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Reported by Kasia Brzezinska, CSaP Policy Intern (Jan - April 2018)
Professor Charles Kennel, CSaP's long-standing Visiting Research Fellow from the University of California San Diego, explained why California’s climate fate is tied up with the behaviour of the Pacific El Nino and La Nina system, how the loss of Arctic sea ice may be changing that system, and how gaining a greater understanding of its processes might enable us to predict extreme weather in future.
Since the giant El Nino of 1998, global warming has experienced a hiatus and it seems that the Pacific ENSO system – responsible for natural weather disasters around the world – has changed in a fundamental way. But it still isn't entirely clear why that change has occurred.
Professor Kennel began his talk by explaining that global surface temperature is a misleading indicator of the risks that we run by allowing climate change to continue. During the hiatus that began after 1998, it seemed that the average temperature of the Earth's surface didn't change significantly, and so it didn't tell us of the risks that had been accumulating during this time. However, these risk have now been revealed in the extreme weather that has recently hit California.
The history of California is written in water and not in ink.
Rather than focusing on global surface temperature alone, Professor Kennel argued that we should turn our attention to the depleting sea ice. He showed how recent numerical simulations suggest that the loss of sea ice may have led to California’s recent drought.
Professor Kennel noted that prior to the hiatus, the temperature change in the Arctic was over land. But during the hiatus, the sea ice melted, which led to the Arctic Ocean warming. And in 1997-1998, there was a rapid increase in the melting of Arctic sea ice and the solar radiant energy absorbed by the ocean. He also added that Arctic Ocean warming may be responsible for creating upper atmosphere winds that are changing the El Nino and La Nina cycle.
This may have caused the prolonged La Nina state which kept the Pacific Ocean cool, and in turn led to California experiencing its greatest drought since record-keeping began.
However, Professor Kennel acknowledged that these changes in the ENSO system are only one aspect of the story explaining the whole global hiatus in warming. The amount of energy stored in the El Nino system and in the volume of water underneath the El Nino system is small compared to the amount of energy that has gone into the global ocean.
But he believes we can explain the phase change in the behaviour of the El Nino system as a coupled interaction between retreating sea ice and stronger La Nina behaviour. This means that with a better understanding of how these processes work, we might be closer to forecasting ENSO-related weather disasters and understanding what will happen when the sea ice is gone.
Professor Kennel summarised his presentation:
A podcast of the seminar is available below:
Climate Seminar Series 2018
The Centre for Science and Policy is working with Professor Charles Kennel, Director emeritus at the Scripps Institution of Oceanography, University of California San Diego, to deliver the 2018 series of climate change seminars hosted by Christ’s College.
For more details of the climate seminars, please click here.