Met Office ARC0027

Written evidence submitted by the Met Office

Introduction

The Met Office is the UK’s National Meteorological Service (NMS), a Public Sector Research Establishment (PSRE) and an Executive Agency of the Department for Science, Innovation and Technology. We are responsible for monitoring and predicting the weather and providing the National Severe Weather Warning Service (NSWWS).

The Met Office Hadley Centre provides climate science and services to help governments, industries and people understand and prepare for climate change, including the monitoring of global and national climate variability and change. Within this, the Met Office Hadley Centre Climate Programme (MOHCCP) delivers policy relevant scientific evidence and advice for the UK Government and beyond to address the societal challenges of climate change, helping to build a more resilient, net-zero future. This work includes conducting research on the Arctic region, in terms of both monitoring long-term changes and improving weather and climate predictions through improved understanding and modelling of Arctic processes.

Met Office scientist, Professor Helene Hewitt OBE presented evidence to the Environmental Audit Sub-Committee on Polar Research during their first oral evidence session for this inquiry on 27 March 2023. This submission builds on the evidence Professor Hewitt presented and responds to specific requests for further information from Committee members.

SECTION 1: THE ARCTIC ENVIRONMENT

Observable realities of changes in the Arctic Environment

The Met Office has undertaken extensive research in both the current and future conditions in the Arctic for sea ice, sea level changes, permafrost thaw and methane. The Met Office also presents evidence in this section from our contributions as lead and co-authors, chapter scientists, and reviewers of the United Nations Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6).

1.1. IPCC and other multilateral assessments:

The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate1, and Chapter 92 in the Working Group 1 IPCC AR6 examined changes in the Arctics ocean, cryosphere and sea level and concluded that over the last 50 years, the Arctic has warmed at more than twice the global rate.

Both reports found a number of conclusive reasons why the Arctic is warming more rapidly than the rest of the world, including:

The loss of ice and snow cover reduces the reflectivity of land and ocean surfaces in the Arctic, causing a greater proportion of incoming solar radiation to be absorbed. This is a positive feedback that acts to enhance warming rates.
Confinement of warming to near the surface in the polar atmosphere which also leads to amplification.
Increases in heat transported from further south into the Arctic by both the atmosphere and the ocean.

1 IPCC (2019) “Summary for Policymakers” in: “IPCC Special Report on the Ocean and Cryosphere in a Changing Climate” Cambridge University Press, Cambridge, UK and New York, NY, USA

2 Hewitt et al., (2021): Ocean, Cryosphere and Sea Level Change. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, pp. 1211–1362, doi:10.1017/9781009157896.011

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Over the last decade, Arctic sea ice area in September is smaller than at any time in the last 1000 years, permafrost warming and thawing has been widespread since the 1980s, and there is high confidence that the Greenland ice sheet has been losing mass since at least the 1990s. There is no evidence to suggest that any of these trends will not continue. This has led to an increase in extreme Arctic heat events, and annual minimum temperatures in the Arctic are increasing at more than three times the global rate3.

The Met Office recently contributed to a review article on the impact of climate change on Arctic sea ice in the context of the Marine Climate Change Impacts Partnership (MCCIP) 4. An update to the MCCIP Arctic sea ice report card was led by the Met Office, involving authors from across the UK and Europe. The MCCIP report card reaffirmed the messages of IPCC AR6, based upon observations and publications updated to 2022.

1.2. Arctic sea ice extent, thinning and loss

As stated in the IPCC report, since satellite records began, there have been decreases in Arctic sea ice area of about 40% at the seasonal minimum in September, and 10% at the seasonal maximum in March. The report found that these decreases are due to both additional melting in the summer period, and also to reduced growth over the winter (as a warmer ocean makes it harder for sea ice to form). As the summer ice cover has reduced, we are seeing more interannual variability as the cover is much more vulnerable to weather systems in the Arctic. The assessment also concluded that human influence is very likely the main driver of the decrease in Arctic sea ice area.

Arctic sea ice fluctuates on a yearly basis with a minimum coverage in September. September sea ice extent is one of the most rapidly changing components of the global climate system. Satellite sensors continue to record a downward trend in Arctic sea ice extent in every month of the year. The decline is highest at the seasonal summer minimum with September extent reducing, on average, by almost 79,000 square kilometres per year5. If the Arctic Ocean becomes seasonally ice-free, this will happen first in September, when Arctic sea ice cover reaches its seasonal minimum.

