AMAP Conference the Arctic As a Messenger for Global Pollution 2011

AMAP Conference The Arctic as a Messenger for Global Pollution 2011

THE RECENT TRAJECTORY OF ARCTIC CLIMATE

John E. Walsh University of Alaska, Fairbanks, Alaska, USA

In the period since the completion of the Arctic Climate Impact Assessment in 2004, the Arctic has experienced its highest temperatures of the instrumental record, even exceeding the warmth of the 1930s and 1940s. Recent paleo-reconstructions also show that Arctic summer temperatures have been higher in the past few decades than at any time in the past 2000 years. The seasonality and location of the maximum warming indicates that the Arctic may have passed the threshold at which absorption of solar radiation during summer limits ice growth the following autumn and winter, initiating a feedback that leads to a substantial increase in Arctic Ocean surface air temperatures. A secondary maximum of warming during springtime is consistent with an earlier loss of terrestrial snow cover in recent years. The spatial pattern of the near-surface warming shows the signature of the Paciﬁc Decadal Oscillation (PDO) in the Paciﬁc sector as well as the inﬂuence of a dipole-like circulation pattern in the Atlantic sector.

The Arctic Ocean has experienced enhanced oceanic heat inﬂows from both the North Atlantic and the North Paciﬁc. The Paciﬁc inﬂows appear to have played a role in the retreat of sea ice in the Paciﬁc sector of the Arctic Ocean. The association between sea ice and enhanced North Atlantic layer heat content is complicated by the strong halocline above the Atlantic layer, so the role of the Atlantic water heat anomalies is still under investigation. Nevertheless, the Atlantic water heat inﬂux to the Arctic Ocean appears to be characterized by increasingly warm pulses separated by brief respites of cooling, as occurred in 2008-2009.

WHAT DOES THE FUTURE HOLD FOR SNOW AND PERMAFROST IN THE ARCTIC AND WHY DO WE CARE? – SWIPA SNOW AND PERMAFROST CHAPTERS

Margareta Johansson1, 2, Terry V. Callaghan2, 3, Oleg Anisimov4, Ross Brown5, Hanne H. Christiansen6, Arne Instanes7, PavelYa Groisman8, Niklas Labba9, Vladimir Radionov10, Vladimir Romanovsky11 and Sharon Smith1

Current trends

Permafrost warming, typically between 0.5 and 2 °C, generally continues in the Arctic. New data show permafrost warming has continued over the past decade in the eastern and High Arctic regions of Canada, in the northern Nordic regions and Svalbard, in the Russian European North and in western Siberia, although there was a reduced rate of warming during the past decade in western North America. Areas with warm, ice-rich permafrost showed lower warming rates than areas with cold permafrost or bedrock. An updated assessment of trends in active-layer thickness (ALT) over the past two decades shows ALT has increased at sites in Scandinavia and the Russian Arctic, but surprisingly, increases in North America have only been reported from the interior of Alaska, and only over the past ﬁve years.

Projected future trends

Snow cover duration is projected to decrease by 10% to 20% over most of the Arctic by 2050. The smallest decreases are found over Siberia (< 10%) and the greatest losses over Alaska and northern Scandinavia (30% to 40%). The earliest and largest future decreases in snow cover duration and accumulation are projected to occur over coastal regions in agreement with observed trends. Slight increases in maximum snow accumulation are projected. Increases of 0 to 15% are projected over much of the Arctic with the largest increases (15% to 30%) over the Siberian sector. Rain-on-snow events are projected to increase in frequency and areal extent over all regions of the Arctic over the next 50 years.

New projections of ground temperature throughout the pan-Arctic area suggest that by the end of the 21st century, late-Holocene permafrost in the Northern Hemisphere may be actively thawing at the southern boundary of the permafrost region and some Late Pleistocene permafrost could start to thaw at some locations. Regional models project that by the end of the 21st century, the upper 2 to 3 metres of permafrost will thaw over 16% to 20% of the area currently underlain by permafrost in Canada and that there will be widespread permafrost degradation over about 57% of the total area of Alaska. In Russia, increases in ground temperature of 0.6 to 1°C by 2020 have been projected.

