The environmental changes around Antarctica are coming so fast it is difficult for researchers, let alone everyone else, to keep up with the studies that are documenting the impacts. It makes reviews like this a valuable synthesis of the types of extrema happening to the region.

I like how the paper looks at the problem from a couple of dimensions. They look at all the themes that are being affected by the changing climate now. This runs from the shrinking ice of all kinds through to oceans, biodiversity as well as atmospheric changes.

Then this is contextualized by climate-induced past changes. Several key knowledge gaps are highlighted, such as sea ice thickness, usefully reminding us that not everything is known about the system.

Because change in Antarctica is not masked by the activities of large local human populations, the impacts are very stark.

The evidence for a cascade of extreme events is exactly the concern identified by the research community for decades. Because of this, the study will need constant updating as the scale of change evolves – there are new studies that have come out even in the short time between when the paper was written and published.

The work is another clear signal from the research community that in order to maintain present levels of quality of life, the majority of our societies need to rapidly and comprehensively shift away from greenhouse gas emitting activity.

This review from Siegert and his team underscores the context of Antarctic extreme events. 2023 is (again) a year of extremes. Whereas in normal years, the Southern Ocean around Antarctica this time of the year is covered by approximately 17 million square kilometres of sea ice, equivalent to an area roughly the size of 63 New Zealands, this year, we are witnessing a staggering loss of an area of about nine New Zealands. 2023 is off the charts, literally.

Described as a "1 in a 7.5 million year event", this extreme sea-ice minimum cannot be solely attributed to natural climate variability; rather, it is driven by excess energy in the climate system, stemming from human-induced greenhouse gas emissions. The consequences are evident through the surge in extreme events globally, from heatwaves and floods to storms, wildfires, and tornadoes – all manifestations of the climate system's attempt to dissipate the surplus energy.

Climate inaction has already set in motion irreversible changes. And while the oceans have been absorbing 90% of the excess energy, they cannot keep up for much longer. Warmer oceans are the likely culprit preventing sea-ice formation around Antarctica, mirroring the gradual decline observed in the Arctic. Understanding these extreme events is vital, as Siegert and his team remind us of the consequences of neglecting climate change.

15 years ago, James Lovelock, co-author of the Gaia Hypothesis, said, "enjoy life while you can: in 20 years global warming will hit the fan". He may have been off by five years.

Coping with a single extreme event is challenging enough; the prospect of dealing with compounded effects of multiple extreme events coming together year after year is worrying and demands immediate attention and action from individuals and policymakers alike.

I appreciate the overview of the different components of Antarctica and changes that we are seeing. Additionally, I hope this work continues to generate awareness and inform people on the impacts of climate change (e.g. Antarctica's contributions to sea level rise have been increasing and will likely continue to do so).

Hopefully this paper generates more science! The authors repeatedly note that an extreme event occurred (e.g. heatwave of 38.5°C higher than average temperatures over East Antarctica in March 2022) but go on to note that no formal attribution of the event has been done.

Scientists can and do calculate the increases in severity and likelihood of extreme events happening due to climate change. For example, New Zealand researchers found that the May 2021 Canterbury floods were 10 - 15% more intense due to human influence. So, I was disappointed to not see any attribution of the extreme events in this work, but hopefully that will come!

I found the author's definition of 'extreme events' confusing. Researchers who work in studying extreme events usually define them as the 5th percentile of events (e.g. a period of rainfall that is heavier than 95% of all rainfall events). This paper seems to imply that processes like 1) meltwater on ice, 2) ice streams (parts of the ice sheet where ice flows more quickly), and 3) winds blowing dust onto ice are all extreme and could be due to climate change. This isn't quite true, all could and would have occurred without human-driven climate change.

The paper does bring up some key points that are likely impacts of warming temperatures (due to burning fossil fuels). Particularly concerning of which are rising sea levels as ice melt quickens and record low sea ice extent, which is at its lowest extent since records became available in 1978.

The paper by Siegert et al is a timely call to us that, as global heating approaches the Paris climate limit of 1.5°C above the pre-industrial global average, Antarctica is experiencing more and more extreme events. In some cases we are getting dangerously close to tipping points, which once crossed will lead to irreversible change with unstoppable consequences for future generations.

Some of the warning signs include the unprecedented heatwave of March 2022 which saw temperatures increase by nearly 40°C over Concordia Station in East Antarctica, and the dramatic decline in winter sea-ice extent since 2016.

This years sea-ice minimum is 20% lower than the average of the last 40 years and is equivalent to sea ice loss of an area nearly 10 times New Zealand. This causes an amplified warming feedback, whereby white sea-ice which reflects 90% of the incoming solar radiation is replaced by dark ocean which absorbs 90% of the radiation. Many researchers are asking if it is now not possible to reverse this trend. Time well tell, but as the southern ocean continues to warm (it has taken up 70% of the heat from human warming so far) the margins of Antarctica’s ice sheets are melting at an accelerating rate. Numerical climate and ice sheet models and evidence from past climate records shows that the West Antarctic Ice Sheet may irreversibly melt if warming is sustained above 1.5°C. Above 2°C of warming, parts of the East Antarctic Ice Sheet will also melt, committing the planet to as much as 20m of global sea-level rise over coming centuries.

