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Testing for the possible influence of unknown climate forcing upon global temperature increases from 1950 to 2000

Sat, 31 Dec 2011 23:00:00 GMT

Title: Testing for the possible influence of unknown climate forcing upon global temperature increases from 1950 to 2000 Authors: Anderson, B. T.; Boston Univ; Boston Univ; Boston Univ; Boston Univ, Dept Earth & Environm, Boston, MA 02215 USA; Knight, J. R.; Hadley Ctr, Met Off, Exeter, Devon, England; Ringer, M. A.; Hadley Ctr, Met Off, Exeter, Devon, England; Yoon, J. H.; Pacific NW Natl Lab, Richland, WA 99352 USA; Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: Global-scale variations in the climate system over the last half of the twentieth century. including long-term increases in global-mean near-surface temperatures. are consistent with concurrent human-induced emissions of radiatively active gases and aerosols. However, such consistency does not preclude the possible influence of other forcing agents, including internal modes of climate variability or unaccounted for aerosol effects. To test whether other unknown forcing agents may have contributed to multidecadal increases in global-mean near-surface temperatures from 1950 to 2000. data pertaining to observed changes in global-scale sea surface temperatures and observed changes in radiatively active atmospheric constituents are incorporated into numerical global climate models. Results indicate that the radiative forcing needed to produce the observed long-term trends in sea surface temperatures-and global-mean near-surface temperatures-is provided predominantly by known changes in greenhouse gases and aerosols. Further, results indicate that less than 10% of the long-term historical increase in global-mean near-surface temperatures over the last half of the twentieth century could have been the result of internal climate variability. In addition. they indicate that less than 25% of the total radiative forcing needed to produce the observed long-term trend in global-mean near-surface temperatures could have been provided by changes in net radiative forcing from unknown sources (either positive or negative). These results, which are derived from simple energy balance requirements. emphasize the important role humans have played in modifying the global climate over the last half of the twentieth century.

Predictability of the mid-latitude Atlantic meridional overturning circulation in a multi-model system

Mon, 31 Dec 2012 23:00:00 GMT

Title: Predictability of the mid-latitude Atlantic meridional overturning circulation in a multi-model system Authors: Pohlmann, H.; Max-Planck-Institut fu ̈r Meteorologie,; Smith, D. M.; Met Office Hadley Centre; Balmaseda, M. A.; ECMWF; Keenlyside, N. S.; Geophysical Institute and Bjerknes Centre, University of Bergen; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Matei, D.; Max-Planck-Institut fu ̈r Meteorologie,; Muller, W. A.; Max-Planck-Institut fu ̈r Meteorologie,; Rogel, P.; CERFACS Abstract: Assessing the skill of the Atlantic meridional overturning circulation (AMOC) in decadal hindcasts (i.e. retrospective predictions) is hampered by a lack of obser- vations for verification. Models are therefore needed to reconstruct the historical AMOC variability. Here we show that ten recent oceanic syntheses provide a common signal of AMOC variability at 45°N, with an increase from the 1960s to the mid-1990s and a decrease thereafter although they disagree on the exact magnitude. This signal corre- lates with observed key processes such as the North Atlantic Oscillation, sub-polar gyre strength, Atlantic sea surface temperature dipole, and Labrador Sea convection that are thought to be related to the AMOC. Furthermore, we find potential predictability of the mid-latitude AMOC for the first 3–6 year means when we validate decadal hindcasts for the past 50 years against the multi-model signal. However, this predictability is not found in models driven only by external radiative changes, demonstrating the need for initialization of decadal climate predictions.

Strengthening of the hydrological cycle in future scenarios: atmospheric energy and water balance perspective

