Wildfire activity driven by the 405-kyr orbital climate cycles in the Middle Jurassic

Abstract

Global changes in the frequency and extent of wildfires are thought related to human-induced climate warming influencing fire weather and ignition probability. However, our understanding is still limited on whether and how pre-anthropogenic natural periodic changes in climate control variations in wildfire behavior over orbital timescales. Here we present a ∼ 2.2-Myr-long record of wildfire activity based on evidence of charcoal and pyrogenic polycyclic aromatic hydrocarbons (PAHs) abundances from the mid-latitude terrestrial sediments of the Middle Jurassic, along with multiproxy climate data including organic carbon isotopes, chemical weathering indices, and clay minerals from the same sediments. Our results show that peaks of wildfire frequency well correspond to seasonal dry climate with cyclicity of ∼405 kyr, suggesting long eccentricity-induced climate cycles forcing of wildfire activity by impact on the fuel load and state. The periods of enhanced wildfire activity were consistent with the phases of orbital-driven increased seasonality in Earth's past, implying that current human-induced climatic change has already led to an increasing in the risk of wildfires despite decreasing Earth's eccentricity.