Recent news stories have focused on the slowdown in the decline of Arctic sea ice and some have interpreted these as ‘good news stories’, but what does the science really show?

As sea ice is a vital aspect of the delicate and complex Earth system, it’s vital we understand exactly what is happening with sea ice as global temperatures continue to rise.

Sea ice should not be confused with icebergs, which break away from glaciers as they reach the ocean.

Sea ice forms when sea water freezes, creating ice floes that float on the surface. Sea ice is found year-round in the Arctic and Southern oceans, where the air is cold enough to freeze salt water.

Unlike land-based ice, when sea ice melts it does not contribute to sea level rise in a significant way, but it still has an impact on the Earth’s systems.

Sea ice helps regulate the Earth’s temperature

Sea ice has a higher ‘albedo’ than the surrounding sea water. This means it is more reflective due to its lighter colour. It reflects solar radiation from the sun back into space helping to keep the planet cool and regulating global temperatures.

When sea ice melts, there is a larger proportion of darker sea surface with a ‘low albedo’, absorbing more of the sun’s heat. This creates a feedback loop which means the planet warms further.

This process creates a ‘positive feedback mechanism’. This refers to changes in a system which creates effects that make that change even stronger. As melted ice exposes more dark ocean water, which absorbs more heat from the sun than ice does, the extra heat causes even more ice to melt, which exposes more dark water, and so on. The process reinforces itself and speeds up.

Sea ice helps drive ocean circulation patterns

Ocean currents, which determine weather patterns around the world and help drive the Earth’s wider carbon cycle, are driven by differences in temperature and salinity of the water. This is referred to as thermohaline circulation.

A complex series of processes take place during the sea ice life cycle. Sea water contains salt, making it more dense than fresh water. When it freezes, the ice crystals can’t retain all the salt and so some is rejected into the water around it, making it denser. When sea ice melts, it releases freshwater into the ocean. These fluxes in salt and freshwater dictate the movement of water within the polar oceans and have implications for wider ocean circulation.

One circulation pattern which is sensitive to declining Arctic sea ice is the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents that includes the gulf stream. The gulf stream relies on cold salty water sinking in the North Atlantic to drives the flow of waters from the Azores up towards northern Europe.

As sea ice in the Arctic melts, the water in the northern Atlantic Sea is becoming increasingly diluted and therefore not as heavy. This change has the potential to divert or even collapse these currents and change the patterns of weather Europe and northern United States have become used to, such as milder winters and warmer summers.

Sea ice is a habitat for some of the Earth’s most beautiful species

Sea ice also provides a habitat for a range of species including polar bears, whales, krill and seals. As it melts, these species are increasingly under pressure.

Key indicators of sea ice health

Scientists monitor sea ice using:

• Extent: The surface area of the sea where the ice is at least 15% ice concentration.
• Thickness: The vertical depth of the ice
• Ice volume: The actual amount of ice in volume.

Observing changes in these indicators helps scientists gain a robust understanding of climate change.

How headlines can misrepresent the science

There have been some viral social media stories suggesting that sea ice hasn’t changed over the decades and that sea ice decline is a myth.

There have been other stories that focus on how sea ice in the Artic is not declining at the rate we would expect considering the Arctic is warming four times faster than the rest of the planet.

These could seem like good news stories.

What the science reveals

• CPOM data show average Arctic sea ice thickness in October has reduced by 0.6 centimetres per year since 2010 suggesting an overall decline in sea ice volume even if extent has not reduced.
• Arctic sea ice has declined in both extent and volume throughout the year, with the most significant losses occurring in late summer, according to ESA satellite data.
• In this article, NASA reported that in 2025 global sea ice coverage was at a record low. This is due to a rapid decline in Antarctic sea ice extent. There is more information about the current state of sea ice cover in this report from NASA.

Explaining a complex system in one sentence

The problem with headlines is that you can’t capture a complex situation in one sentence, and sea ice is a dynamic and expansive puzzle.

