Modeling seasonal variability in Arctic cloud and water vapor feedbacks

The Arctic is among the regions where climate is changing most rapidly today. Climate change there is amplified by a variety of positive feedbacks, many of which are linked with changes in water vapor, cloud cover, and other cloud properties. Global climate models indicate that these feedbacks will lead to enhanced warming of Arctic surface air temperature relative to the global average in response to increasing atmospheric greenhouse gases. We use a global climate model to examine several of these feedbacks, how they vary by season, and how they might change during the 21st century. One feedback loop begins with a temperature increase that produces an increase in water vapor which in turn increases the downward longwave radiation and surface air temperature. A similar feedback is associated with increases in cloud cover and cloud optical depth. We next examine how these feedbacks vary by season and find that they are particularly pronounced during autumn, winter, and spring, leading to enhanced temperature increases during these seasons. We also examine how these feedbacks change during the 21st century.