Abstract
We present the chain of mechanisms linking free radical catalytic loss of stratospheric ozone, specifically over the central United States in summer, to increased climate forcing by CO2 and CH4 from fossil fuel use. This case directly engages detailed knowledge, emerging from in situ aircraft observations over the polar regions in winter, defining the temperature and water vapor dependence of the kinetics of heterogeneous catalytic conversion of inorganic chlorine (HCl and ClONO2) to free radical form (ClO). Analysis is placed in the context of irreversible changes to specific subsystems of the climate, most notably coupled feedbacks that link rapid changes in the Arctic with the discovery that convective storms over the central US in summer both suppress temperatures and inject water vapor deep into the stratosphere. This places the lower stratosphere over the US in summer within the same photochemical catalytic domain as the lower stratosphere of the Arctic in winter engaging the risk of amplifying the rate limiting step in the ClO dimer catalytic mechanism by some six orders of magnitude. This transitions the catalytic loss rate of ozone in lower stratosphere over the United States in summer from HOx radical control to ClOx radical control, increasing the overall ozone loss rate by some two orders of magnitude over that of the unperturbed state. Thus we address, through a combination of observations and modeling, the mechanistic foundation defining why stratospheric ozone, vulnerable to increased climate forcing, is one of the most delicate aspects of habitability on the planet.
Highlights
CO2 and CH4 release from melting permafrost and methane clathrateCompounding the central role that the Arctic plays in setting the time scale for irreversibility regarding the global climate structure, are coupled feedbacks between the increasing temperatures resulting from increased heat flow into the Arctic Basin, and associated carbon release from melting permafrost and methane clathrates.[5,6] The thinning and loss of the Arctic ice cap, as well as thawing permafrost, tap into the large carbon reservoirs containing both CH4 within clathrates and organic carbon within the terrestrial permafrost system
We present the chain of mechanisms linking free radical catalytic loss of stratospheric ozone, over the central United States in summer, to increased climate forcing by CO2 and CH4 from fossil fuel use
The analysis presented here of the sensitivity of lower stratospheric ozone over the US in summer builds on four decades of developments linking chlorine and bromine radicals to ozone loss in the polar regions,[44,45,55] and to ozone depletion at mid-latitudes resulting from the coupling of volcanic aerosols and temperature variability to anthropogenic chlorine and bromine,[22,24,25,56] as well as analyses of the consequences from sulfate addition to the stratosphere from geoengineering via solar radiation management.[29,30,31,32]
Summary
Compounding the central role that the Arctic plays in setting the time scale for irreversibility regarding the global climate structure, are coupled feedbacks between the increasing temperatures resulting from increased heat flow into the Arctic Basin, and associated carbon release from melting permafrost and methane clathrates.[5,6] The thinning and loss of the Arctic ice cap, as well as thawing permafrost, tap into the large carbon reservoirs containing both CH4 within clathrates and organic carbon within the terrestrial permafrost system. This destabilizes the ice structure and accelerates the decomposition of the glacial system by weakening the horizontal confinement of the ice structure such that it collapses outward and downward. Coupling of radical catalyzed loss of stratospheric ozone to climate forcing by increased CO2 and CH4 in the atmosphere
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