House of Commons - Protecting the Arctic - Environmental Audit Committee

Protecting the Arctic - Environmental Audit Committee Contents

2 The impact of climate change on the Arctic

6. The Arctic is a diverse region encompassing a seasonally-changing frozen ocean surrounded by continents where permafrost and tundra give way to vast expanses of boreal forest. Climatic conditions—temperature, precipitation, wind speeds and the prevalence of sea ice in coastal areas—vary at similar latitudes. For instance, average temperatures in January are -6.7°C in Tromsø, Norway but -28.1°C in Fairbanks, Alaska.[1] "The extent of snow, ice over water, and the dynamics of glaciers and ice streams vary greatly over short timescales and from place to place", whereas "the extent of permafrost and large ice sheets vary and change over decadal timescales and large areas".[2]

7. Distinguishing long-term impacts of climate change from natural variability requires data from many locations in the Arctic over many years and careful analysis. There is evidence, nevertheless, that the Arctic is warming twice as fast as anywhere else on the planet, with average warming north of 60°N of 1-2°C since the 1960s.[3] Evidence from lake sediments, tree-rings and ice cores suggest that temperatures in recent decades have been higher than at any time in the past 2,000 years.[4]

8. Henry Bellingham MP, the then Foreign and Commonwealth Office Parliamentary Under Secretary and lead Minister responsible for the Arctic, told us that the Government believed that climate change "poses the biggest single threat to the Arctic environment".[5] The effects of climate change are already being felt in the Arctic, and "are likely to continue more profoundly than perhaps anywhere else on Earth".[6] The ice-cap retreating was not the only consequence of climate change in the Arctic. The extent and duration of snow cover has decreased, largely as a result of snow melting earlier in the spring.[7] Precipitation has increased by 80% over the last century, with much of the increase falling as rain.[8] Temperatures in the permafrost have risen by up to 2°C over the past three decades.[9] Glaciers are melting.[10] Rivers' discharge to the sea has increased, reducing the salinity and density in the North Atlantic. Ice cover on lakes and rivers is breaking up earlier than previously observed.[11]

9. The biggest change, however, is in the size of the Arctic ice-cap. Sea-ice has been declining at least since satellite records began[12] and is one of the most serious consequences of global warming.[13] The rate of decline is currently about 3% per decade for the maximum winter extent (March) and about 10-12% per decade for the minimum summer extent (September).[14] The six lowest September ice extents have occurred in the last six years,[15] including September 2012 which was the lowest ice extent on record (Figure 1, page 10).[16]

10. The latest biennial Arctic Report Card notes that "there are now a sufficient number of years of data to indicate a shift in the Arctic Ocean system since 2006 ... characterised by the persistent decline in the thickness and summer extent of the sea ice cover, and a warmer, fresher upper ocean".[17] Warming in the Arctic was not just as a result of increased CO2 emissions, but also increases in other greenhouse gasses such as methane and black carbon aerosols, and a decline in cooling sulphate aerosols.[18] While most emissions driving climate change in the Arctic do not primarily originate in the Arctic, changes there will have impacts for the global climate, giving everyone a clear stake in the Region's future.[19]

11. Increased precipitation, shorter and warmer winters, and substantial decreases in snow and ice cover are likely to persist for centuries.[20] Even with the most "aggressive mitigation scenarios", there would still be a significant loss of Arctic sea ice by the end of the century.[21] Whereas increasing concentrations of greenhouse gasses are "projected to contribute to additional Arctic warming of about 4-7°C over the next 100 years".[22] Professor Tim Lenton of the University of Exeter told us that the current situation met the Intergovernmental Panel on Climate Change's definition of "dangerous change".[23] Professor Peter Wadhams of the University of Cambridge told us that all the environmental trends of air temperatures, changes in the ocean, and changes in the sea-ice were heading in the "same direction", and that "the direction is very clear: We are going to get into a ghastly situation for the planet at some point and whether it is happening next year or it is going to take a few decades is the only question".[24] John Nissen of the Arctic Methane Emergency Group linked extreme weather patterns in recent years to a "decrease in stability as the Arctic warms relative to the rest of the planet".[25] A reduction in emissions, however, "would allow ecosystems and human societies as a whole to adapt more readily, reducing overall impacts and costs",[26] and is necessary to limit further global warming and avoid more severe effects in the Arctic and across the globe.[27]

