Event summary: Policy implications of cryosphere science for the 1.5°C target event.

This event was held in conjunction with the non-partisan International Cryosphere Climate Initiative (ICCI), as one of a series of “Cryosphere 1.5°C Briefings”. These bring together leading IPCC and other academics together with stakeholders such as national climate negotiators and domestic policy makers on the policy implications at all levels arising from the latest science focused on cryosphere (snow and ice) regions including climate negotiations at COP 26.

Insufficient emissions reductions could lead to warming scenarios beyond 1.5°C that trigger global changes and feedbacks in the cryosphere that may be rapid and to some degree irreversible (several tens of thousands of years). The most significant dynamics include sea-level rise from polar ice sheets; polar ocean acidification; mountain glacier loss; permafrost thaw and related CO2/methane emissions; and, Arctic sea ice loss. All these changes will impose dramatic impacts on the global climate system, as well as local people and ecosystems.

Speakers

• Professor Julie Brigham-Grette, UMass-Amherst and past Chair, U.S. Polar Research Board (Ice Sheets/SLR)
• Dr Heidi Sevestre, University Centre in Svalbard (Mountain Glaciers and Snow)
• Professor Julienne Stroeve, University College London/University of Manitoba/NSIDC (Sea Ice)
• Dr Helen Findlay, Plymouth Marine Laboratory (Polar and High Latitude Oceans)
• Dr Gustaf Hugelius, Bolin Centre for Climate Research, Stockholm University (Permafrost)
• Pam Pearson, former U.S. climate negotiator and Director, ICCI (Policy Implications)
• Dr Joeri Rogelj, Grantham Institute/Imperial College (SR1.5 Emissions Pathways)
• Beth Viola, Holland and Knight, Clinton NSC and Gore Climate Advisor (U.S. Transition/Climate Change)
• Dr Sarah Honour, Head of Climate Science, Department for Business, Energy and Industrial Strategy (BEIS)

Chair’s welcome

Lord Teverson welcomed the attendees and highlighted the importance of understanding changes in the cryosphere in the lead up to COP 26. He highlighted the work of the House of Lords Select Committee on the Arctic, and the impacts of changes in the cryosphere including retreat of ice sheets, changes in albedo, melting permafrost and the release of methane and the need to consider the possible effects of climate feedbacks.

Professor Julie Brigham-Grette – ice sheets

UMass-Amherst and Chair, U.S. Polar Research Board

Study of past climate change, the natural variability of the geologic past and understanding of how glacial systems, the atmosphere, the oceans responded in the past to climate change, can tell us about our future. Using data from ancient shorelines from around the world from Alaska, Scandinavia, South America and Australia like bathtub rings around coasts, tells us that in a warmer world sea level rise is becoming irreversible. During the 20th Century, global mean sea level has been increasing and this rise is accelerating. We are already committed to two to three metres of sea level rise in the coming centuries with only a 1°C temperature rise.

This much like the last interglacial when sea level was even higher because of global factors that interacted with the cryosphere much like greenhouse gases today. However, global sea level will rise even more if global temperatures go above 1.5°C. Keeping the world below a 1.5°C rise will slow down the rate of sea level rise. All studies show that the Greenland ice sheet will dominate sea level rise in coming decades due to the surface melt especially when we lose the summer Arctic sea ice within the next 25 years. It’s one of those feedbacks that makes preserving the sea ice so important. This study shows the extent of surface lowering in a scenario above 2°C.

Antarctica is also a serious concern. Under a low emissions scenario sea level will continue to rise but at a lower rate. A good outcome at this lower emission scenario would be Antarctica only contributing centimetres to sea level rise in the coming century. The longer we stay at higher temperature, the higher sea level will go and the greater the chance future generations will be locked into higher sea levels that will challenge society. During the last deglaciation, from about 14.7 to 13.5 thousand years ago, sea level rose from 16 to 25 metres in only 400 years, rates of 40 to 60mm per year, so it’s not impossible for it to happen again if it happened before. There is high agreement that Antarctic ice sheet loss could be irreversible for decades to millennia.

