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. 2021;165(1):12.
doi: 10.1007/s10584-021-03001-7. Epub 2021 Mar 8.

Observations of greenhouse gases as climate indicators

Lori Bruhwiler  1 , Sourish Basu  2   3 , James H Butler  1 , Abhishek Chatterjee  2   3 , Ed Dlugokencky  1 , Melissa A Kenney  4 , Allison McComiskey  5 , Stephen A Montzka  1 , Diane Stanitski  1
Affiliations

Observations of greenhouse gases as climate indicators

Lori Bruhwiler et al. Clim Change. 2021.

Abstract

Humans have significantly altered the energy balance of the Earth's climate system mainly not only by extracting and burning fossil fuels but also by altering the biosphere and using halocarbons. The 3rd US National Climate Assessment pointed to a need for a system of indicators of climate and global change based on long-term data that could be used to support assessments and this led to the development of the National Climate Indicators System (NCIS). Here we identify a representative set of key atmospheric indicators of changes in atmospheric radiative forcing due to greenhouse gases (GHGs), and we evaluate atmospheric composition measurements, including non-CO2 GHGs for use as climate change indicators in support of the US National Climate Assessment. GHG abundances and their changes over time can provide valuable information on the success of climate mitigation policies, as well as insights into possible carbon-climate feedback processes that may ultimately affect the success of those policies. To ensure that reliable information for assessing GHG emission changes can be provided on policy-relevant scales, expanded observational efforts are needed. Furthermore, the ability to detect trends resulting from changing emissions requires a commitment to supporting long-term observations. Long-term measurements of greenhouse gases, aerosols, and clouds and related climate indicators used with a dimming/brightening index could provide a foundation for quantifying forcing and its attribution and reducing error in existing indicators that do not account for complicated cloud processes.

Keywords: Anthropogenic emissions; Atmospheric composition; Greenhouse gases; Radiative forcing.

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Conflict of interest statement

Conflict of interestThe authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Conceptual model for greenhouse gas (GHG) climate indicators. Indicators proposed in this study are atmospheric concentrations of non-CO2 GHGs (CO2 is already included in the National Climate Indicator System (NCIS)). Atmospheric GHG concentrations are directly observable and can be monitored over time. They can also be used to estimate radiative forcing. The Annual Greenhouse Gas Index (AGGI) is also included in the NCIS and quantifies the change in radiative forcing due to GHGs relative to 1990. Solid arrows indicate sources and sinks of atmospheric GHGs. Observations constraining these processes could be useful future climate indicators, but fluxes of GHGs are at present difficult to quantify at large spatial and temporal scales
Fig. 2
Fig. 2
Global average abundances of the major, well-mixed, long-lived greenhouse gases—carbon dioxide, methane, nitrous oxide, CFC-12, and CFC-11—from the NOAA global air sampling network are plotted since the beginning of 1979
Fig. 3
Fig. 3
Radiative forcing, relative to 1750, for long-lived greenhouse gases. The NOAA Annual Greenhouse Gas Index (AGGI), which is indexed to 1 for 1990, is shown on the right axis
Fig. 4
Fig. 4
(Top) De-seasonalized global average anthropogenic CO2 (red), estimated by subtracting the pre- industrial value of 280 ppm. The black curve shows an exponential fit to observations using the fit parameters of Hofmann et al. (2009) that results in an emission doubling time of about 30 years. (Bottom) The difference between the exponential fit of Hofmann et al. (2009) and observed global average CO2
See this image and copyright information in PMC

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