Not only is the extent of Arctic sea ice reducing, but it is also thinning6, and the area of thick multiyear ice that has survived at least one summer has significantly reduced7. The loss of thick multi-year ice means that the average thickness of Arctic sea ice is decreasing overall. A recent synthesis of in-situ and satellite data from 1958-2018

indicates an Arctic‐wide thinning of 2m (or 66% relative to pre-1990) over the past six decades8. A combination of satellite and submarine data has been used to estimate a decrease of average ice thickness in the central Arctic from 3.64 m to 1.89 m over the period 1980 to 2008 which gives an approximate average rate of thinning of 60 cm per decade.9

Climate models suggest that the Arctic becomes ice-free during summer as temperatures increase, and that ice cover returns to its previous state when the temperature is reduced again10. Other studies have shown that the

3 IPCC (2021) “Summary for Policymakers” in: “Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change”, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 3−32

4 Blockley et al. (2020) Impacts of climate change on Arctic sea ice MCCIP Science Review 2020, pp. 208–227

5 Or around 11.5% per decade when referenced to the long-term (1981–2010) mean September extent of 6.88 million km2 - www.eumetsat.int/osi-saf

6 Lindsay and Schweiger (2015) Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations The Cryosphere, 9, 269–283, https://doi.org/010.5194/tc-9-269-2015

7 R Kwok (2018 Arctic sea ice thickness, volume, and multiyear ice coverage: losses and coupled variability (1958–2018) Environ. Res. Lett. 13 105005 www.iopscience.iop.org/article/10.1088/1748-9326/aae3ec

8 Ibid.

9 www.metoffice.gov.uk/research/climate/cryosphere-oceans/sea-ice/index

10 Ridley et al., (2012) How reversible is sea ice loss?, The Cryosphere, 6, 193-198; Ridley and Blockley, (2018) Brief Communication: The significance for the IPCC targets of 1.5 °Cand 2.0 °C temperature rise for an ice-free Arctic, The Cryosphere Discussions, 1-8.

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decline in Arctic sea ice extent is related to atmospheric CO2 concentration11 and suggest that if global temperatures were to level out sea ice extent would stabilise12.

Many impacts will likely be felt irrespective of the precise date when the Arctic is declared seasonally ice-free. The loss of Arctic summer sea ice could be an important ecological threshold because many animal species rely on the presence of sea ice, ranging from algae13 to large mammals such as the polar bear14. The decline in Arctic sea ice cover could also have socioeconomic impacts, including increased human activity in the Arctic owing to easier access for shipping, and longer ice-free seasons in all areas of the Arctic15.

1.3. Sea level change and measurement processes

By using tidal gauge record, we can see that sea-level change in the Arctic is largely influenced by movement of the Earth’s crust or ‘glacial isostatic adjustment’16. The vertical land motion affects the rate of sea-level change and this has resulted in both land uplift and land subsidence (see Fig. 2 in annex). Locally, in these areas where there is a lot of vertical movement, the impact of climate change on sea level rise will not be so noticeable as tectonic plate movement will be the dominant process. For comparison, global mean sea-level rise shows rates of about 1.3 mm per year for 1901-1971, increasing to 1.9 for 1971-2006, and further increasing to 3.7 mm per year for 2006-201817. Local factors, such as ocean circulation changes and additional vertical land motion processes may also play a role in shaping tide gauge records.

Many of the processes that lead to sea level rise are well-understood, such as the expansion of the ocean as it warms. However, key processes that determine the future rate of ice loss from the Greenland and Antarctic ice sheets are poorly understood. Ice sheets are inhospitable and difficult to access with has resulted in less scientific observation in comparison to other areas. This, in addition to the long timescales needed to observe glacial change, leads to uncertainty in future projections and the likelihood of outcomes. The uncertainty increases at higher levels of global warming (caused by high climate sensitivity18 or a high emissions pathway) if the change in ice sheets becomes irreversible.

There are several scientific challenges with measuring Arctic sea-level rise using satellite observations, such as seasonal to permanent sea-ice cover, lack of regional coverage of satellites and satellite instrument’s ability to measure ice. Sea level changes in the Arctic respond to the same global drivers of sea level, notably expanding as temperatures increase19 and increasing in mass from melting land-based ice sheets and glaciers. Additionally, local sea-level changes are influenced by the reduction in ice mass over Greenland changing the earth’s gravity, rotation, and deformation20. This means that some regions of the Arctic will experience a reduction in sea-level rise or sea-level fall.