Processes controlling the rate of ice sheet loss and the extent of ice sheet instability could increase the extent of contribution to sea level rise. The loss of ice shelf buttressing is the key factor, and slowing emissions will slow the loss of ice shelves. Sea level rise will challenge adaptation responses regionally and worldwide. The largest impacts will be on flat low-lying coastlines, including around parts of the UK. With a 1°C temperature rise we see 3m sea level rise, 1.5°C around 5m and 2 to 3°C, 10 to 20 metres of sea level rise. The different levels around Liverpool, London, Manchester and Glasgow emphasises how flat these areas are. Given the knowledge of past we can state confidently that slowing the rate of emissions will slow the rate of sea level rise, keep communities out of harm’s way and give them time to respond. The choices we make now determine the trajectory of sea level of rise. Just imagine a sea level rise 85 cm higher than today, when today’s school children are 85 years old will it be worse or better for them, we now have to make that choice for them.

Dr Heidi Sevestre – mountain glaciers and snow

University Centre in Svalbard

Glaciers are important for societies, even though they are smaller than the ice sheets. They were the largest contributors to sea level rise in the 20th Century as glaciers melt across the world, and this ice loss is accelerating. While the largest glaciers can contribute significantly to sea level rise, in terms of water supply the smallest ones have the most significant influence on human populations. Glaciers and snow often play similar roles for supplying benefits to communities and in ecosystems.

The main service provided by snow and ice is freshwater when they melt partially or totally, which can be used for drinking water, sanitation, irrigation and hydroelectricity. In some regions, such as tropical areas near the Northern Andes, glaciers are the only consistent and reliable water supply for local and indigenous people. In other regions, seasonal snow is among the most important water resources, such as in the South-western US. When glaciers melt and less snow falls every year it leads to a range of impacts, such as a heightened risk of natural disasters, difficulties for local economies connected to winter recreation activities, the loss of climate archives and reductions in human wellbeing with the loss of cultural heritage.

Projections for glaciers in different regions up to 2300 based on different emission scenarios suggest a range of outcomes depending on the emission trajectories followed. There are still some tropical region glaciers left in the Northern Andes, East Africa and Papua New Guinea, but unfortunately a temperature rise of 1°C is already too much for most, and very few glaciers will survive beyond 1.5°C. For mid-latitude glaciers where ice loss is also accelerating, if the high emissions scenario continues to be followed all the ice in these regions will be gone by 2300.

If global temperatures remain at or below 1.5°C glaciers would retain 20 to 45% of their mass by 2300. In central Europe (the Alps), there could be some regrowth of glaciers if temperatures remain at or below 1.5°C. For high latitude and high-altitude glaciers, the differences between emission scenarios is large, with much more ice kept by 2300 if the low emission scenario is followed. If the high emission scenario occurs, there is almost a complete loss of ice in Eastern and Central Asia where hundreds of millions of people rely on this water supply.

In the case of snow, observations show the persistence of snow is changing all over the world, snow seasons are getting shorter every year with snow covering less ground than before. In the UK, economic impacts related to reductions in seasonal snow cover are significant: less snow cover affects the quantity and quality of river flows; it also means less protection for overwintering crops and vegetation from frost; warmer winters leads to drier soils and vegetation more vulnerable to wildfires; and, impacts winter sport and tourism. The only way to preserve as much snow and ice as possible, and to protect water resources, is to urgently reduce emissions and follow a 1.5°C pathway.

Professor Julienne Stroeve – sea ice

University College London/University of Manitoba/NSIDC

Today the Arctic Ocean looks very different, even to Arctic sea ice conditions we saw in the late 1980s. We have an Arctic Ocean with open water all along the Eurasian and North American sectors in the summertime, whereas there used to be sea ice that persisted throughout the year. There is half the amount of sea ice we had just 40 or 50 years ago, and large parts of the Arctic Ocean are completely ice free. While the summer sea ice minimum receives a lot of attention in the media, sea ice loss is not limited to summer.

Data on deviations in sea ice conditions from 1981 to 2010 highlight that since the mid-2000’s every month shows below average ice conditions relative to the 30-year climatology. This also shows that the largest departures from average conditions that have been seen have not just occurred in September 2012, which was quite anomalous, but this October (2020) was the largest departure from average conditions ever recorded. Even May and November 2016 were larger departures than those seen in 2012. Because ice conditions were so unusual this year in the Laptev Sea, the Northern Sea route along the Russian coast was open until the end of October.

