While 2023 made headlines for smashing global temperature records, last year also saw some truly remarkable events in the Antarctic.
After crashing to a record-low summer extent in February, sea ice around the southern continent regrew extremely slowly.
By July, when sea ice should be approaching its maximum winter coverage, there was an area of ice “missing” that was bigger than Algeria – the world’s 10th largest country.
When the annual maximum extent arrived – early – it was the smallest on record by a “wide margin”.
This made 2023 the second record-breaking year in a row, continuing the recent erratic swings in sea ice cover that had otherwise been preceded by several decades of steady, gradual increase.
In our new paper, published in the Royal Meteorological Society’s journal Weather, my coauthor and I explore what happened to sea ice in 2023, what caused the dramatic events and what the implications are for the future.
The importance of Antarctic sea ice
Antarctic sea ice is a critical puzzle piece in the regional and global climate picture.
The frozen continent as a whole acts as the Earth’s principal refrigerator, reflecting the sun’s energy from its bright, white mirror-like surface, helping keep temperatures cool.
Sea ice formation around its coastline acts as an engine for ocean currents and influences weather patterns that can have far-reaching effects.
Floating ice also acts as a buffer that can protect the exposed edges of the ice sheet from the destructive action of waves, meaning that it can curb Antarctica’s contribution to sea level rise. By influencing the availability of water from the open ocean, it also affects how much snow can fall to replenish the ice sheet’s losses.
And sea ice is vitally important for marine life, as demonstrated by the “catastrophic breeding failure” of Emperor penguin chicks following the (then) record-low sea ice coverage in 2022.
Long-term trends
Thanks to satellite data, scientists have a detailed picture of how Arctic and Antarctic sea ice have behaved since the late 1970s. And for Antarctica, this picture has been something of a puzzle.
Between 1979 and 2015, average Antarctic sea ice extent – the area of ocean with at least 15% sea ice cover – increased slightly, but fairly steadily. This is in stark contrast to the Arctic, where sea ice at the minimum summer extent plummeted by nearly 12% per decade.
Then, after a record high year in 2014, Antarctic sea ice extent dropped to a record low in 2017. Several years of low sea ice came after that, with the summer minimum record smashed in 2022, when it fell below 2m square kilometres for the first time.
How extreme was 2023?
Antarctic sea ice waxes and wanes throughout the year, reaching a minimum in February at the end of the southern-hemisphere summer and a maximum in September after a long, cold winter.
This seasonal expansion causes the area covered by sea ice to grow six-fold within a single year – as the chart below shows. It depicts Antarctic sea ice extent for each day of 2023 (blue line), along with how it compares to the historical range (blue shading) and the record low for the time of year (dotted line).
Antarctic daily sea ice extent from the US National Snow and Ice Data Center. The bold lines show daily 2023 values, the shaded area indicates the two standard deviation range in historical values between 1979 and 2010. The dotted line shows the record low. Chart by Carbon Brief.
As the chart shows, 2023 was an exceptional year in the satellite record, remaining well below average for the entire year.
The year started with a record-breaking minimum extent of 1.79m km2 in February 2023, which was 10% lower than the already record-breaking 2022.
Although the autumn freeze-up started off as usual, from April the seasonal expansion of sea ice was very slow. By July, the total sea ice extent was 13.5m km2 – 15% lower than average for the month.
The area of “missing” sea ice for the month of July, relative to the 1981–2010 average, was nearly two-and-a-half million square kilometres – an area larger than Algeria.
The period of extreme departure from average persisted from mid-May until mid-November, with conditions recovering a little, meaning that by the end of the year, they were no longer record-breaking.
Overall, the largest deviations from average conditions in 2023 were recorded in winter (June to August). To see this in context, the chart below shows winter sea ice extent from 1979 to 2023 and highlights how dramatically low winter sea ice was last year.
In addition, the table below shows the average winter sea ice extent and the anomaly – that is, the departure from the 1981-2010 average. It is clear that at 2.34m km2, the anomaly in the winter of 2023 was larger than in any other year. The next largest was 0.93m km2 in 2022.
| Year | JJA mean extent (million km2) | JJA anomaly (million km2) |
|---|---|---|
| 2023 | 13.34 | -2.34 |
| 2022 | 14.75 | -0.93 |
| 2002 | 14.95 | -0.73 |
| 2017 | 14.97 | -0.71 |
| 1986 | 15.00 | -0.69 |
Table showing the top five years with largest negative winter sea ice extent anomalies with respect to 1981–2010, ranked from lowest sea ice extent to highest. All extents and anomalies are shown in millions of square kilometres. Source: Gilbert & Homes (2024)
Drivers of low sea ice conditions
There is no single cause of record-low sea ice conditions, but it is likely that a combination of oceanic and atmospheric factors conspired to produce 2023’s record sea ice conditions.