IMPACT ON UK WEATHER FROM CLIMATE CHANGE IN THE ARCTIC

12. Climatic change in the Arctic is affecting the UK's weather. Professor Wadhams told us that the open water left by the retreating ice in summers could lead to "radically changed" weather patterns around the northern hemisphere.[28] Britain was warming more slowly when compared with the rest of continental Europe as the decrease in the thermo-haline circulation meant that less heat was being brought to Britain by the Gulf Stream.[29] Professor Lenton told us that the loss of ice around Finland and the North of Norway in the Barents and Kara Seas in winter in particular was "correlated with so-called blocking events and the extreme cold winters in Europe". These changes we would "see on a seasonal time-scale and can have quite big impacts".[30]

13. The Government's Climate Change Risk Assessment, published in January 2012, noted a potential benefit in terms of "shorter shipping routes and reduced transportation costs due to less Arctic ice" (paragraph 107), but did not note any specific risks to the UK over the coming years.[31] Professor Julia Slingo, Chief Scientist at the Met Office, believed that this may be because the Risk Assessment was built on models developed in the early part of this decade which did not have the "sophistication of the Arctic sea-ice modelling that we have now". Professor Slingo agreed that the depletion of ice could "plausibly impact on our winter weather, and lead to colder winters over northern Europe" but it was "only one of a number of factors, ... it is not a dominant driver of winter weather, particularly over the UK".[32] The UK has had a number of years with low rainfall[33] and Professor Slingo told us that she was concerned that if we continue to have a sequence of cold winters this could be "damaging, even with wet summers going alongside them" because the replenishment of aquifers generally occurs through the winter.[34]

Effects on wildlife

14. The Arctic region is one of the last true wildernesses on Earth. The impact of humans has been limited to date and unique ecosystems have developed there with a number of endemic species such as the polar bear.[35] Many globally significant populations of animals can be found in the Arctic, including over half of the world's shorebird species, 80% of goose populations, several million reindeer,[36] beluga whales and narwhals.[37] Sea-ice is an important element in the Arctic ecosystem for some species,[38] from bacteria and unicellular algae on the underside of the ice to large mammals such as the polar bear and ringed seals.[39]

15. Half of the marine area of the Arctic is covered by seasonal ice in winter, turning into open water in the summer.[40] This drives large migrations,[41] meaning that a significant proportion of Arctic biodiversity is shared with other parts of the world, especially the UK.[42] The cold waters, high in nutrients, attract large numbers of migratory[43] grey and humpback whales and harp and hooded seals.[44] 15% of the world's migratory bird species spend their breeding season in the Arctic.[45]

16. Arctic ecosystems appear to be particularly vulnerable to the effects of climate change,[46] although they are still poorly understood and long-term data are sparse.[47] For instance, of the 19 sub-populations of polar bears, there were only reliable data to assess the trend in numbers of seven.[48] The Arctic Council's Biodiversity Assessment, due to be published in Spring 2013, aims to provide baseline data on Arctic wildlife. Nevertheless, disappearing sea ice and changing water temperatures were already "having a profound impact on many species".[49] A recent Arctic Council assessment found that the impact of climate change on marine animals and birds was likely to be "profound".[50] There are fewer polar bears because they are finding it more difficult to hunt for food in the south of their ranges.[51] Walruses are also being forced to hunt in deeper water, where access to food is much more difficult.[52] Ecosystems would be affected by permafrost degradation, with existing lakes drained but also new wetlands created.[53] Herds of reindeer have declined by one-third since the 1990s as their access to food sources, breeding grounds, and historic migration routes have been altered.[54] Precipitation was increasingly falling as rain during the winter, which created an ice-crust over the snow, affecting grazing animals.[55] Increased 'greening' of the land is affecting the animals it supports.[56] Species specifically adapted to the Arctic climate are especially at risk, including many species of moss and lichens, lemmings, voles, arctic fox and snowy owl.[57] Increasing levels of ultraviolet radiation in the Arctic due to stratospheric ozone depletion is also a risk to wildlife.[58] The impact of climate change on biodiversity could be magnified by other factors such as the presence of contaminants, habitat fragmentation, industrial development and unsustainable harvests.[59]

