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Observations of anthropogenic global warming

Papers on global warming and Earth’s rotation

Posted by Ari Jokimäki on May 25, 2011

This is a list of papers on global warming effects to Earth’s rotation. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

GRACE era secular trends in Earth rotation parameters: A global scale impact of the global warming process? – Roy & Peltier (2011) “Recent trends in the two primary anomalies in the rotational state of the planet are analyzed in detail, namely those associated with the speed and direction of polar wander and with the non-tidal acceleration of the rate of axial rotation (via the measurement of the changing oblateness of the Earth’s shape). It is demonstrated that a significant change in the secular trends in both of these independent parameters became evident subsequent to approximately 1992. It is suggested that both parameters might have come to be substantially influenced by mass loss from both the great polar ice sheets, and from the very large number of small ice-sheets and glaciers that are also being influenced by the global warming phenomenon. The modern values for the secular drifts in those parameters that we estimate are appropriate to the period during which measurements have been made by the satellites of the Gravity Recovery and Climate Experiment (GRACE). These changes in secular rates might greatly assist in understanding why the GRACE-inferred values of the time derivatives of the degree two and order one Stokes coefficients differ so significantly from those associated with Late Quaternary ice-age influence.” Roy, K., and W. R. Peltier (2011), Geophys. Res. Lett., 38, L10306, doi:10.1029/2011GL047282.

Ocean bottom pressure changes lead to a decreasing length-of-day in a warming climate – Landerer et al. (2007) “We use a coupled climate model to evaluate ocean bottom pressure changes in the IPCC-A1B climate scenario. Ocean warming in the 21st and 22nd centuries causes secular oceanic bottom pressure anomalies. The essential feature is a net mass transfer onto shallow shelf areas from the deeper ocean areas, which exhibit negative bottom pressure anomalies. We develop a simple mass redistribution model that explains this mechanism. Regionally, however, distinct patterns of bottom pressure anomalies emerge due to spatially inhomogeneous warming and ocean circulation changes. Most prominently, the Arctic Ocean shelves experience an above-average bottom pressure increase. We find a net transfer of mass from the Southern to the Northern Hemisphere, and a net movement of mass closer towards Earth’s axis of rotation. Thus, ocean warming and the ensuing mass redistribution change the length-of-day by −0.12 ms within 200 years, demonstrating that the oceans are capable of exciting nontidal length-of-day changes on decadal and longer timescales.” Landerer, F. W., J. H. Jungclaus, and J. Marotzke (2007), Geophys. Res. Lett., 34, L06307, doi:10.1029/2006GL029106.

The 60-year solar modulation of global air temperature: the Earth’s rotation and atmospheric circulation connection – Mazzarella (2007) “Spectral analysis of geomagnetic activity, global air temperature, Earth’s rotation rate and zonal circulation, when smoothed from secular trend and periods shorter than 23 years, shows a concentration of energy around the 60-year period explaining more than 80% of the entire variance. This information has enabled the set-up of a cascade physical model that integrates the Sun-atmosphere-Earth system as a single unit and ties solar corpuscular radiation to global warming through Earth’s rotation and atmospheric circulation. Our results suggest that changes in geomagnetic activity, and in the Earth’s rotation, could be used as long- and short-term indicators, respectively, of future changes in global air temperature.” A. Mazzarella, Theoretical and Applied Climatology, Volume 88, Numbers 3-4, 193-199, DOI: 10.1007/s00704-005-0219-z.

Earth rotation/polar motion excitations from atmospheric models – Salstein (2005) “We review both the characteristics of the angular momentum signals that excite Earth rotation variations as calculated from global analyses of the atmosphere, as well as the ability of the current generation of global atmospheric models to simulate such signals. We are interested in results for the planetary axial component, whose fluctuations are related to length of day, and the two equatorial components, related to polar motion. Model results are compared with the analyses of the atmosphere that are produced by weather forecast centers, both contemporaneously and retrospectively, which are also known as operational analyses and reanalyses, repectively. Results from simulations by a group of atmospheric general circulation models forced by time-variable sea surface temperatures over a one- to two-decade period enable us to assess the current state-of-the-art in simulating atmospheric excitations of Earth rotation. These models have become increasingly skillful in this regard on both seasonal and interannual timescales, with much of the latter related to the dominant El Niño-Southern Oscillation atmosphere-ocean signal. Recently, some atmospheric general circulation models have also been run to simulate much of the last century. Several realizations of such a model for a period covering the 20th century, for example, have been used to estimate excitations of the Earth rotation on a number of time scales. Information from all these simulations of the past is useful in the design of atmosphere, or atmosphere-ocean coupled, models that can serve as tools to forecast the future, including those with scenarios of projected increases in greenhouse gases; such models could produce changes in Earth rotation or polar motion parameters.” Salstein, David A., Artificial Satellites – Journal of Planetary Geodesy (ISSN 0208-841X), Vol. 40, No. 1, p. 35 – 46 (2005). In: Proceedings of the seminar “Earth rotation and satellite geodesy from astrometry to GNSS”, Warsaw, September, 18-19, 2003. Part III: Earth rotation.