11 Notz and Stroeve, (2016) Observed Arctic sea ice loss directly follows anthropogenic CO2 emission, Science, 354, 747-750 https://doi.org/10.1126/science.aag2345; Notz and Marotzke, (2012) Observations reveal external driver for Arctic sea-ice retreat, Geophysical Research Letters, vol. 39, l08502, doi:10.1029/2012gl051094

12 Ridley, J. K., Blockley, E. et al. (2018) The sea ice model component of HadGEM3-GC3.1, Geosci. Model Dev., 11, 713–723, https://doi.org/10.5194/gmd- 11-713-2018

13 Søreide et al., (2010) Timing of blooms, algal food quality and Calanus glacialis reproduction and growth in a changing Arctic Global Change Biology, 16, 3154-3163 https://doi.org/10.1111/j.1365-2486.2010.02175.x

14 Amstrup et al. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence. Nature 468, 955–958 (2010). https://doi.org/10.1038/nature09653

15 Meier et al., (2014) Arctic sea ice in transformation: A review of recent observed changes and impacts on biology and human activity, Review of Geophysics, 52, 185-217

16 Ongoing movement of land that was once covered by ice-age glaciers, often referred to as “post-glacial rebound”.

17 IPCC (2021)

18 www.metoffice.gov.uk/research/climate/understanding-climate/climate-sensitivity-explained

19 Thermal expansion of the water column.

20 Shape, size, or volume of an area of the Earth's crust.

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1.4. Permafrost thaw

Permafrost - ground that is frozen for periods of two years or more - lies under approximately 22% of the land in the Northern Hemisphere21. Increases in permafrost temperatures have been observed in polar regions22 with

increases of up to about 1 °C per decade in cold permafrost and less than 0.3 °C per decade in warmer permafrost. Met Office scientists assessed the permafrost in the current generation of Earth System Models and showed, that, whilst the northern-high latitude air temperatures are relatively well simulated by climate models, the present-day permafrost extent varies considerably between models23. Projections of future change suggest the permafrost volume in the top 2m of the soil could decrease by 10% to 40 % per degree Celsius. Permafrost contains more than twice as much carbon as is currently in the atmosphere and under degradation24 it will release additional carbon in the form of CH4 and CO225. Improvements in the representation of permafrost processes in Earth System Models are required to more fully quantify the feedback of permafrost carbon loss onto the global climate.

Likely consequences of permafrost degradation in the Arctic include changes to hydrology, with both wetting and drying, with the melting of ground ice causing subsidence and landscape changes. Both of these effects are likely to damage infrastructure and increase maintenance costs. Current observed infrastructure damage is substantial and is projected to continue, with 30–50% of critical circumpolar infrastructure thought to be at risk by 205026.

Another consequence of permafrost thawing is the release of naturally occurring mercury bound to plant organic matter. Although the amount and location of mercury that could be released is uncertain, projections estimate increase mercury concentrations entering food chains and water supplies.27

1.5. Methane

Using a new methane emissions-driven model28, two studies indicate that methane mitigation and methane removal slow the rate of global mean surface warming and delay peak temperatures29. In the Arctic, the climate benefit from methane mitigation is greater than that in global mean temperature due to Arctic amplification3031. This suggests that methane mitigation/removal has a role in Arctic climate mitigation although mitigation efforts also need to focus on carbon dioxide emissions.

The global atmospheric methane growth rate observed in 2020 was unprecedented since routine systematic methane observations began in 1983. This record growth rate was surpassed in 2021. Observations from November 2022 now indicate that atmospheric methane concentrations have reached a record high32. However, studies of the record growth rate in 2020 suggest that it was due to both increases in wetland emissions – the

21 Westermann et al. (2019). Northern Hemisphere permafrost map based on TTOP modelling for 2000–2016 at 1 km2 scale. Earth-Science Reviews, 193, 299–316. https://doi.org/10.1016/j.earscirev.2019.04.023

22 Smith et al. (2022) The changing thermal state of permafrost. Nature Reviews Earth & Environment, 3(1), 10-23. www.nature.com/articles/s43017-021- 00240-1

