August 17, 2020 | Published by |

Picture: Photo topping Washington Post Pulitzer prizewinning story. Credit: Bonnie Jo Mount.

We are pleased to announce that the Heatwaves and Cold Air Outbreaks research program has won its first Pulitzer Prize. Okay, that’s not quite true, but a Washington Post series on the world’s climate hotspots, 2°C: Beyond the Limit, did. A story on marine heatwaves off Tasmania, On land Australia’s rising heat is ‘apocalyptic’. In the ocean it’s worse, was part of the series that featured our own Prof Neil Holbrook and many colleagues across the Australian oceanography and climate community. It’s impressive to see this work get such recognition.

Closer to home, as we move towards the next IPCC report and examine the new range of CMIP6 models that will play a large part in its projections, our researchers have been looking closely at how well these new models reproduce conditions over Australia.

Working with researchers in CSIRO and the Bureau of Meteorology, we found they show small improvements over the previous generation (CMIP5; developed in ~2012), including better reproduction of land and marine heatwaves and sea-level rise as well as improved relationships between Australia’s climate drivers and rainfall. The issues around increased climate sensitivity shown in some of the CMIP6 models also appeared in some of our Australian projections, although this aspect continues to be investigated internationally to determine the reason for these differences.

A key component of our modelling research is focused on reducing errors and ensuring that physical processes are simulated accurately. As part of this ongoing process, CLEX researchers addressed the error compensation issue for temperature extremes by defining a novel performance metric that identifies those models that can simulate temperature extremes well and simulate them well for the right reasons. This investigation compared additive errors in CMIP5 and CMIP6 models. We found the overall performance of an ensemble improves when increasing the horizontal resolution largely due to improvements in synoptic-scale variability. We also found that CMIP6 improvements relative to CMIP5 surpass those expected from the increase in horizontal resolution alone, suggesting model improvements associated with the representation of physical processes.

One of the most challenging areas in climate models is downscaling, which is the modelling of climate processes over regional areas. This scale is important for policymakers to be able to make accurate decisions about adapting to climate in different areas. However, this work uses regional climate models (RCM) that are more expensive in terms of time and computing resources when compared to global climate models (GCM). To determine if RCMs produced more valuable results compared to GCMs, CLEX researchers simulated the Australian climate using both. They found overall, RCMs simulated the Australian climate more accurately than GCMs, particularly for some regions like the heavily populated and economically important east coast. This research was also the first to develop a method that shows where and when RCMs simultaneously add value to modelled representations of the present-day climate while at the same time making different projections about future climate change compared to GCMs. When RCMs show both of these attributes, it suggests that they confer plausible improvements in future climate projections, relative to GCMs. The researchers called this new quantity the ‘realised added value’ shown by RCMs.

Another new metric developed by the Heatwaves and Cold Air Outbreaks team is cumulative heat. It came from the first comprehensive worldwide assessment of heatwaves down to regional levels, which has revealed that in nearly every part of the world heatwaves have been increasing in frequency and duration since the 1950s. The new cumulative heat metric reveals exactly how much heat is packed into individual heatwaves and heatwave seasons.

It’s not just heatwaves that are changing but also fire seasons. A regional study of how prescribed burning days may change in the future produced an unexpected result. It found that along the east coast from Queensland right round to South Australia days suitable for prescribed burning would change very little and, in some places, would even increase. What did change was when the weather was suitable, shifting from autumn to winter and early spring. Unfortunately, this also corresponded to changes in inversion layers, which keeps smoke and pollution closer to the ground.

But heatwaves don’t just exist on land. Our oceans are subject to long-lasting heatwaves that have profound impacts on ecologies and fisheries around the world. They even impact the foundations of the ocean food chain with new research from CLEX showing how nutrient variation in combination with marine heatwaves will affect ocean productivity. Marine heatwaves are expected to expand and intensify in coming decades due to climate change, while nutrient-poor waters are projected to expand globally. These findings suggest that weaker blooms during marine heatwaves will, therefore, become more common and widespread.

The impacts of marine heatwaves have resulted in a call from international researchers led by CLEX investigators that highlights the need for the development of systems to predict marine heatwaves. The authors said there is a need for streamlined and simple information and forecasts that can be widely shared with stakeholders, preferably via a central point where information and news is provided in a consistent and accessible manner. If this was introduced marine-resource users and managers of fisheries, aquaculture and conservation would be able to take action to minimise damage, such as harvesting or relocating farmed species or providing short term protections like cooling or shading.

And CLEX researchers are already moving on this front. Along with other colleagues, they investigated the large-scale drivers that led to the development of marine heatwaves off southeast Australia observed from 1994-2016, including the extreme 2015/16 event. They found about half of marine heatwaves in this region were primarily due to the intensification of the East Australian Current Extension, bringing warmer water with it. The slow-moving waves that generated this can’t be seen by the naked eye but the change in wave heights they generate can be detected by satellites. This work means it may be possible to forecast major marine heatwave events around Tasmania up to 2-3 years in advance.

As well as looking forward, our researchers have been looking backwards in an effort to extend Australia’s meteorological record. Joelle Gergis and Linden Ashcroft have been leading a project to dust-off forgotten old weather journals from Adelaide as part of a process to create the longest continuous daily temperature record in Australia, and one of the longest in the Southern Hemisphere. This has also led to the creation of a citizen science project, Climate History Australia, that aims to get Australians involved in transferring the data from journals into the digital realm.

Linden has also become editor-in-chief of the Geoscience Data Journal which focuses, as the name suggests, on scientific data, producing open-access peer-reviewed data sets. This is important work that improves the scientific record, provides version control for the community and allows major datasets to be fully described, cited and discovered.

In another form of outreach to the wider community, Sanaa Hobeichi has added CLEX School Resources Developer to her research roles. This new role is part of the Knowledge Brokerage Team led by Ian Macadam. Sanaa will be responsible for ensuring that the Centre delivers educational resources on climate science and/or weather that are tailored to the needs of secondary school Maths and Science teachers. Finally, even amidst the pandemic, we have added a new student to our ranks. We welcomed Marzie Naserikia who has started her PhD with us supervised by Melissa Hart and Negin Nazarian.