PDB3: USE OF BOOTSTRAP IN A COST-OF-ILLNESS STUDY TO DERIVE ACCURACY OF ESTIMATES

Farrando, Jordi;Febles, Maria Dolors ;Henrich, Jordi;Tarrasó, Olga ;Fuertes, J.C.;Pérez, S

On the early response of the climate system to a meltwater input from Greenland

The early response of the atmosphere–ocean system to meltwater runoff originating from the Greenland ice sheet is studied using a coupled atmosphere–ocean general circulation model (AOGCM). For this purpose, AOGCM ensemble simulations without and with associated ocean freshening around Greenland are compared. For freshwater perturbations initiated in northern winter, the mean response for the first three months shows the emergence of negative sea surface temperature (SST) anomalies in the Denmark Strait, in association with enhanced oceanic advection by the East Greenland Current. The response also shows negative SST anomalies in the North Atlantic associated with enhanced westerlies at the ocean surface. Additionally, the baroclinic atmospheric cyclonic circulation east of Greenland intensifies, and anticyclonic circulations with equivalent barotropic structures develop over western Europe and the North Pacific Ocean. Simulations by the atmospheric component of the AOGCM indicate that atmosphere–ocean interactions contribute significantly to enhance the response. The sensitivity of the coupled system response to the timing of freshwater perturbation is also studied. For freshwater perturbations initialized in northern summer, the response during the following winter is similar, but stronger in magnitude. In the Northern Hemisphere, the atmospheric response resembles the Arctic Oscillation (AO) mode of variability. The association between anomalies in the Denmark Strait SSTs and in the atmosphere east of Greenland is consistent with that observed during previous great salinity anomaly (GSA) events. The results obtained highlight the importance of atmosphere–ocean interaction in the early climate response to Greenland melting, the teleconnections with the North Pacific and the contribution of GSA events to North Atlantic Oscillation (NAO) variability

Sea surface freshwater flux estimates from GECCO, HOAPS and NCEP

Surface net freshwater flux fields, estimated from the GECCO ocean state estimation effort over the 50 yr period 1951-2001, are compared to purely satellite-based HOAPS freshwater flux estimates and to the NCEP atmospheric re-analysis net surface freshwater flux fields to assess the quality of all flux products and to improve our understanding of the time-mean surface freshwater flux distribution as well as its temporal variability. Surface flux fields are adjusted by the GECCO state estimation procedure together with initial temperature and salinity conditions so that the model simulation becomes consistent with ocean observations. The entirely independent HOAPS net surface freshwater flux fields result from the difference between SSM/I based precipitation estimates and fields of evaporation resulting from a bulk aerodynamic approach using SSM/I data and the Pathfinder SST. All three products agree well on a global scale. However, overall GECCO seems to have moved away from the NCEP/NCAR first guess surface fluxes and is often closer to the HOAPS data set. This holds for the time mean as well as for the seasonal cycle

Role of Perturbing Ocean Initial Condition in Simulated Regional Sea Level Change

Multiple lines of observational evidence indicate that the global climate has been getting warmer since the early 20th century. This warmer climate has led to a global mean sea level rise of about 18 cm during the 20th century, and over 6 cm for the first 15 years of the 21st century. Regionally the sea level rise is not uniform due in large part to internal climate variability. To better serve the community, the uncertainties of predicting/projecting regional sea level changes associated with internal climate variability need to be quantified. Previous research on this topic has used single-model large ensembles with perturbed atmospheric initial conditions (ICs). Here we compare uncertainties associated with perturbing ICs in just the atmosphere and just the ocean using a state-of-the-art coupled climate model. We find that by perturbing the oceanic ICs, the uncertainties in regional sea level changes increase compared to those with perturbed atmospheric ICs. Thus, in order for us to better assess the full spectrum of the impacts of such internal climate variability on regional and global sea level rise, approaches that involve perturbing both atmospheric and oceanic initial conditions are necessary