17. Some Arctic species often have very long lifespans and slow reproduction rates,[60] and "relatively simple ecosystem structures and short growing seasons limit the resilience of the natural environment, and make environmental recovery harder to achieve".[61] This makes the Arctic environment "highly sensitive to damage" of a kind that would be likely to have long-term impacts.[62] Climate change could cause a mismatch between the timing of reproduction of certain species and food availability.[63]

18. In the longer term, the composition of Arctic ecosystems will change. There will be a northward movement of some species, including some fish.[64] As the Arctic become ice-free in summers, new species are expected to take advantage of the high summer light levels in the upper layers of the oceans.[65] Migrating invasive species might displace native Arctic inhabitants.[66]

19. A reduction in sea-ice and rising sea levels could increase coastal erosion as higher waves and storm surges reach the shore.[67] Two-thirds of the Arctic coastline is protected by ice, and melting land-fast ice could lead to rapid erosion.[68] This will affect people as well as animals. Habitat changes, chemical pollution, overfishing, land use changes, population increases and cultural and economic changes are amplifying the impacts of climate change on the health and wellbeing of Arctic communities.[69] Many indigenous peoples depend on hunting Arctic mammals, herding reindeer and fishing, not only for food, but as part of their cultural and social identity.[70] Changes in species' ranges and availability present "serious challenges to human health and food security and possibly the survival of some cultures".[71]

Tipping points

20. These climate change effects on the Arctic might be exacerbated and accelerated if 'tipping points' are breached—these are points at which rapid changes take place out of proportion to the amount of climate change driving them as a result of 'positive feedbacks'.[72] They could lead to rapid or longer term changes depending on the climate system involved.[73] Some 'tipping points' may be reversible and others may not.[74] We explore the likelihood of such tipping points below.

THE RETREATING ARCTIC ICE-CAP

21. The Arctic Ocean ice-cap has a seasonal cycle, reaching its maximum extent in March and minimum extent in September.[75] Since the 1950s the summer extent of ice has been retreating year on year, at a rate of 4% per decade.[76] But since the early 2000s this rate has increased to 10-12%.[77] The amount of "older, thicker multi-year ice continues to decrease"[78] and "modelling indicates that the total area of ice may be more variable year to year as more areas of ice become susceptible to melting completely during the summer".[79] Alongside rising temperatures, there are a number of other factors forcing this retreat that are still not fully understood, including climate-driven changes in atmospheric and ocean circulation patterns and a reduction in summertime cloud levels.[80]

22. The retreating ice-cap represents a potential tipping point because the heat of sunlight is more readily absorbed when falling on water than on ice (ice has a higher 'albedo' than water), causing further warming and further ice retreat in turn. Professor Wadhams calculated that the open water left by the retreating ice-cap warms up to 4-5°C during the summer, delaying the onset of autumn freezing and warming the seabed, helping to melt offshore permafrost.[81] Faster wind speeds and bigger waves were also a consequence of larger stretches of open water, which break the ice up into floes and increase the melt rate.[82] The Arctic Methane Emergency Group were concerned that "the rate of warming of the Arctic could double or even triple, once the Arctic Ocean is ice-free in September. And it could double again, once the ocean is ice-free for half the year".[83]

23. Professor Lenton believed that there was some evidence that sea-ice retreat may have already passed a tipping point. The last six summers had the six lowest recorded ice extents, with a "step up in the amplitude of the seasonal cycle of sea-ice variability", which could "perhaps [be] seen as passing some kind of tipping point or threshold". But he recognised that there was also "plenty of argument about whether there is really a tipping point", depending on whether a loss of summer ice would prevent ice reforming in winter.[84] Professor Wadhams told us that once the summer sea-ice disappears the oceans would warm up and their structure would change to the point where if the climate cools again it would be difficult for ice to form again. He did not think that there would be an "oscillation" back and forth; it would be a "one-way street".[85] John Nissen of the Arctic Methane Emergency Group believed that "the imminent collapse of Arctic sea-ice poses a new emergency situation, ... it threatens an irreversible transition towards abrupt and catastrophic climate change".[86] However, the Met Office believed that its modelling suggested that Arctic sea-ice loss would be "broadly reversible if the underlying warming were reversed".[87]