According to the Russian Federal Agency for Maritime and River Transport, the first ten months of 2020 saw an increase in transit shipping between Asia and Europe of 83% compared too last year. Big changes are happening both in the Eurasian and North American sectors. There is a lot of year to year variability in the sea ice cover and the ability to predict record lows from one year to the next remains limited, but we do know that the long term decline is strongly linked to how much CO2 is in the atmosphere. In our 2016 study, the relationship is defined that for every metric tonne of CO2 that we add to the atmosphere we melt 3m2 of sea ice. This study allowed more certainty about estimates to be placed on how much CO2 can be added to the atmosphere before ice free conditions start to be seen.

At just an additional 700 Gt of carbon, sea ice will drop below 1 million km2 in September, which is often the threshold used by scientists to define when most of the Arctic Ocean becomes ice free. At our current emission rates of 35 to 45 Gt of carbon each year this transition will likely happen before the middle of this century. Similarly, because global warming is linked to atmospheric CO2, this linear relationship also holds for temperature.

Even at a target of 1.5°C of warming above pre-industrial temperatures there is the possibility for some icefree conditions to occur occasionally. At by 1.7°C there will be consistent ice-free Septembers, and the number of months with ice free conditions will increase then with additional warming. If we reach 3°C of warming, there will be 5 months of ice-free conditions in the Arctic, a huge climate shift that hasn’t happened in tens if not hundreds of thousands of years. These predictions are based on observations, but climate simulation models of what happens under business as usual scenarios compared to drastic reductions in CO2 emissions informing the next IPPC report.

They suggest trajectories for March to September for the extent and volume of the sea ice the latter reflecting the thickness of the sea ice. These show ice free Septembers are likely from the middle of the century, regardless of emission scenarios. If you look at the spread of the different emission scenarios they overlap, so that by 2040/50 all these emission scenarios suggest the potential for ice free summers to occur. However, if emissions were to be drastically reduced and a more conservative scenario followed, then sea ice can be recovered.

The loss of the sea ice in September will not be permanent and can be brought back. It is important to reduce emissions if some sea ice is to be kept in the Arctic Ocean. If business as usual scenarios are followed, it will be very thin sea ice that easily melts, which will affect the ecology of the Arctic Ocean. Sea ice thickness affects the amount of light reaching the sea surface, playing an important role in under ice algae and phytoplankton blooms that are at the base of the food web in the Arctic. Thinning ice may allow more light through, this can initiate the timing of under ice algae blooms, which will also be affected by nutrient availability, with the phenology dramatically altered by changes in the sea ice environment.

What happens in the Arctic doesn’t just stay in the Arctic. Reductions in sea ice means the oceans will absorb the solar energy that would have been previously reflected, causing the Arctic to warm up faster than the rest of the planet. When you have enhanced warming in the Arctic compared to lower latitudes it alters the temperature gradients between regions changing large scale atmospheric and oceanic circulation patterns. We already see slowing of Westerly winds in response to this enhanced Arctic warming, which may weaken the jet stream, with weather patterns persisting longer and extreme heat, drought, cold or intensive rain staying in one place longer. There has been an uptick in extreme weather events in the last couple of decades that appears to be linked to enhanced warming in the Arctic due to the loss of sea ice cover.

First discussion break

At this point the chair initiated the first discussion break giving attendees an opportunity to address the first three panel experts. During the discussion the following points were addressed:

• The ‘Karl Popper’ question, if people were sceptical that might be asked, is what level of change in the data would disprove the model, in other words how many years would it take of glaciers growing, the Arctic improving for the models to be adjusted – if there isn’t a way of disproving the modelling, people become suspicious that it may be self-reinforcing.
• While most of the changes happening to the cryosphere are irreversible when it comes to glaciers it would take temperature going back to preindustrial levels to be able to grow back.
• There is a lot of natural climate variability in the system so even when you are looking at trajectories of sea ice loss it’s not unusual to see recoveries for decades at a time, but this does not mean it won’t disappear if more greenhouse gases and added to the atmosphere and warming continues. Some of differences in the model and what they predict can be challenging in terms of uncertainties, but we don’t really need the models to tell you what level of warming or CO2 concentrations can we reach before you lose the sea ice and that we have control over that.
• The geological record is the ground truthing of what can happen. We have very good examples in the recent geological history that document precisely what happens when you warm up the world. So that is our playbook, our scientific guidebook that shows what happens and what are the consequences.

