It is the first time climate scientists have produced robust results from modelling to conclude that climate change has a substantial impact on the El Niño-Southern Oscillation (ENSO) cycle in the future. But a 2010 study by scientists from NASA and NOAA provided some signs.
So, a stronger El Niño is likely to bring more intense drying which may exacerbate drought and bushfire weather. In the central pacific island nation of Kiribati El Niño will bring more intense rain and floods. More intense Winter rain and floods may be felt in California, northwest Mexico and southwest United States, as well as down the west coast of South America, and even further afield.
El Niño intensity growing
A 2010 study by Tong Lee of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Michael McPhaden of NOAA's Pacific Marine Environmental Laboratory, Seattle found that since 1982 the intensity of El Niños in the central Pacific, based upon sea surface temperatures, has nearly doubled, with the most intense event occurring in 2009-10. But no significant rise in sea surface temperatures were observed during neutral and La Nina phases of ENSO.
"These results suggest climate change may already be affecting El Niño by shifting the center of action from the eastern to the central Pacific," said McPhaden. "El Niño's impact on global weather patterns is different if ocean warming occurs primarily in the central Pacific, instead of the eastern Pacific.
Tong Lee concluded, "It is important to know if the increasing intensity and frequency of these central Pacific El Niños are due to natural variations in climate or to climate change caused by human-produced greenhouse gas emissions," he said.
So the question was still open whether and how climate change was impacting ENSO.
Climate Change contributes to El Niño intensity after 2050
"Although this issue has been investigated many times during the past 20 years, there is very little consensus on future changes in ENSO, apart from an expectation that ENSO will continue to be a dominant source of year-to-year variability." said Dr Scott Power and colleagues in this new study.
Using the most recent climate models with four different scenarios for CO2 and other greenhouse gases, robust results for the later half of the century were achieved showing a noticeable intensification of El Niño driven drying in the western Pacific Ocean and rainfall increases in the central and eastern equatorial Pacific.
"Experiments with an Atmospheric General Circulation Model reveal that robust projected changes in precipitation anomalies during El Niño years are primarily determined by a nonlinear response to surface global warming." say the scientists in the study extract.
The study was lead by Senior Principal Research Scientist at the Australian Bureau of Meteorology, Dr Scott Power and published in Nature as Robust twenty-first-century projections of El Niño and related precipitation variability (abstract)
"The future of ENSO and the disruption it causes to the climate of the earth, its people and its ecosystems are clearer now than ever before." said Dr Scott Power in an interview at The Conversation.
Dr Power was Coordinating Lead Author of Chapter 11, Fifth Assessment Report, IPCC Working Group 1, and gave the keynote presentation at an AMOS meeting in Melbourne on 3 October 2013 discussing the latest IPCC report.
In an interview with Richard Ewart from Radio Australia, Scott Power explained the research:
"What we have found in the latest generation of climate models, we've been examining a large number of them, we find that in a majority of those models you tend to get an intensification of those two things: during El Niño conditions you get even drier conditions in the far west and even wetter conditions in the central and eastern part of the pacific. So at this stage we have been focussing on the large scale features of the change. That is what we describe in the paper. We don't actually get down to 'what does this mean for individual countries'. Although, it is quite clear that in that large expansive region where rainfall tends to go up, covering thousands of kilometres, that incorporates most of Kiribas."
When asked if the probability of climatic disasters are more likely due to this intensification of El Niño Dr Scott chose his words carefully:
"Specifically, what we can say is that during El Niño events rainfall tends to increase in the central and eastern Pacific. So what our results show that increase will tend to be even greater. I don't think it is an unreasonable inference to say that if there is a risk of a flood in a certain country in association with rainfall increases, then that risk would be inflated, all other things being equal. But, in reality we didn't actually investigate what the implications were relating to flood. We just examined exclusively changes in ocean temperatures and changes in precipitation only."
Scott Power highlighted that the Pacific Ocean has had a warming trend for a considerable period. Indeed, in November 2011 the Bureau of Meteorology and CSIRO published a major report on Pacific climate change: temperatures rise, sea levels increase, rainfall changing. He concluded his interview on Radio Australia saying:
"But now we know from the science, from the IPCC report that came out a couple of weeks ago and the work we have done with many of the island nations done over the last several years. That we know the Pacific has been warming up, at all the islands across the region and we know that the oceans have been warming up, sea levels have been rising, there has been lots of variability but there have been these underlining trends: higher temperatures, higher sea levels.
So what we have been examining, what we have been talking about in our Nature article is the impact of humans on the climate system. So that is not going to occur on its own. It will still come wrapped up in this naturally occurring variability. So the future climate, just like the recent climate, won't be just a function of naturally occurring oscillations or cycles as you say. It is going to be a function of those natural cycles but also anthropogenically forced or human forced changes as well."
Watch an Australian Broadcasting Corporation interview discussing the new scientific findings with Dr Scott Power from BOM on youtube.
The recent hot weather - Australia has already had extreme heatwaves over Summer and Autumn, the hottest September on record by a large margin, the hottest 12 months on record, and is well on track for the hottest calendar year - comes even though the ENSO cycle is currently in neutral and follows two years where a strong La Nina brought significant rains and floods to Australia, so much so that it put a significant bump in the sea level rise trend.
The last strong El Niño year was in 1997-1998 when temperatures peaked here in Australia and globally and climate deniers often cherry pick as the start of a period to illustrate there has been little recent atmospheric warming, even though there is strong evidence the planet as a whole has continued warming with much of the heat being absorbed by the oceans. See Professor Any Pittman's article: Is global warming in a hiatus?
"It is sobering to see that we're setting these records in non-El Niño years," Dr Power said according to a Sydney Morning Herald report, "The magnitude of the changes [on future El Niño periods] will critically depend on the amount of emissions that the world ultimately ends up producing over coming decades," he said.
A recent study from the University of Hawaii showed that cities around the globe will depart their historical level of climate variability starting from 2020. The world's oceans were assessed as having already crossed this threshold in 2008.
Sources:
- Scott Power, François Delage, Christine Chung, Greg Kociuba & Kevin Keay, Robust twenty-first-century projections of El Niño and related precipitation variability (abstract), Nature (2013) doi:10.1038/nature12580
- Richard Ewart, ABC Radio Australia Pacific Beat program, 15 October 2013 - Research shows climate change is causing issues for El Niño
- Interview at the Conversation, 14 October 2013 - Australia to see worse drought thanks to intensifying El Niño
- Tong Lee and Michael J. McPhaden, Increasing intensity of El Niño in the central-equatorial Pacific (abstract), Geophysical Research Letters, DOI: 10.1029/2010GL044007
- NASA news, 25 August 2010 - NASA/NOAA Study Finds El Niños are Growing Stronger
- Image - Deviations from normal sea surface temperatures (left) and sea surface heights (right) at the peak of the 2009-2010 central Pacific El Niño, as measured by NOAA polar orbiting satellites and NASA's Jason-1 spacecraft, respectively. The warmest temperatures and highest sea levels were located in the central equatorial Pacific. Image credit: NASA/JPL-NOAA
No comments:
Post a Comment