2026-03-24 マサチューセッツ工科大学（MIT）
MIT researchers developed a model to study how some natural, methane-cleansing molecules known as the “atmosphere’s detergent” will shift in a changing climate.Credits:Image: MIT News; iStock
＜関連情報＞
- https://news.mit.edu/2026/complicated-future-methane-cleansing-molecule-0324
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025MS005248
不確実な自然排出は、理想的な地表温暖化に伴う対流圏ヒドロキシルラジカル（OH）の増加を抑制する Uncertain Natural Emissions Dampen the Increase in Tropospheric Hydroxyl Radical (OH) With Idealized Surface Warming
Qindan Zhu, Nicole Neumann, Arlene M. Fiore, Robert Pincus, Jian Guan, George Milly, Clare E. Singer, Brian Medeiros, Paolo Giani
Journal of Advances in Modeling Earth Systems Published: 24 March 2026
DOI:https://doi.org/10.1029/2025MS005248
Abstract
The hydroxyl radical (OH) defines the oxidative capacity of the atmosphere and determines the lifetime of reactive greenhouse gases, including methane. The response of OH to climate warming is influenced by uncertain and compensating processes involving meteorological factors and temperature-sensitive natural emissions, including soil N<?XML:NAMESPACE PREFIX = “[default] http://www.w3.org/1998/Math/MathML” NS = “http://www.w3.org/1998/Math/MathML” /> (SN) and biogenic volatile organic compounds (BVOC) emissions. However, separating individual processes that control the OH response to warming is challenging given the high dimensionality of both climate dynamics and emissions in fully coupled chemistry-climate models. Here, we create an idealized chemistry-climate model, Aqua-chem, by prescribing annual mean emissions and zonally symmetric sea surface temperatures. We show that the net OH response to an idealized 2 K surface warming in Aqua-chem depends on competing effects of moistening (a robust response to warming) and temperature-sensitive BVOC emissions (a highly uncertain response). The 2 K surface warming increases water vapor, resulting in an increase in tropospheric OH through primary OH production (ozone photolysis followed by reaction of D with O). Temperature-sensitive SN emissions further enhance OH via the NO + H reaction, but this additional increase is outweighed by the increase in temperature-sensitive BVOC emissions. Amplified OH losses, through reactions with BVOCs and their oxidation byproducts, strongly dampen the increase due to atmospheric moistening with rising surface temperature. Our study underscores the importance of accurately quantifying the temperature sensitivity of natural emissions in order to constrain the OH response to climate warming.
Plain Language Summary
Methane is mainly removed from the atmosphere through the reaction with the hydroxyl radical (OH). As the climate warms, changes in OH directly impact how quickly methane is broken down, affecting the methane budget. However, OH is controlled by a complex, non-linear system that involves both climate dynamics and atmospheric chemistry, making it difficult to predict how OH will respond to warming. In this project, we developed an idealized chemistry-climate model, Aqua-chem, which simplifies the climate dynamics while preserving the full complexity of atmospheric chemistry. This model allows us to quickly and effectively assess how OH responds to changes in surface temperature. Our results show that rising surface temperature increases water vapor, a key limiting factor for OH production in much of the atmosphere. However, warming also leads to higher biogenic emissions of reactive carbon compounds, which increase the OH loss frequency. Ultimately, the sign and magnitude of OH changes under climate warming are shaped by these two competing effects, the increase in OH due to moistening and the decrease in OH due to enhanced biogenic emissions.