Dr Helen Findlay – polar and high latitude oceans

Plymouth Marine Laboratory

The Arctic Ocean is becoming warmer, fresher and more acidic. Arctic Ocean surface waters have warmed since the 1980s, in winter the sea ice extent is greatest but there is still a warming trend in the European sector. However, the greatest warming trend we see is about half a degree per decade occurring in the summer during the sea ice minimum.

Ocean warming is amplified by ice loss feedback and the albedo effect, while ice reflects sunlight darker waters absorb more heat, but in turn that ice loss is amplified by transport of warmer waters into the Arctic – ocean warming and ice loss are very interlinked and feedback on each other. They also have other ocean impacts; for instance, they result in increased river run-off that causes a freshening of the ocean, which is of concern in the Arctic Ocean because so many rivers run to it. This in turn affects carbon and nutrient budgets, with knock on implications for the Arctic food web. All these impacts are significantly reduced under low emissions scenarios of a 1.5°C world.

Ocean acidification, the absorption of CO2 into the ocean where it forms a weak acid called carbonic acid, occurs more in colder waters that absorb more CO2; they are also more susceptible to its effects as less buffering occurs at colder temperatures. A change in acidity can affect organisms and species on many different levels. The most obvious is that carbonic acid is corrosive to calcium carbonate minerals; so, any organism that produces carbonite shells or skeletons, such as a mussel, a clam, an oyster or a coral will be susceptible to these corrosive waters.

This makes it more difficult to repair their shells and structures and much more likely that any exposed structures will dissolve. The extent of corrosive waters under a high emissions scenario will cover almost all the Arctic and Antarctic oceans by the end of the century with surface waters corrosive to these structures all year round, but not under a low emissions pathway. However, we already see such conditions occurring on a temporary seasonal basis and causing damage to organisms.

There is observational evidence of impacts, such as on Pteropods, a small free-swimming species of snail, which is a primary food source for many fish including salmon. Pitting and scarring of their shells is already occurring under today’s CO2 levels. Acidification can only be reduced by reducing CO2 emissions. It is intimately linked with how much CO2 continues to dissolve in the oceans. It will take thousands of years for carbonate chemistry to return to its present state and tens of thousands of years to return to a normal state.

An example of how these changes might affect an ecologically important and regionally relevant fish species is the cod. Freshening water will change the nutrient budget, which could impact plankton production and food availability, ocean acidification has been shown to negatively affect cod reproduction and this could force cod to stay further south. Warming water will bring other species in, forcing cod north.

This totality of effects will restrict cod populations to very small proportion of its current habitat. A recent study looked at the implications of warming and acidification on cod stocks, and determined that these stresses together would put fisheries at danger of collapse under high emission scenarios. Fishing effort would need to be drastically reduced to maintain any profitability for that stock. Keeping emissions to 1.5°C is critical for minimising risks to polar ecosystems and the benefits they provide us with.

Dr Gustaf Hugelius – permafrost

Bolin Centre for Climate Research, Stockholm University

Permafrost is the permanently frozen ground that exists across the Arctic. There is a feedback where climate change thaws the permafrost, which then collapses releasing organic material that has been frozen for millennia that microbes start consuming, releasing CO2 and CH4. Permafrost melt is accelerating, but started with the current 1°C increase from the pre-industrial period and has accelerated over the last few decades.

A rapid thaw can be observed with satellites and with models from 2003 and 2017. There has been a very substantial loss of permafrost during these years. It has accelerated even more over the past few summers with the heatwaves we have had. When the permafrost thaw is accelerating like this, substantial amounts of greenhouse gases are emitted. These levels are significant enough to decrease the amount of the carbon budget that can be emitted by humans while staying within 1.5°C and 2°C targets.

The emissions from permafrost were not accounted for when these budgets were calculated, adding urgency to the problem that the permafrost will emit even more CO2 and CH4 with higher temperatures. By the end of this century under a 1.5°C emissions scenario permafrost will emit roughly as much as India does today. At 2°C of warming its roughly equivalent to what the EU-28 emits today. For the high emission warming scenarios of 3 or 4°C by the end of the century, permafrost emissions will be the equivalent of the US or China today.

Permafrost is often called the ‘sleeping giant’, which is an appropriate analogy because of the huge area and large carbon stores involved. It is also a system that responds slowly but inevitably. The emissions that are triggered with thawing now will continue for centuries regardless of future emissions, even if human greenhouse gas emissions are stopped or slowed down.