• Some headlines focus on sea ice extent, which is only one indicator of sea ice coverage, ignoring thickness and volume. Even if the extent of the sea ice remains the same from one year to the next, if it is only half as thick, then the total volume of ice has also halved. The Arctic is losing its thickest multi-year ice, with the ice pack becoming increasingly seasonal. This means that overall there is less sea ice, and therefore more freshwater in the ocean. 
• Decline in sea ice may appear to slow down due to ‘seasonal variability’, which are ‘short-term variations’ while the overarching long-term trend, monitored over many decades, may still be one of decline. Scientists use climate model simulations to help understand and predict the behaviour of sea ice. Models show that as Arctic sea ice declines over multiple decades, we can expect periods of no change or even growth, due to natural variability within the climate system.
• As Julienne Stroeve points out in this article, even though sea ice melts during the summer, new ice forms again in winter when temperatures drop. A growth that can obfuscate some of the ice lost in summer. As winters get shorter, there will be less time for the ice to grow, and it won’t grow as thick meaning this “buffer” replacing lost ice is reducing.

The bigger picture

When media outlets report on scientific studies relating to changes in the cryosphere, the focus might be on one element. The problem with this is it might paint a picture of the state of Earth’s ice that may not reveal the full story.

Anthropogenic Global Warming (AGW), long-term warming of the Earth’s climate due to human activities such as burning fossil fuels, is undeniably taking place. The WMO recently declared 2024 as the hottest year on record, and you can see a graph showing global temperatures since 1860 to see how temperatures have, and are rising over centuries.

The Earth’s ice still sees natural cyclical changes caused by ocean currents, short-term weather patterns and atmospheric conditions. This means sea ice extent may recover in the winters, but the long-term trend due to warming remains true.

Over the last three decades sea ice in the Arctic has declined during the summer months and winter ice is newer and thinner. Despite seasonal ups and downs, the net loss of ice is accelerating.

These trends are worrying, but there are some positives we can focus on.

Although the challenge is great, the world is equipped to tackle that challenge.

Monitoring sea ice is rapidly improving, and scientists are getting increasingly better at understanding these huge and dynamic areas of ice. This means we can better project future outcomes and plan and mitigate for future changes.

The fact that sea ice still shows seasonal recovery during winters means there is still the opportunity to protect it through working towards net zero and limiting global warming.

With increasingly sophisticated satellite missions and models, multi-agency projects and powerful movements pressing for change, we can adapt and protect our changing planet.

Featured image credit: Amy Swiggs

A new study published today in The Cryosphere revives and refines decades-old satellite altimetry data, offering the potential for a sharper view of how Greenland and Antarctica have changed.

Led by Maya Raghunath Suryawanshi (CPOM, Lancaster University and Interdisciplinary Centre for Water Research) the researchers used current state-of-the-art techniques to reprocess ERS-1, ERS-2 and Envisat altimeter data, dating from the early 1990s. This produced more accurate records of ice sheet elevation spanning two decades which is crucial for understanding long-term trends in ice loss.

As melting polar ice sheets are a key driver of sea level rise, monitoring and assessing these huge, remote and inhospitable terrains is vital if we are going to adapt to changing sea levels in the future. Understanding how quickly they are melting, and why, depends on data from past decades.

Over the last thirty years, satellite missions have enabled scientists to map the polar regions with increasing precision. Radar altimetry works by timing how long it takes radar pulses to bounce off the ice surface and return to the satellite. This allows researchers to track changes in ice elevation and, by extension, ice mass over time as well as the processes driving change.

Methods for processing satellite altimetry data have improved and been refined over time. It is therefore important to return to previous datasets using updated techniques to improve the quality of this long-term satellite record. This enhances confidence in our record of ice sheet change, places current observations within a longer-term context, and helps inform our understanding of potential future behaviour of the ice sheets.

Image credit: Suryawanshi et al, The Cryosphere

Suryawanshi and the team used the very latest techniques and algorithms when completing their processing. They then performed comprehensive assessments of these new datasets using airborne data to verify their results. The study demonstrated the improvements in data quality achieved by their new processing as they found their results were in closer agreement with this airborne data.

The team has also created a user-friendly version of this dataset which is free to access the European Space Agency website via https://earth.esa.int/eogateway/catalog/tdp-for-land-ice (ESA, 2023).

The research was performed as part of the ESA-funded Fundamental Data Records for Altimetry (FDR4ALT) project, and represents a collaboration between CPOM (led from Northumbria University), The Lancaster Environment Centre (Lancaster University), Interdisciplinary Centre for Water Research, Indian Institute of Science and Collecte Localisation Satellites.