24. In recent months, further research results on the volume (rather than extent) of the ice have added weight to the possibility of approaching ice-free Arctic summers. Although the extent of ice had been reliably measured since the 1970s,[88] the thickness of the ice-cap was more difficult to measure because it cannot be easily observed from satellites.[89] Measuring the thickness had been undertaken using submarines, which had showed that the ice-cap had reduced by about 45% since the 1970s.[90] The Pan-Arctic Ice-Ocean Modelling and Assimilation System (PIOMAS), at the University of Washington,[91] calculated in 2011 that the volume of ice in Septembers had decreased by 75% since 1979.[92] Professor Wadhams believed that the data was "held in high regard" by many experts in the field.[93] He and John Nissen took issue[94] with Professor Slingo who, giving evidence in March 2012, told us that "there is a decline in ice ... but to say we have lost 75% of the volume is inconsistent with our assessments". She was looking forward to new measurements from the CryoSat-2 satellite, which she believed would give a better sense of the thickness of the ice.[95]

25. There were different estimates of when the Arctic would become ice-free[96] in summer, depending on what model was employed.[97] Professor Lenton told us in February that it was "highly unlikely" that the Arctic could be ice-free in the next few summers. His "best guess" was "sometime in the 2030s, maybe 2040s".[98] Professor Wadhams believed that, taking account of the thinning of the ice-cap, "it is very much quicker, perhaps needing only 4 years".[99] He believed that the rate of retreat and thinning had "greatly exceeded" the predictions of most models, except PIOMAS.[100] The Arctic Methane Emergency Group's extrapolation of data on the volume of summer ice from the PIOMAS model, following an exponential reduction trend-line, suggested that Septembers would be ice-free from 2015.[101]

26. On the other hand, Professor Slingo told us that a recently completed Met Office assessment (which we saw in draft in the course of our inquiry and was subsequently published in September 2012)[102] had indicated that the earliest date at which the Arctic would be ice-free during the summer would be between 2025 and 2030, and "certainly not in the next few years...".[103] The climate models on which these predictions are based were "capable of capturing the observed decline in ice extent", however they "do not generally show ice loss at the current rate until later in the 21st century" and "low ice events", such as observed in 2007 and 2012, were "unusual in the models, occurring only once in every 100 years". The Met Office assessment noted that others' projections of a seasonally ice-free Arctic by as early as 2013 was "based on extrapolating model output [and] have to be viewed with scepticism". It noted that there were "plausible mechanisms" for more rapid change in the Arctic than current models predict, but "further observations are required to establish if any of these mechanisms are occurring". The Met Office concluded that an ongoing assessment of the likelihood of rapid change was required, taking account of the "constantly developing evidence".[104] Professor Slingo told us that as the Arctic warms and the sea ice becomes thinner, "you do expect the extent … will become more volatile".[105] Understanding of "how the Arctic Ocean takes up heat, and how that then affects the sea ice behaviour" was still being developed, but she believed that the models used were "capturing the trend and the volatility quite well", although they would not capture particular events (such as El Nino) which could drive Arctic circulation changes.[106]

27. Since our evidence sessions, some preliminary analysis of data from the CryoSat-2 satellite was broadcast in August 2012,[107] which supported predictions that the Arctic would become ice-free during the summer sooner rather than later. The European Space Agency's CryoSat-2 satellite was launched in 2010 to monitor the changes in the thickness of the Arctic sea-ice and the ice sheets on Greenland and Antarctica.[108] Professor Seymour Laxon of the Centre for Polar Observation and Modelling—leading the analysis of the Cryosat-2 data—told us that preliminary analysis of the Cryosat-2 data combined with that of NASA's ICESat satellite, showed that between 2003 and 2011 the volume of summer sea ice in October/November had reduced from ~14,000 to ~7,000 cubic kilometres (a 50% decrease). Averaged over the period, up to 900 cubic kilometres of summer sea-ice was lost a year.[109] He told us that these data "suggest a decrease ... at least as large as that simulated by PIOMAS, and possibly higher".[110] The Met Office believed that evidence pointed to weather patterns having influenced the rapid loss of sea ice over this summer. The changes in sea-ice volume shown in recent estimates "only extends over a few years" and was not "representative of a long term trend".[111] Although we recognise the Met Office's[112] and Professor Laxon's concerns about extrapolating trends in volume loss into the future,[113] a simple calculation based on this data points to the Arctic becoming ice-free in the summer within a decade.[114]

28. There is growing evidence that the damaging effects of climate change are being felt strongly in the Arctic. The ice-cap is retreating. In September 2012 it had reached its lowest extent since satellite records began, and new evidence shows that it is also thinning faster than previously thought. The general view that the ice-cap is not at risk of a summer collapse in the next few years may need to be revisited and revised. A collapse not only threatens the unique ecosystems there, but would have damaging ramifications for regional and global climate.