23 Burke et al. (2020) Evaluating permafrost physics in the Coupled Model Intercomparison Project 6 (CMIP6) models and their sensitivity to climate change

The Cryosphere 14, 3155–3174, https://doi.org/10.5194/tc-14-3155-2020

24 Top-down thawing, subsidence, and loss of area.

25 Schuur et al. (2015) Climate change and the permafrost carbon feedback Nature, 520, 171–179 https://doi.org/10.1038/nature14338

26 Hjort et al. (2022) Impacts of permafrost degradation on infrastructure Nat Rev Earth Environ 3, 24–38 https://doi.org/10.1038/s43017-021-00247-8

27 Schaefer et al. (2020) Potential impacts of mercury released from thawing permafrost Nature communications, 11(1), 4650 https://doi.org/10.1038/s41467-020-18398-5

28 A capability to fully model the global methane cycle, providing essential evidence to underpin climate mitigation policy. Folberth et al. (2022) Description and Evaluation of an Emission-Driven and Fully Coupled Methane Cycle in UKESM1 J. Adv. Model. Earth Syst. 14(7) doi:10.1029/2021MS002982.

29 Staniaszek et al. (2022) The role of future anthropogenic methane emissions in air quality and climate npj Clim. Atmos. Sci. 5, 21 doi:10.1038/s41612-022- 00247-5; Abernethy, S. (2021) Methane removal and the proportional reductions in surface temperature and ozone Philos. Trans. R. Soc. A, 379, 20210104, doi:10.1098/rsta.2021.0104.

30 When the magnitude of the reduction in Arctic surface temperatures is greater than the reduction in global mean temperature

31 Staniaszek et al. (2022)

32 Lan et al. (2023) Trends in globally-averaged CH4, N2O, and SF6 determined from NOAA Global Monitoring Laboratory measurements. Version 2023-03, doi:10.15138/P8XG-AA10.

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largest natural source of methane – and reduced emissions of nitrogen oxides33. Nitrogen oxide emissions from transportation decreased during lockdowns associated with the global Covid-19 pandemic, causing an increase in methane lifetime and potentially explaining half of the methane growth rate34. Emission estimates35 provide evidence that both 2020 and 2021 growth rates can be attributed to emissions, in particular from tropical wetlands. While some observations suggest increases in Arctic methane emissions, there is no evidence that the Arctic is contributing significantly to the global methane levels.

Impact of changes in the Arctic for the UK

The consequences of changes in the Arctic have been much debated. IPCC AR6 reported a lack of agreement between different studies on the impact of Arctic sea ice loss on midlatitude weather and this remains a topic of ongoing research. Since publication of the IPCC report, Met Office scientists have led and published new research which gives current best estimates of the effect of the Arctic changes on the yearly variations in UK winters of around 10%, and concluded that the effect could be small.

Arctic climate changes could also have an indirect impact on UK climate through changes to the Atlantic Ocean overturning circulation (AMOC), which brings warm waters to the ocean west of the UK. The AMOC is influenced by changes in long-lived greenhouse gases, such as carbon dioxide, and short-lived influences, such as aerosols and methane. The magnitude of these influences, and the role of the Arctic in AMOC changes, are still uncertain and a topic of ongoing research by Met Office scientists in collaboration with the wider international climate science community36.

1.6. Impact of Arctic sea ice loss on UK weather

Arctic sea ice extent is expected to continue to decline as the climate changes. The impact of Arctic sea ice loss on atmospheric circulation has been much-debated over the past decade, due to differences between observations and models.

To gain further insight, coordinated model experiments were proposed by the Polar Amplification Model Intercomparison Project (PAMIP)37. Met Office analysis of PAMIP simulations38 - performed by 16 different models

- did reveal a robust weakening of the mid-latitude westerly winds in response to future Arctic sea ice loss39. Weakening of these winds has previously been associated with severe cold winters in the Northern Hemisphere. However, this analysis finds the relationship between Arctic ice loss and westerly winds is weak, and can only account for around 10% of the yearly variations in UK winters, although it is similar in magnitude to, and opposes, the strengthened westerly winds expected in response to increases in greenhouse gases. Arctic warmth also