Funding information

This study was primarily funded by the European Space Agency and UKRI NERC.

Publication information

Title: ‘New radar altimetry datasets of Greenland and Antarctic surface elevation, 1991–2012’

Authors: Maya Raghunath Suryawanshi, Malcolm McMillan, Jennifer Maddalena, Fanny Piras, Jérémie Aublanc, Jean-Alexis Daguzé, Clara Grau, and Qi Huang

DOI: https://doi.org/10.5194/tc-19-2855-2025

New Story Image credit: Suryawanshi et al, The Cryosphere

Resolute Bay is part of the Qikigtaaluk Region at the northern end of Canada’s Northwest passage. One of the coldest inhabited places on Earth, it is also the stunning location of recent fieldwork involving CPOM scientists.

In April 2025 the all-female field team of polar scientists from UCL, including Julienne Stroeve, Rosemary Willatt, Carmen Nab and Alicia Fallows, with an airborne team led by Christian Haas from AWI, visited Resolute Bay to investigate the use of Ku- and Ka-band frequency radar and different polarisations on ice and snow.

Watch the team in action in this video case study.

What is KuKa?

KuKa is a dual-frequency radar operating at Ku-band (12-18 GHz) and Ka-band (30-40 GHz) frequencies.

KuKa radar can work in two ways; estimating the distance from the sensor to a surface looking straight down (using Altimeter mode); and also when looking at an incidence angle (using Scatterometer Mode). It can collect information about the polarisation of the waves, which is referred to as ‘Polarimetric Capability’ (You can find out more about this in this paper by Stroeve et al.) Scientists have found that polarisation can help to determine snow depth on Arctic and Antarctic sea ice, which could also help with estimation of sea ice thickness.

The team tested KuKa radar at two sea ice locations, on tundra, and on the frozen freshwater Resolute Lake, towing the KuKa radar on a qamutiik (traditional Inuit sled) at all four sites.

A Magnaprobe was used to determine the snow depth at many points along the same track as the KuKa was tested. A SnowMicroPen (SMP), was used to gain information on the penetration resistance of the snow and build understanding of the snowpack formation.

The Magnaprobe is a rod-like tool used in snow research which is pushed into the snow until it encounters resistance at the ice surface, thereby measuring the snow depth. A SnowMicroPen (SMP) is a device which estimates the snow structure, strength and density, by using a sensor to measure the penetration force in high resolution at intervals, while being forced through the snow.

The team dug snow pits to help identify the snow depth, measure temperature and salinity throughout the snowpack, and to understand physical properties of the snow. They also drilled at several locations, to take measurements of the sea ice thickness and lake ice thickness.

A broadband electromagnetic sensor (GEM) was used to estimate the total snow and ice thickness, and a drone and terrestrial laser scanner were used to create a 3D profile of the snow surface roughness and for images.

The team could then compare the data they gained from the Kuka device, against the measurements they took manually at the same locations.

This field campaign helps build a better understanding of how snow and ice properties affect radar signals, and retrieval of snow and ice thickness, therefore providing insights for future satellite missions such as the European Space Agency’s (ESA) upcoming CRISTAL space mission.

The concept of the CRISTAL mission is to combine Ku- and Ka-band data for simultaneous snow and ice freeboard measurements. A new technique using polarimetric information, discovered using KuKa, is also under development. This involves analysing how the electromagnetic waves scatter off a surface, which helps scientists to distinguish between the differing surfaces (ice, water or snow) in more detail.

Why is this important?

Field campaigns like these are crucial in understanding how Kuka radar can be used to provide increasingly accurate measurements of the Earth’s ice.

These missions provide information on the Earth system, including the polar regions which we use to assess ice mass balance, associated sea level rise as well as gain a clearer understanding of how global weather patterns are affected by melting ice. This scientific understanding is vital is we are to live and thrive in a changing climate.

Who funded this research?

This field campaign was part of the NERC DEFIANT project. It received funding from the European Union’s Horizon 2020 research and innovation programme via project CRiceS. This research was also supported by the Polar Continental Shelf Program. ESA NEOMI grant 4000139243/22/NL/SD supports development of the polarimetric altimetry concept.

