estimated for a mountainous 28 x 55 km region of predominantly coniferous forests in western Montana. A simple geographic information system integrated topographic, soils, vegetation, and climatic data at a 1.1 -km scale size defined by the satellite sensor pixel size. Leaf area index (LAI) of the forest was estimated with data from the NOAA (National Oceanic and Atmospheric Administration) Advanced Very High Resolution Radiometer (AVHRR). Daily microclimate of each cell was estimated from ground and satellite data and interpolated using MT-CLIM, a mountain microclimate simulator. A forest ecosystem simulation model, FOREST-BGC. was used to calculate ET and PSN daily for each cell. Ranges of estimated LA1 (4-U) ET (25-60 cm/yr), and PSN (9-20 Mg ha^-1 yr^-1) across the landscape follow the trends expected in both magnitude and spatial pattern. These estimates compared well with field measurements of related variables, although absolute validation of these predictions is not now possible at large spatial scales.” Ecology, Vol. 70, No. 4 (Aug., 1989), pp. 1090-1101. [Full text]

Relating seasonal patterns of the AVHRR vegetation index to simulated photosynthesis and transpiration of forests in different climates – Running & Nemani (1988) “Recent research has suggested that the Normalized Difference Vegetation Index (NDVI) calculated from the AVHRR sensor is directly related to photosynthesis (PSN), transpiration (TRAN), and aboveground net primary production (ANPP) of terrestrial vegetation. Weekly NDVI data for 1983–1984 were retrieved for seven sites of diverse climate in North America. The sites were Fairbanks, AK, Seattle, WA, Missoula, MT, Madison, WI, Knoxville, TN, Jacksonville, FL, and Tucson, AZ. Meteorological data from ground stations were retrieved to drive an ecosystem simulation model (FOREST-BGC) calculating daily canopy PSN and TRAN and annual ANPP of a hypothetical forest stand for the corresponding period at each site. Correlations of annual integrated NDVI across all sites for both years were: annual PSN, R² = 0.87; annual TRAN, R² = 0.77; annual ANPP, R² = 0.72. Correlation between weekly NDVI and PSN was variable; with high latitude wet sites, R² = 0.77–0.84. On sites with less seasonal amplitude of NDVI and PSN, or on sites with substantial seasonal water stress correlations ranged from R² = 0.08 to 0.64. Correlations of weekly NDVI with TRAN followed the same pattern as PSN, but were slightly lower. The tendency of raw NDVI data to overpredict PSN and TRAN on water limited sites was partially corrected using an “aridity index” of annual radiation/annual precipitation that could be computed from general climatological data for improving large scale NDVI maps of PSN and TRAN. The spatial subsampling done for the global vegetation index (GVI) precludes following specific study sites through the growing season. We conclude that estimates of vegetation productivity using the GVI should only be done as annual integrations until unsubsampled local area coverage (LAC) NDVI data can be tested against forest PSN, TRAN, and ANPP, measured at shorter time intervals.” Remote Sensing of Environment, Volume 24, Issue 2, March 1988, Pages 347-367, doi:10.1016/0034-4257(88)90034-X. [Full text]

North American vegetation patterns observed with the NOAA-7 advanced very high resolution radiometer – Goward et al. (1985) “Spectral vegetation index measurements derived from remotely sensed observations show great promise as a means to improve knowledge of land vegetation patterns. The daily, global observations acquired by the Advanced Very High Resolution Radiometer, a sensor on the current series of U.S. National Oceanic and Atmospheric Administration meteorological satellites, may be particularly well suited for global studies of vegetation. Preliminary results from analysis of North American observations, extending from April to November 1982, show that the vegetation index patterns observed correspond to the known seasonality of North American natural and cultivated vegetation. Integration of the observations over the growing season produced measurements that are related to net primary productivity patterns of the major North American natural vegetation formations. Regions of intense cultivation were observed as anomalous areas in the integrated growing season measurements. These anomalies can be explained by contrasts between cultivation practices and natural vegetation phenology. Major new information on seasonality, annual extent and interannual variability of vegetation photosynthetic activity at continental and global scales can be derived from these satellite observations.” Plant Ecology, Volume 64, Number 1, 3-14, DOI: 10.1007/BF00033449. [Full text]

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Science shocker: Drought drives decade-long decline in plant growth – Climate Progress (2010)

Papers on oil companies and climate change

This is a list of papers on the oil companies and climate change. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

The oxymoron of ‘sustainable oil production’: the case of the Norwegian oil industry – Ihlen (2009) “Many oil companies have adopted the concept of sustainable development and claim that their production is sustainable. This might seem odd given that the oil industry depletes a non-renewable resource and that oil production also contributes to climate change. This paper analyses how the industry attempts to resolve this paradox, using the Norwegian oil industry as a case study. It is demonstrated how four rhetorical operations are used. By employing the topic of definition, the industry argues that it is sustainable because it (1) strives to cut its emissions and (2) manages oil resources with a long-term perspective until such time as technology will provide solutions. The industry then uses the topic of comparison to (3) discredit other energy sources as ‘unrealistic’ options and (4) compare the production in Norway with more polluting oil production elsewhere. Understanding this type of rhetoric is crucial for validating or criticizing the sustainability claims of the industry.”

