Climate Change in the Arctic: What Are the Signs and What Is Predicted?

It is well established that much of the Arctic has warmed during recent decades at rates faster than most of the rest of the world.  The warming is supported by corresponding changes in sea ice, permafrost, and glaciers.  In this presentation, we will use the geographical and seasonal patterns of recent Arctic change to identify the roles of three drivers: the radiative forcing by increased greenhouse gas concentrations, the snow/ice-albedo-temperature feedback, and natural variations within the climate system.  The latter include prominent modes of the atmospheric circulation..     Global climate models run with prescribed increases of greenhouse gas concentrations provide a vehicle for identifying the greenhouse signal in climate change.  Composite fields based on ensembles of model simulations eliminate much of the natural variability, thereby quantifying the background warming upon which natural variations will be superimposed. However, the prominence of natural variability raises a key question that will be addressed here:  What are the odds that the Arctic will be warmer during the next N-year period than during the most recent N-year period?