El Nino Conditions. Warm water pool approaches South American coast. Absence of cold upwelling increases warming.
Geophysicists recently discovered that El Niño events in the central Pacific Ocean increase global average surface temperatures less than El Niño events located in the eastern Pacific.
These central Pacific El Niño events may have contributed to decades-long slowdowns in the rate of climate change. That slowdown helped fuel climate change skeptics over the past few years as the pause in warming gained media attention.
A shift in this year's El Niño may change all that.
Since 1900, five distinct slowdowns in global surface warming occurred despite the influence of increasing greenhouse gas levels on the climate, wrote the authors of a recent paper in Geophysical Research Letters. During each of these heating hiatuses, three to four El Niño events occurred. However all of these events were located in the central Pacific.
Every year of the warming slowdowns hosted Pacific Ocean conditions classified as neutral, central Pacific El Niño, mixed or La Niña. No eastern Pacific El Niño events occurred during slowdowns.
Four El Niño and three La Niña events have occurred since 1998. All of the El Niño events occurred in the central Pacific. Natural variability in Pacific Ocean conditions may explain this trend towards central Pacific events. La Niña has dominated since then, cooling the atmosphere.
But now a shift in the average state of the Pacific could tip the scales towards El Niño events in the eastern Pacific, which would lead to periods of even higher global surface temperatures on top of the already warming climate.
Geophysicists from the University of British Colombia used sea surface temperature records from 1880 to 1911 to analyze the influence of different types of El Niño events.
El Niño and La Niña form two parts of the El Niño Southern Oscillation (ENSO), which is a cycle of variations in air pressure and surface temperature of the tropical Pacific Ocean. El Niño events involve warmer waters and higher air pressure, resulting in heavy rains along the west coast of South America and warm, dry winters in the northern United States among other effects.
La Niña events involve cooler Pacific Ocean temperatures and lower air pressure. The west coast of South America can suffer severe drought during La Niña.