Special Thanks

Thank you to local guide and bear guard, Sheldon, for his expert knowledge and for keeping the team safe on this fieldwork.

Glossary of terms:

Freeboard – the vertical distance between sea level and the top of the ice or snow.
A broadband EM sensor (GEM) – a geophysical electromagnetic induction sensor.
Site transects – the path (or line) along which the team recorded their observations and measurements.
Salinity – the amount of dissolved salt in the water.
Magnaprobe – a rod-like tool used in snow research which is pushed into the snow until it encounters resistance, thereby measuring the snow depth.
SnowMicroPen (SMP) – a device which measures measures the snow structure, strength and density, by using a sensor to measure the penetration force in high resolution at intervals, while being forced through the snow.
KuKa – a dual-frequency radar operating at Ku-band (12-18 GHz) and Ka-band (30-40 GHz) frequencies. KuKa radar can work in two ways; estimating the distance from the sensor to a surface (using Altimeter mode); and also measuring more uneven or rough surfaces (using Scatterometer Mode).
Polarimetric Capability – The ability of KuKa to measure how the electromagnetic waves scatter off a surface, which helps scientists to distinguish between the differing surfaces (ice, water or snow) in more detail.
NERC – Natural Environment Research Council
DEFIANT – Research Programme, led by BAS and funded by NERC – Drivers and Effects of Fluctuations in sea Ice in the ANTarctic. Read more.

Key Publications Relating to the topic

• Stroeve et al. (2020)
• Stroeve et al. (2020)
• Nandan et al. (2023)
• Willatt et al. (2023)
• Willatt et al. (2025)

Ice Sheets and Sea Level Rise – what we know and why it matters

Mean sea level has risen by 11.5cm since the early 1990s, due to the melting of land ice, changes in land-water storage (when water originally contained on land mass moves into the oceans) and thermal expansion of the oceans (water expanding as it warms).

Sea level rise is already affecting the UK, increasing coastal erosion and flooding, in particular during storm surges. This puts coastal communities, habitats and key infrastructure, such as power stations, at risk.

Monitoring the Ice Sheets

The Earth’s colossal ice sheets, in Greenland and Antarctica, are major contributors to sea level rise.

Thanks to advancements in Earth Observation satellite missions, technologies and computer modelling capabilities, we can now monitor these ice sheets accurately and project future scenarios. However, significant uncertainties remain around how the ice sheets are going to behave in the coming decades.

Insights from the Experts

In the ‘Sea Level Uncertainties From the Ice Sheets’ webinar (16 July) organised by the UK National Climate Science Partnership, Dr Inès Otosaka (CPOM) and Dr Rosie Williams from the British Antarctic Survey (BAS) shared key findings.

Ice sheets are melting, and this is accelerating

Dr Otosaka explained:

• The Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) led by CPOM has been utilising data from satellite missions to monitor the mass balance of the ice sheets and their contribution to sea levels.
• The Greenland and Antarctic ice sheets are contributing a quarter of all sea level rise and are driving its acceleration. Since 1979, ice sheets have added 3.2cm to sea level rise and the pace of loss is increasing.
• Greenland is melting faster than Antarctica now, but Antarctica is seeing mass loss in the West.
• Ice loss is tracking at the upper end of IPCC projections.

Why so much uncertainty?

Dr Williams explained that:

• Different models and climate forcings produce varying results.
• Subsurface processes such as under-ice melting are hard to observe from space.
• Smaller scale processes can have large impacts, for instance calving and fracturing of the ice sheet as they are taking place at inaccessible places and no laws around general calving currently exist.
• Instability processes such as Marine Ice Cliff Instability (MICI) are still not fully understood.

Rosie went on to explain some of the High Impact Low Likelihood (HILL) scenarios produced by the IPCC.

• The contribution of Antarctic ice melt will dominate all other sources of sea level rise in the coming years due to Marine Ice Cliff Instability.
• By 2100 we could see almost 2m of sea level rise.

The cost of inaction

The UK, and many other countries around the world, are vulnerable to the impacts of sea level rise, so we need to understand better what’s coming and when.

If we fail to adapt appropriately to sea level rise by 2050 the cost could exceed £24 billion a year, in comparison to the projected cost of £3.41 billion/year for ideal adaptation (Rising et al., 2022).