Recent studies have pointed to the important role of ocean processes and heat stored below the surface, which have kept sea ice extent low since 2016. Warm sea surface temperatures in the Southern Ocean during the first half of 2023 probably also partly explain both the record minimum extent in February and the slow freeze-up afterwards.
But Antarctic sea ice is also closely controlled by atmospheric circulation. One such circulation pattern is the Amundsen Sea Low, which is a low-pressure weather system that consistently forms off the coast of West Antarctica. Exactly where it is and how low the atmospheric pressure gets can control winds and temperature in the region, impacting the movement, breakup, formation and destruction of sea ice.
The pattern in sea ice in 2023 was closely tied to the behaviour of the Amundsen Sea Low, which was unusually deep and far to the east in winter when the sea ice anomalies were at their peak.
This situation tends to blow warm air towards the coast and push sea ice back, limiting sea ice growth during the freeze-up season.
Other large-scale weather patterns – such as the Southern Annular Mode and El Niño-Southern Oscillation have historically contributed to the ups-and-downs observed in Antarctic sea ice, but they do not seem to have had a major influence in 2023.
These weather patterns can interact to either amplify or suppress sea ice changes by affecting the ways that sea ice moves, melts and freezes.
Links with climate change
Deciphering the role of climate change in Antarctic sea ice trends is much more complicated than in the Arctic because conditions are impacted by so many competing factors.
However, the sheer magnitude of 2023’s sea ice lows suggests that something unusual is happening.
Sea ice conditions during 2023 were far outside the bounds of normality, but it is difficult to say exactly how far. That is because the satellite record is relatively short (45 years) and the system is highly variable. In addition, climate change is already impacting the Southern Ocean in complex ways, making an estimation of what is “normal” impossible.
Climate models project a decline in Antarctic sea ice in response to greenhouse gas emissions and rising temperatures. However, until 2015 this prediction was largely at odds with what scientists were seeing – in part due to the complexity and uncertainty of the processes involved, and the impractically high detail required to accurately represent sea ice in models.
However, despite their limitations, it seems inescapable that models will ultimately be correct about Antarctic sea ice decline. Human emissions are raising temperatures in the Southern Ocean, and studies show a link between ocean warming and low Antarctic sea-ice extents.
Several papers – including one discussed in a previous Carbon Brief guest post – have argued that recent record-low sea ice years may be a taste of what is to come.
With 2024 likely to be another year of high global average temperatures and weather extremes, it may emerge as another year of low Antarctic sea ice. Although current sea ice extent is no longer the lowest on record, conditions are still well below the 1981-2010 average, and this situation may well persist into the 2024 melt season.
So, while it is too early to say conclusively that the recent sea-ice lows are the beginning of a regime shift in Antarctic sea ice, it seems inevitable that it will eventually decline in response to human-caused climate change.
For now, all scientists can say for certain is that the events of 2023 were entirely remarkable and unlike anything seen in the satellite record.
The post Guest post: Why 2023 was an exceptional year for Antarctic sea ice appeared first on Carbon Brief.
Guest post: Why 2023 was an exceptional year for Antarctic sea ice
Drought and heatwaves occurring together – known as “compound” events – have “surged” across the world since the early 2000s, a new study shows.
Compound drought and heat events (CDHEs) can have devastating effects, creating the ideal conditions for intense wildfires, such as Australia’s “Black Summer” of 2019-20 where bushfires burned 24m hectares and killed 33 people.
The research, published in Science Advances, finds that the increase in CDHEs is predominantly being driven by events that start with a heatwave.
The global area affected by such “heatwave-led” compound events has more than doubled between 1980-2001 and 2002-23, the study says.
The rapid increase in these events over the last 23 years cannot be explained solely by global warming, the authors note.
Since the late 1990s, feedbacks between the land and the atmosphere have become stronger, making heatwaves more likely to trigger drought conditions, they explain.
One of the study authors tells Carbon Brief that societies must pay greater attention to compound events, which can “cause severe impacts on ecosystems, agriculture and society”.
Compound events
CDHEs are extreme weather events where drought and heatwave conditions occur simultaneously – or shortly after each other – in the same region.
These events are often triggered by large-scale weather patterns, such as “blocking” highs, which can produce “prolonged” hot and dry conditions, according to the study.
