Date:
Wed, 17/05/201712:00-13:30
Location:
Danciger B building, Seminar room
Lecturer: Prof. Eli Tziperman
Affiliation:
Department of Earth and Planetary Sciences,
and School of Engineering and Applied Sciences,
Harvard University
Abstract:
Two warm climate mysteries will be discussed and explained as the result of two different cloud feedbacks. The motivation, apart from future climate scenarios, is evidence of an exceptionally warm climate about 50 Million years ago (Eocene) allowing crocodiles and palm trees, which cannot withstand subfreezing temperatures, to thrive in northern North America, where current winter temperatures can be -40C.
First, we consider the process of Arctic air formation currently occurring over northern North America during the winter season's polar night, and leading to cold outbreaks further south. We propose that Arctic air formation may be shut off in a warmer climate by a low-cloud feedback. We further show that the idea also explains recent climate observations and future climate projections, both showing an unexplained enhanced and surface-intensified warming over high-latitude continental areas.
Second, it is proposed that in a warmer, higher CO2 world, the Arctic ocean and atmosphere may be kept warm even during the polar night winter season due to deep atmospheric convection and high clouds which are typical of the tropics at present. The proposed convective cloud feedback will be shown to also be at work in future model projections of global warming, resulting in the elimination of Arctic sea ice even during winter.
Affiliation:
Department of Earth and Planetary Sciences,
and School of Engineering and Applied Sciences,
Harvard University
Abstract:
Two warm climate mysteries will be discussed and explained as the result of two different cloud feedbacks. The motivation, apart from future climate scenarios, is evidence of an exceptionally warm climate about 50 Million years ago (Eocene) allowing crocodiles and palm trees, which cannot withstand subfreezing temperatures, to thrive in northern North America, where current winter temperatures can be -40C.
First, we consider the process of Arctic air formation currently occurring over northern North America during the winter season's polar night, and leading to cold outbreaks further south. We propose that Arctic air formation may be shut off in a warmer climate by a low-cloud feedback. We further show that the idea also explains recent climate observations and future climate projections, both showing an unexplained enhanced and surface-intensified warming over high-latitude continental areas.
Second, it is proposed that in a warmer, higher CO2 world, the Arctic ocean and atmosphere may be kept warm even during the polar night winter season due to deep atmospheric convection and high clouds which are typical of the tropics at present. The proposed convective cloud feedback will be shown to also be at work in future model projections of global warming, resulting in the elimination of Arctic sea ice even during winter.