GML Seminars

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Upcoming Seminars

Title:	Ice core measurements of atmospheric methane reveal linkages between global methane biogeochemistry and climate
Speaker:	Ben Riddle-Young Ben Riddle-Young is a postdoctoral researcher at CIRES working with the NOAA GML Carbon Cycle Greenhouse Gases group. He studies global-scale greenhouse gas dynamics on paleo and modern timescales. Ben received his PhD from Oregon State University in 2023, which mainly focused on using ice cores to understand the drivers of past atmospheric methane variability and how they were related to corresponding climate changes. He likes to spend his free time either outdoors skiing or backpacking, or indoors cooking and playing with his new kittens.
Date/Time:	Wednesday, May 14, 2025 01:00 PM
Location:	David Skaggs Research Center, Room GC402 Google Meet
Abstract Constraining the causes of past atmospheric methane (CH₄) variability is critical for understanding links between CH₄, climate, and terrestrial biogeochemical cycling. Ice core records reveal a 400 ppb CH4 rise across the last deglaciation and more rapid changes during the last glacial period and deglaciation that were synchronous with abrupt climate variations known as Dansgaard–Oeschger (DO) and Heinrich Events (HE). The drivers of these CH₄ variations remain unknown but can be constrained using the CH₄ interpolar difference (IPD), which is sensitive to the latitudinal distribution of emissions, and the stable isotopic composition of CH₄, which is sensitive to changes in different isotopically distinguishable emission categories (microbial, pyrogenic, and geologic). We first present a new CH₄ IPD record across the last deglaciation, with substantially improved temporal resolution, chronology, and a critical correction for CH₄ production in Greenland samples. Box model analyses suggest that tropical sources dominated abrupt CH₄ variability, highlighting their sensitivity to abrupt climate change and shifting tropical rainfall patterns. Northern extratropical emissions began increasing ~16,000 years ago, likely via wetland expansion and/or permafrost degradation induced by high-latitude warming, and contributed <25 Tg/yr (45% of the total emission increase) to the abrupt CH₄ rise coincident with rapid northern warming at the onset of DO1. Next, we present multi-decadal-scale measurements of δ13C–CH4 and δD–CH4 from Antarctic ice cores and identify abrupt, 1‰ and 0.5‰ enrichments in δ13C–CH4 synchronous with HE and DO CH4 increases, respectively. δD–CH4 varied little across the abrupt changes. Using box models to interpret these data, we propose that abrupt shifts in tropical rainfall associated with HEs and DO Events enhanced 13C-enriched pyrogenic CH4 emissions, and by extension global wildfire extent, by 90–150%. Carbon cycle box modeling experiments suggest that the resulting released terrestrial carbon may have caused one-third to all of the abrupt CO2 increases associated with HEs. These new constraints on deglacial climate–CH4 cycle interactions can improve the understanding of possible present and future feedbacks.

Title:	(TBD) Observation and modeling of ozone-depleting substances and replacement emissions
Speaker:	Megan Lickley
Date/Time:	Wednesday, June 11, 2025

Title:	(TBD) Arctic climate feedback and observations
Speaker:	Jen Kay
Date/Time:	Wednesday, June 25, 2025

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