In other words, even if we cap warming by 2100 and regardless of whether warming is stabilised at 1.5, 2 or 4°C, the permafrost will keep responding for multiple centuries after that. The thaw that we initiate now will be committing future generations to having to combat emissions and having to use negative emissions technologies to draw carbon emissions back down even if other human emissions have ceased.

Pam Pearson – policy implications

Former U.S. climate negotiator and director, International Cryosphere Climate Initiative (ICCI)

What are the implications of this evidence for emissions reductions, and why should policymakers care about these dynamics when there many other immediate challenges? Why can’t this wait? All of these dynamics you’ve just heard about kick in between a 1 and 2°C increase in temperature, so the reason this is urgent is that even at 1.1°C, we are already in the danger zone; and risks only get worse and increase from here on in.

Taking a longer perspective reminds people of how much things have changed over the last 150 years. Up to the preindustrial period covering hundreds of thousands of years of multiple glacial and interglacial periods, CO2 has only varied between 180ppm and 280 ppm. The last time we were above 400ppm, you need to go back 3 million years. When the cottage I live in was built in around 1870, CO2 was at 290ppm, essentially still at preindustrial levels after a couple of centuries of burning coal.

Only about 50 years later by 1918, levels had gone past 300 and were about 305ppm. We have now gone past 400 and the peak this year was at 418ppm, so it really has been a very radical change in this period, equivalent to millions of years. CO2 has continued to rise and there is no negotiating with the melting point of ice, and in the next decade we need to respect those real physical limits.

The loss of Arctic sea ice at 1.7°C is reversible depending on how warm the Arctic Ocean gets; you may start to get thick multi-annual ice within 40 to 50 years. However, sea level rise and permafrost loss are irreversible. With glaciers there is almost a totally loss globally around 2°C. This could be reversed within hundreds of years, but would take longer if the glaciers completely disappear. If the 1.5°C target is achieved, it will possible to retain some remnants at midlatitudes, and it would be easier to restore the glaciers.

Some of these effects are irreversible in human timescales of 5000 years or more. For instance, permafrost will continue to melt as temperatures rise, and will produce emissions for several centuries after the thaw initiates. This means we are committing future generations to negative emissions for several centuries, even if we achieve net zero within desired timeframes. With polar ocean acidification these colder polar waters are acidifying more quickly, which is entirely determined by peak CO2. We are already seeing shell damage today at 400ppm. That will expand greatly beyond 450ppm and it will take 50, 000 to 70,000 years to reverse that (in other words irreversible).

In the case of ice sheets and sea level rise, there is a growing time delayed risk above 1°C. Once certain thresholds are reached, with rising temperature and duration above 2°C, we will be committed to extreme sea level rises of 15 to 20m of sea level rise in coming centuries. The level of damage is determined by peak temperature. 2°C is not a safe level. Restoration to lower temperatures gives partial ice sheet restoration at best. Every tenth of a degree matters and the zone between 1 and 2°C is critical. To have any chance of staying within 1.5°C, the IPCC have highlighted that emissions will have to halve in the next decade. This means about a 5% reduction per year. That is hard message, but COVID-19 has shown what happens when we ignore the science.

Second discussion break

At this point a second discussion break took place. During this discussion the following points were addressed:

• If we reach net zero by 2050 during the second half of this century, then it looks like a lot of these impacts discussed today are going to continue for centuries afterwards. What opportunities will negative emissions technologies present in the 22nd Century to reverse some of these?
• Are the timescales involved part of reason why people find it difficult to engage with the issue of ice loss and climate change more generally?
• It does make it more difficult and because these regions are far away, trying to get people to understand it will still impact them directly. Despite the timescales, the youth movements have moved the debate on appreciably with a significant shift just over the past couple of years. There has been some modelling of negative emissions that suggests these impacts will not be reversible in the 22nd century, they will need to kick in around 2060, and it can only complement not replace very tough mitigation.
• There is no technical solution that will hinder the melt of permafrost itself, it is too big a problem to tackle with a direct engineering solution. Nature based solutions will be needed elsewhere or technologies that directly draw emissions from the atmosphere over the very long term. To halt these negative trends, we need rapid action, negative emissions are not a solution compared to reducing emissions rapidly from other sources.
• The oceans are a big store, so anything that happens there takes centuries to bounce back particularly when we are talking about acidification impacts. A whole sequence of changes occurs in ocean chemistry just through the addition of CO2, so it takes geological timescales to buffer that. You need to add extensive amounts of carbonate system to change it back to anything like to what we have seen in the recent past. Negative emissions may help but we are still talking about immensely long timescales. Engaging with loss on these timescales is extremely difficult, but the large-scale impacts that have started to occur are cutting through, although as they become ever more obvious to people it will be too late.

