Cambiamenti Climatici Research Articles

Performance of State‐of‐the‐Art C3S European Seasonal Climate Forecast Models for Mean and Extreme Precipitation Over Africa

AbstractSeasonal hydrological forecasts at high spatial and temporal resolution can help manage water resources and mitigate impacts of extreme events but are dependent on skillful and operational seasonal forecasts from climate models. In this study, we evaluate precipitation forecasts from five operational climate models with a potential to drive hydrological forecasts: European Centre for Medium‐Range Weather Forecasts (ECMWF), UK Met Office (UK‐Met), Météo France, Deutscher Wetterdienst, and Centro Euro‐Mediterraneo sui Cambiamenti Climatici. The Multi‐Source Weighted‐Ensemble Precipitation is used as a reference data set to evaluate the model skill. The performance of individual models is evaluated on daily, weekly, monthly, seasonal, and climatological periods, and for selected target months, lead‐times and drought events, and compared to unweighted and skill‐weighted multi‐model ensemble mean forecast. For all models, the lead 1‐month forecast can replicate the climatological mean, monthly mean, and monthly anomaly precipitation, although much of this skill originates from the first week of the forecast. The skill drops rapidly for lead 2‐month and longer and is highest in drier regions and seasons. The forecast skill of monthly meteorological drought events at lead 1‐month is modest. All models represent the monthly variation in the length of wet and dry spell days at lead 1‐month, but the skill is weak for heavy and very heavy precipitation days. ECMWF is found to be the most skillful model, followed by the UK‐Met, although the multi‐model weighted average provides the highest performance compared to individual models and the un‐weighted multi‐model mean.

Variability of Rainfall Over the Coastal Area In Bangladesh by Using Climate Model

The study attempt to understand the variability of rainfall by looking into the previous and future climate of the coastal area in Bangladesh from 1850 to 2100 by using the climate model (CMCC-CM- the Centro Euro-Mediterraneo Sui Cambiamenti Climatici Climate Model) of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). Rainfall data were collected from CMCC-CM by R programming for two GHGs emission scenarios (RCP 4.5 and RCP 8.5) referred to as ‘Representative Concentration Pathways (RCPs)’. The analysis has been conducted based on four seasons and an annual basis by plotting model data in MS Excel and R programming. The model shows that the average annual rainfall will increase from 1055.6 mm (during 1850-1900) to 1368.1mm (during 2051-2100) for RCP 4.5 while it will reach 1569.7mm (during 2050-2100) for RCP 8.5. Rainfall is also increasing for all seasons except winter. In winter season, the average rainfall will increase from 35.37mm (during 1850-1900) to 41.75mm (during 2051-2100) for RCP 4.5, where it will decrease from 35.37mm (during 1850-1900) to 22.55mm (during 2051-2100) for RCP 8.5 in the study area. The increasing and decreasing trend are more in high GHGs emission scenarios than in the medium, which will be alarming. Accordingly, this projection will be helpful to understand the adverse impacts of climatic elements and take short and long-term planning of decision-makers in that area. J. Asiat. Soc. Bangladesh, Sci. 47(2): 149-160, December 2021

Recent Advances of a Box Model to Represent the Estuarine Dynamics: Time‐Variable Estuary Length and Eddy Diffusivity

AbstractThis study starts from a two‐layer 1D Estuary Box Model (EBM), the so called Centro Euro‐Mediterraneo sui Cambiamenti Climatici (CMCC) EBM (Verri et al., 2020, https://doi.org/10.1016/j.ocemod.2020.101587), devised to offer a proper representation of the net river release in a coupled modeling framework with hydrology models and ocean models reaching the mesoscale. Two key advances are proposed in the present study: (I) the estuary length and (II) the horizontal eddy diffusivity coefficient are no longer considered as static parameters to calibrate but two non‐dimensional equations have been introduced in order to make them time‐variable. The Goro branch of the Po river delta is considered as case study of “salt‐wedge estuary” flowing into a microtidal sea. Regarding the estuary length, a non‐dimensional equation has been tested and validated. This equation provides a time dependent estuary box volume which is more realistic choice. This time‐variable estuary length represents the length of the salt wedge intrusion. Regarding the horizontal eddy diffusivity, the static eddy coefficient adopted in the previous version of the model is a coarse assumption. Thus a non‐dimensional equation for this coefficient has been tested and validated. It makes the eddy diffusivity dependent on the velocity shear, the salinity gradient and the estuary geometry. The proposed dynamic formula is found to enhance the model capability to reproduce the salinity at the estuary mouth. Overall the high statistical performance in terms of RMSE and correlation coefficient, the short CPU time and the minimal calibration encourage to use the CMCC EBM in coupled mode with both mesoscale‐resolving ocean and hydrology models to produce operational forecasts and climate scenarios.