Eﬀects of ongoing and projected changes in snow and permafrost

Changes in snow accumulation and melt, evaporation, and runoﬀ as well as short- and longterm water storage changes are expected to dramatically change the hydrological regime of the Arctic. Also, the hydrology will change due to thawing permafrost resulting in either drying or waterlogging. The net hydrological balance that determines ecosystem processes and biogeochemical cycling is hence uncertain.

Since the publication of the Arctic Climate Impact Assessment (ACIA, 2005) and the Fourth Assessment of the Intergovernmental Panel on Climate Change (Solomon et al., 2007), knowledge about the preservation and activity of life in permafrost has increased. Furthermore, recent work has shown that carbon pools in permafrost soils are much larger than previously recognized: around 1400 to1850 gigatonnes (Gt) is located in terrestrial permafrost regions.

Although model projections suggest that tundra is likely to remain a weak sink of atmospheric carbon dioxide (CO2), there are great uncertainties and the emissions of methane (CH4) and nitrous oxide (N2O) (much stronger greenhouse gases than CO2) from permafrost areas have the potential to substantially increase radiative forcing.

In addition, Arctic coastal seas underlain by subsea permafrost host an extremely large carbon pool: the Arctic continental shelf could contain around 1300 Gt of carbon, of which 800 Gt is CH4, some of which could be available for sudden release under the appropriate conditions. A release of only 1% of this reservoir would more than triple the atmospheric mixing ratio of CH4, potentially triggering abrupt climate change.

While thawing permafrost is likely to provide a positive feedback to climate change through increased greenhouse gas emission, there is some evidence that changing snow cover in spring is a result of the positive feedback due largely to a decreasing albedo.

FROM THE CRYOSPHERE TO THE CLIMATE SYSTEM – SYNTHESIS OF FEEDBACKS AND INTERACTIONS

Terry V. Callaghan1, 2,Margareta Johansson1, 3, Jeﬀ Key4, Terry Prowse5, Maria Ananicheva6 and Alexander Klepikov7

Changes in Arctic climate are a result of complex interactions and feedbacks among the cryosphere, atmosphere, ocean and biosphere. Feedback processes are responses to a driving mechanism that subsequently accelerate (positive feedback) or retard (negative feedback) the original driving process. Some are direct, but others are complex and indirect. Individual feedbacks operate over diﬀerent time scales and their eﬀects can vary from local to global spatial scales. Some feedbacks driven by climate warming are negative and result in climate cooling whereas others are positive and lead to further warming.

An overall assessment of the net eﬀect of many diﬀerent potential feedbacks on climate change has not yet been achieved.

Here we summarise the feedbacks of a changing Arctic cryosphere presented in the SWIPA Report, describe interactions that span the various cryospheric components, and preliminarily assess their relative magnitudes. We reveal that:

• In the cryosphere-climate system there are more feedbacks that are likely to result in warming than lead to cooling.

• Several positive feedbacks are ﬁnite: warming due to reduced albedo will no longer increase in areas that have totally lost snow or ice cover.

• Feedbacks operate at diﬀerent spatial scales. Many of the feedbacks, such as those operating through albedo and evapotranspiration, will have signiﬁcant local effects that together could result in a global impact. Some processes such as CO2 ﬂuxes are likely to have very small global eﬀects but uncertainty is high. Others, such as subsea methane emissions, could have large global eﬀects.

• Some cryospheric processes in the Arctic have teleconnections elsewhere, for example, the loss of sea ice north of Eurasia may result in a cooling eﬀect overeastern Asia, and changes in snow cover aﬀect atmospheric circulation. Conversely, major changes in the cryosphere have been largely a result of large-scale processes, particularly atmospheric and oceanic circulation.

• There are also interactions between the elements of thecryosphere acting through the atmosphere and ocean.

• The cryospheric components of the Arctic play a pivotal role in freshwater generation, its intra-Arctic storage, and routing to the North Atlantic where it can produce an important feedback to regional and global climate. With continued climate warming it is highly likely that the cryospheric components will play an increasingly important role.

• Terrestrial snow cover, sea ice and permafrost are involved in multiple temporal and spatial feedback regimes whereas land ice is involved in fewer feedbacks.

• General circulation models (GCMs) do not include all major feedbacks, in part because they do not include all processes that lead to feedbacks (e.g., freshwater runoﬀ from glaciers and ice sheets). Further, the feedbacks may not be accurately parameterized in the models.