Dr Joeri Rogelj – SR1.5 emissions pathways

Imperial College London

Our choices today matter for how many climate impacts we will be experiencing over the course of this century and we have been hearing why limiting temperatures to 1.5°C matters. Taking insights from the IPCC Special Report on Global Warming of 1.5°C, it is clear that no sector is off the hook and we need to act quickly – staying within 1.5°C will require rapid, far-reaching and unprecedented changes.

Rapid means within the next decade, by 2030 we have to see very strong emissions reductions compared to where we are today, noting that at present emissions are still going up, even with the downward blip caused by the COVID pandemic. We need to have changes in all sectors: in the way we produce energy, the way we use land for food production, in the way we move around, in the way we build properties, heat our houses, or design our cities, and in the way we produce the products that we use. Finally, we need to see these actions across all stakeholders, businesses and countries. Because this is a global problem, global emissions need to go down, and this obviously needs global solutions.

The emission reductions required to meet 1.5°C involve a very steep decline in the near term, by around 2030 we already have halved emissions compared to 2010, then, roughly at mid-century we meet net zero and finally, in the second half of the century, the world moves into net negative emissions through the use of negative emission technologies to slowly reverse the amount of warming that we are experiencing. Emissions from some sectors that society depends on might not reach zero because technologies or methods to do this have not yet been identified. For example, some emissions of nitrous oxide and methane from agricultural activities at present can’t be eliminated.

The letter sent by the UK Committee on Climate Change to the UK Government on what its Nationally Defined Contribution should be, recommends a reduction in all greenhouse gases. For context, the numbers presented here are only in terms of CO2. The UK’s mid-century net-zero target is also applicable to all GHG emissions. The big question of course is whether these changes are feasible. The IPCC was asked this question and although there can be no clear yes or no answer to it, it suggested six areas that need to be considered (environmental feasibility, technological feasibility, economic feasibility, institutional feasibility, geophysical feasibility and social/cultural feasibility).

Science can address some of these areas, we understand the physics, how our earth system works, we understand how technologies develop and we understand economics; and science can state that the changes in these areas are feasible. However, there are two dimensions where scientists can’t call the shots, about whether our political systems can bring about this change and whether our social and cultural systems can, that is, if societies are willing to change their behaviours that are currently resulting in pollution. We are looking to our representatives and political systems to make these decisions, supported by civil society, and to make these very strong reductions happen. As scientists we can only provide the information and the evidence but are looking to society to follow through on this.

Beth Viola – U.S. transition/climate change

Holland and Knight, Clinton NSC and Gore/Obama climate advisor

The incoming US administration is already working on its climate policies, with John Kerry appointed Special Presidential Envoy for Climate Change, a cabinetlevel position in the Executive Office of the President of the United States for the first time, which includes sitting on the National Security Council reporting to the President. The campaign had climate change as one of its four priority pillars, and President-elect Biden’s agenda is that the US needs to hit net zero by 2020.

The ‘build back better’ plan is an aggressive approach to achieving this target, which will require congressional help to implement the relevant measures. There is likely to be a split congress that makes it more difficult for President-elect Biden to achieve this agenda, but the appointment of John Kerry means the US will be re-engaging with the international community on climate change. One of the first things likely to happen is a re-commitment to the Paris agreement, and the transition team is already working on what the nationally defined contribution will contain as a commitment from the US and what can be achieved without congressional help.

It is also anticipated that a domestic climate tsar will be appointed, with the energy and environment team announced after the health appointments are made. The tsar will be a high-level person working out of the White House to achieve the domestic climate policy targets all of which will signal the Presidentelect’s commitment to addressing climate change. He has stated that he will host a climate summit shortly after he assumes office with other global leaders so he can make clear the US is committed to re-engaging and re-establishing leadership on these issues globally.