Increasing Atlantic Ocean Heat Transport in the Latest Generation Coupled Ocean‐Atmosphere Models: The Role of Air‐Sea Interaction

AbstractRecent increases in resolution of coupled ocean‐atmosphere models have the potential to improve the representation of poleward heat transport within the climate system. Here we examine the interplay between model resolution‐dependent changes in Atlantic Ocean heat transport (AOHT) and surface heat fluxes. The different roles of changes in atmospheric and ocean resolution are isolated using three different climate models (The Centro Euro‐Mediterraneo sui Cambiamenti Climatici Climate Model 2, Hadley Centre Global Environmental Model 3 – Global Coupled configuration 2, and European Community Earth‐System Model 3.1) and comparing runs in which (a) only the ocean resolution changes, (b) only the atmosphere resolution changes, and (c) both change. Enhancing ocean resolution from eddy parameterized to eddy permitting increases the AOHT throughout the basin, values changing from 1.0 to 1.2 PW at 26°N, bringing the AOHT into the range of estimates from the RAPID observing array. This increase in AOHT is associated with higher North Atlantic sea surface temperatures and increased ocean heat loss to the atmosphere. Increasing the atmospheric resolution alone has little impact on the AOHT due to regionally compensating changes in the components of the net heat flux. Finally, in a fourth experiment the impact of resolution changes in both components and the transition to an eddy‐resolving ocean is assessed. This additional resolution increase is accompanied by a further change in the AOHT and improves agreement with observations in the tropics but not the subpolar regions. However, unlike with the increase to the eddy‐permitting ocean, when the greatest AOHT change occurs in the subtropics and subpolar region, the most significant increase now occurs in the tropics.

Tropical Cyclone Interaction with the Ocean: The Role of High-Frequency (Subdaily) Coupled Processes

Through tropical cyclone (TC) activity the ocean and the atmosphere exchange a large amount of energy. In this work possible improvements introduced by a higher coupling frequency are tested between the two components of a climate model in the representation of TC intensity and TC–ocean feedbacks. The analysis is based on the new Centro Euro-Mediterraneo per I Cambiamenti Climatici Climate Model (CMCC-CM2-VHR), capable of representing realistic TCs up to category-5 storms. A significant role of the negative sea surface temperature (SST) feedback, leading to a weakening of the cyclone intensity, is made apparent by the improved representation of high-frequency coupled processes. The first part of this study demonstrates that a more realistic representation of strong TC count is obtained by coupling atmosphere and ocean components at hourly instead of daily frequency. Coherently, the positive bias of the annually averaged power dissipation index associated with TCs is reduced by one order of magnitude when coupling at the hourly frequency, compared to both forced mode and daily coupling frequency results. The second part of this work shows a case study (a modeled category-5 typhoon) analysis to verify the impact of a more realistic representation of the high-frequency coupling in representing the TC effect on the ocean; the theoretical subsurface warming induced by TCs is well represented when coupling the two components at the higher frequency. This work demonstrates that an increased horizontal resolution of model components is not sufficient to ensure a realistic representation of intense and fast-moving systems, such as tropical and extratropical cyclones, but a concurrent increase in coupling frequency is required.