33 Peng et al. Wetland emission and atmospheric sink changes explain methane growth in 2020 Nature 612, 477–482 https://doi.org/10.1038/s41586-022- 05447-w ; Stevenson (2022) COVID-19 lockdown emission reductions have the potential to explain over half of the coincident increase in global atmospheric methane Atmos. Chem. Phys. 22, 14243–14252, https://doi.org/10.5194/acp-22-14243-2022

34 Stevenson et al. (2022)

35 Rößger et al. (2022) Seasonal increase of methane emissions linked to warming in Siberian tundra. Nat. Clim. Chang. 12, 1031–1036 https://doi.org/10.1038/s41558-022-01512-4

36 Hassan, T. et al. (2022) Air quality improvements are projected to weaken the Atlantic meridional overturning circulation through radiative forcing effects Commun. Earth Environ., 3, 149, doi:10.1038/s43247-022-00476-9; Jackson et al. (2020) Impact of ocean resolution and mean state on the rate of AMOC weakening. Clim Dyn 55, 1711–1732 https://doi.org/10.1007/s00382-020-05345-9; Menary et al. (2020) Aerosol-Forced AMOC Changes in CMIP6 Historical Simulations Geophysical, Research Letters, 47,14 https://doi.org/10.1029/2020GL088166

37 Smith et al. (2019) The Polar Amplification Model Intercomparison Project (PAMIP) contribution to CMIP6: investigating the causes and consequences of polar amplification. Geosci. Model Dev. 12, 1139–1164 doi.org/10.5194/gmd-12-1139-2019

38 Smith et al. (2022) Robust but weak winter atmospheric circulation response to future Arctic sea ice loss Nature Communications, 13, 727,

doi:10.1038/s41467-022-28283-y

39 Ibid

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spreads to lower latitudes, opposing the cooling effect of the weakened westerly winds40, meaning the net effect on UK winter temperatures may be small.

1.7. Sea level changes

The observed climatic and environmental changes in the Arctic will affect both global and local sea-level change throughout the world, through loss of ice from the Greenland ice sheet and glaciers in the Arctic region. The Greenland ice sheet is expected to contribute up to 18 cm to global mean sea level rise this century. As highlighted previously, due to limited scientific understanding of ice sheet processes, we cannot rule out global sea-level rise in excess of 2m from Greenland ice sheet loss alone by 2300, under current high warming scenarios41. However, gravitational effects and the spatial pattern of sea level change42 associated with ice mass loss from Greenland mean that the UK will experience almost zero local rise from this source – and even a fall in sea level for some locations – compared to other parts of the world43.

Despite limited expected impacts for the UK, UK Overseas Territories could subject to substantial sea level rise from Greenland ice sheet loss. Conversely, The Antarctic ice sheet is the more important driver of future sea-level rise for the UK, and regional sea level rise around UK coastlines will be strongly affected by loss of the Antarctic ice sheet (see Fig 1. in annex).

SECTION 2: THE UK’S ARCTIC INTERESTS

Risks to the climate and environment in the Arctic

Increased activity in the Arctic presents risks to the climate and environment. This, in turn, increases the need for reliable forecasts and accurate environmental weather guidance to support safe business and operational practice.

2.1. Consequences of extractive industries

The IPCC has high confidence that industrial emissions have been growing faster since 2000 than emissions in any other sector, driven by increased basic materials extraction and production44. The retreat of sea ice will provide access to new Arctic resources. It is estimated that 22% of undiscovered fossil fuel reserves are located north of the Arctic Circle, 30% of which is natural gas, and 13% of which is oil45. Other natural resources that will become increasingly accessible and exportable include an estimated $1 trillion worth of precious metals and minerals, fisheries, and renewable energy sources46.

The extraction, processing and utilisation of these increasingly accessible Arctic resources will almost certainly contribute to the further release of greenhouse gas emissions and associated warming.

40 Screen (2017) The missing Northern European winter cooling response to Arctic sea ice loss Nature Communications, 8, 14603 https://doi.org/10.1038/ncomms14603

41 Nick et al. (2013) Future sea-level rise from Greenland’s main outlet glaciers in a warming climate Nature 497, 235–238 https://doi.org/10.1038/nature12068

42 As ice melts and water enters the oceans, the mass of the planet is moved around and its shape is changed. This is among the factors that alter the way the Earth wobbles on its axis. This can also impact regional variation of sea level rise

43 This primarily due to the effects of Greenland ice mass loss on Earth’s gravity field and the relative proximity of the UK (Figure 1 in the annex), as explained in more detail in the UKCP18 Marine Report (Palmer et al, 2018).

