Originally posted on the BAS website

20 May, 2024 Press releases

Scientists at the British Antarctic Survey (BAS) have found that the record-low levels of sea ice around Antarctica in 2023 were extremely unlikely to happen without the influence of climate change. This low was a one-in-a-2000-year event without climate change and four times more likely under its effects. The results are published this week (20 May) in the journal Geophysical Research Letters.  

In 2023, Antarctic sea ice reached historically low levels, with over 2 million square kilometres less ice than usual during winter – equivalent to about ten times the size of the UK. This drastic reduction followed decades of steady growth in sea ice up to 2015, making the sudden decline even more surprising. 

Using a large climate dataset called CMIP6, BAS researchers investigated this unprecedented sea ice loss. They analysed data from 18 different climate models to understand the probability of such a significant reduction in sea ice and its connection to climate change. 

Lead author Rachel Diamond explained that while 2023’s extreme low sea ice was made more likely by climate change, it was still considered very rare according to the models.  

She says: 

“This is the first time this large set of climate models has been used to find out how unlikely 2023’s low sea ice actually was. We only have forty-five years of satellite measurements of sea ice, which makes it extremely difficult to evaluate changes in sea ice extent. This is where climate models come into their own.

According to the models, the record-breaking minimum sea ice extent would be a one- in-a-2000-year event without climate change. This tells us that the event was very extreme – anything less than one-in-100 is considered exceptionally unlikely.”

Caroline Holmes, a co-author on the study, said: 

“Strong climate change – i.e. the temperature changes we’re already seeing, and those expected if emissions continue to rise rapidly – in the models makes it four times more likely that we see such a big decline in sea ice extent. This suggests that 2023’s extreme low was made more likely by climate change.” 

The researchers also used the models to look at how well sea ice is likely to recover. By looking at similar events in the models, the authors found that after such extreme sea ice loss, not all of the sea ice around Antarctica returns – even after twenty years. This adds model evidence to existing observational evidence that the last few years’ low sea ice could signal a lasting regime shift in the Southern Ocean. 

Louise Sime, a co-author on the study, says: 

“The impacts of Antarctic sea ice staying low for over twenty years would be profound, including on local and global weather and on unique Southern Ocean ecosystems – including whales and penguins.” 

Satellite records of Antarctic sea ice began in late 1978 and between then and 2015, Antarctic sea ice extent increased slightly and steadily. In 2017, Antarctic sea ice reached a record low, and has been followed by several years of relatively low sea ice extent. 

There are many complex and interacting factors that influence Antarctic sea ice, making it hard to get a clear understanding of why 2023 was such a record-breaking year. Recent studies have highlighted the important role of ocean processes and heat stored below the surface, and warm sea surface temperatures during the first half of 2023 may also have contributed. Strong variations in north-to-south winds and storm systems also played a role. 

Antarctic sea ice is a critical factor in our overall understanding of climate change. Sea ice formation around the Antarctic acts as an engine for ocean currents and influences weather patterns. It also protects the exposed edges of the ice shelves from waves, curbing Antarctica’s contribution to sea level rise. Sea ice is also vitally important for marine life – scientists have observed catastrophic breeding failures of emperor penguin colonies because of low sea ice in recent years.   

Studies like this one are therefore critical to find out how likely rapid sea-ice losses are, and if sea ice is likely to stay low over the coming decades. 

CMIP6 models rarely simulate Antarctic winter sea-ice anomalies as large as observed in 2023 by Diamond, R., et al is published today in Geophysical Research Letters.  

Originally posted on the BAS website

Scientists at British Antarctic Survey have found that the number of warm weather events in the South Orkney Islands have significantly increased in frequency over the last 75 years. Using newly available historical data, scientists have identified the atmospheric factors behind the warm events in the region, shedding new light on the climate change trends that are affecting sub-Antarctic islands. 

The scientists found that the warm trends in these islands were closely linked to an increase in extreme warm-event occurrence. These extreme weather events were generated by anomalous large-scale atmospheric circulation patterns. Atmospheric rivers – long, narrow plumes of water vapor in the atmosphere – picked up and then transferred a great amount of heat and water vapour from tropical or subtropical ocean. These interacted with the mountainous topography of the South Orkney Islands, which led to increased melting of ice and snow in the region. 

The isolated and mountainous South Orkney Islands are important to Antarctic ecological systems and biodiversity, and extreme warm air temperatures over these islands could result in ecosystem change. The islands are also surrounded by the waters of the Weddell-Scotia confluence zone – dynamic and productive waters that impact global ocean circulation.