PERMAFROST THAWING

29. Permanently frozen ground, or permafrost, covers 10.5 million square kilometres of the Arctic.[115] Thawing permafrost—on land or potentially in the shallow seas—could represent a tipping point. 'Positive feedback' would come from organic matter contained within it decomposing and generating heat and releasing methane—a greenhouse gas which would drive further permafrost thawing.[116] Methane is a relatively short-lived greenhouse gas[117] but has a warming effect 72 times more than CO2 over 20 years.[118]

30. John Nissen of the Arctic Methane Emergency Group told us that "methane is a real problem and it is never really addressed". He believed that "because of its potency as a greenhouse gas, we only need release of 1% of ... the Arctic potential methane—that is about 35 billion tonnes—and that would triple the current rate of global warming". He believed that "it is difficult to see how civilisation could survive such a thing".[119]

31. Professor Lenton told us, however, that from the Hadley Centre's model their "best estimate is we may get 0.1°C of extra warming at the end of the century from the loss of methane from the northern high latitudes".[120] He believed that the present lack of evidence to the contrary meant that methane released from permafrost "is not on the list of tipping elements", but that different regional areas of permafrost might be at risk at different times.[121] The Yedoma area of Siberia was a particularly "rich" store of carbon that could "undergo self-sustaining collapse, due to an internally generated source of heat released by bio-chemical decomposition of the carbon, triggering further melting in a runaway positive feedback", but 9°C of regional warming would be required to pass such a tipping point.[122]

32. Methane released from permafrost on land requires bacterial and microbial action, and is sensitive to temperature rise.[123] Under the sea, existing stores of methane could be abruptly released.[124] An increase in methane had been linked to mass extinctions in the past[125] but, Professor Lenton told us, that methane release had been over "thousands and tens of thousands of years".[126] Professor Wadhams believed that the summer retreat of the ice from the Arctic continental shelves[127] was allowing the surface layer of the ocean to warm up and "bringing temperatures of up to 5°C right down to the seabed".[128] This was accelerating the melt of offshore permafrost and releasing methane trapped in methane hydrates (comprising methane water and ice).[129] Large plumes of methane were appearing "all over the summer Arctic shelves" giving "a very big boost to global warming".[130] John Nissen of AMEG told us that 50 gigatonnes of methane were trapped in the East Siberian Arctic Shelf, which if released would raise atmospheric methane levels eleven or twelve times, causing "abrupt and catastrophic climate change within a few decades".[131]

33. Professor Slingo differentiated between the methane hydrates in the Arctic shelves and the "deep hydrates that would take millennial timescales to destabilise". She believed that based on modelling estimates "we are not looking at catastrophic releases of methane", although it was "still very early science". She thought that there was uncertainty about how far heating of the upper level of the ocean could dissipate downwards in the water column, and that "there is still a big debate as to how much the actual continental shelf itself will warm".[132] Apart from one or two regions, observed increases in sea-floor temperatures had at the most been only about 0.1^oC.[133] She also told us that research indicated that where there was methane coming out of the continental shelf in those one or two areas, "there is a general consensus that only a small fraction of methane, when it is released through this gradual process of warming of the continental shelf, actually reaches the surface".[134] John Nissen and Professor Wadhams disputed that view.[135] The Arctic Methane Emergency Group were also concerned that if methane hydrate became unstable it could pose a hazard to oil drilling.[136]

34. There is a range of views on the rate at which methane is being released in the Arctic as a result of climate warming there, and whether and how soon that might constitute a tipping point. Given its particular potency as a greenhouse gas, however, there is a potentially serious risk for global climate change from any significant methane release in the Arctic. We discuss below whether such risks warrant specific interventions (paragraphs 46-55).