44 IPCC (2022). Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Cambridge University Press, Cambridge, UK and New York, NY, USA. Ch 11 htps://doi.org/10.1017/9781009157926.013

45 Gautier et al. (2009) Assessment of undiscovered oil and gas in the Arctic Science, 324 (5931) 1175-1179 https://doi.org/10.1126/science.1169467

46National Intelligence Council (2021) Climate Change and International Responses Increasing Challenges to US National Security Through 2040.

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2.2. Consequences of greater maritime mobility

Sub-zero temperatures in the Arctic restrict shipping due to sea ice but enable the passage of ground vehicles over perennially frozen soil and water surfaces47. Maritime mobility will almost certainly increase as a result of sea ice reductions, whereas mobility over land may decrease48 due to permafrost thaw and increased depth of snow cover49.

Ice-free summers and an extension of the navigable period in the Arctic Ocean will increase maritime traffic in the Arctic. This will increase the exposure of global shipping to the hazards of the High North, including geographic remoteness, and rapidly changing weather50. More operational forecasting services may therefore be required to ensure the safety of businesses and personnel operating in the Arctic, including search and rescue. The international community has already begun to respond to risks of this nature. For example, the International

Maritime Organization’s Polar Code, which came into effect in 2017, includes mandatory guidance on ship design, equipment, search and rescue and environmental protection.

The consequences of unsafe shipping practices in the Arctic include greater likelihood of oil spills and associated environmental damages, disruption to local ecosystems, and loss of human life. With port infrastructure typically designed to either last over a century or be readily adaptable over the same period, the potential of sea-level fall introduces different challenges to port accessibility in the Arctic region.

SECTION 3: THE UK’S CONTRIBUTION TO THE ARCTIC THROUGH SCIENTIFIC RESEARCH

Arctic research informing Government policy

3.1. Weather forecasting for increased Arctic accessibility and activity

With changing defence and security requirements for the Arctic, the Met Office have expanded our Arctic monitoring and research to respond to a Ministry of Defence (MOD) and Foreign, Commonwealth and Development Office (FCDO) request for increased meteorological support to activities in the Arctic region. A short piece of initial scoping work, funded partly by MOD and partly through the BEIS Tactical Fund, is nearing completion. This work has focused on expanding the Arctic weather forecasting capabilities of the Met Office and understanding the implications of a changing Arctic environment on the region’s accessibility and the hazards experienced.

Benefits to the UK of supporting Arctic research activity

Partnering the UK’s leading climate-science expertise with the local knowledge and intelligence of Arctic allies has the potential to increase our understanding of the impacts of Arctic changes for the UK, to bolster our position as a global science superpower and to support the development of effective climate mitigation and adaptation plans.

3.2. Strengthening partnerships

47Stephenson et al. (2011) Divergent long-term trajectories of human access to the Arctic Nature Climate Change, 1, 156-160 https://doi.org/10.1038/nclimate1120

48 IPCC (2014)

49Gädeke et al. (2021) Climate change reduces winter overland travel across the Pan-Arctic even under low-end global warming scenarios Environmental Research Letters. 16, 024049 https://doi.org/10.1088/1748-9326/abdcf2

50 Emmerson et al (2012) Arctic Opening: Opportunity and Risk in the High North.

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In developing the science behind the UK’s national capabilities in climate, weather and ocean modelling, it is important to recognise that there are limits to the resources that can be committed to Arctic-specific developments, versus other priorities. Collaboration with allies who are experienced in operating in the Arctic offers benefits in both in terms of science and diplomacy. To date, partnerships with countries such as Canada, United States and Norway have resulted in valuable data exchange and community software developments,

increasing the UK’s access to information that informs and strengthens UK resilience strategies, supporting UK safety.

An example of beneficial Arctic science partnerships is the BEIS Tactical Fund (see section 3.1). The Met Office hosted and led an Arctic forecasting workshop bringing together colleagues from the United States, Canada, Denmark, Norway and Finland. The workshop participants demonstrated enthusiasm for future collaboration on operational meteorology and oceanography and multi-lateral knowledge-sharing, which is being followed up through a sequence of bilateral meetings.