The previous administration disassembled much of the federal government and there are very few federal employees left that work on these issues. A lot of the scientists have left the agencies, along with key administrators, and many of the political appointments at the top of these organisations were never made. The top priority of the incoming administration will be to rebuild the federal government and there will be an emphasis on building out those agencies and employees most relevant to climate change.

The other part of this will be executive orders. The leverage of the existing government will be used including existing programmes to encourage and expand innovative technologies for mitigating climate change. There is also a ground swell of opinion from business on the need to engage with UNFCCC processes, and a lot of support for the administration to address climate issues.

Dr Sarah Honour – UK policy

Head of Climate Science, Department for Business, Energy and Industrial Strategy (BEIS)

The previous speakers have highlighted both the importance and vulnerability of the cryosphere. It is home to millions of people as well as to rich and diverse ecosystems that are some of the most sensitive to changes in climate and already suffering effects. The science is clear and the best way to protect these communities and ecosystems is to scale up efforts to stay within 1.5°C as well as increasing resilience to impacts we know can’t be avoided.

The upcoming COP President, the UK, takes these issues seriously and is also in a position to make a real difference. Delivering a successful COP26 is one of the UK’s top international priorities in 2021. For our Presidency we will aim to achieve the goals of the Paris Agreement through three main mechanisms, through the setting of national ambitions, the negotiations themselves and wider public campaigns. So first on ambitions, set on the best available science we are working with climate vulnerable countries to encourage others to come forward with the best available reductions in plans, including nationally determined contributions, long term strategies as well as to set net zero goals.

It is only be delivering such plans we will be able to limit temperatures in line with the Paris Agreement and reduce the risk of passing dangerous tipping points and causing damage to the cryosphere and to the wider planet. Secondly, the UK is committed to seeking an agreement on the Paris rule book, to make sure that the agreement is fully implemented. It is also seeking a strong negotiated outcome that accelerates climate action that also supports the UNFCCC process itself. Science will be an important underpinning; to the UK presidency, it is key that we listen to the scientists and actions are based on the evidence.

The UK Presidency will champion this approach and will also look for opportunities to create dialogue between the scientific experts and negotiators. Thirdly we need everyone to act, so we are working more widely across five campaigns to bring together governments, businesses and civil society to accelerate the transition in the global economy giving countries the confidence they need to commit to ambitious plans. These areas, some of which are directly relevant to the cryosphere, such as nature-based adaptation and resilience, as well as others including net zero emission vehicles, energy transition and finance will show leadership and broker non-state actor commitments to support delivery of increased global ambition.

It would also be remiss not to emphasise another important part of our presidency, which is championing a diverse and inclusive COP. Indigenous people account for around 10% of the Arctic population, and a substantial number of those are in high mountain regions. Their lives and livelihoods are most affected by the climatic changes and their experience and knowledge is vital in creating long lasting solutions that protect and preserve the land; they understand the land far better than we do. We are working with indigenous groups to amplify their voices and enable a fuller meaningful participation. We are committed to using these diverse voices to help deliver a COP that is truly for all of society.

Despite the postponement of COP are work continues, in less than a fortnight’s time, the UN, UK and France will be hosting a virtual leaders ambition summit. This will provide a platform for leaders to come forward with new ambitious nationally defined contributions, long term strategies to net zero as well as new climate finance pledges and ambitious adaptation plans. As the Prime Minister set out in the ten-point plan speech last month, this is a huge opportunity to build back better after the COVID-19 crisis. The UK will be using the time we have now and between COP26 next year to advocate ambition and highlight the latest science, this will lay the outcome that will show that the net zero transition is inevitable and accelerating, and will help preserve the cryosphere and planet for future generations.

Final discussion break

In the final discussion break attendees were able to ask remaining questions to the expert panel. The points addressed included:

