Abstract
AbstractWe calculate ozone radiative forcing (RF) and stratospheric temperature adjustments for the period 1850–2014 using the newly available Coupled Model Intercomparison Project phase 6 (CMIP6) ozone data set. The CMIP6 total ozone RF (1850s to 2000s) is 0.28 ± 0.17 W m−2 (which is 80% higher than our CMIP5 estimation), and 0.30 ± 0.17 W m−2 out to the present day (2014). The total ozone RF grows rapidly until the 1970s, slows toward the 2000s, and shows a renewed growth thereafter. Since the 1990s the shortwave RF exceeds the longwave RF. Global stratospheric ozone RF is positive between 1930 and 1970 and then turns negative but remains positive in the Northern Hemisphere throughout. Derived stratospheric temperature changes show a localized cooling in the subtropical lower stratosphere due to tropospheric ozone increases and cooling in the upper stratosphere due to ozone depletion by more than 1 K already prior to the satellite era (1980) and by more than 2 K out to the present day (2014).
Highlights
The radiative forcing (RF) due to changes in tropospheric and stratospheric ozone is the third largest greenhouse gas contributor to RF since preindustrial (PI) times (Myhre et al, 2013)
Global Estimates of Ozone RF We investigate first the global-mean tropospheric and stratospheric ozone RF using Coupled Model Intercomparison Project phase 6 (CMIP6) and compare it with Coupled Model Intercomparison Project phase 5 (CMIP5) calculations for the 2000s decade (Table 1)
The total ozone RF is 80% greater using CMIP6 ozone: 0.28 W m−2 compared to 0.15 W m−2 using CMIP5
Summary
The radiative forcing (RF) due to changes in tropospheric and stratospheric ozone is the third largest greenhouse gas contributor to RF since preindustrial (PI) times (Myhre et al, 2013). The horizontal and vertical inhomogeneity in ozone makes it more difficult to observe and characterize its distribution and trends, even for recent times. These difficulties become progressively larger further back in time, and there is little information, except for a few surface sites in the last nineteenth century (Cooper et al, 2014). At least since the middle of the twentieth century, ozone has been increasing in the troposphere and decreasing in the stratosphere, due to the combined effects of air pollutants and ozone depleting substances, making the net forcing a residual of opposing terms
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