The Met Office has already benefitted from collaborations in the Arctic as an active member of The Five Eyes (FVEYS) group "MET5" (for which we are currently chair). As like-minded allied nations, we have been able to share and co- develop meteorological and ocean information, data, products and services, which has enabled us to operate more effectively in the defence and security arena and increase military safety.

The Met Office would support any UK efforts to understand the impacts of increased accessibility in the Arctic (see section 2.2) being conducted in close partnership with allies. A coordinated national response across both civilian and military organisations should enhance outcomes. For example, to develop partnerships and understand the potential benefits of this shared capability, Met Office delegates recently visited Canadian civilian and military scientific and forecasting centres and will shortly be visiting the Finnish Meteorological Institute.

3.3. Improving weather impact mitigation

Through our work with the BEIS Tactical Fund, the Met Office have made recommendations and identified next steps for enhancing our expertise in understanding weather conditions in the Arctic across all timescales. This will support the UK’s safe activity and ability to mitigate weather impacts in the region, now and in the future, including military operations.

3.4. Improving weather and climate models

The Met Office is always improving the representation of different processes in the models. For the Arctic, this includes improved representation of permafrost and interactive ice sheets so that we can more accurately model how the Greenland ice sheet changes and its resulting impact on the UK and global climate. In response to a request from MOD, and interest from international partners such as the US Government, the Met Office is also exploring how to improve performance of all of our ocean models to inform activity in the maritime domain, including in the Arctic Ocean. By improving our weather and climate models, the Met Office can deepen our understanding of the Arctic, improve our forecasting capabilities and better support the UK in developing resilience and adaptation strategies.

As research, technology and computing power advances, climate models are likely to improve, both in terms of accuracy and detail. For example, more specific potential impacts of climate change could be provided at a regional and local level to inform climate mitigation and adaption planning. Improvements in the ongoing process representation, numerical scheme and data assimilation in the models predicting atmosphere and ocean on

short-medium ranges (up to two weeks ahead) could have substantial impact on our ability to improve forecast skill in the Arctic. The latest generation of Met Office global models include grid schemes that incorporate polar cells, and both global and regional systems can be operated as coupled atmosphere-ocean forecasting

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frameworks51. Properly representing the two-way feedbacks between atmosphere and ocean is critical in a region where ice-cover, and therefore the boundary between land and sea, will vary massively between seasons.

The Ocean Data Assimilation Group at the Met Office are developing improved schemes to correctly initialise the modelled sea-ice edge, whilst use of the WAVEWATCH III wave model52 should enable the Met Office to track and implement some of the latest science parameterizations of wave-ice interactions53. Work is at an early stage to enable the Met Office global ocean model to better represent shallow, tidal, shelf seas areas, including representation of how tides propagate under ice-covered waters.

UK Arctic science research used in multilateral assessments

3.5. UK science profiled through IPCC contributions

Across many areas, the UK are leading contributors of Arctic science in the IPCC assessment process. The Met Office hold leadership roles in IPCC process via all levels in the organisation, including science leadership, expert scientific assessment, and technical support roles. Met Office scientist, Prof Helene Hewitt OBE, represented the UK as Coordinating Lead Author for Chapter 9 of the IPCC 2021 Sixth Assessment Report, examining the ocean, cryosphere and sea level change, including in the Arctic and polar regions54. Other contributions to IPCC from the UK derive from inputs to the assessment process itself: observational data, model output and peer-reviewed scientific papers. Results from these inputs are visible in both text and figures of the IPCC reports. For the Sixth Assessment Report, the Met Office contributed one author for the Synthesis report, two Coordinating Lead Authors, three Lead Authors, and one Review Editor, as well as many contributing authors and reviewers for the underlying reports.

3.6. Other multi-lateral collaborations

As part of a collaboration with the University of Leeds, the Met Office contributed to the 2021 assessment report on Arctic climate change55 by the Arctic Assessment and Monitoring Programme, a working group of the Arctic Council. For the first time, simulations using the UK’s Earth system model (UKESM1) were performed, which enabled results to be provided for the assessment of the impact of different short lived climate forcers on the Arctic climate and air quality. The results showed that future mitigation of air pollutants, which also act as short-lived climate forcers, will likely lead to significant benefits to regional air quality but could enhance warming rates over the Arctic, mainly from sulphur reductions. However, targeted reductions of certain sources of black carbon and methane could offset the enhanced Arctic warming rates by the mid-21st century.