C-GLORSv5: an improved multipurpose global ocean eddy-permitting physical reanalysis

Abstract. Global ocean reanalyses combine in situ and satellite ocean observations with a general circulation ocean model to estimate the time-evolving state of the ocean, and they represent a valuable tool for a variety of applications, ranging from climate monitoring and process studies to downstream applications, initialization of long-range forecasts and regional studies. The purpose of this paper is to document the recent upgrade of C-GLORS (version 5), the latest ocean reanalysis produced at the Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) that covers the meteorological satellite era (1980–present) and it is being updated in delayed time mode. The reanalysis is run at eddy-permitting resolution (1∕4° horizontal resolution and 50 vertical levels) and consists of a three-dimensional variational data assimilation system, a surface nudging and a bias correction scheme. With respect to the previous version (v4), C-GLORSv5 contains a number of improvements. In particular, background- and observation-error covariances have been retuned, allowing a flow-dependent inflation in the globally averaged background-error variance. An additional constraint on the Arctic sea-ice thickness was introduced, leading to a realistic ice volume evolution. Finally, the bias correction scheme and the initialization strategy were retuned. Results document that the new reanalysis outperforms the previous version in many aspects, especially in representing the variability of global heat content and associated steric sea level in the last decade, the top 80 m ocean temperature biases and root mean square errors, and the Atlantic Ocean meridional overturning circulation; slight worsening in the high-latitude salinity and deep ocean temperature emerge though, providing the motivation for further tuning of the reanalysis system. The dataset is available in NetCDF format at doi:10.1594/PANGAEA.857995.

Projecting changes in Tanzania rainfall for the 21st century

A non-homogeneous hidden Markov model (NHMM) is developed using a 40-year record (1950–1990) of daily rainfall at 11 stations in Tanzania and National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) re-analysis atmospheric fields of a number of meteorological variables. The following atmospheric fields, temperature at 1000 hPa, geo-potential height at 1000 hPa, meridional winds and zonal winds at 850 hPa, and zonal winds at the equator from 10 to 1000 hPa, in a region defined by 25°S–25°N and 25°–75°E are identified as appropriate predictors for the downscaling of the seasonal regime of daily rainfall in Tanzania. The NHMM is used to predict future rainfall patterns under a comparatively high greenhouse gas emissions scenario [Representative Concentration Pathway 8.5 (RCP8.5)], using predictors from the CMCC-CMS (Centro Mediterraneo sui Cambiamenti Climatici) simulations from 1950 to 2100. Instead of pre-specifying a fixed rainy season, the model considers seasonality of precipitation to be determined by the 21st century simulations of the atmospheric variables used as predictors. The future downscaled precipitation simulations for the RCP8.5 scenario indicate that in the 21st century Tanzania may experience: (1) a slight decrease in the number of wet days and seasonal rainfall in MAM and JJAS, but not in OND; (2) a reduction of annual total rainfall; and (3) an intensification of the frequency and intensity of extreme rainfall, as identified by 90th, 95th, and 99th percentiles.

The Representation of Atmospheric Blocking and the Associated Low-Frequency Variability in Two Seasonal Prediction Systems

Abstract Primarily as a response to boundary forcings, certain components of the atmospheric intraseasonal variability are potentially predictable. Particularly referring to the extratropics, the current generation of seasonal forecasting systems is making advancements in predicting these components by realistically initializing many components of the climate system, using higher resolution and utilizing large ensemble sizes. The operational seasonal prediction system of the Met Office (UKMO) and the corresponding system of the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) are analyzed in terms of their representation of different aspects of extratropical low-frequency variability. The UKMO system achieves unprecedented high scores in predicting the winter mean phase of the North Atlantic Oscillation (NAO; correlation 0.62) and the Pacific–North American pattern (PNA; correlation 0.82). The CMCC system, despite its smaller ensemble size and coarser resolution, also exhibits significant skill (0.42 for NAO, 0.51 for PNA). Low-frequency variability is underrepresented in both models, particularly in the eastern North Atlantic. Consequently, their intrinsic variability patterns (sectoral EOFs) are somewhat different from the observed patterns. Regarding the representation of wintertime Northern Hemisphere blocking, after bias correction both systems exhibit a realistic climatology of blocking frequency. In this assessment, instantaneous blocking and large-scale persistent blocking events are identified using daily geopotential height fields at 500 hPa. The blocking signature on the circulation and the dependence of blocking frequency on the NAO are also quite realistic for both systems. Finally, the Met Office system exhibits significant skill in predicting the winter mean frequency of blocking that relates to the NAO.