• The likely re-engagement with science by the incoming US administration was welcomed. It was also highlighted that the formation of POST was based on the US Congress Office of Technology Assessment (OTA), which existed from 1972 to 1995, and has a similar role of producing objective and authoritative analysis of the complex scientific and technical issues. The ongoing need for such analysis was emphasised along with encouragement to consider the need for such a resource again in the US.
• Freshwaters containing meltwater from areas of permafrost flowing into the Arctic contain large amounts of sediment, the turbidity from which might have implications for fisheries. Salinity is one of the factors that will be affected in the Arctic but in terms of river flows the problem is trying to work out the different types of compound that rivers are taking into the ocean. Turbidity will increase and have effects on food webs but how this will directly affect fish stocks is not as well-known as it could be. The big question around river input is the change in the nutrient budget as well, so not only will you affect turbidity and light, but also stratification (how well the ocean is mixed). If the river is running through nutrient rich areas the resulting nutrient load could have a knock-on effect for eutrophication, causing changes in oxygen, which is a real worry for the Arctic oceans. In some areas of river influenced areas along the Canadian and Alaskan coasts affected by big rivers such as the Yukon, experience quite low oxygen levels already and quite high nutrient flow. There are areas that are going to be drastically changed but there is still a lot of work to be done trying to work out what fisheries will be impacted as it is very complex with so many stressors and changes occurring in the ocean at the same time. However, it will cause a change in the food web and that will cause a change in what food species are present for fish species and the subsequent stocks available for us to fish. So, there will be a change, but how that change manifests itself is still to be determined.
• Mountain glaciers can create micro-climates around them that not only influence the temperature and humidity around them where they are, but also the water they release every summer is key for biodiversity. We can see in the areas around tropical glaciers that these are the areas where we find the highest biodiversity and high numbers of endemic species. If the glaciers disappear so will the water resources that are important for these ecosystems and also the microclimates connected to the glaciers.
• The understanding of ice sheets at risk of irreversible retreat was raised. The US and UK are combining in a massive study of parts of the Western Antarctic Ice Sheet (WAIS) because we now have a good idea of the bathymetry or shape of the basin under this ice sheet, how far back it goes and deeper it gets. This means when the ice shelves disappear, the flow of the ice behind it accelerates. For example, on the Larsen B ice shelf out on the Antarctic Peninsula that let go about a decade ago, the ice flow behind it accelerated five or six times over in terms of its rate of speed. We are watching and monitoring the demise of the Thwaite and Pine Island glacier ice shelves because of concerns that they are going into deeper and deeper basins, so it will be a non-stop run-away ice flow. This is also happening in 3 or 4 of the major outlet glaciers in Greenland. These glaciers are retreating into deeper basins, which means they can only accelerate in their flow. A couple of basins in East Antarctica also have this topography, which are even bigger, such as the Wilkes Basin being studied by a New Zealand project.
• There are a lot of biodiversity and other issues associated with permafrost, such as migratory birds that are losing their habitat with the thaw. About half the lakes in the world are in the permafrost region and small ponds are disappearing that are used by these species. Another growing concern is that we have recently found that almost half of the world’s mercury is locked into permafrost, and mercury is a toxin if it is released into the environment. Pulses are being released as the permafrost thaws at very high levels that might affect fish species or the communities or others that consume those fish.
• There are interactions between biodiversity, which is under stress because of climate change and other human activities, and the mitigation strategies we pursue. Just to get to net zero and halt global warming we will need a certain amount of carbon dioxide removal and this removal often requires land for afforestation, energy crops or for other reasons. That land has to come from somewhere, so depending on how much we reduce emissions and how much we rely on carbon dioxide removal, and what solutions we rely on, so we do we use nature base solutions, do we plant monocultures or do we use biodiversity to restore ecosystems? This will have strong knock on effects on local biodiversity. So the solutions are linked to the side effects we are trying to avoid.
• The key difference between the Arctic and the Antarctica is that the Arctic is an ocean surrounded by land, which has been covered by snow and ice that reflected the sunlight and heat out to space. As the sea ice retreats the oceans absorb more of this heat, in the winter the oceans release this heat before the ice can form. This results in amplified warming in the Arctic in the autumn and winter driven by the heat from the oceans. In the springtime, there are changes in atmospheric circulation that brings up warm air to the North, but the main driver of the increase in Arctic temperatures is the loss of ice and snow cover from land.
• While these cryosphere regions have great intrinsic values, their loss will have much wider impacts on the rest of the planet. For example, biodiversity will be lost elsewhere due to sea level rise, with changes in weather patterns because of sea ice loss or because of extreme storms, and these will be the main impacts on biodiversity in terms of scale. What happens in the Arctic does not stay in the Arctic, as has been said previously.
• Regarding COVID-19 and data gaps arising in research, there are big delays with programmes being cancelled and it is influencing the ability to collect data to do research. Everything is on hold in a lot of places, so there will be gaps but everyone is eager to get back out there.