The recent report from the WMO predicts that we will be at 1.5°C in the next 5 years. This together with the increased occurrence of extreme weather events in Antarctica and elsewhere, has heightened global concern, and has shown that the policy repsonse so far has been inadequate to address the climate crisis. The IPCC in their latest synthesis report reminds us that there are still multiple feasible pathways to avoid 2°C of global warming, but we must all act now at pace and scale.

This is an effective and very useful high-level summary of Antarctica’s vulnerability to the current climate shifts. All of the statements are in line with the current scientific consensus, with no unsubstantiated statements as far as I’m aware. In describing both the size and potential impact of Antarctica’s climate vulnerabilities, the paper presents a measured and balanced assessment which, while sobering, in no way overstates the situation.

Antarctica is a delicately-balanced system, highly sensitive to changes that elsewhere would be considered small or even insignificant. That’s because even small shifts are enough to cross the freezing point, and therefore change the physical state of the environment. The heatwave of 2022 saw temperatures nearly 40˚C higher than normal in parts of East Antarctica, delivering +7˚C and liquid rain to the Australian Casey station.

Antarctic sea ice – the apron of frozen ocean around Antarctica that forms each winter and breaks up again each summer – has been highly dynamic over the entire satellite record (i.e. since 1979). But that variability has really ramped up in the past decade. In that time, we have seen both record highs and lows of total sea ice extent, with many months falling outside of the range of variability that had been seen prior to 2010. This makes is very difficult to predict what will happen next, but the fact that a record low of 2022 was followed by an even more significant drop in 2023 is very real cause for concern. This is because sea ice performs a whole host of functions that moderate our climate (listed below). For context, the present area of ‘missing’ sea ice is around 20% of the total sea ice extent, roughly equal to 10x the area of New Zealand.

The Southern Ocean is a complex system with a changes cascading through multiple parts of the system and potentially feeding back on itself through multiple mechanisms. This makes it very difficult to predict exactly how things will play out.

Christchurch is presently hosting a meeting of the world’s top Antarctic biologists. The recent extreme events and the rapid rate of change in Antarctica have alarmed the international scientific community. The result will be a statement, ‘The Christchurch Communique’, signed by hundreds of Antarctic scientists, calling on all nations to “intensify and exceed their current commitments to greenhouse gas emissions reductions.” because “an immediate increase in ambition is required to reach net zero...”

Why should New Zealanders care?

"New Zealand’s climate is strongly influenced by heat and moisture carried by the ocean. The Southern Ocean has taken up most of the extra heat from human activities and the tropics are pushing southward. This means that, across the latitudes that NZ occupies, there are stronger gradients, more energy, and more propensity for the atmosphere to take up moisture from the ocean. NZ is therefore in the firing line of a more energetic ocean/atmosphere system, capable of delivering more intense storm and rain events, with increasing frequency."

The five most important effects that sea ice has on the global climate system:

1. "Albedo Effect: The vast sheet of white reflects ~90% of incoming solar radiation back out to space (even more if it has snow on top), preventing it from being absorbed to heat up our system. In contrast, the dark ocean waters that it forms from absorb ~90% of that heat. As more heat is absorbed, it makes it less likely for ice to form so more heat is absorbed rather than reflected. This is a ‘self-reinforcing’ process.
2. Ocean Overturning: The huge volumes of cold salty that are produced as a by-product of sea ice formation drive global ocean overturning, controlling how heat and nutrients are distributed throughout the global ocean. ~40% of all ocean waters can be traced back to Antarctic sea ice formation
3. Drawdown of heat: This process of deep sinking also draws heat out of the atmosphere to deliver it to the deep ocean. To date, the global oceans have taken up 93% of the extra heat in the climate system from human activities (compared with ~1% taken up by the atmosphere). And the Southern Ocean has taken up ~2/3 of that.
4. Drawdown of CO2: In a similar way, CO2 is drawn down out of the atmosphere and delivered to the deepest ocean basins. However, the return flow also brings CO2 that has been stored down deep back up to the surface. So the net effect is a small number which is the balance between two very large numbers. At present the net effect is drawdown of CO2 by the Southern Ocean, but this could change as things get stormier.
5. Ecosystem support: the vast surface of the sea ice provides a surface for algae to grow on – these perform a similar function to grass meadows in terrestrial ecosystems. So sea ice provides the foundational support for the entire marine food web. Also, Emperor Penguins need the sea ice to breed on, so as the sea ice declines, we expect to see them in similar decline. If we stay on track with current rates of emissions, Emperors are predicted to decline by >80% by 2100.