Initializing decadal climate predictions with the GECCO oceanic synthesis

This study aims at improving the forecast skill of climate predictions through the use of ocean synthesis data for initial conditions of a coupled climate model. For this purpose, the coupled model of the Max Planck Institute (MPI) for Meteorology, which consists of the atmosphere model ECHAM5 and the MPI Ocean Model (MPI-OM), is initialized with oceanic synthesis fields available from the German contribution to Estimating the Circulation and Climate of the Ocean (GECCO) project. The use of an anomaly coupling scheme during the initialization avoids the main problems with drift in the climate predictions. Thus, the coupled model is continuously forced to follow the density anomalies of the GECCO synthesis over the period 1952-2001. Hindcast experiments are initialized from this experiment at constant intervals. The results show predictive skill through the initialization up to the decadal time scale, particularly over the North Atlantic. Viewed over the time scales analyzed here (annual, 5-yr, and 10-yr mean), greater skill for the North Atlantic sea surface temperature (SST) is obtained in the hindcast experiments than in either a damped persistence or trend forecast. The Atlantic meridional overturning circulation hindcast closely follows that of the GECCO oceanic synthesis. Hindcasts of global-mean temperature do not obtain greater skill than either damped persistence or a trend forecast, owing to the SST errors in the GECCO synthesis, outside the North Atlantic. An ensemble of forecast experiments is subsequently performed over the period 2002-11. North Atlantic SST from the forecast experiment agrees well with observations until the year 2007, and it is higher than if simulated without the oceanic initialization (averaged over the forecast period). The results confirm that both the initial and the boundary conditions must be accounted for in decadal climate predictions

Science directions in a post-COP21-world of transient climate change: enabling regional to local predictions in support of reliable climate information

During recent decades, through theoretical considerations and analyses of observations andmodel simulations, the scientific community has fundamentally advanced our understanding of thecoupled climate system, thereby establishing that humans affect the Earth’s climate. Resulting from thisremarkable accomplishment, the COP21 agreement marks a historic turning point for climate research bycalling for actionable regional climate change information on time scales from seasonal to centuries for thebenefit of humanity, as well as living and nonliving elements of the Earth environment. Out of the underlyingUnited National Framework Convention on climate Change process, improving seamless regional climateforecast capabilities emerges as a key challenge for the international research community. Addressing itrequires a multiscale approach to climate predictions. Here we offer a vision that emphasizes enhancedscientific understanding of regional to local climate processes as the foundation for progress. The scientificchallenge is extreme due to the rich complexity of interactions and feedbacks between regional andglobal processes, each of which affects the global climate trajectory. To gain the necessary scientific insightand to turn it into actionable climate information require technical development, international coordination,and a close interaction between the science and stakeholder communities

Sea level changes mechanisms in the MPI-ESM under FAFMIP forcing conditions

Mechanistic causes for sea level (SL) change patterns are analyzed as they emerge from the Coupled Model Intercomparison Project Phase 6 (CMIP6) endorsed Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) coupled climate experiments imposing individual forcing anomalies in wind stress, heatflux and freshwater flux to the Max-Planck-Institute Earth System Model (MPI-ESM). It appears that the heat flux perturbations have the largest effect on the sea level. In contrast, the direct impact of momentum and freshwater flux anomalies on SL anomalies appear to be limited to some region e.g. the Southern Ocean, Arctic Ocean and to some extent the North Pacific and North Atlantic Ocean. We find that thermosteric changes dominate the total SL change over large parts of the global ocean, except north of 60 °N where halosteric changes prevail. An analysis of added and redistributed components of heat and freshwater further suggests that the added component dominates the thermosteric SL and the redistributed component dominates the halosteric SL. Due to feedback processes a superposition of all forcing components together leads to the simulated sea level changes in each individual experiment. As a result, large surface heat flux anomalies over the Atlantic lead to wind stress change outside of the Atlantic through teleconnections, which in turn appear to be the primary driving agent for changes of sea level outside of the Atlantic in all three experiments. The associated wind driven Sverdrup stream function implicates that outside of the Atlantic most of the feedback can be explained by changes in the Sverdrup circulation