Sat, 31 Dec 2011 23:00:00 GMT

Title: Strengthening of the hydrological cycle in future scenarios: atmospheric energy and water balance perspective Authors: Alessandri, A.; ENEA; Fogli, P. G.; CMCC; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Zeng, N.; University of Mariland Abstract: Future climate scenarios experiencing global warming are expected to strengthen the hydrological cycle during the 21st century (21C). We analyze the strengthening of the global-scale increase in precipitation from the perspective of changes in whole atmospheric water and energy balances. By combining energy and water equations for the whole atmosphere, we obtain constraints for the changes in surface fluxes and partitioning at the surface between sensible and latent components. We investigate the differences in the strengthening of the hydrological cycle in two centennial simulations performed with an Earth system model forced with specified atmospheric concentration pathways. Alongside the Special Report on Emissions Scenario (SRES) A1B, which is a medium-high non-mitigation scenario, we consider a new aggressive-mitigation scenario (E1) with reduced fossil fuel use for energy production aimed at stabilizing global warming below 2 K. Our results show that the mitigation scenario effectively constrains the global warming with a stabilization below 2 K with respect to the 1950–2000 historical period. On the other hand, the E1 precipitation does not follow the temperature field toward a stabilization path but continues to increase over the mitigation period. Quite unexpectedly, the mitigation scenario is shown to strengthen the hydrological cycle even more than SRES A1B till around 2070. We show that this is mostly a consequence of the larger increase in the negative radiative imbalance of atmosphere in E1 compared to A1B. This appears to be primarily related to decreased sulfate aerosol concentration in E1, which considerably reduces atmospheric absorption of solar radiation compared to A1B. The last decades of the 21C show a marked increase in global precipitation in A1B compared to E1, despite the fact that the two scenarios display almost the same overall increase of radiative imbalance with respect to the 20th century. Our results show that radiative cooling is weakly effective in A1B throughout the 21C. Two distinct mechanisms characterize the diverse strengthening of the hydrological cycle in the middle and end- 21C. It is only through a very large perturbation of surface fluxes that A1B achieves a larger increase in global precipitation in the last decades of the 21C. Our energy/water budget analysis shows that this behavior is ultimately due to a bifurcation in the Bowen ratio change between the two scenarios. This work warns that mitigation policies that promote aerosol abatement, may lead to an unexpected stronger intensification of the hydrological cycle and associated changes that may last for decades after global warming is effectively mitigated. On the other hand, it is also suggested that predictable components of the radiative forcing by aerosols may have the potential to effectively contribute to the decadal-scale predictability of changes in the hydrological strength.

