Ancient warm climate showed weaker response to orbital cycles than today
New climate modeling reveals that during the warm Miocene period 20 million years ago, Earth's temperature responded less dramatically to orbital variations than in today's climate. The finding suggests that high-ice, cold climates amplify orbital forcing effects through feedback mechanisms—knowledge critical for predicting how modern climate will respond to natural cycles as ice sheets shrink.
Originaltitel: Weakened Miocene temperature response to orbital forcing compared to the modern-day
Abstract. Although orbital signal is widely identified in Miocene proxy records, the climate mechanisms linking insolation changes to regional temperature within this warm, low-ice period remains not well known. Here we use fully coupled climate model simulations to assess temperature response to maximum and minimum boreal summer insolation under Miocene and pre-industrial (PI) conditions. Under both conditions, temperature exhibits broadly anti-phased responses to increased and decreased insolation, but the Miocene response is overall weaker, with regionally dependent contrasts and reduced symmetry between two orbital cases. Three notable Miocene-PI differences emerge: (1) reduced boreal continental sensitivity in the Miocene due to dampened albedo, water-vapor and cloud feedbacks in a warmer, low-ice climate; (2) stronger Miocene cooling over tropical North Africa under high insolation, driven by intensified hydrological and moisture-feedbacks supported by a wider Tethys Sea; (3) reversed Southern Ocean anomalies under low insolation, where poleward-restricted Miocene sea ice enables winter insolation changes to trigger positive ice-albedo feedbacks. These results demonstrate that background climate state strongly modulates orbital-scale responses and provide important context for interpreting Miocene proxy records and long-term changes in Earth's climate sensitivity through the Neogene.