Earth Systems

An important question for climate change science is possible shifts in the extremes of regional water cycle, especially changes in patterns, intensity and/or frequency of extreme precipitation events. In this study, an analogue method is developed to help detect extreme precipitation events and their potential changes under future climate regimes without relying on the highly uncertain modeled precipitation. Our approach is based on the use of composite maps to identify the distinct synoptic and large-scale atmospheric conditions that lead to extreme precipitation events at local scales. The analysis of extreme daily precipitation events, exemplified in the south-central United States, is carried out using 62-yr (1948-2010) CPC gridded station data and NASA’s Modern Era Retrospective-analysis for Research and Applications (MERRA). Various aspects of the daily extremes are examined, including their historical ranking, associated common circulation features at upper and lower levels of the atmosphere, and moisture plumes. The scheme is first evaluated for the multiple climate model simulations of the 20th century from Coupled Model Intercomparison Project Phase 5 (CMIP5) archive to determine whether the statistical nature of modeled precipitation events (i.e. the numbers of occurrences over each season) could well correspond to that of the observed. Further, the approach will be applied to the CMIP5 multi-model projections of various climate change scenarios (i.e. Representative Concentration Pathways (RCP) scenarios) in the next century to assess the potential changes in the probability of extreme precipitation events. The research results from this study should be of particular significance to help society develop adaptive strategies and prevent catastrophic losses.

Changes in extratropical storm tracks associated with climate change can directly affect the transport of momentum, energy and water vapor as well as impact the carbon cycle and modify the ocean circulation. For these reasons quantifying the possible range of changes in storm-track intensity is very relevant. In this paper, we analyze the transient eddy kinetic energy from six simulations using the MIT IGSM-CAM framework. The MIT IGSM-CAM framework links the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) version 3 to the MIT Integrated Global System Model (IGSM) version 2.3, an intermediate complexity fully coupled earth system model that allows simulation of critical feedbacks among its various components, including the atmosphere (represented by a zonal-mean statistical-dynamical model), ocean, land, urban processes and human activities. An essential feature of the MIT IGSM-CAM is the flexibility to vary the climate parameters of the framework (climate sensitivity, net aerosol forcing and ocean heat uptake rate). The simulations presented in this paper were carried out for two emission scenarios (a “Business as usual” scenario and a 660 ppm of CO2-eq stabilization) and three sets of climate parameters. The three values of climate sensitivity chosen are median and the bounds of the 90% probability interval of the probability distribution obtained by comparing the observed 20th century climate change with simulations by the IGSM with a wide range of climate parameters values. The associated aerosol forcing values were chosen to ensure a good agreement of the simulations with the observed climate change over the 20th century. Because the concentrations of sulfate aerosols significantly decrease over the 21st century in both emissions scenarios, climate changes obtained in these six simulations provide a good approximation for the median, and the 5th and 95th percentiles of the probability distribution of 21st century climate change.

John Marshall, the Cecil and Ida Green Professor of Oceanography in MIT’s Department of Earth, Atmospheric and Planetary Sciences and the Director of MIT's Climate Modeling Initiative, spoke with the MIT Club of Northern California about the role oceans play in global climate change.

What’s the science behind climate change, and how can we combat a warming climate? Those are complex questions that MIT faculty are actively pursuing. In this podcast, four MIT professors— Dan Cziczo, Kerry Emanuel, Christopher Knittel, and Andrew Whittle—will discuss their climate research on areas including hurricane activity, coastal flooding, carbon dioxide, and economic policy.

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