Abstract
We analyze monthly tropical near surface air temperature and Mauna Loa Observatory carbon dioxide (CO2) data within 1960–2016 to identify different carbon cycle responses for two El Nino types: El Ninos originating in the central tropical Pacific (CP El Nino) and El Ninos originating in the eastern tropical Pacific (EP El Nino). We find significant differences between the two types of El Nino events with respect to time delay of the CO2 rise rate that follows the increase in tropical near surface air temperatures caused by El Nino events. The average time lag of the CP El Nino is 4.0 ± 1.7 months, while the mean time lag of EP El Nino is found to be 8.5 ± 2.3 months. The average lag of all considered 1960–2016 El Ninos is 5.2 ± 2.7 months. In contrast the sensitivity of the CO2 growth rate to tropical near surface air temperature increase is determined to be about the same for both El Nino types equal to 2.8 ± 0.9 ppm yr−1 K−1 (or 5.9 ± 1.9 GtC yr−1 K−1). Our results should be useful for the understanding of the carbon cycle and constraining it in climate models.
Highlights
The El Nino-Southern Oscillation (ENSO) is one of the largest modes of climate variability, which is connected to a natural warming/cooling of the tropical PacificOcean that occurs about every three to seven years.Previous research has demonstrated that ENSO can arise from non-linear atmosphere–ocean interaction and that the ENSO has implications for temperature and rainfall in many parts of the globe (e.g. Yeh et al 2009, Jimenez-Munon et al 2016, Jacox et al 2016, Lee et al 2010, Lee and Julien 2016, Cobon et al 2016, Ng et al 2017)
We analyze monthly tropical near surface air temperature and Mauna Loa Observatory carbon dioxide (CO2 ) data within 1960–2016 to identify different carbon cycle responses for two El Nino types: El Ninos originating in the central tropical Pacific (CP El Nino) and El Ninos originating in the eastern tropical Pacific (EP El Nino)
The average warming produced by the EP El Nino was about 50% higher (0.6 ◦ C compared to 0.4 ◦ C) than the average of the CP El Nino events
Summary
The El Nino-Southern Oscillation (ENSO) is one of the largest modes of climate variability, which is connected to a natural warming/cooling of the tropical Pacific. El Nino events has been the subject of several investigations using observations and climate models with an incorporated carbon cycle, including expected El. Nino changes, in some models, under an increasing atmospheric CO2 (Keeling et al 1995, Meehl and Washington 1996, Jones et al 2001, Richards 2013, Christensen et al 2013, Cox et al 2013, Taschetto et al2014, Kim et al 2016, Sterner and Johansson 2017). In some models, under an increasing atmospheric CO2 (Keeling et al 1995, Meehl and Washington 1996, Jones et al 2001, Richards 2013, Christensen et al 2013, Cox et al 2013, Taschetto et al2014, Kim et al 2016, Sterner and Johansson 2017) Most of these analyses assume a single El Nino type. Shown as a peak in NINO4 index, with the main feature being an advection of waters from the warm pool in the west. El Nino to be of a mixed character, with predominantly EP consequences
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