Bedmap2: improved ice bed, surface and thickness datasets for Antarctica

Mon, 31 Dec 2012 23:00:00 GMT

Title: Bedmap2: improved ice bed, surface and thickness datasets for Antarctica Authors: Fretwell, P.; British Antarctic Survey, Cambridge, UK; Pritchard, H. D.; British Antarctic Survey, Cambridge, UK; Vaughan, D. G.; British Antarctic Survey, Cambridge, UK; Bamber, J. L.; School of Geographical Sciences, University of Bristol, UK; Barrand, N. E.; British Antarctic Survey, Cambridge, UK; Bell, R.; Lamont-Doherty Earth Observatory of Columbia University, Palisades, USA; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bingham, R. G.; School of Geosciences, University of Aberdeen, UK; Blankenship, D. D.; Institute for Geophysics, University of Texas at Austin, USA; Casassa, G.; Centro de Estudios Cientificos, Santiago, Chile; Catania, G.; Institute for Geophysics, University of Texas at Austin, USA; Callens, D.; Laboratoire de Glaciologie, Universit´e Libre de Bruxelles, Brussels, Belgium; Conway, H.; Earth and Space Sciences, University of Washington, Seattle, USA; Cook, A. J.; Department of Geography, Swansea University, Swansea, UK; Corr, H. F. J.; British Antarctic Survey, Cambridge, UK; Damaske, D.; Federal Institute for Geosciences and Natural Resources, Hannover, Germany; Damm, V.; Federal Institute for Geosciences and Natural Resources, Hannover, Germany; Ferraccioli, F.; British Antarctic Survey, Cambridge, UK; Forsberg, R.; National Space Institute, Technical University of Denmark, Denmark; Fujita, S.; National Institute of Polar Research, Tokyo, Japan; Gim, Y.; Jet Propulsion Laboratory. California Institute of Technology, Pasadena, USA; Gogineni, P.; Electrical Engineering & Computer Science, University of Kansas, Lawrence, USA; Griggs, J. A.; School of Geographical Sciences, University of Bristol, UK; Hindmarsh, R. C. A.; British Antarctic Survey, Cambridge, UK; Holmlund, P.; Stockholm University, Stockholm, Sweden; Holt, J. W.; Institute for Geophysics, University of Texas at Austin, USA; Jacobel, R. W.; St. Olaf College, Northfield, MN 55057, USA; Jenkins, A.; British Antarctic Survey, Cambridge, UK; Jokat, W.; Alfred Wegener Institute, Bremerhaven, Germany; Jordan, T.; British Antarctic Survey, Cambridge, UK; King, E. C.; British Antarctic Survey, Cambridge, UK; Kohler, J.; Norwegian Polar Institute, Fram Centre, Tromsø, Norway; Krabill, W.; NASA Wallops Flight Facility, Virginia, USA; Riger-Kusk, M.; College of Science, University of Canterbury, Christchurch, New Zealand; Langley, K. A.; Department of Geosciences, University of Oslo, Norway; Leitchenkov, G.; Institute for Geology and Mineral Resources of the World Ocean, St.-Petersburg, Russia; Leuschen, C.; Electrical Engineering & Computer Science, University of Kansas, Lawrence, USA; Luyendyk, B. P.; Earth Research Institute, University of California in Santa Barbara, USA; Matsuoka, K.; Norwegian Polar Institute, Tromso, Norway; Mouginot, J.; Department of Earth System Science, University of California, Irvine, USA; Nitsche, F. O.; Lamont-Doherty Earth Observatory of Columbia University, Palisades, USA; Nogi, Y.; National Institute of Polar Research, Tokyo, Japan; Nost, O. A.; Norwegian Polar Institute, Tromso, Norway; Popov, S. V.; Polar Marine Geosurvey Expedition, St.-Petersburg, Russia; Rignot, E.; School of Physical Sciences, University of California, Irvine, USA; Rippin, D. M.; Environment Department, University of York, Heslington, York, YO10 5DD, UK; Rivera, A.; Centro de Estudios Cientificos, Santiago, Chile; Roberts, J.; Department of Sustainability, Environment, Water, Population and Communities, Australian Antarctic Division, Hobart, Tasmania, Australia; Ross, N.; School of Geography, Politics and Sociology, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK; Siegert, M. J.; School of Geographical Sciences, University of Bristol, UK; Smith, A. M.; British Antarctic Survey, Cambridge, UK; Steinhage, D.; Alfred Wegener Institute, Bremerhaven, Germany; Studinger, M.; NASA Goddard Space Flight Center, Greenbelt, USA; Sun, B.; Polar Research Institute of China, Shanghai, China; Tinto, B. K.; Lamont-Doherty Earth Observatory of Columbia University, Palisades, USA; Welch, B. C.; Alfred Wegener Institute, Bremerhaven, Germany; Wilson, D.; Institute for Crustal Studies, University of California in Santa Barbara, USA; Young, D. A.; Institute for Geophysics, University of Texas at Austin, USA; Xiangbin, C.; Polar Research Institute of China, Shanghai, China; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60 S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved datacoverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72m lower and the area of ice sheet grounded on bed below sea level is increased by 10 %. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets.

ENSO and its effects on the atmospheric heating processes

Tue, 28 Feb 2012 23:00:00 GMT

Title: ENSO and its effects on the atmospheric heating processes Authors: Miyakoda, K.; Princeton University; Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Ploshay, J.; GFDL, NJ, USA Abstract: El Nino-Southern Oscillation (ENSO) is an important air-sea coupled phenomenon that plays a dominant role in the variability of the tropical regions. Observations, atmospheric and oceanic reanalysis datasets are used to classify ENSO and non-ENSO years to investigate the typical features of its periodicity and atmospheric circulation patterns. Among non-ENSO years, we have analyzed a group, called type-II years, with very small SST anomalies in summer that tend to weaken the correlation between ENSO and precipitation in the equatorial regions. A unique character of ENSO is studied in terms of the quasi-biennial periodicity of SST and heat content (HC) fields over the Pacific-Indian Oceans. While the SST tends to have higher biennial frequency along the Equator, the HC maximizes it into two centers in the western Pacific sector. The north-western center, located east of Mindanao, is strongly correlated with SST in the NINO3 region. The classification of El Nino and La Nina years, based on NINO3 SST and north-western Pacific HC respectively, has been used to identify and describe temperature and wind patterns over an extended-ENSO region that includes the tropical Pacific and Indian Oceans. The description of the spatial patterns within the atmospheric ENSO circulation has been extended to tropospheric moisture fields and low-level moisture divergence during November–December–January, differentiating the role of El Nino, when large amounts of condensational heat are concentrated in the central Pacific, from La Nina that tends to mainly redistribute heat to Maritime Continents and higher latitudes. The influence of the described mechanisms on equatorial convection in the context of the variability of ENSO on longer timescales for the end of the 20th century is questioned. However, the inaccuracy of the atmospheric reanalysis products in terms of precipitation and the shorter time length of more reliable datasets hamper a final conclusion on this issue.