Low-frequency excitation of length of day and polar motion by the atmosphere – de Viron et al. (2004) “Results of a 100-year run of the Hadley Centre general circulation model are used to compute monthly values of the three components of atmospheric torque on the Earth and of the associated atmospheric angular momentum series. All these results are compared with equivalent ones from the National Center for Environmental Prediction/National Center for Atmospheric Research reanalyses for the overlap period since 1948. We find some important differences; consequently, our results should be taken as an order of magnitude of the effect. We also compute the effect of the atmosphere on length of day (LOD) and polar motion by the use of both the torque and the angular momentum approaches. We find comparable amplitude with both torque and angular momentum for the polar motion; the axial torque, however, related to LOD, appears to be unphysical. The excitation of long-period LOD variation is in phase with the observed variation but much smaller. The low-frequency polar motion is only coherent with the observation at certain particular periods.” de Viron, O., D. Salstein, C. Bizouard, and L. Fernandez (2004), J. Geophys. Res., 109, B03408, doi:10.1029/2003JB002817.

CO2-Induced Changes in Atmospheric Angular Momentum in CMIP2 Experiments – Räisänen (2003) “The response of atmospheric angular momentum to a gradual doubling of CO2 is studied using 16 model experiments participating in the second phase of the Coupled Model Intercomparison Project (CMIP2). The relative angular momentum associated with atmospheric zonal winds increases in all but one of the models, although the magnitude of the change varies widely. About 90% of the 16-model mean increase comes from increasing westerly winds in the stratosphere and the uppermost low-latitude troposphere above 200 hPa. This increase in westerly winds reflects a steepening of the meridional temperature gradient near the tropopause and in the upper troposphere. The simulated temperature gradient at this height increases partly as an indirect consequence of the poleward decrease in the tropopause height, and partly because convection induces a maximum in warming in the tropical upper troposphere. The change in the omega angular momentum associated with the surface pressure distribution is in most models smaller than the change in the relative angular momentum, although its exact value is sensitive to the method of calculation.” Räisänen, Jouni, 2003, J. Climate, 16, 132–143. [Full text]

Unusual Behavior in Atmospheric Angular Momentum during the 1965 and 1972 El Niños – Huang et al. (2003) “The global atmospheric angular momentum (AAM) is known to increase with tropical eastern Pacific sea surface temperature (SST) anomalies during El Niño events. Using a reanalysis dataset, the ratio of the monthly AAM anomaly to El Niño SST anomaly (based on the Niño-3.4 index) is found to be approximately 1 angular momentum unit (=1025 kg m2 s−1) per degree Celsius for most post-1975 El Niños. This ratio is much smaller, however, during the 1965/66 and 1972/73 El Niños, raising the possibilities that either the early reanalysis data are in error due to sparse observations, or the atmospheric response to the two early El Niños was unusual. The possibility of a severe data problem in the reanalysis is ruled out by cross-validating the AAM time series with independent measurements of length of day. The latitudinal structures of the zonal wind anomalies in 1965/66 and 1972/73 are examined for both the reanalysis and a set of general circulation model (GCM) simulations. Multiple GCM runs with specified SST produce a more positive ensemble-mean AAM anomaly in 1965 than its counterpart in the reanalysis. The GCM-simulated ensemble-mean zonal wind anomaly resembles the canonical El Niño response with accelerations of subtropical zonal jets in both hemispheres, a pattern that is almost absent in the reanalysis. On the other hand, a large spread exists among the individual ensemble members in the 1965/66 GCM simulations. Although the majority of the individual ensemble members shows the canonical El Niño response, two outliers (out of 12 runs) exhibit very small zonal wind responses in the Northern Hemisphere similar to the reanalysis. Thus, the observed AAM anomaly during 1965/66 is interpreted as an outlier with atmospheric noise being strong enough to overwhelm the canonical El Niño response. The low AAM in the 1972/73 event is related in the reanalysis to a significantly negative zonal wind response on the equator. This signal is robustly reproduced, although with a slightly smaller amplitude, in the ensemble mean and all individual ensemble members in the GCM simulations. The small ensemble standard deviation and large ensemble-mean response on the equator indicate that the negative response is due to the lower-boundary forcing related to the SST anomaly. The fact that the AAM anomaly in 1972/73 is not well correlated with the Niño-3.4 index, then, indicates that SST anomalies outside the conventional El Niño region may be responsible for the low AAM. The uncharacteristically low values of global AAM in 1965/66 and 1972/73 contribute to a low mean for the decade before 1975, which, combined with high AAM in the post-1980 era, produces a significant upward trend in AAM in the second half of the twentieth century. If the weak AAM anomalies during the two pre-1975 El Niños are due to random noise or incidental non-El Niño influences, taking them at face value would result in an overestimate of about 15%–20% in the multidecadal trend of AAM due to boundary forcing alone. Notably, a multidecadal trend in AAM is also simulated in the ensemble mean of the multiple GCM runs, but its magnitude is smaller than the observed counterpart and more consistent with the multidecadal trend of the Niño-3.4 index. The implications of these findings for climate change detection are discussed.” Huang, Huei-Ping, Klaus M. Weickmann, Richard D. Rosen, 2003, J. Climate, 16, 2526–2539. [Full text]

