Increasing carbon dioxide concentration in the upper atmosphere observed by SABER

Abstract

Carbon dioxide measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument between 2002 and 2014 were analyzed to reveal the rate of increase of CO2 in the mesosphere and lower thermosphere. The CO2 data show a trend of ~5% per decade at ~80 km and below, in good agreement with the tropospheric trend observed at Mauna Loa. Above 80 km, the SABER CO2 trend is larger than in the lower atmosphere, reaching ~12% per decade at 110 km. The large relative trend in the upper atmosphere is consistent with results from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS). On the other hand, the CO2 trend deduced from the Whole Atmosphere Community Climate Model remains close to 5% everywhere. The spatial coverage of the SABER instrument allows us to analyze the CO2 trend as a function of latitude for the first time. The trend is larger in the Northern Hemisphere than in the Southern Hemisphere mesopause above 80 km. The agreement between SABER and ACE‐FTS suggests that the rate of increase of CO2 in the upper atmosphere over the past 13 years is considerably larger than can be explained by chemistry‐climate models.

Carbon dioxide trends in the mesosphere and lower thermosphere

“…The first term represents a constant residual CO 2 , the second term is the linear trend, and the last term is the dependency on solar activity in which s(t) is represented by the F 10.7 index. The QBO was not considered since QBO effects on CO 2 trends in the MLT region are very small [ Yue et al ., ; Garcia et al ., ]. Vertical profiles of CO 2 linear trends are then presented in pressure coordinates.…”

“… Multiple linear regressions (MLR) . A MLR procedure is applied to the residual time series, considering a linear trend in CO 2 , dependency on solar cycle variability using the F 10.7 solar activity index, and in some cases, additional dependency on the quasi‐biannual oscillation (QBO) represented by the 30 mb mean zonal wind at the equator [e.g., Yue et al ., ]. The MLR model used in this study is as follows: where t is time.…”

“…The average CO 2 trend in the lower atmosphere is ~5%/decade for the most recent decades. CO 2 trends derived from SABER measurements appeared to confirm the results obtained from ACE‐FTS [ Yue et al ., ]. Current state‐of‐the‐art upper atmosphere general circulation models and whole atmosphere models, however, cannot reproduce this altitude differential CO 2 trend [ Emmert et al ., ; Yue et al ., ; Garcia et al ., ].…”

Extreme enrichment in atmospheric 15 N 15 N

“…The anthropogenic CO 2 rise has recently been detected in the lower thermosphere by satellites ( 31 , 32 ), suggesting that gases emitted at the surface can enter the thermosphere within several hundred years and vice versa. The atmosphere’s Δ 30 value therefore carries signatures of both gas-phase and biological processing of N 2 .…”

Impacts of SABER CO2‐based eddy diffusion coefficients in the lower thermosphere on the ionosphere/thermosphere

“…Global-mean CO 2 is chemically inert in the MLT region as evidenced by its global-mean lifetimes with respect to photolysis, molecular diffusion, and eddy diffusion [Liang et al, 2007;Garcia et al, 2014, Figure 9]. Furthermore, CO 2 is a highly recommended tracer for the estimation of the climatological trend in global-mean eddy diffusion [Emmert et al, 2012;Yue et al, 2015;Garcia et al, 2016].…”