The CIRCE simulations: Regional Climate Change Projections with Realistic Representation of the Mediterranean Sea

Mon, 31 Dec 2012 23:00:00 GMT

Title: The CIRCE simulations: Regional Climate Change Projections with Realistic Representation of the Mediterranean Sea Authors: Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Somot, L.; CNRM-GAME; Li, L.; CNRS-LMD; Artale, V.; ENEA; Adani, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Bellucci, A.; CMCC; Braun, A.; CNRM-GAME; Calmanti, S.; ENEA; Carillo, A.; ENEA; Dell'Aquila, A.; ENEA; Deque, M.; CNRM-GAME; Dubois, C.; CNRM-GAME; Elizade, A.; MPI; Harzallah, A.; INSTM; Jacob, D.; MPI; L'Hévéder, D.; CNRS-LMD; May, W.; DMI; Oddo, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Ruti, P.; ENEA; Sanna, A.; CMCC; Sannino, G.; ENEA; Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Savault, F.; CNRM-GAME; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: In this article we describe an innovative multi-model system developed within the CIRCE EU-FP6 Project and used to produce simulations of the Mediterranean Sea regional climate. The models include high-resolution Mediterranean Sea components, which allow to assess the role of the basin, and in particular of the air-sea feedbacks in the climate of the region. The models have been integrated from 1951 to 2050, using observed radiative forcings during the first half of the simulation period and the IPCC SRES A1B scenario during the second half. The projections show a substantial warming (about 1.5°-2°C) and a significant decrease of precipitation (about 5%) in the region for the scenario period. However, locally the changes might be even larger. In the same period, the projected surface net heat loss decreases, leading to a weaker cooling of the Mediterranean Sea by the atmosphere, whereas the water budget appears to increase, leading the basin to loose more water through its surface than in the past. These results are overall consistent with the findings of previous scenario simulations, such as PRUDENCE, ENSEMBLES and CMIP3. The agreement suggests that these findings are robust to substantial changes in the configuration of the models used to make the simulations. Finally, the models produce a 2021-2050 mean steric sea-level rise that ranges between +7 cm and +12 cm, with respect to the period of reference.

Climatology of the Central-Northern Adriatic Sea

Sat, 31 Dec 2011 23:00:00 GMT

Title: Climatology of the Central-Northern Adriatic Sea Authors: Russo, Aniello; Carniel, Sandro; Sclavo, Mauro; Krzelj, Maja Editors: InTech Abstract: It is well know that the ocean processes exert a great influence on global climate as well as affect the local climate of coastal areas (Russo et al., 2002). Within the Mediterranean region (see Fig. 1a), the presence of the Adriatic Sea influences the atmospheric properties of the surrounding regions over long and short time-scales, and has obviously a relevant influence on human activities and ecosystems (Boldrin et al., 2009).This Chapter will describe the main climatological characteristics of the northern-central Adriatic Sea (see Figure 1b) assessed on a human time-scale, i.e. the last few decades.

Decadal Climate Predictions with a coupled OAGCM initialized with oceanic reanalyses