THE GREENLAND ICE-SHEET

35. Most of Greenland is permanently covered in ice.[137] Unlike with sea ice, any reduction in the Greenland Ice-sheet mass contributes directly to global sea levels.[138] The ice sheet contains approximately 2.85 million cubic kilometres of freshwater,[139] equivalent to 7 metres of global sea level rise.[140] Up until the 1990s only a tiny proportion of this overall volume melted each year, and much of that was compensated for by fresh snowfall on Greenland.[141] Recently, however, the rate of ice-sheet loss has accelerated as a direct result of the warming Arctic climate.[142]

36. Measurements in 2009 show there have been quite large and rapid changes in surface melting and ice discharge.[143] Measurements by NASA satellites showed that nearly 97% of the Greenland ice-sheet surface had thawed at some point during July 2012.[144] The retreat of the summer sea ice from around Greenland warms up Greenland, and means that the Greenland ice-sheet melts more rapidly.[145] The contribution from the Greenland ice-sheet melt now is "about as great as all the rest of the retreating glaciers in the world put together",[146] and the current net loss represents enough water to supply more than one billion city-dwellers.[147] Professor Wadhams believed that this will mean that "over the next century the rise in global sea levels will probably be greater than predicted by [the Intergovernmental Panel on Climate Change] ... quite a lot more than one metre instead of less than 70 centimetres".[148]

37. Professor Lenton pointed out that predictions of what degree of future global warming would result in an irreversible retreat of the ice-sheet ranged from between 0.7°C and 6°C. There could be "multiple stable states" for the ice-sheet volume and "multiple tipping points", starting with a retreat of the ice-sheet onto the land, but there was insufficient information to prove that this process was already underway.[149] Other research indicated that the original ice sheet volume could only be regained if the losses were no greater than 10-20%.[150]

38. Satellite images showed an area twice the size of Manhattan had broken away from the Petermann glacier in July 2012.[151] A recent Danish research project suggests that the ice-sheet may be melting in "spurts", making global sea rise difficult to predict.[152] More generally, the interactions between ocean, snow, ice and the atmosphere are not fully understood, making predictions in this area difficult.[153]

THE THERMO-HALINE CIRCULATION

39. The Atlantic thermo-haline ocean circulation acts as a conveyor belt bringing warm water to the Arctic and transporting cooler water back to the tropics. It is composed of wind-driven surface currents (in this case the Gulf Stream) and deep ocean circulations. In the Arctic, water sinks in the Greenland and Labrador Seas and then flows southwards.[154]

40. Some evidence points to additional freshwater from ice-melt reducing the salinity of the Arctic Ocean[155] which, coupled with temperature changes, is slowing down the circulation.[156] The Greenland Sea sinking current had "diminished very significantly" in the last 10 years because ice-formation had stopped there (ice-formation was needed to enhance the density of the [remaining] water and help it sink).[157] Professor Wadhams told us that previously a "see-saw" was evident, whereby if the Labrador Sea convection got weaker, the Greenland Sea convection got stronger, and vice-versa. However, he told us that there was some evidence that there was a weakening of both sinks, leading to the whole circulation weakening.[158] A change in circulation patterns could represent a tipping point,[159] resulting in changed regional and global climate.[160]

41. However, any change to the circulation "was a slow process [and was] not going to change things rapidly".[161] Professor Lenton explained that currents could shut off potentially from one year to the next, but "to truly see the consequences climatically play out, ... much longer time scales are involved, up to centuries".[162] Professor Slingo did not think that there would be "very large changes" in the thermo-haline circulation "within the next century".[163] Professor Lenton believed that such predictions were based on assumptions that the circulation patterns were stable, but that these might need to be revisited to reflect recent work suggesting that there may be "multiple states" for the Atlantic circulation. He believed that rather than a total collapse of the thermo-haline circulation, a relatively near-term collapse of the Labrador Sea convection could result in the overall weakening of the wider regional thermo-haline circulation.[164]

42. John Nissen believed that a switching off the thermo-haline circulation might reduce warm waters flowing into the Arctic, but he accepted that this would be a disaster for the UK's climate.[165] Professor Wadhams told us that this would not be sufficient on its own to "bring back the ice".[166]

BOREAL FORESTS

43. The lengthening of the snow-free season is encouraging shrub growth in the tundra, and also 'greening' of the boreal forest further south.[167] Whilst a greater amount of vegetation is likely to increase carbon uptake from the atmosphere, the reduced reflectivity of the land surface (albedo) is likely to outweigh this, causing further warming.[168] Some models project that by 2100 the tree-line will have advanced north by as much as 500 km, resulting in a loss of 51% of the tundra habitat.[169] However, Professor Lenton did not expect this to be a tipping point.[170]