Prof Sang-Wook Yeh is one of the study authors and a professor at the Ewha Womans University in South Korea. He tells Carbon Brief:
“When heatwaves and droughts occur together, the two hazards reinforce each other through land-atmosphere interactions. This amplifies surface heating and soil moisture deficits, making compound events more intense and damaging than single hazards.”
CDHEs can begin with either a heatwave or a drought.
The sequence of these extremes is important, the study says, as they have different drivers and impacts.
For example, in a CDHE where the heatwave was the precursor, increased direct sunshine causes more moisture loss from soils and plants, leading to a drought.
Conversely, in an event where the drought was the precursor, the lack of soil moisture means that less of the sun’s energy goes into evaporation and more goes into warming the Earth’s surface. This produces favourable conditions for heatwaves.
The study shows that the majority of CDHEs globally start out as a drought.
In recent years, there has been increasing focus on these events due to the devastating impact they have on agriculture, ecosystems and public health.
In Russia in the summer of 2010, a compound drought-heatwave event – and the associated wildfires – caused the death of nearly 55,000 people, the study notes.
The record-breaking Pacific north-west “heat dome” in 2021 triggered extreme drought conditions that caused “significant declines” in wheat yields, as well as in barley, canola and fruit production in British Columbia and Alberta, Canada, says the study.
Increasing events
To assess how CDHEs are changing, the researchers use daily reanalysis data to identify droughts and heatwaves events. (Reanalysis data combines past observations with climate models to create a historical climate record.) Then, using an algorithm, they analyse how these events overlap in both time and space.
The study covers the period from 1980 to 2023 and the world’s land surface, excluding polar regions where CDHEs are rare.
The research finds that the area of land affected by CDHEs has “increased substantially” since the early 2000s.
Heatwave-led events have been the main contributor to this increase, the study says, with their spatial extent rising 110% between 1980-2001 and 2002-23, compared to a 59% increase for drought-led events.
The map below shows the global distribution of CDHEs over 1980-2023. The charts show the percentage of the land surface affected by a heatwave-led CDHE (red) or a drought-led CDHE (yellow) in a given year (left) and relative increase in each CDHE type (right).
The study finds that CDHEs have occurred most frequently in northern South America, the southern US, eastern Europe, central Africa and south Asia.
Threshold passed
The authors explain that the increase in heatwave-led CDHEs is related to rising global temperatures, but that this does not tell the whole story.
In the earlier 22-year period of 1980-2001, the study finds that the spatial extent of heatwave-led CDHEs rises by 1.6% per 1C of global temperature rise. For the more-recent period of 2022-23, this increases “nearly eightfold” to 13.1%.
The change suggests that the rapid increase in the heatwave-led CDHEs occurred after the global average temperature “surpasse[d] a certain temperature threshold”, the paper says.
This threshold is an absolute global average temperature of 14.3C, the authors estimate (based on an 11-year average), which the world passed around the year 2000.
Investigating the recent surge in heatwave-leading CDHEs further, the researchers find a “regime shift” in land-atmosphere dynamics “toward a persistently intensified state after the late 1990s”.
In other words, the way that drier soils drive higher surface temperatures, and vice versa, is becoming stronger, resulting in more heatwave-led compound events.
Daily data
The research has some advantages over other previous studies, Yeh says. For instance, the new work uses daily estimations of CDHEs, compared to monthly data used in past research. This is “important for capturing the detailed occurrence” of these events, says Yeh.
He adds that another advantage of their study is that it distinguishes the sequence of droughts and heatwaves, which allows them to “better understand the differences” in the characteristics of CDHEs.
Dr Meryem Tanarhte is a climate scientist at the University Hassan II in Morocco, and Dr Ruth Cerezo Mota is a climatologist and a researcher at the National Autonomous University of Mexico. Both scientists, who were not involved in the study, agree that the daily estimations give a clearer picture of how CDHEs are changing.
Cerezo-Mota adds that another major contribution of the study is its global focus. She tells Carbon Brief that in some regions, such as Mexico and Africa, there is a lack of studies on CDHEs:
“Not because the events do not occur, but perhaps because [these regions] do not have all the data or the expertise to do so.”
However, she notes that the reanalysis data used by the study does have limitations with how it represents rainfall in some parts of the world.
Compound impacts
The study notes that if CDHEs continue to intensify – particularly events where heatwaves are the precursors – they could drive declining crop productivity, increased wildfire frequency and severe public health crises.
These impacts could be “much more rapid and severe as global warming continues”, Yeh tells Carbon Brief.
Tanarhte notes that these events can be forecasted up to 10 days ahead in many regions. Furthermore, she says, the strongest impacts can be prevented “through preparedness and adaptation”, including through “water management for agriculture, heatwave mitigation measures and wildfire mitigation”.
