Kevin Trenberth on El Niño – A Tracking Of The Evolution Of His Perspective On This Issue Since 1997

Kevin Trenberth is recognized as one the pioneers in developing an improved understanding of El Niños. Thus, it is informative to see how his viewpoint has evolved over time. I have reproduced material from several sources below which document this evolution in his thinking on this climate feature.

First, in 1997 it was written in a report on his research (see), that

“El Niño and global warming

El Nino has been showing up more often since the late 1970s, with a prolonged episode from 1990 to 1995 and another quickly building up now. According to NCAR atmospheric scientist Kevin Trenberth, one possible explanation is that the warm pool in the tropical western Pacific Ocean may be growing larger. Climate models are not yet accurate enough in simulating El Nino to clearly attribute these changes to global warming. However, even without affecting how often El Nino occurs or how long it stays around, global climate warming is likely to intensify the extremes of flooding and drought already experienced in different parts of the world during a normal El Nino and its inverse, La Nina. Trenberth believes that global warming and El Nino reinforce each other in their impact on the environment and society, primarily through their combined effects on the hydrological cycle and the repercussions for water supplies.”

In 1999 in a news article (see) it was written

“What about the future of El Nino? According to NCAR senior scientist Kevin Trenberth, ENSO’s impacts may be enhanced by human-produced climate change. El Ninos have been unusually frequent since the mid- 1970s. The same period has seen a dramatic rise in global temperature. The year 1998 set a global record and was one of the United States’ two warmest years since records began in the late 1800s.

Trenberth has found that the global mean temperature peaks three to four months after the peak in El Nino. “It is no coincidence that the exceptional warmth in the first seven months of 1998 occurred as the Pacific Ocean lost heat following the peak of the 1997-98 El Nino in December 1997,” notes Trenberth. During El Ninos, warm waters spread across the tropical Pacific, evaporating large amounts of water vapor that release heat when the vapor condenses into clouds and rain. Thus, El Nino events tend to transfer heat from ocean to atmosphere, warming the globe about 0.1 degree Celsius for each standard deviation of departure from average temperatures in the Southern Oscillation index, according to Trenberth.

Trenberth theorizes that much of the additional heat trapped by increasing amounts of greenhouse gases may be going into the oceans. It is later released through El Ninos that are larger, more frequent, or less efficient in releasing the ocean-stored heat……”

Then in 2001 it was reported (see)

“Trenberth’s research was published in the “Letters” section of the Journal of Climate. According to Journal guidelines, “Letters provide rapid and high-profile publication of brief and timely contributions to the climatological community.” So apparently, the discovery of the TNI is a major breakthrough in climate science. And in a year or two, when the next El Niño event takes hold, which it undoubtedly will, prepare yourself for an endless barrage of global warming–El Niño stories. It’s all about the TNI. “[Note: as written in this article “The Trans-Niño Index  (TNI)is the difference in standardized sea-surface temperature departures between the eastern tropical Pacific and the western/central tropical Pacific. The TNI is highest when temperatures are below normal in the central/eastern Pacific and above normal off the Peruvian coast”].

In 2002, in An Essay by Dr. Kevin E. Trenberth, he wrote

“How El Niño changes as climate changes and global warming progresses is a critical question of great importance for many regions of the globe. While our exploratory analyses are suggestive and form useful hypotheses for future work, climate models do not yet simulate El Niño well enough and are too different from each other to have any confidence in their projections. This itself is an indication of a lack of adequate understanding of some aspects of El Niño and its role in the global climate system. Accordingly, we continue to seek improved analyses of the past and associated diagnostic studies that will clarify the role of El Niño and improve its prediction. A focus for some of the research is quantitative diagnostic estimates of the energetics of El Niño, so that we can track how the heat builds up in the ocean and is subsequently redistributed and dissipated during the El Niño event. The underlying hypothesis is that El Niño exists and plays a role in the Pacific Ocean as a means of removing heat from the equatorial regions of the ocean, where it would otherwise build up. An implication of this, if correct, is that further heat buildup from increasing greenhouse gases in the atmosphere would lead to increased magnitudes and/or frequency of El Niño events. Nevertheless, we do not expect this to be simple, and nature always seems to be able to come up with surprises as to just what the future holds”

There is no more recent publications that I have found with respect to any further evolution of his thinking with respect to El Niños. Nonetheless, between 1997 to 2002, his prespective on this climate feature changed.  

This evolution of scientific thinking, as we learn more on the complexity of the climate system, is the hallmark of a scientist who is willing to alter their viewpoints as new information arrives. Keven Trenberth should be recognized for making the candid statement that nature always seems to be able to come up with surprises as to just what the future holds.”

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