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Sources of fluctuations
Despite the Paris Agreement and many countries and organizations adhering to their commitments to reduce greenhouse gas emissions, the concentration of atmospheric carbon dioxide is still increasing alarmingly. On the other hand, unfortunately, countries like China and India have continued to burn coal and build power plants based on this fuel. These policies have caused the emission of greenhouse gases by these two countries to be more than the amount of reduction that happened in other regions.
The increase in global temperature is a step-like process. 1998 was the warmest year of the 20th century after the great El Niño of 1997-1998. After 1998, there was a multi-year hiatus (from 2001 to 2014) in the global warming process, causing a lot of noise from people who called it a myth.
The great El Nino of 2014-2015 ended the hiatus in global warming, and 2015 became the warmest year on Earth so far; But a year later, this title was given in 2016.
Many annual fluctuations are associated with El Niño cycles; But that’s not all. Further analyzes show that the decadal oscillations of the Pacific Ocean follow changes in the amount of heat stored in different depths of this ocean. These changes are known as the Pacific Interdecadal Oscillation. The Pacific Decadal Oscillation can be considered as the Northern Hemisphere version of the Pacific Interdecadal Oscillation.
With the decadal oscillation of the Pacific Ocean, major changes in prevailing winds, sea level pressure, sea water level, rainfall and location of storms occurred throughout this ocean and its border countries. These changes spread to the southern oceans and from the Arctic to the Atlantic Ocean.
The mentioned effects are greater in winter in each hemisphere. There is very good but incomplete evidence that changes in the winds of ocean currents and ocean convection and overturning lead to changes in the amount of heat absorbed in the deep ocean during the negative phase of the quiet decadal oscillation.
Therefore, during the positive phase of the ten-year oscillation of the Pacific Ocean, more heat is stored in the 300 meters above the ocean and can affect the global temperature. During the negative phase, more heat penetrates below 300 meters and leads to the overall warming of the oceans; But it disappears on the surface.
During El Nino, heat stored deep in the western equatorial Pacific is transported around and returned to the atmosphere, causing a small global warming.
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