Recent Earth Oblateness Variations: Unraveling Climate and Postglacial Rebound Effects – Dickey et al. (2002) “Earth’s dynamic oblateness (J 2) has been decreasing due to postglacial rebound (PGR). However, J 2 began to increase in 1997, indicating a pronounced global-scale mass redistribution within Earth’s system. We have determined that the observed increases in J 2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the Southern, Pacific, and Indian oceans. When these effects are removed, the residual trend in J 2 (–2.9 x 10−11 year−1) becomes consistent with previous estimates of PGR from satellite and eclipse data. The climatic significance of these rapid shifts in glacial and oceanic mass, however, remains to be investigated.” Jean O. Dickey, Steven L. Marcus, Olivier de Viron and Ichiro Fukumori, Science 6 December 2002: Vol. 298 no. 5600 pp. 1975-1977, DOI: 10.1126/science.1077777.

Effect of global warming on the length-of-day – Viron et al. (2002) “The anthropogenic increase in greenhouse gas concentrations in the Earth atmosphere will probably induce important modifications of the global circulation in the atmosphere and ocean. Due to the angular momentum conservation of the Earth-atmosphere-ocean system, variation of the length-of-day (LOD) can be expected. By using the outputs of the models participating to the Coupled Model Intercomparison Project (CMIP-2), we reach the following conclusions: (1) the models globally agree to an increase of the LOD of the order of 1 μs/year, (2) the effect is mostly associated with an increase of the mean zonal wind, of which about one third is compensated by a change in mass repartition.” de Viron, O., V. Dehant, H. Goosse, and M. Crucifix (2002), Geophys. Res. Lett., 29(7), 1146, doi:10.1029/2001GL013672.

Ocean angular momentum signals in a climate model and implications for Earth rotation – Ponte et al. (2002) “Estimates of ocean angular momentum (OAM) provide an integrated measure of variability in ocean circulation and mass fields and can be directly related to observed changes in Earth rotation. We use output from a climate model to calculate 240 years of 3-monthly OAM values (two equatorial terms L1 and L2, related to polar motion or wobble, and axial term L3, related to length of day variations) representing the period 1860-2100. Control and forced runs permit the study of the effects of natural and anthropogenically forced climate variability on OAM. All OAM components exhibit a clear annual cycle, with large decadal modulations in amplitude, and also longer period fluctuations, all associated with natural climate variability in the model. Anthropogenically induced signals, inferred from the differences between forced and control runs, include an upward trend in L3, related to inhomogeneous ocean warming and increases in the transport of the Antarctic Circumpolar Current, and a significantly weaker seasonal cycle in L2 in the second half of the record, related primarily to changes in seasonal bottom pressure variability in the Southern Ocean and North Pacific. Variability in mass fields is in general more important to OAM signals than changes in circulation at the seasonal and longer periods analyzed. Relation of OAM signals to changes in surface atmospheric forcing are discussed. The important role of the oceans as an excitation source for the annual, Chandler and Markowitz wobbles, is confirmed. Natural climate variability in OAM and related excitation is likely to measurably affect the Earth rotation, but anthropogenically induced effects are comparatively weak.” R. Ponte, J. Rajamony and J. Gregory, Climate Dynamics, Volume 19, Number 2, 181-190, DOI: 10.1007/s00382-001-0216-6.