3.7. UK international science leadership

Models developed by the Met Office and our UK partners are recognised as among the best weather and climate models in the world. Our climate models include representation of the atmosphere, the ocean, the sea ice and all the linkages between them. In that sense, they are the best tools available for investigating interactions between the changing Arctic and the UK.

51Further information on coupled atmosphere-ocean forecasting can be found here - https://www.metoffice.gov.uk/research/weather/ocean- forecasting/coupled-development

52 https://www.metoffice.gov.uk/research/weather/ocean-forecasting/ocean-waves

53 https://www.metoffice.gov.uk/weather/learn-about/weather/oceans/ocean-modelling-for-marine-forecasting

54 Hewitt et al., (2021): Ocean, Cryosphere and Sea Level Change

55 AMAP (2021). Arctic Climate Change Update 2021: Key Trends and Impacts. Summary for Policy-makers. Arctic Monitoring and Assessment Programme (AMAP), Tromsø, Norway. Pp16 www.amap.no/documents/doc/arctic-climate-change-update-2021-key-trends-and-impacts.-summary-for-policy- makers/3508

Met Office ARC0027

As the IPCC Sixth Assessment draws to a close, work will now start for the Seventh Assessment. One of the key contributions to the IPCC assessment process is the Coupled Model Intercomparison Project (CMIP). The Met Office is one of the modelling centres that has contributed to CMIP over many cycles. In CMIP7, Met Office is now one of the co-chairs of CMIP as well co-chair of the infrastructure panel and members of task teams. This level of leadership is allowing the Met Office to influence the direction of CMIP towards the next IPCC report.

April 2023

ANNEX

Further information on sea ice:

Sea ice and the cryosphere – The Met Office

Further information on sea level changes (past and future):

Further information on methane:

New methodology for understanding benefits of methane removal - Met Office
A Significant Advancement in Modeling the Global Methane Cycle - Eos
Methane is the second most important greenhouse gas after carbon dioxide56 and changes in its anthropogenic emissions have contributed 0.5 °C to the global mean temperature rise observed to date57. Methane also contributes to the formation of tropospheric ozone; when present close to the surface, ozone can harm human health and agriculture58.
Work carried out as part of the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP) shows that methane mitigation is important to consider alongside other short-lived atmospheric components such as ozone and aerosols – termed Near-Term Climate Forcers (NTCFs). For example, reducing aerosols to improve air quality causes increased surface warming and precipitation, and a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a major influence on the climate of western Europe.

Further information on the IPCC:

Climate Change 2021: The Physical Science Basis | Climate Change 2021: The Physical Science Basis (ipcc.ch)
Special Report on the Ocean and Cryosphere in a Changing Climate — (ipcc.ch)
The IPCC (Intergovernmental Panel on Climate Change) is the United Nations body for assessing the science related to climate change. IPCC provides policymakers with:

Scientific assessments on climate change
Impacts and potential risks
Adaptation options (how can we adapt to what is already changing)
Mitigation options (how can we prevent more changes from happening)

The Department for Energy Security and Net Zero fund Met Office participation in IPCC as authors, chapter scientists, reviewers and our work contributing.

56 IPCC (2021)

57 Ibid.

58 United Nations Environment Programme and Climate and Clean Air Coalition (2021). Global Methane Assessment: Benefits and Costs of Mitigating Methane Emissions. Nairobi, United Nations Environment Programme https://www.unep.org/resources/report/global-methane-assessment-benefits-and- costs-mitigating-methane-emissions

Met Office ARC0027

Figure 2: Comparison tide gauge observations (black) and satellite altimeter observations (grey) with sea-level projections for Reykjavik, Iceland (left) and Newlyn, UK (right), using the RCP2.6 (blue) and RCP8.5 (red) pathways. The shading indicates the 5th – 95th percentile estimate of the Palmer et al (2020) analysis, and the dotted lines the 5th – 95th percentile projections from IPCC SROCC. Unlike the UK, which will experience rising sea levels and where the uncertainty in RCP is a significant contribution to the overall uncertainty by 2100, Reykjavik (and other regions close to Greenland) may experience sea-level fall, with uncertainty being dominated by uncertainty in the model representations of key processes.60

60 Figure reproduced from Palmer et al (2020) Exploring the drivers of global and local sea‐level change over the 21st century and beyond Earth's Future, 8, e2019EF001413. https://doi.org/10.1029/2019EF001413