Hua Lu, lead author of both papers, said: 

“The warming trends we’ve uncovered have real implications for the sensitive biodiversity of the South Orkney Islands. Signy Island supports one of the richest and most diverse ecosystems in the Southern Ocean. Although these islands are remote and isolated, they demonstrate how Earth’s climate systems connect us all. As historic climate patterns shift, we need to be ready for the knock-on impact on the natural environment and on people around the world.” 

The findings are some of the early outputs of the SURFEIT programme, which aims to improve scientific models of interactions between the atmosphere, water, snow and ice, and our ability to predict extreme event weather changes in Antarctica.

These new findings are based on meteorological records from two research stations in the South Orkney Islands: British Antarctic Survey’s Signy Research Station, and the Argentine Orcadas Base. The continuous meteorological records from 1947 to 1995 at Signy Station was made possible by a digitisation project supported by the Diversity in UK Polar Science initiative. For the first time, these newly available historical Signy records have been used for uncovering long-term temperature trends and extreme warm events in the region.

Originally posted on the website of the British Antarctic Survey on 05/10/2023

British Antarctic Survey glaciologist Hamish Pritchard has won the 2023 Harry Otten Prize for Innovation in Meteorology. His idea, Lakes as snowfall sensors: solving the precipitation problem in the mountain cryosphere, proposes that lakes can be used as pressure-sensing surfaces to produce accurate observations of the water content of snowfall – simply, cheaply, autonomously, and over large areas.

With standard water-pressure sensors submerged on a lakebed, the mass of winter snow precipitation as it reaches the lake surface can be recorded, while avoiding biases that appear with other instruments that interact with snow as it falls or accumulates.

Hamish explained the importance of understanding changes to mountain glaciers: “For hundreds of millions of people, snow is a really important source of fresh water. When winter snow melts each year, the water allows crops to be grown through the spring and summer in the plains below. But snow is right on the frontline of climate change, so this water supply is changing fast and is under threat. To plan for these changes we need good climate models that get snowfall right, and for that, we need snowfall measurements that are more accurate and cover much larger areas than we currently have. This new lake method provides such measurements.”

The jury awarded the first prize of €25,000 during the Annual Meeting of the European Meteorological Society in Bratislava.

Hamish Pritchard, pictured on field work in the Himalayas (British Antarctic Survey)

Pam Emch, Chair of the Board of the Harry Otten Foundation, commented: “The idea put forward by Hamish Pritchard can help cost effectively address and improve the quantification of precipitation that falls as snow. An improvement in this measurement has applicability not only in meteorology, but also in water resources planning and management and could potentially be utilized for remote sensing instrumentation/observation calibration/validation.”

The jury received 18 applications for the prize with lead authors from at least 14 different countries in Europe, Africa, Australia, and the U.S.A. The Harry Otten Prize is awarded every two years.

Photo by Hamish Pritchard

The above photo shows a remote instrument set up on Signy Island to record and transmit measurements of lake water pressure. In winter we will use these to measure how much snow is falling on Signy, over an area much larger than is possible with conventional snow gauges. This is part of the SURFEIT project.

This story was originally published on the British Antarctic Survey website on 02/02/2023

Understanding ice loss from Antarctica and its contribution to global sea-level rise is a key ambition for SURFEIT

Researchers at British Antarctic Survey (BAS) will develop new and ambitious ideas to tackle critical global environmental challenges, such as global sea-level rise from Antarctica, thanks to new funding.

The investment from the Natural Environment Research Council (NERC) has been awarded to BAS for the new science programme SURface FluxEs In AnTarctica (SURFEIT), to the value of £2.3m.

SURFEIT, led by BAS and working with international partners, will improve predictions of future global sea level rise that is driven by loss of ice from Antarctica. The specific focus is on interactions between the atmosphere and ice; the SURFEIT team will:

• improve how polar clouds are represented in climate models;
• use pre-existing, and new observations alongside climate model output to help improve the understanding of changes in snowfall over Antarctica;
• ensure that small-scale and extreme-event weather changes in Antarctica can be accurately predicted;
• improve how earth and ice system model components link together, so that better predictions can be made of when Antarctic ice may fracture, and so raise global sea level.

Dr Iain Williams, NERC Director of Strategic Partnerships, said:

“This exciting investment in internationally collaborative research programmes will significantly advance our understanding of the drivers and responses to global environmental change. Many of the environmental science challenges we face are global in nature and require an international and transboundary response. By bringing together expertise in earth, ecological, ocean, polar, and atmospheric sciences, from NERC’s research centres with colleagues from across the globe, we can develop understanding that will help us mitigate and adapt to the changes caused by global warming.”

The NERC National Capability International programme will focus on research excellence and global public good.