It is vital we understand the potential scenarios and can recognise when we are confronted with one. This is why there is an urgent need to continue to monitor and model the ice sheets.

What we can do

Despite the risks, there is still hope. The worst-case scenarios are not inevitable. Research conducted by the TerraFIRMA team using the UK Earth System Model (UKESM) simulations shows that every degree of warming matters when it comes to sea level rise.

If we act now to reduce emissions, boost our capabilities in monitoring and modelling the ice, and develop Early Warning Systems, we can still aim to thrive in a changing climate.

Watch the full presentation to find out more…

On Wednesday at the European Space Agency’s Living Planet Symposium 2025 we had a fantastic celebration of a very special satellite mission: CryoSat.

CryoSat-2 is very close to our hearts here at the UK Centre for Observation and Modelling (CPOM), due to the crucial role the intrepid Earth Explorer plays in gathering data on the Earth’s ice sheets, sea ice, ice shelves and glaciers. Without this information, we wouldn’t have made the significant leaps forward in polar and climate science over the last two decades.

In the session ‘Celebrating 15 Years of CryoSat for climate science’ led by Tommaso Parrinello (Aeolus and CryoSat Mission Manager, ESA) we heard from a range of scientists on the importance of this mission and how it has contributed to our understanding of the cryosphere, its impact on the wider Earth systems and sea level rise, as well as how it will continue to shape the future of climate science.

To mark this special occasion, we have put together this list of 10 cool things we love about CryoSat-2 from yesterday’s fascinating series of talks on the mission.

1. The idea for CryoSat was conceived by Sir Duncan Wingham, CPOM’s founding Director, but the first satellite was lost in a launch failure in 2005. Thankfully it was rebuilt and launched successfully five years later in 2010.
2. CryoSat’s original mission objectives were to monitor polar ice sheets and arctic sea ice, but today a large proportion of scientific papers using CryoSat data is on topics outside of the cryosphere, noted Andrew Shepherd in his presentation.
3. CryoSat has been instrumental in monitoring global ice losses! In 2021 a study led by CPOM’s Tom Slater showed that Earth is losing 1 trillion tonnes of ice each year. The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) Project led by CPOM’s Inès Otosaka now produces annual assessments of ice sheet mass balance, taking advantage of CryoSat data alongside other satellite missions.
4. CryoSat even works on Canadian ice caps, said Professor Rene Forsberg! CryoSat can capture information on smaller ice caps and glaciers due to the advancement of the swath processing technique. Swath processing uses interferometry to map ‘broad swaths of surface elevation’ allowing for higher resolution (less than one kilometre) elevation measurements.
5. In 2023, CryoSat went global on glaciers! The first global assessment of global glacier mass change with radar altimetry was produced (Jakob & Gourmelen, 2023). This year the GLAMBIE project produced updated figures on glacier loss showing that from 2000 – 2023 glaciers across the globe lost 6542 billion tonnes of ice, contributing 18 mm to global sea level rise.
6. CryoSat-2 and ICESat-2 are complementary! A recent study led by CPOM’s Nitin Ravinder showed that CryoSat and ICESat-2 measured Greenland ice sheet elevation change measurements agree with each other to within 3%, confirming that results from these satellites can be combined to produce a more reliable view of ice sheets.
7. There is a CryoTEMPO product suite which uses CryoSat-2 data to produce easily accessible, user-friendly data products for a variety of thematic areas such as sea ice, land ice, polar oceans, coastal oceans and inland water.
8. CryoSat provides insights on sea level rise. Anny Cazenave (LEGOS) gave a wonderful overview on how CryoSat-2 has supported our understanding of sea level rise, sharing insights on altimetry-based sea level trends (2011-2022) AVISO.
9. Dr Livia Jakob (Earthwave) introduced us to the CryoSat Companion now available through ChatGPT! This new AI assistant supports people in using and understanding the data. It even told us an icy joke during the presentation.
10. CryoSat is inspiration of the new CRISTAL mission due to launch in 2027. Set to be a considerable advancement for polar science due to it’s dual-frequency Interferometric Radar altimeter for Ice and Snow (IRIS).

But this is just the tip of the iceberg (sorry!). There’s still so much to learn from CryoSat, and you can do that by following updates from @esa_cryosat on X.

CryoSat’s journey is not over yet, by any means!