A blocking view of the stratosphere‐troposphere coupling

AbstractDynamical influence from the stratosphere is known to play a role in shaping the wintertime tropospheric circulation patterns. Observations suggest that this influence is strongest following weak and strong polar vortex events, termed sudden stratospheric warmings (SSWs) and vortex intensification (VI) events, respectively. In this work, stratosphere‐troposphere coupling is studied through the modulation by extreme vortex events of the Northern Hemispheric tropospheric blocking frequency and eddy‐driven jet displacements. This is done using three reanalysis data sets and the Centro Euro‐Mediterraneo sui Cambiamenti Climatici Climate Model with a resolved Stratosphere (CMCC‐CMS) coupled model control run. Reanalysis results suggest the existence of distinct patterns of blocking activity following extreme vortex events. Over the Atlantic basin, SSWs are shown to lead by about 20–50 days the occurrence of increased/reduced blocking frequency on the poleward/equatorward side of the Atlantic jet stream. Anomalies of the opposite sense, with poleward reduction and equatorward enhancement of the blocking frequency, occur following VI events. The response over the Pacific sector is less clear. Compared to reanalyses, CMCC‐CMS shows a similar but weaker response, especially over the Atlantic: a possible explanation is identified in the different structure of the polar vortex and weaker wind shear anomalies with respect to reanalysis. We finally highlight that patterns identified following vortex extremes show similarities with the Northern Annular Mode over the Atlantic but not over the Pacific. This suggests that the stratosphere‐troposphere coupling is more a regional than annular feature.

Estimation and Impact of Nonuniform Horizontal Correlation Length Scales for Global Ocean Physical Analyses

Abstract Optimally modeling background-error horizontal correlations is crucial in ocean data assimilation. This paper investigates the impact of releasing the assumption of uniform background-error correlations in a global ocean variational analysis system. Spatially varying horizontal correlations are introduced in the recursive filter operator, which is used for modeling horizontal covariances in the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) analysis system. The horizontal correlation length scales (HCLSs) were defined on the full three-dimensional model space and computed from both a dataset of monthly anomalies with respect to the monthly climatology and through the so-called National Meteorological Center (NMC) method. Different formulas for estimating the correlation length scale are also discussed and applied to the two forecast error datasets. The new formulation is tested within a 12-yr period (2000–11) in the ½° resolution system. The comparison with the data assimilation system using uniform background-error horizontal correlations indicates the superiority of the former, especially in eddy-dominated areas. Verification skill scores report a significant reduction of RMSE, and the use of nonuniform length scales improves the representation of the eddy kinetic energy at midlatitudes, suggesting that uniform, latitude, or Rossby radius-dependent formulations are insufficient to represent the geographical variations of the background-error correlations. Furthermore, a small tuning of the globally uniform value of the length scale was found to have a small impact on the analysis system. The use of either anomalies or NMC-derived correlation length scales also has a marginal effect with respect to the use of nonuniform HCLSs. On the other hand, the application of overestimated length scales has proved to be detrimental to the analysis system in all areas and for all parameters.

The climate of the Mediterranean region: research progress and climate change impacts

