PAOC Colloquium: Trude Storelvmo (Yale)

Title: Mixed-phase clouds and climate - a close and complicated relationship

Abstract: Clouds in Earth's atmosphere can be composed of liquid droplet, ice crystals, or a combination of the two. Clouds' thermodynamic phase is largely controlled by temperature, but other factors, most notably ice-nucleating aerosol particles, can also have a significant effect. Because cloud radiative properties are crucially dependent on cloud phase, any cloud phase change, no matter the cause, is bound to have a very powerful impact on Earth’s radiation budget. It has been hypothesized that anthropogenic aerosol emissions have impacted mixed-phase clouds since pre-industrial times, and thus imposed a potentially large radiative forcing on Earth’s climate. Estimates of how aerosol emissions could have influenced the radiation budget via mixed-phase clouds have recently started to emerge, but so far provide ambiguous forcing estimates, both in terms of magnitude and sign. Intuitively we also expect cloud phase changes to accompany a warming climate, given that temperature exerts a dominant influence on cloud phase. Recent work has revealed that such cloud phase changes represent a very important cloud-climate feedback in both past and future climates, particularly at mid- and high latitudes, and that this particular feedback mechanism has likely been misrepresented in many climate models to date. I will review progress in our understanding of the role of mixed-phase clouds in both climate forcings and feedbacks, from the seminal work of the mid-20th century pioneers in cloud physics to the recent breakthroughs made possible by modern satellite missions. I’ll end with my view of what is needed next in order to shed new light on the complicated relationship between mixed-phase clouds and climate.

About the Speaker: I am an atmospheric scientist, focusing my research on the role of aerosol particles and clouds in Earth’s climate. I am particularly interested in how aerosol particles affect climate by acting as cloud condensation nuclei and ice nuclei. I also work on question related to cloud-climate feedback mechanisms and climate engineering involving aerosols and/or clouds.  Aerosol/cloud effects are arguable among the most uncertain and poorly constrained influences on the climate system, and will represent a tremendous challenge to the scientific community in years to come.

About this Series: The PAOC Colloquium is a weekly interdisciplinary seminar series that brings together the whole PAOC community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, but also talks about e.g. societal impacts of climatic processes. The seminars generally take place on Monday from 12-1pm. Lunch is provided to encourage students and post-docs to meet with the speaker. Besides the seminar and lunch, individual meetings with professors, post-docs, and students are arranged.