Trend in Atmospheric Angular Momentum in a Transient Climate Change Simulation with Greenhouse Gas and Aerosol Forcing – Huang et al. (2001) “The authors investigate the change of atmospheric angular momentum (AAM) in long, transient, coupled atmosphere–ocean model simulations with increasing atmospheric greenhouse gas concentration and sulfate aerosol loading. A significant increase of global AAM, on the order of 4 × 1025 kg m2 s-1 for 3 × CO2–1 × CO2, was simulated by the Canadian Centre for Climate Modelling and Analysis (CCCma) coupled model. The increase was mainly contributed by the relative component of total AAM in the form of an acceleration of zonal mean zonal wind in the tropical–subtropical upper troposphere. Thus, under strong global warming, a superrotational state emerged in the tropical upper troposphere. The trend in zonal mean zonal wind in the meridional plane was characterized by 1) a tropical–subtropical pattern with two maxima near 30° in the upper troposphere, and 2) a tripole pattern in the Southern Hemisphere extending through the entire troposphere and having a positive maximum at 60°S. The implication of the projected increase of global AAM for future changes of the length of day is discussed. The CCCma coupled global warming simulation, like many previous studies, shows a significant increase of tropical SST and includes a zonally asymmetric component that resembles El Niño SST anomalies. In the CCCma transient simulations, even though the tropical SST and global AAM both increased nonlinearly with time, the ratio of their time increments ΔAAM/ΔSST remained approximately constant at about 0.9 × 1025 kg m2 s-1 (°C)-1. This number is close to its counterpart for the observed global AAM response to El Niño. It is suggested that this ratio may be useful as an index for intercomparisons of different coupled model simulations.” Huang, Huei-Ping, Klaus M. Weickmann, C. Juno Hsu, 2001, J. Climate, 14, 1525–1534, doi: 10.1175/1520-0442(2001)0142.0.CO;2. [Full text]

The influence of global warming in Earth rotation speed – del Rio (1999) “The tendency of the atmospheric angular momentum (AAM) is investigated using a 49-year set of monthly AAM data for the period January 1949-December 1997. This data set is constructed with zonal wind values from the reanalyses of NCEP/NCAR, used in conjunction with a variety of operationally produced AAM time series with different independent sources and lengths over 1976-1997. In all the analyzed AAM series the linear trend is found to be positive. Since the angular momentum of the atmosphere-earth system is conserved this corresponds to a net loss of angular momentum by the solid earth, therefore decreasing the Earth rotation speed and increasing the length of day (LOD). The AAM rise is significant to the budget of angular momentum of the global atmosphere-earth system; its value in milliseconds/century (ms/cy) is +0.56 ms/cy, corresponding to one-third of the estimated increase in LOD (+1.7 ms/cy). The major contribution to this secular trend in AAM comes from the equatorial Tropopause. This is consistent with results from a previous study using a simplified aqua-planet model to investigate the AAM variations due to near equatorial warming conditions. During the same time interval, 1949-1997, the global marine + land-surface temperature increases by about 0.79 °C/cy, showing a linear correspondence between surface temperature increase and global AAM of about 0.07 ms per 0.1 °C. These results imply that atmospheric angular momentum may be used as an independent index of the global atmosphere’s dynamical response to the greenhouse forcing, and as such, the length of day may be used as an indirect indicator of global warming.” Abarca del Rio, R., Ann. Geophys., 17, 806-811, doi:10.1007/s00585-999-0806-x, 1999. [Full text]

Response of Zonal Winds and Atmospheric Angular Momentum to a Doubling Of CO2 – Rosen & Gutowski (1992) “The possible impact of doubling CO2 on the zonal-mean zonal winds and the angular momentum of the atmosphere is examined using general circulation model output archived by the Goddard Institute for Space Studies, the National Center for Atmospheric Research, and the Geophysical Fluid Dynamics Laboratory. Whereas the emphasis in most previous studies with these models has been placed on the temperature and precipitation changes expected from a doubled-CO2 scenario, the intent here is to investigate some of the dynamical consequences predicted by them models, especially within the tropics where the zonal-wind and temperature changes are less tightly coupled than elsewhere. Comparisons among the three models of the difference in zonal-mean zonal winds between 2×CO2 and 1×CO2 simulations indicate a common tendency when CO2 is doubled for winds to become more easterly in much of the tropics during June-July-August. Less of a consensus for the tropics emerges for December-January-February, perhaps as a result of differences among the models’ basic climatologies for the zonal-wind field. In general, however, changes predicted for the zonal winds in the tropics and elsewhere are comparable to the interannual variability currently observed, suggesting that these changes ought to become detectable eventually. Largely because of the tropical wind changes, decreases in the troposphere’s relative angular momentum accompany a doubling of CO2 in all the model runs. The amplitude of the decrease is typically a considerable fraction of a model’s seasonal cycle and, in some cases, is large enough that a measurable change in the length of day could result. Although the possibility of an anthropogenic effect on earth’s rotation is noteworthy, such a prediction must be regarded as tentative in light of the shortcomings found in the models’ zonal-wind climatologies and the differences in their zonal-mean responses.” Rosen, Richard D., William J. Gutowski, 1992, J. Climate, 5, 1391–1404. doi: 10.1175/1520-0442(1992)0052.0.CO;2. [Full text]