This special issue was proposed at the second MedCLIVAR conference (which was held in Madrid, Spain, 26–29 September 2012) and has received a wide range of contributions covering different and complementary topics: paleo-climate, present climate variability and trends, extremes, climate projections, and impacts of future climate change on the regional environment and societies. All these topics (see Lionello et al. 2012b, for a synthesis) are subject of a rapidly evolving research, which has the sensitivity of the Mediterranean region to climate change as a main motivation. In fact, in the last decades in the Mediterranean region, temperatures have risen faster than the global average and model projections agree on its future warming and drying, with a likely increase of heat waves and dry spells. Further, countries around the Mediterranean basin are characterized by strong differences, as shown by various socioeconomic and environmental indicators, such as per capita gross domestic product (GDP), energy supply, CO2 emissions, and water availability. Environmental issues are exacerbated by societal aspect, as the whole region is densely populated with many Middle East and North African (MENA) countries expected to double their population by the mid-twenty-first century. A growing dependence on irrigation in MENA countries will likely increase their economic and social vulnerability, because of future reduced total water availability and rapidly growing competing urban water demands. This issue is an outcome of the work carried on within the MedCLIVAR network. It describes recent progresses on the understanding of the climate of the Mediterranean region and the impacts of its future evolution on the environment and people. MedCLIVAR (Mediterranean CLImate VARiability) has been running continuously for about 10 years. It was initially proposed at the 2003 European Geosciences Union assembly in Nice (France), endorsed by the international Climate Variability and Predictability (CLIVAR) office in 2005, and supported by the European Science Foundation for the period 2006–2011. This special issue is the latest contribution to the MedCLIVAR dissemination activity, which has already produced three books (Lionello et al. 2006; Vicente-Serrano and Trigo 2011; Lionello 2012) and 4 special issues (Lionello et al. 2008; Jones et al. 2011; Lionello 2012; P. Lionello (&) DISTeBA, University of Salento, CMCC – Centro EuroMediterraneo sui Cambiamenti Climatici, via per Monteroni 165, Block M, 73100 Lecce, Italy e-mail: piero.lionello@unisalento.it

Intensity-Duration-Frequency (IDF) rainfall curves, for data series and climate projection in African cities.

Changes in the hydrologic cycle due to increase in greenhouse gases cause variations in intensity, duration, and frequency of precipitation events. Quantifying the potential effects of climate change and adapting to them is one way to reduce urban vulnerability. Since rainfall characteristics are often used to design water structures, reviewing and updating rainfall characteristics (i.e., Intensity–Duration–Frequency (IDF) curves) for future climate scenarios is necessary (Reg Environ Change 13(1 Supplement):25-33, 2013).The present study regards the evaluation of the IDF curves for three case studies: Addis Ababa (Ethiopia), Dar Es Salaam (Tanzania) and Douala (Cameroon). Starting from daily rainfall observed data, to define the IDF curves and the extreme values in a smaller time window (10′, 30′, 1 h, 3 h, 6 h, 12 h), disaggregation techniques of the collected data have been used, in order to generate a synthetic sequence of rainfall, with statistical properties similar to the recorded data. Then, the rainfall pattern of the three test cities was analyzed and IDF curves were evaluated.In order to estimate the contingent influence of climate change on the IDF curves, the described procedure was applied to the climate (rainfall) simulations over the time period 2010–2050, provided by CMCC (Centro Euro-Mediterraneo sui Cambiamenti Climatici). The evaluation of the IDF curves allowed to frame the rainfall evolution of the three case studies, considering initially only historical data, then taking into account the climate projections, in order to verify the changes in rainfall patterns. The same set of data and projections was also used for evaluating the Probable Maximum Precipitation (PMP).

VALUE AT RISK (VaR)

The value at risk (VaR) measures the risk of loss associated to financial assets. For a given time period (normally ranging from 1 to 10 days), and with a given probability confidence (generally equal to 95% or 99%); this measure represents the maximum loss the investor can suffer when holding financial assets. The time horizon used to calculate the VaR depends on the investment duration; the value at risk is used to compute the minimum capital requirements necessary to compensate losses resulting from market risk, according to the BIS banking regulation. Value at risk (VaR) measures the risk of loss associated to financial assets. For a given time period (normally ranging from 1 to 10 days), and with a given probability level (generally equal to 95% or 99%), this measure represents the maximum loss the investor can suffer when holding financial assets. This loss derives from a model implementation, and reflects the interaction of a number of factors assumed correlated one with the other. The time horizon chosen to calculate VaR is in accordance with the investment duration or with the minimum time length needed to disinvest in case of loss. The VaR is used also, and perhaps mostly, to determine the minimum capital requirements necessary to compensate for losses resulting from market risk. This measure ap1 Melania MICHETTI, Researcher at the Centro Euro-Mediterraneo per i Cambiamenti Climatici – CMCC.

