The Climate Variability program has seen an extraordinary amount of activity over the past four months with new arrivals, a clutch of thesis submissions, awards, research voyages and a wealth of research.
Perhaps the highlight of our research effort during this period came from a former PhD student who has now moved on to the Bureau of Meteorology, (soon to be confirmed as Dr) Mandy Freund. Working with her supervisors she produced a world first 400-year-long observational record of El Niño events using coral cores. What made this particularly rewarding was that many people considered such an approach to be impossible. This dataset has immense value as, until now, researchers had relied almost exclusively on the instrumental record, which was too short to determine if recent changes in El Niño activity were out of the ordinary. Mandy’s research showed that indeed they were, particularly in the past 30 years, and that there were shifts in location and potentially the intensity of recent El Niños.
One of the striking parts of research in the Climate Variability group is how often our results show the interconnectedness of climate and weather events around the globe. A perfect example of this was work by Andrea Taschetto and Alex Sen Gupta with South American colleagues that revealed strong convection over the Indian Ocean was responsible for the 2013/14 drought in South America and the accompanying marine heatwave. The research indicated that this was not the first time Indian Ocean convection had played a role in drought events over South America and it was likely to again.
This interconnectedness of our climate reoccurred in multiple papers over the past four months. The strength of trade winds as they blow across the Pacific was found by our researchers to have the capacity to accelerate or decelerate global warming. Intriguingly, the strength of the trade winds was linked to a low frequency climate phenomenon, the Interdecadal Pacific Oscillation, which is now entering a positive phase. This suggests Pacific trade winds would slow leading to accelerated global warming.
The Indian Ocean reared its head again as a distant influencer on global climate, when CLEX researchers found through coupled model runs that it likely played the lead role in the rapid decline of Antarctic sea-ice in 2016, a loss that has yet to recover. However, the wide range of variation in sea-ice found during these model runs suggested this sharp decline was the result of natural variation rather than climate change.
Meanwhile the decline of sea-ice in the Arctic is indeed strongly linked to human caused climate change. Working with colleagues from Norway, Amelie Meyer found that the disappearance of old ice in this region wasn’t just caused by summer melting but that winter storms and warm water intrusions from the Atlantic Ocean were playing an important role. Her research found winter storms over the Arctic leave a legacy that breaks up the ice, melts it from beneath and has led to constant ongoing decline in old ice that far exceeds the period of the storms.
Intriguingly in another area of the Arctic and working with another team, Amelie Meyer and colleagues found limits on these warm water intrusions. Using ocean gliders to capture observations of the warm water intrusions of the Spitzbergen Current, they found small, very cold eddies formed by melting freshwater acted to prevent deeper penetration of these currents, rapidly cooling the Current.
Not every link in the climate system is so clear-cut. In some cases a correlation does not necessarily equate to causation. PhD student Zoe Gillett and a team of international researchers found this out when they investigated a correspondence between southern ozone hole observations during spring and extremely hot summer temperatures in Australia. Our researchers found that ocean temperatures were key to the variations of the spring ozone hole and also for the consequent warmer summers in Australia. So, while the ozone hole didn’t necessary cause the warmer temperatures, as some suspected, it is now a useful tool that may help us improve seasonal predictions.
Amidst this broader research, there has also been continuous progress on improving our climate models. Chief Investigator Craig Bishop and his team have been applying high-level data assimilation techniques that have confirmed the long-term cooling of Antarctica over the past millennia and has produced a statistical approach that will allow future researchers to identify the most robust paleo-reconstructions of El Niño Southern Oscillation events.
In what may seem, at first glance, an unrelated piece of research, our researchers have produced a new method that improves our understanding of the way waves of all types move through the ocean and within local areas. The key here is that waves actually play a role in shifting currents and eddies. These interactions shift ocean heat that impacts the atmosphere above them and therefore need to be properly represented in climate models. It is yet again an example of the interconnected nature of our climate.
But as some of the above highlights suggest, not all our research is carried out with climate models. Recently, Helen Phillips led a multidisciplinary team aboard the RV Investigator that left Fremantle to investigate changes in the eastern Indian Ocean since the 1960s. The voyage was the Australian contribution to the Second International Indian Ocean Expedition, led by Prof Lynnath Beckley of Murdoch University. CLEX students Maxime Marin (UTAS) and Earl Duran (UNSW) were part of Helen’s team.
The other side of our research into climate is a focus on key global reports. We have two chief investigators who are chapter lead authors Nerilie Abram (Chapter 1 – Framing and Context of the Report) and Nathan Bindoff (Chapter 5 – Changing ocean, marine ecosystems and dependent communities) for the IPCC Special Report on Oceans and Cryosphere in a Changing Climate. The final report and summary for policymakers will be released on September 23.
Another chief investigator, Peter Strutton, along with Associate Investigator Shayne McGregor and Partner Investigator Harry Hendon were lead authors on the second Tropical Pacific Observing System Report. The report calls for “for an expanded motivation for and redesign of the backbone Tropical Pacific Observing System. You can find the report here.
Beyond all the research and reports, perhaps one of the most rewarding parts of the CLEX journey is seeing our students graduate and take the next step in their extraordinary careers in climate science.
Over the past four months we saw Luwei Yang submit her PhD thesis, The Impact of Lee Waves on the Southern Ocean Circulation and its Sensitivity to Wind Stress. In that same period we had three Honours students complete their thesis – Ruth Moorman (ANU), Xiaoxuan Jiang and Ziyan Zhang (both from University of Tasmania).
We also welcomed a new student, Sarah Jackson, who will be supervised by ANU Chief Investigator Nerilie Abram.
Along with students we also added two new postdocs – Diego Carrio and Francesco Sardelli, who will be working with Craig Bishop. Diego’s work is related to the performance of new and innovative data assimilation algorithms for discovering model trajectories that closely track observations while Francesco will be working on new directions in data assimilation.
Finally, we must acknowledge the triumphs of our teams in terms of recognition by their peers. We were delighted when Adele Morrison was awarded the Meyers Medal for early career research excellence. It’s the third time a Centre of Excellence ECR has won the medal.
We also saw Annette Stellema and Rishav Goyal receive honourable mentions among a packed field for best poster at AMOS-ICTMO. All in all, it has been an incredibly busy and impressive four months and we look forward to the rest of 2019, which is on track to be just as notable.