Accurate climate projections are of great societal relevance (e.g., in assessing the risk from heavy rainfall events) and scientific interest (e.g., in understanding the dynamics of the climate system). These projections rely on global climate models that typically have grid spacing of a few tens to a hundred kilometers and thus, cannot resolve processes that occur on smaller scales (i.e., subgrid processes). Because subgrid processes, such as convection and clouds, have important consequences for Earth's climate, there is a need to represent them using parameterizations. These parameterizations approximate the effects of unresolved processes on the resolved fields. Traditional parameterizations rely partly on physics but also on simple conceptual models and heuristic approximations, and they are a major source of uncertainties in climate models and climate projections (Bony
The ocean is a reservoir for CFC-11, a major ozone-depleting chemical. Anthropogenic production of CFC-11 dramatically decreased in the 1990s under the Montreal Protocol, which stipulated a global phase out of production by 2010. However, studies raise questions about current overall emission levels and indicate unexpected increases of CFC-11 emissions of about 10 Gg ⋅ yr−1 after 2013 (based upon measured atmospheric concentrations and an assumed atmospheric lifetime). These findings heighten the need to understand processes that could affect the CFC-11 lifetime, including ocean fluxes. We evaluate how ocean uptake and release through 2300 affects CFC-11 lifetimes, emission estimates, and the long-term return of CFC-11 from the ocean reservoir. We show that ocean uptake yields a shorter total lifetime and larger inferred emission of atmospheric CFC-11 from 1930 to 2075 compared to estimates using only atmospheric processes. Ocean flux changes over time result in small but not completely negligible effects on the calculated unexpected emissions change (decreasing it by 0.4 ± 0.3 Gg ⋅ yr−1). Moreover, it is expected that the ocean will eventually become a source of CFC-11, increasing its total lifetime thereafter. Ocean outgassing should produce detectable increases in global atmospheric CFC-11 abundances by the mid-2100s, with emission of around 0.5 Gg ⋅ yr−1; this should not be confused with illicit production at that time. An illustrative model projection suggests that climate change is expected to make the ocean a weaker reservoir for CFC-11, advancing the detectable change in the global atmospheric mixing ratio by about 5 yr.
This study evaluates formaldehyde (HCHO) over the U.S. from 2006 to 2015 by comparing ground monitor data from the Air Quality System (AQS) and a satellite retrieval from the Ozone Monitoring Instrument (OMI). Our comparison focuses on the utility of satellite data to inform patterns, trends, and processes of ground-based HCHO across the U.S. We find that cities with higher levels of biogenic volatile organic compound (BVOC) emissions, including primary HCHO, exhibit larger HCHO diurnal amplitudes in surface observations. These differences in hour-to-hour variability in surface HCHO suggests that satellite agreement with ground-based data may depend on the distribution of emission sources. On a seasonal basis, OMI exhibits the highest correlation with AQS in summer and the lowest correlation in winter. The ratios of HCHO in summer versus other seasons show pronounced seasonal variability in OMI, likely due to seasonal changes in the vertical HCHO distribution. The seasonal variability in HCHO from satellite is more pronounced than at the surface, with seasonal variability 20–100% larger in satellite than surface observations. The seasonal variability also has a latitude dependency, with more variability in higher latitude regions. OMI agrees with AQS on the interannual variability in certain periods, whereas AQS and OMI do not show a consistent decadal trend. This is possibly due to a rather large interannual variability in HCHO, which makes the small decadal drift less significant. Temperature also explains part of the interannual variabilities. Small temperature variations in the western U.S. are reflected with more quiescent HCHO interannual variability in that region. The decrease in summertime HCHO in the southeast U.S. could also be partially explained by a small and negative trend in local temperatures.
Understanding global emissions of long-lived trace gases requires careful interpretation of in situ measurements. Emissions can be inferred from observed changes in atmospheric mole fractions along with an assumed atmospheric lifetime (WMO, 2003(WMO, , 2018. However, sparse networks of in situ trace gas measurements together with large uncertainties in atmospheric lifetimes (Ko et al., 2013) can lead to large uncertainties in inferred emissions (Lickley, 2021). Experts have long looked to hemispheric differences in mole fractions of these chemicals as evidence to support conclusions about changes in anthropogenic emissions (Lovelock et al., 1973). However, recent work illustrates the importance of stratosphere -troposphere fluxes in driving anomalies of in situ trace gas measurements (Laube et al., 2020;Nevison et al., 2011;Ray et al., 2020;Ruiz et al., 2021). Ray et al. (2020) use modeling experiments to show that observed anomalies in North-South hemisphere differences (NH-SH) in CFC-11, CFC-12, and N 2 O tropospheric mole fractions are associated with stratospheric anomalies driven by the Quasi Biennial Oscillation (QBO). This association has yet to be validated or quantified with stratospheric measurements, limiting our ability to interpret
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