Contrasting Biogenic Isoprene Emission Responses to La Niña and El Niño Driven by Temperature: Insights from HCHO-Based Global Inversion.

Isoprene strongly influences atmospheric chemistry by consuming hydroxyl radicals, forming secondary organic aerosols, and affecting methane's lifetime. Accurate monitoring of its emissions is thus essential for understanding biosphere-atmosphere feedbacks, particularly under climate extremes. We develop a regression-based inversion framework to estimate global monthly biogenic isoprene emissions (2019-2024), integrating TROPOspheric Monitoring Instrument (TROPOMI) HCHO columns and LMDZ-INCA atmospheric transport model. Our inversion yields a global annual mean emission of 456 ± 249 TgC yr-1, with a minimum in 2022 (437 TgC, 1.4σ below multiyear mean) and a peak in 2024 (477 TgC, 1.5σ above), closely tracking global annual land surface temperature variations (R = 0.95). Emission anomalies are most pronounced in tropical regions contributing over 80% of global total anomalies during the 2020-2023 La Niña (-30 TgC), 2023-2024 El Niño (+11 TgC), and 2024 Northern Hemisphere extreme warming events (+15 TgC). Attribution analysis confirms surface temperature as the dominant driver of biogenic isoprene anomalies, with increasing sensitivity in Northern high-latitude zones under warming conditions. The updated emissions improve spatial agreement and reduce bias in LMDZ-INCA simulations against independent satellite-based isoprene and ground-based HCHO observations. This work delivers the first HCHO-constrained global isoprene emission data set through 2024, supporting air quality, oxidant budget, and climate feedback studies.