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Approach :

  • Define ENSO. (give diagram)
  • Describe the relation between ENSO & ozone depletion.
  • Conclusion

The El-Nino Southern Oscillation (ENSO) is a recurring climate pattern involving temperature changes of waters in the central & eastern tropical Pacific Ocean. This patterns triggers changes in temperature and precipitation.

La Nino Conditions

The recent wildfires in California & Australia are glaring instances of how the ENSO is fuelling forest fires. In California, typically, rainfall is enhanced by El Nino and suppressed by La Nina. But due to climate change disruptions, this wet – dry cycle has been amplified leading to more vegetation growth in wetter years, subsequently providing more fire fuel during the drought years.

Increased forest fires caused by ENSO is responsible for the short term spike in methyl bromide, a ozone depleting substance. Methyl bromide is an odourless, colourless gas having both natural and industrial sources. According to US Environment Protection Agency, about 50-95% of it naturally enters atmosphere from oceans & forest fires.

A recent study has found a strong correlation between ENSO and increased atmospheric concentration of methyl bromide. Increased forest fires during the warm phase of ENSO (El Nino) can explain the inter-annual variations in methyl bromide levels. More than 46% of the annual variations of atmospheric methyl bromide is attributed to global fires. Thus, a complex interplay exists between ENSO and ozone depletion.

In early 1980s, scientists noticed a dramatic thinning of ozone layer over Antarctica. Since the Montreal Protocol (1987), the ozone has been gradually recovering, with the hole expected to recover by 2050. However, if the future ENSOs become stronger or more frequent, then the added methyl bromide can delay the ozone hole recovery.

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