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1. Relation between ENSO and Global Warming
2. Relation between El Nino, La Nina and Greenhouse gas |
1. ENSO and Global Warming
During the last several decades, the number of El Niño events increased, and the number of La Niña events decreased, although observation of ENSO for much longer is needed to detect robust changes. The question is whether this is a random fluctuation or a normal instance of variation for that phenomenon or the result of global climate changes toward global warming.
The studies of historical data show the recent El Niño variation is most likely linked to global warming. For example, one of the most recent results, even after subtracting the positive influence of decadal variation, is shown to be possibly present in the ENSO trend, the amplitude of the ENSO variability in the observed data still increases, by as much as 60% in the last 50 years.
The exact changes happening to ENSO in the future is uncertain: Different models make different predictions. It may be that the observed phenomenon of more frequent and stronger El Niño events occurs only in the initial phase of the global warming, and then (e.g., after the lower layers of the ocean get warmer, as well), El Niño will become weaker than it was. It may also be that the stabilizing and destabilizing forces influencing the phenomenon will eventually compensate for each other. More research is needed to provide a better answer to that question. The ENSO is considered to be a potential tipping element in Earth's climate.
The studies of historical data show the recent El Niño variation is most likely linked to global warming. For example, one of the most recent results, even after subtracting the positive influence of decadal variation, is shown to be possibly present in the ENSO trend, the amplitude of the ENSO variability in the observed data still increases, by as much as 60% in the last 50 years.
The exact changes happening to ENSO in the future is uncertain: Different models make different predictions. It may be that the observed phenomenon of more frequent and stronger El Niño events occurs only in the initial phase of the global warming, and then (e.g., after the lower layers of the ocean get warmer, as well), El Niño will become weaker than it was. It may also be that the stabilizing and destabilizing forces influencing the phenomenon will eventually compensate for each other. More research is needed to provide a better answer to that question. The ENSO is considered to be a potential tipping element in Earth's climate.
2. El Nino, La Nina
and Greenhouse Gas Emissions
Nitrous oxide (N2O) is not only a major greenhouse gas[i] but is also associated with stratospheric ozone depletion[ii]. The ozone-depletion potential of N2O currently dominates that of other ozone-depleting substances following the reduction in chlorofluorocarbon emissions[iii]. Microbial production in soils account for nearly 60% of total N2O production[iv][v], although anthropogenic sources (including agricultural soil) contributes approximately 1/3 of total N2O source[vi][vii][viii].
NH4 is produced via biomass decomposition, while the process of nitrification – which is temperature and moisture dependent – NO3 is produced from NH4 and in between, N2O is created. Denitrification, a process of converting NO3 into N2, is also soil temperature and moisture dependent and it occurs under and anaerobic state[ix].
NH4 is produced via biomass decomposition, while the process of nitrification – which is temperature and moisture dependent – NO3 is produced from NH4 and in between, N2O is created. Denitrification, a process of converting NO3 into N2, is also soil temperature and moisture dependent and it occurs under and anaerobic state[ix].
Studies have shown that there are decreased N2O emissions in the beginning of El Niño events and increased emissions during most of the La Nina, as well as after the dip in El Niño events. There are high correlations between emissions and volumetric water content (VWC) in the equatorial regions and between soil N2O emissions and soil temperature in the upper Northern Hemisphere regions. Heat waves and drought caused by El Niño also cause a reduction in gross primary production (GPP), the rate at which solar energy is converted to chemical energy by producers in an ecosystem, due to stomatal closure. The effect is a reduction in soil N2O emissions during El Niño years[x] and the reverse is observed during La Nina events.
Although there is no conclusive evidence thus far that El Niño has become more frequent due to anthropogenic climate change, enhanced precipitation variability associated with ENSO events are still possible. Climate models that generate ENSO-like sea-surface temperature (SST) variability in simulations with increased greenhouse gas concentrations found that El Niño events became more frequent and La Niña events more intensive[xi]. However the lack of knowledge about future ENSO behaviour makes any assessments of future climate uncertain.
Although there is no conclusive evidence thus far that El Niño has become more frequent due to anthropogenic climate change, enhanced precipitation variability associated with ENSO events are still possible. Climate models that generate ENSO-like sea-surface temperature (SST) variability in simulations with increased greenhouse gas concentrations found that El Niño events became more frequent and La Niña events more intensive[xi]. However the lack of knowledge about future ENSO behaviour makes any assessments of future climate uncertain.