An integrated assessment of Super & Smart Grids.

By Elena Claire Ricci Fondazione Eni Enrico Mattei (FEEM), Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) elena.ricci@cmcc.it SUMMARY We assess the optimality of investments in power grid innovation, under both technological options of Super and Smart Grids, using the WITCH model in the version that includes Super-Grids. Super Grids allow to produce and trade electricity generated by large scale concentrated solar power (CSP) plants in highly productive areas that are connected to the demand centres through High Voltage Direct Current (HVDC) cables. We extend the model to include also Smart-Grids that allow: i) to increase the share of renewable power manageable by the power network, ii) to reduce the costs of customer relationships via Smart Meters; iii) residential consumer to generate electricity via micro-photovoltaic plants, and iv) residential consumer to generate virtual electricity via consumption management. We find that it becomes optimal to invest in grid innovation, in order to start gaining the management benefits and taking advantage of consumer generating opportunities (of electricity and “nega-watts”), starting in 2010 and to exploit the increased possible penetration of renewable energy sources from 2035. Long-distance CSP generation becomes optimal only from 2040, and trade from 2050; but it reaches very high shares in the second half of the century, especially when penetration limits are imposed on nuclear power and on carbon capture and storage operations (CCS). On the whole, climate policy costs can be reduced by large percentages, up to 48%, 34%, 24% for the USA, Western Europe, Eastern Europe, respectively, with respect to corresponding scenarios without the grid innovation via Super and Smart Grid option and with limits on nuclear power, CCS, and CSP import. The analysis is then extended to compare these options considering, at least qualitatively, the differentiated impacts on the environment, technology, organization, society, local and national economies and geopolitics.

Madden‐Julian Oscillation in a climate model with a well‐resolved stratosphere

This work evaluates how well a coupled ocean‐atmospheric climate model with a well‐resolved stratosphere captures the observed Madden‐Julian Oscillation (MJO) signal in the upper troposphere and lower stratosphere. The model is the Centro Euro‐Mediterraneo per i Cambiamenti Climatici (CMCC) coupled modeling system (CMCC‐CMS) with 95 atmospheric levels. CMCC‐CMS produces MJO composites of precipitation that are very similar to those of the observations and the ERA‐40 reanalysis product. Furthermore, model precipitation is found to propagate eastward near the observed speed. There is also strong agreement in the tropics and subtropics in the temperature and flows at 100 and 200 hPa upon comparing the composites based on the full 340 years of model output and those for the past 20 years of the model output with those of the ERA‐40 reanalysis. At the 100 hPa level the temperature anomalies in the model output and reanalysis propagate eastward at about 7 m s–1 at the equator, 25°N and 65°N. Longitude and height cross sections at 25°N suggest vertically propagating Rossby waves up to near the 10 hPa level in both the model and observations. Latitude and height cross sections of temperature and zonal and meridional winds indicate strong vertical propagation in the tropics in both the model and reanalysis. Overall, the CMCC‐CMS model shows MJO characteristics in the tropical and subtropical troposphere and lower stratosphere that are in very good agreement with observed analyses.

Tropical Cyclone Count Forecasting Using a Dynamical Seasonal Prediction System: Sensitivity to Improved Ocean Initialization