The study recommends reassessing current risk management strategies for these compound events. It also suggests incorporating the sequences of drought and heatwaves into compound event analysis frameworks “to enhance climate risk management”.
Cerezo-Mota says that it is clear that the world needs to be prepared for the increased occurrence of these events. She tells Carbon Brief:
“These [risk assessments and strategies] need to be carried out at the local level to understand the complexities of each region.”
The post Heatwaves driving recent ‘surge’ in compound drought and heat extremes appeared first on Carbon Brief.
Heatwaves driving recent ‘surge’ in compound drought and heat extremes
Greenhouse Gases
DeBriefed 6 March 2026: Iran energy crisis | China climate plan | Bristol’s ‘pioneering’ wind turbine
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Energy crisis
ENERGY SPIKE: US-Israeli attacks on Iran and subsequent counterattacks across the Middle East have sent energy prices “soaring”, according to Reuters. The newswire reported that the region “accounts for just under a third of global oil production and almost a fifth of gas”. The Guardian noted that shipping traffic through the strait of Hormuz, which normally ferries 20% of the world’s oil, “all but ground to a halt”. The Financial Times reported that attacks by Iran on Middle East energy facilities – notably in Qatar – triggered the “biggest rise in gas prices since Russia’s full-scale invasion of Ukraine”.
‘RISK’ AND ‘BENEFITS’: Bloomberg reported on increases in diesel prices in Europe and the US, speculating that rising fuel costs could be “a risk for president Donald Trump”. US gas producers are “poised to benefit from the big disruption in global supply”, according to CNBC. Indian government sources told the Economic Times that Russia is prepared to “fulfil India’s energy demands”. China Daily quoted experts who said “China’s energy security remains fundamentally unshaken”, thanks to “emergency stockpiles and a wide array of import channels”.
‘ESSENTIAL’ RENEWABLES: Energy analysts said governments should cut their fossil-fuel reliance by investing in renewables, “rather than just seeking non-Gulf oil and gas suppliers”, reported Climate Home News. This message was echoed by UK business secretary Peter Kyle, who said “doubling down on renewables” was “essential” amid “regional instability”, according to the Daily Telegraph.
China’s climate plan
PEAK COAL?: China has set out its next “five-year plan” at the annual “two sessions” meeting of the National People’s Congress, including its climate strategy out to 2030, according to the Hong Kong-based South China Morning Post. The plan called for China to cut its carbon emissions per unit of gross domestic product (GDP) by 17% from 2026 to 2030, which “may allow for continued increase in emissions given the rate of GDP growth”, reported Reuters. The newswire added that the plan also had targets to reach peak coal in the next five years and replace 30m tonnes per year of coal with renewables.
ACTIVE YET PRUDENT: Bloomberg described the new plan as “cautious”, stating that it “frustrat[es] hopes for tighter policy that would drive the nation to peak carbon emissions well before president Xi Jinping’s 2030 deadline”. Carbon Brief has just published an in-depth analysis of the plan. China Daily reported that the strategy “highlights measures to promote the climate targets of peaking carbon dioxide emissions before 2030”, which China said it would work towards “actively yet prudently”.
Around the world
- EU RULES: The European Commission has proposed new “made in Europe” rules to support domestic low-carbon industries, “against fierce competition from China”, reported Agence France-Presse. Carbon Brief examined what it means for climate efforts.
- RECORD HEAT: The US National Oceanic and Atmospheric Administration has said there is a 50-60% chance that the El Niño weather pattern could return this year, amplifying the effect of global warming and potentially driving temperatures to “record highs”, according to Euronews.
- FLAGSHIP FUND: The African Development Bank’s “flagship clean energy fund” plans to more than double its financing to $2.5bn for African renewables over the next two years, reported the Associated Press.
- NO WITHDRAWAL: Vanuatu has defied US efforts to force the Pacific-island nation to drop a UN draft resolution calling on the world to implement a landmark International Court of Justice (ICJ) ruling on climate, according to the Guardian.
98
The number of nations that submitted their national reports on tackling nature loss to the UN on time – just half of the 196 countries that are part of the UN biodiversity treaty – according to analysis by Carbon Brief.
Latest climate research
- Sea levels are already “much higher than assumed” in most assessments of the threat posed by sea-level rise, due to “inadequate” modelling assumptions | Nature
- Accelerating human-caused global warming could see the Paris Agreement’s 1.5C limit crossed before 2030 | Geophysical Research Letters covered by Carbon Brief
- Future “super El Niño events” could “significantly lower” solar power generation due to a reduction in solar irradiance in key regions, such as California and east China |