EARLY WARNING ON TIPPING POINTS

44. Although there is some information on the likelihood of crossing some Arctic climate tipping points, "substantial uncertainty remains"[171] and there is "still a long way to go in correctly identifying tipping points and assessing their proximity".[172] Professor Lenton told us that it would be difficult to develop a suite of early warning signs for changes in the Arctic because there was inadequate monitoring.[173] Professor Wadhams told us that although "there are disagreements about the speed at which changes are happening and will happen", the "direction of them I think everybody is agreed on".[174] Similarly, Professor Lenton believed there was consensus that climate forcing is going to trigger some tipping points within the next century, and he could not rule out that some tipping points may already have been crossed.[175]

45. In the absence of urgent action on climate change, there may be a number of tipping points in climate-driven systems in the Arctic, which threaten to rapidly escalate the danger for the whole planet. A collapse of summer sea-ice, increased methane emissions from thawing permafrost, runaway melting of the Greenland ice-sheet, and a collapse of the thermo-haline circulation, may all be approaching in the Arctic and will have disastrous consequences for global climate and sea levels. These together comprise a wake-up call to reinvigorate efforts to tackle climate change. A lack of consensus on precisely how fast any tipping points are approaching in the Arctic should not be used as an argument for inaction; rather it demonstrates the need for continued and sustained research to underpin further action. The UK makes an essential contribution to Arctic science, which we discuss in Part 4, and we look to the Government to continue supporting Arctic science as a key component of its work on climate change.

Potential interventions

46. We examined potential interventions that might yield positive outcomes on Arctic climate change in the near term—'geo-engineering' and reducing black carbon.

GEO-ENGINEERING

47. The Arctic Methane Emergency Group called for urgent intervention by governments to avoid tipping points being reached.[176] Given that there was "nothing in nature that can come to our help",[177] the Group called on governments to "intervene by cooling the Arctic, principally by using geo-engineering techniques; ... [these] techniques have natural analogues which suggest that they should be safe and effective ... if their deployment [avoided] unwanted side-effects".[178] They called for the urgent application of a combination of three geo-engineering technologies: spraying aerosols into the stratosphere to reflect sunlight away, cloud brightening using salt-spray also to increase reflection, and cloud removal to allow heat radiation into space. They also called for the use of methane capture technologies such as 'methane mats'.[179]

48. There was some differences of view in the evidence we received about whether geo-engineering in principle was a credible long-term solution. Professor Wadhams saw geo-engineering as a "sticking plaster" until the forcing of climate warming is tackled,[180] and John Nissen believed that the costs would be "hundreds of millions rather than many billions per year".[181] On the other hand, if such applications were subsequently stopped, the planet would warm up more quickly to where it would have been without geo-engineering, rather than the gradual warming otherwise expected.[182] Professor Lenton told us that "if you go down that path, you are committing not just the next generation but tens of generations potentially to keep doing that". He believed that it was important that economic modelling of geo-engineering costs included the "possible damages or risk factors" and a "critical look at those very few existing studies as to whether they have really quantified [them]".[183]

49. There was consensus that even if geo-engineering techniques could be used, they first required further development and were not ready for immediate deployment.[184] Professor John Latham of University Corporation for Atmospheric Research, Boulder, USA and colleagues believed that as "key climate processes remain poorly understood, existing models are unable to provide a reliable means of quantifying the magnitude of changes that may occur".[185] Professor Lenton told us that advocates of geo-engineering techniques who suggest "meddling with Arctic cloud cover", do not necessarily realise that during the dark Arctic winter clouds generally warmed rather than cooled the atmosphere.[186] Overall, due diligence was needed to understand all the consequences of such techniques,[187] including impacts on rainfall,[188]weather patterns[189] and reduced incoming sunlight.[190] Professor Latham and colleagues believed that any geo-engineering scheme "needs to have its concepts rigorously challenged and then undergo rigorous, peer reviewed testing and scrutiny before any consideration of its use takes place".[191]

50. Geo-engineering techniques for the Arctic at present do not offer a credible long-term solution for tackling climate change. Further research is needed to understand how such techniques work and their wider impacts on climate systems. In the meantime, therefore, we remain unconvinced that using 'technical fixes' is the right approach and efforts should not be diverted from tackling the fundamental drivers of global climate change.