Oil Companies and Climate Change: Inconsistencies between Strategy Formulation and Implementation? – Sæverud & Skjærseth (2007) “This article examines major oil companies in terms of climate strategies and their implementation. More specifıcally, it takes a critical look at Shell, BP, and ExxonMobil, and the relationship between rhetoric and action regarding investments in climate-friendly activities. Empirical evidence indicates a generally high degree of consistency between what these companies say and what they do, but interesting differences are also found: ExxonMobil has done somewhat more than its climate strategy formulations would suggest; Shell has done somewhat less; whereas BP’s activities are mainly in line with its statements. Factors at three levels contribute to explaining these differences: (1) the company level, 2) the political framework conditions in the various regions where the companies operate, 3) international climate cooperation. The fındings and explanations, although restricted to the three oil companies with regard to climate change, provide insight into the relationship between corporate strategies and implementation more generally. They offer understanding and analytical categories for assessing how well and why such multinational entities put into practice stated objectives.” [Full text]

Strategic Responses to Global Climate Change: Conflicting Pressures on Multinationals in the Oil Industry – Levy & Kolk (2002) “MNCs are increasingly facing global environmental issues demanding coordinated market and non-market strategic responses. The home country institutional context and individual company histories can create divergent pressures on strategy for MNCs based in different countries; however, the location of MNCs in global industries and their participation in ‘global issues arenas’ create issue-level fields within which strategic convergence might also be expected. This paper analyzes the responses of oil MNCs to climate change and finds that local context influenced initial corporate reactions, but that convergent pressures predominate as the issue matures.” [Full text]

The oil industry and climate change: strategies and ethical dilemmas – van den Hove et al. (2002) “This paper explores the different climate change strategies chosen by three major multinational oil corporations: ExxonMobil, TotalFinaElf and BP Amoco. They are referred to, as the `fight against emission constraints,’ `wait and see,’ and `proactive’ strategies, respectively. The justifications given to support these strategies are identified. They cover the business, scientific, political, economic, technological and social dimensions. In a business ethics framework, the issue of climate change brings forth an ethical dilemma for the oil industry, in the form of a tension between profits and CO₂ emissions. The strategies are analysed as three attitudes towards this dilemma: (i) placing priority on the business consequences while weakening the perception that anthropogenic greenhouse gas emissions are causing climate change; (ii) avoiding responsibility; and (iii) placing priority on the need for a modification of the business process while limiting the negative effect in terms of business consequences. In conclusion, we propose that beyond the ethical issues proper to climate change itself, additional ethical issues are raised if society at large is instrumentalised by an industry in its search for profit. Publicly gauging and valorising the ethical commitment of a corporation appear as ways of inducing more collaborative and proactive attitudes by business actors.”

Winds of Change: Corporate Strategy, Climate change and Oil Multinationals – Kolk & Levy (2001) “Behind pessimistic expectations regarding the future of an international climate treaty, substantial changes can be observed in company positions. Multinationals in the oil and car industries are increasingly moving toward support for the Kyoto Protocol, and take measures to address climate change. This article analyses developments in the oil industry over the past few years, observing considerable shifts in corporate climate strategies. It compares British Petroleum, Royal Dutch Shell, Texaco and ExxonMobil, of which currently only the latter strongly opposes a climate treaty. BP and Shell have moved decisively toward supporting emission reductions and investing in renewable energy, while Texaco has begun to move in a similar direction. Divergent behaviour can be explained in terms of company-specific factors, particularly corporate histories of profitability and location, market assessments, degrees of centralization and the presence of climate scientists. Ongoing stakeholder pressures, which focus on ‘first-mover’ BP, are evaluated.” [Full text]

Climate Change and the Oil Industry: Common Problems, Different Strategies – Skjærseth & Skodvin (2001) “This analysis shows that there are striking differences in the ways European-based and US-based oil companies have responded to the climate issue—here represented by the Royal Dutch/Shell Group and Exxon Mobil—and that one major source of explanation for this difference is found in the national political contexts of the companies’ home-base countries. The importance of political context implies that the conditions for changing oil companies’ climate strategies are likely to be located in the political context rather than in the companies themselves.” [Full text]

Beauty and the beast? BP’s and Exxon’s positions on global climate change – Rowlands (2000) “The author attempts first to determine whether there are significant differences among the major oil companies’ positions on global climate change, and second to discover the reasons behind any differences found. The investigation focuses upon Exxon and BP Amoco—two of the world’s largest oil companies. The differences between the two, with regard to their attitudes and actions on global climate change, are striking: whereas Exxon is continuing to act as one might initially expect (resisting proactive policies on climate change), BP Amoco appears more willing to contemplate a world that uses less oil. Attempts to explain these differences focus upon the companies’ respective interests, their management structures, and their nationalities. It appears that all factors are important, at least to some degree. The paper concludes with a discussion of research limitations and suggestions.”

Closely related

Papers on AGW denialism.