Global Sea Level and Earth Rotation – Peltier (1988) “Recent analyses of long time scale secular variations of sea level, based on tide gauge observations, have established that sea level is apparently rising at a globally averaged rate somewhat in excess of 1 millimeter per year. It has been suggested that the nonsteric component of this secular rate might be explicable in terms of ongoing mass loss from the small ice sheets and glaciers of the world. Satellite laser ranging and very long baseline interferometry data may be used to deliver strong constraints on this important scenario because of the information that these systems provide on variations of the length of day and of the position of the rotation pole with respect to the earth’s surface geography. These data demonstrate that the hypothesis of mass loss is plausible if the Barents Sea was covered by a substantial ice sheet at the last maximum of the current ice age 18,000 years ago.” W. R. Peltier, Science 13 May 1988: Vol. 240 no. 4854 pp. 895-901, DOI: 10.1126/science.240.4854.895.

An El Niño Signal in Atmospheric Angular Momentum and Earth Rotation – Rosen et al. (1984) “Anomalously high values of atmospheric angular momentum and length of day were observed in late January 1983. This signal in the time series of these two coupled quantities appears to have been a consequence of the equatorial Pacific Ocean warming event of 1982-1983.” Richard D. Rosen, David A. Salstein, T. Marshall Eubanks, Jean O. Dickey and J. Alan Steppe, Science 27 July 1984: Vol. 225 no. 4660 pp. 411-414, DOI: 10.1126/science.225.4660.411.

Atmospheric angular momentum fluctuations and changes in the length of the day – Hide et al. (1980) “Fluctuations in the angular momentum of the Earth’s atmosphere correspond fairly well with equal and opposite fluctuations in the angular momentum of the Earth’s ‘solid’ mantle. A decrease of 20% of the relative angular momentum of the atmosphere during the second half of May 1979 was accompanied by a speeding up of the rotation of the mantle causing the length of the day (l.o.d.) to decrease by 0.6 10-3 s. Although motions in the Earth’s liquid core produce the more pronounced ‘decade’ variations in the l.o.d. there is no evidence that core motions produce l.o.d. variations on much shorter time-scales.” R. Hide, N. T. Birch, L. V. Morrison, D. J. Shea & A. A. White, Nature 286, 114 – 117 (10 July 1980); doi:10.1038/286114a0.

Long Term Variations in the Length of Day and Climatic Change – Lambeck & Cazenave (1976) “The long-period (greater than about 10 yr) variations in the length-of-day (LOD) observed since 1820 show a marked similarity with variations observed in various climatic indices; periods of acceleration of the Earth corresponding to years of increasing intensity of the zonal circulation and to global-surface warming: periods of deceleration corresponding to years of decreasing zonal-circulation intensity and to a global decrease in surface temperatures. The long-period atmospheric excitation functions for near-surface geostrophic winds, for changes in the atmospheric mass distribution and for eustatic variations in sea level have been evaluated and correlate well with the observed changes in the LOD; although their total effect represents only about 10 per cent of the required excitation. The computed excitation lags the LOD variations by about 10–15 yr. Upper atmospheric winds or other meteorological related factors appear to be quite inadequate to provide the additional driving force that is required if the LOD changes are of meteorological origin. Instead, it appears that the LOD fluctuations and the climatic variations on a time scale of 20–30 yr may have a common origin as has been suggested by Anderson. That is, the results suggest that indirect solid Earth effects on climate may be important.” Kurt Lambeck, Amy Cazenave, Geophysical Journal of the Royal Astronomical Society, Volume 46, Issue 3, pages 555–573, September 1976. [Full text]

One Response to “Papers on global warming and Earth’s rotation”

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