Abstract This study investigates the predictability of tropical cyclone (TC) seasonal count anomalies using the Centro Euro-Mediterraneo per i Cambiamenti Climatici–Istituto Nazionale di Geofisica e Vulcanologia (CMCC-INGV) Seasonal Prediction System (SPS). To this aim, nine-member ensemble forecasts for the period 1992–2001 for two starting dates per year were performed. The skill in reproducing the observed TC counts has been evaluated after the application of a TC location and tracking detection method to the retrospective forecasts. The SPS displays good skill in predicting the observed TC count anomalies, particularly over the tropical Pacific and Atlantic Oceans. The simulated TC activity exhibits realistic geographical distribution and interannual variability, thus indicating that the model is able to reproduce the major basic mechanisms that link the TCs’ occurrence with the large-scale circulation. TC count anomalies prediction has been found to be sensitive to the subsurface assimilation in the ocean for initialization. Comparing the results with control simulations performed without assimilated initial conditions, the results indicate that the assimilation significantly improves the prediction of the TC count anomalies over the eastern North Pacific Ocean (ENP) and northern Indian Ocean (NI) during boreal summer. During the austral counterpart, significant progresses over the area surrounding Australia (AUS) and in terms of the probabilistic quality of the predictions also over the southern Indian Ocean (SI) were evidenced. The analysis shows that the improvement in the prediction of anomalous TC counts follows the enhancement in forecasting daily anomalies in sea surface temperature due to subsurface ocean initialization. Furthermore, the skill changes appear to be in part related to forecast differences in convective available potential energy (CAPE) over the ENP and the North Atlantic Ocean (ATL), in wind shear over the NI, and in both CAPE and wind shear over the SI.

Global ocean re-analyses for climate applications

One of the main objectives of the global ocean modelling activities at Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) is the production of global ocean re-analyses over multidecadal periods to reconstruct the state of the ocean and the large scale circulation over the recent past. The re-analyses are used for climate applications and for the assessment of the benefits of assimilating ocean observations on seasonal and longer predictions. Here we present the main characteristics of an optimal interpolation based assimilation system used to produce a set of global ocean re-analyses validated against a set of high quality in situ observations and independent data. Differences among the experiments of the set are analyzed in terms of improvements in the method used to assimilate the data and the quality of observations themselves. For example, the integrated ocean heat content, which can be taken as an indicator of climate changes, is examined to detect possible sources of uncertainty of its long-term changes. Global and basin scale upper ocean heat content exhibits warming trends over the last few decades that still depend in a significant way on the assimilated observations and the formulation of the background covariances. However, all the re-analyses show a global warming trend of the oceanic uppermost 700 m over the last five decades that falls within the range of the most recent observation-based estimates. The largest discrepancies between our estimates and observational based ones are confined in the upwelling regions of the Pacific and Atlantic Oceans. Finally, the results show that the climatological heat and salt transports as a function of latitude also fall within the range of the estimates based on observations and atmospheric re-analyses.

The INGV–CMCC Seasonal Prediction System: Improved Ocean Initial Conditions

Abstract The development of the Istituto Nazionale di Geofisica e Vulcanologia (INGV)–Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) Seasonal Prediction System (SPS) is documented. In this SPS the ocean initial-conditions estimation includes a reduced-order optimal interpolation procedure for the assimilation of temperature and salinity profiles at the global scale. Nine-member ensemble forecasts have been produced for the period 1991–2003 for two starting dates per year in order to assess the impact of the subsurface assimilation in the ocean for initialization. Comparing the results with control simulations (i.e., without assimilation of subsurface profiles during ocean initialization), it is shown that the improved ocean initialization increases the skill in the prediction of tropical Pacific sea surface temperatures of the system for boreal winter forecasts. Considering the forecast of the 1997/98 El Niño, the data assimilation in the ocean initial conditions leads to a considerable improvement in the representation of its onset and development. The results presented in this paper indicate a better prediction of global-scale surface climate anomalies for the forecasts started in November, probably because of the improvement in the tropical Pacific. For boreal winter, significant increases in the capability of the system to discriminate above-normal and below-normal temperature anomalies are shown in both the tropics and extratropics.

Il metano emesso dalle piante modifica il ruolo delle foreste nei cambiamenti climatici?

A recent paper published in Nature (Keppler et al. 2006) reports the remarkable discovery that terrestrial plants emit CH4 under aerobic conditions. This interesting paper raised an intensive discussion on whether these emissions could significantly change the role of forest ecosystems in mitigating climate change. By critically revising the methodology applied, we conclude that the approach of scaling up emissions from the leaf level to the globe is scientifically questionable and tends to overestimate considerably the global estimates, especially for forest biomes. In any case, the CH4 plant emissions would reduce the climatic benefit of afforestation/reforestation programs by only a few percent as maximum. Finally, the controversial role of scientific journalism in the relationship between science and society is briefly discussed.