Mon, 31 Dec 2012 23:00:00 GMT

Title: Decadal Climate Predictions with a coupled OAGCM initialized with oceanic reanalyses Authors: Bellucci, A.; CMCC; Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Storto, A.; CMCC; Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Cagnazzo, C.; CMCC; Fogli, P. G.; CMCC; Manzini, E.; MPI; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: We investigate the effects of realistic oceanic initial conditions on a set of decadal climate predictions performed with a state-of-the-art coupled ocean-atmo- sphere general circulation model. The decadal predictions are performed in both retrospective (hindcast) and forecast modes. Specifically, the full set of prediction experiments consists of 3-member ensembles of 30-year simulations, starting at 5-year intervals from 1960 to 2005, using his- torical radiative forcing conditions for the 1960–2005 period, followed by RCP4.5 scenario settings for the 2006–2035 period. The ocean initial states are provided by ocean reanalyses differing by assimilation methods and assimilated data, but obtained with the same ocean model. The use of alternative ocean reanalyses yields the required perturbation of the full three-dimensional ocean state aimed at generating the ensemble members spread. A full- value initialization technique is adopted. The predictive skill of the system appears to be driven to large extent by trends in the radiative forcing. However, after detrending, a residual skill over specific regions of the ocean emerges in the near-term. Specifically, natural fluctuations in the North Atlantic sea-surface temperature (SST) associated with large-scale multi-decadal variability modes are predictable in the 2–5 year range. This is consistent with significant predictive skill found in the Atlantic meridional overturn- ing circulation over a similar timescale. The dependency of forecast skill on ocean initialization is analysed, revealing a strong impact of details of ocean data assimilation products on the system predictive skill. This points to the need of reducing the large uncertainties that currently affect global ocean reanalyses, in the perspective of providing reliable near-term climate predictions.

Tropical Cyclone Effects on Arctic Sea Ice Variability

Sat, 31 Dec 2011 23:00:00 GMT

Title: Tropical Cyclone Effects on Arctic Sea Ice Variability Authors: Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: In recent years increasing interest has been put on the role that intense Tropical Cyclones can play in the climate system. The following study is aimed at highlighting the effects of strong Tropical Cyclones over the Tropical Atlantic on the mean climate. Their composite effect on the surface winds is made apparent by a wide cyclonic perturbation that affects a large portion of the Atlantic tropical Ocean. Teleconnection patterns, which are visible in the Sea Level Pressure anomalies associated with this Tropical Composite Cyclone, appear to link the activity of the hurricanes to the Arctic Ocean. A significant negative correlation between the energy dissipated by hurricanes in the Tropical atmosphere and the sea ice cover along the Transpolar Drift Stream path, has also been found.

Effect of surface albedo, water vapour, and atmospheric aerosols on the cloud-free shortwave radiative budget in the Arctic

Sat, 31 Dec 2011 23:00:00 GMT

Title: Effect of surface albedo, water vapour, and atmospheric aerosols on the cloud-free shortwave radiative budget in the Arctic Authors: Di Biagio, C.; ENEA, Laboratory for Earth Observations and Analyses, Via Anguillarese 301, 00123 Rome, Italy; Di Sarra, A.; ENEA, Laboratory for Earth Observations and Analyses, Via Anguillarese 301, 00123 Rome, Italy; Eriksen, P.; DMI, Danish Meteorological Institute, Danish Climate Centre, Lyngbyvej 100, 2100 Copenhagen, Denmark; Ascanius, S. E.; DMI, Danish Meteorological Institute, Qaanaaq, Greenland; Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Holben, B.; NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Abstract: This study is based on ground-based measurements of downward surface shortwave irradiance (SW), columnar water vapour (wv), and aerosol optical depth (s) obtained at Thule Air Base (Greenland) in 2007–2010, together with MODIS observations of the surface shortwave albedo (A). Radiative transfer model calculations are used in combination with measurements to separate the radiative effect of A (∆SWA), wv (DSWwv), and aerosols (∆SWs) in modulating SW in cloud-free conditions. The shortwave radiation at the surface is mainly affected by water vapour absorption, which produces a reduction of SW as low as -100 Wm-2 (-18%). The seasonal change of A produces an increase of SW by up to +25 Wm-2 (+4.5%). The annual mean radiative effect is estimated to be -(21–22) Wm-2 for wv, and +(2–3) Wm-2 for A. An increase by +0.065 cm in the annual mean wv, to which corresponds an absolute increase in ∆SWwv by 0.93 Wm-2 (4.3%), has been observed to occur between 2007 and 2010. In the same period, the annual mean A has decreased by -0.027, with a corresponding decrease in ∆SWA by 0.41 Wm-2 (-14.9%). Atmospheric aerosols produce a reduction of SW as low as -32 Wm-2 (-6.7%). The instantaneous aerosol radiative forcing (RFs) reaches values of -28 Wm-2 and shows a strong dependency on surface albedo. The derived radiative forcing efficiency (FEs) for solar zenith angles between 55 and 70 is estimated to be (-120.6 ± 4.3) for 0.1