BLACK CARBON

51. A more realistic and lower-risk intervention would be to tackle black carbon. Black carbon is a component of soot which arises from the incomplete combustion of fossil fuels and organic matter.[192] Major sources of black carbon include diesel engines, commercial and domestic burning, domestic wood and biomass burning, and land or agricultural burning.[193] Soot from fires in boreal forest fires, which have increased in frequency, could also be a source.[194] The depositing of these microscopic dark particles onto snow and ice reduces the albedo effect (allowing the absorption of more sunlight),[195] which is having a greater effect in the Arctic than black particles in the atmosphere.[196]

52. Professor Lenton told us that there was a lack of an "evidence base to tie down how strong the black carbon warming effects in the Arctic region are" but he thought that it made a "significant contribution".[197] Professor Wadhams thought that black carbon was probably the third biggest contributor to warming in the Arctic, after CO2 and methane.[198] It had been estimated that a steep increase in black carbon and a decline in reflective sulphates had together accounted for up to 70% of Arctic warming since 1976.[199] Research was continuing to establish the sources of black carbon,[200] but it was estimated that more than half the black carbon that reaches the Arctic originated in the EU.[201] Ed Dearnley from ClientEarth told us that the greatest potential for black carbon reductions was from China, Russia and the EU.[202]

53. In contrast to CO2 and methane, black carbon has a very short atmospheric lifespan and ClientEarth believed that reducing emissions of black carbon has the "potential to deliver rapid climate change mitigation". It believed that "reducing black carbon and other short-lived climate 'forcers' could reduce regional warming in the Arctic by approximately two-thirds over the next 30 years".[203] Professor Lenton believed a good case for tackling black carbon could be made based on the health benefits alone, but tackling black carbon could make a "measurable difference" to the Arctic against a lack of progress on the "big CO2 problem".[204]

54. ClientEarth suggested a number of actions that the Government should take to tackle black carbon, including strengthening of the Gothenburg Protocol.[205] The Protocol sets national emissions ceilings for a variety of pollutants.[206] The Protocol was revised in 2012 and for the first time introduced an emissions reduction target for fine particulate matter ('PM2.5').[207] The UK agreed a PM2.5 reduction target of approximately 30% by 2020 (from a 2005 baseline), which Defra believed was "substantial".[208] Defra told us that as black carbon is a component of particulate matter, reductions in emissions of PM2.5 will also reduce black carbon.[209] Existing targets in the UK and EU for particulate matter could also contribute themselves to reducing black carbon emissions. Alan Andrews of ClientEarth told us that "we just need to make sure [air pollution legislation] is enforced properly".[210] We examined the Government's efforts to improve air quality in a 2011 Report, and found that the UK is still failing to meet European targets for safe air pollution limits across many parts of the country and that the step change called for has not happened. We recommended, among other things, that a Ministerial Group is set up to oversee delivery of a new cross government air quality strategy, a national framework of low emissions zones is set up, and a public awareness campaign is launched.[211]

55. There are significant risks of increased depositing of black carbon on Arctic snow and ice as new commercial opportunities in shipping, resource extraction and other industrial activities opened up.[212] ClientEarth believed that international shipping was a "comparatively poorly regulated sector for particulate matter emissions" and that black carbon and other emissions from shipping in the Arctic "may increase by as much as a factor of two or three by 2050 unless control measures are put in place".[213] Alan Andrews told us that it was difficult to get agreement at the International Maritime Organization on environmental protection as it had a "huge number of competing interests" from nations with very large shipping interests.[214] There is no international regulation of greenhouse gasses from ships and shipping is not included within the EU Emissions Trading System. In January 2012 the EU launched a consultation to gather ideas on options to reduce emissions from shipping,[215] in line with its commitment to include emissions from shipping within the existing EU reduction commitment if international action was not agreed.[216] The risks to ecosystems from the effects of Arctic warming and potential climate tipping points that we have discussed in this Part, together with the additional risks from energy and shipping development which we discuss in Part 3, make it imperative that any readily available opportunity to make a difference is grasped. Tackling emissions from shipping is such an opportunity, and the Government must engage positively with the EU's efforts to look at options for doing this. We examine in Part 4 the scope for the Government to influence other countries' efforts to reduce black carbon.