Warm climate surprises: from the suppression of cold events in a warmer future climate to a possible wet future for California in spite of persistent drought projections

by Eli Tziperman

Harvard University
at Physics Colloquium

Mon, 20 Dec 2021, 16:10
Ilse Katz Institute for Nanoscale Science & Technology (51), room 015


First half: Arctic air formation over northern North America and Europe during the winter season's polar night leads to extreme cold outbreaks further south. We propose that such Arctic air formation may be suppressed in a warmer climate by a low-cloud feedback. This may explain the existence of frost-intolerant animals and trees such as crocodiles and palm trees that thrived in northern North America 50 Million years ago (Eocene), where current winter temperatures could be as low as −40C, which cannot be explained by an increased CO2 alone. The proposed mechanism also explains recent climate observations and future climate projections, both showing an unexplained enhanced and surface-intensified warming over high-latitude continental areas.

Second half: the Pliocene (5.3–3 Myr), characterized by warmer temperatures and similar CO2 concentrations to present day, is considered a useful analog for future warming scenarios. Geological evidence suggests that at that time, many modern-day desert regions such as the South-West United States, including Death Valley in California, received higher levels of rainfall and supported large lakes and wetter vegetation types. These wetter conditions have been difficult to reconcile with model predictions of 21st century drying over the same areas. We show that this discrepancy between past evidence and future projections may be due to the models missing an important feedback: Increasing sea surface temperature (SST) due to a weakening of the California coastal upwelling leads to wetter conditions over nearby land, and wetter land leads to a weakening of the wind that forces the upwelling. The mechanism and consequences are discussed.

Created on 13-12-2021 by Kats, Yevgeny (katsye)
Updaded on 13-12-2021 by Kats, Yevgeny (katsye)