The overall net eﬀect of all the feedbacks is diﬃcult to assess because of the variability in spatial and temporal scales over which they operate and the calculation of the net eﬀects of all feedbacks requires complex modelling. The lack of full coupling between surface dynamics and the atmosphere is a major gap in current GCMs that remains a priority for future research.

IS THE NORTHERN HIGH LATITUDE LAND-BASED CO2 SINK WEAKENING ?

Daniel J. Hayes1, A. David McGuire2, David W. Kicklighter3, Kevin R. Gurney4 and J.M. Melillo31

Oak Ridge National Laboratory, Oak Ridge, TN, USA • 2

Studies compiled by the Arctic Monitoring and Assessment Programme supported Arctic Carbon Cycle Assessment indicate that, historically, terrestrial ecosystems of the northern high latitude region may have been responsible for up to 60% of the global net land-based sink for atmospheric CO2. However, these regions have recently experienced remarkable modiﬁcation of the major driving forces of the carbon cycle, including surface air temperature warming that is signiﬁcantly greater than the global average and associated increases in the frequency and severity of disturbances. Whether arctic tundra and boreal forest ecosystems will continue to sequester atmospheric CO2 in the face of these dramatic changes is unknown.

Here we show the results of model simulations that estimate a 41 Tg C yr-1 sink in the boreal land regions from 1997 to 2006, which represents a 73% reduction in the strength of the sink estimated for previous decades in the late 20th Century. Our results, along with those from a subset of atmospheric inversion models, suggest that CO2 uptake by the region in previous decades may not be as strong as previously estimated.

Our simulation experiments attribute the recent decline in sink strength as the combined result of 1) weakening sinks due to warming-induced increases in soil organic matter decomposition and 2) strengthening sources from pyrogenic CO2 emissions as a result of the substantial area of boreal forest burned in wildﬁres across the region in recent years. Such changes create positive feedbacks to the climate system that accelerate global warming, putting further pressure on emission reductions to achieve atmospheric stabilization targets.

ARCTIC FUTURE SCENARIO SIMULATIONS AND RAPID SEA ICE REDUCTIONS IN A COUPLED REGIONAL CLIMATE MODEL

TorbenKoenigk and Ralf DöscherSMHI/Rossby Centre, Sweden

Global climate models show large discrepancies in predictions of present and future climate in the Arctic, and consequently, large uncertainties. In order to complete the puzzle of future Arctic climate change and analyze the mechanisms and impacts, a number of regional Arctic scenario experiments are performed with the Rossby Centre Atmosphere Ocean climate model (RCAO). The regional simulations are based on A1B scenario simulations of the last IPCC Assessment Report from the Norwegian Bergen Climate Model (BCM) and the German Max-Planck-Institute climate model (ECHAM) and diﬀer both in the treatments of sea surface salinity and lateral boundary conditions. The results are compared to each other and to the original data of the global models.

The large-scale change patterns of sea level pressure and air temperature are mainly dominated by the changes in the global models but locally signiﬁcant modiﬁcations occur in the regional simulations. Generally, SLP is reduced in most of the Arctic by 1 to 3 hPa until years 2060-2080.

Air temperature increases by 2 to 4 Kelvin in most Arctic regions but up to 10 Kelvin where winter sea ice disappears. In these regions, the response in the regional simulations seems to be more pronounced than in the global simulations.

The regional simulations show lower summer sea ice extents and a stronger decrease than the global simulations. Around 2040, the summer sea ice has almost disappeared for the ﬁrst time and from 2060 on, summers have almost no ice left. The sea ice variability in the regional simulation is higher and several periods occur with low summer ice extent and partial recovery thereafter. These rapid change events are analyzed in detail. Rapid change events of summer sea ice extent can be generated by speciﬁc large scale forcing conditions during the winter before the summer event preconditioning the coming summer or by the summer atmospheric forcing. On average, rapid change events are characterized by increased winter temperature over ice and increased melting from both the top and bottom of the ice leading to reduced ice thicknesses in the winter before the event.

Composites of speciﬁc atmosphere and sea ice conditions reveal that the most extreme drops in sea ice extent occur in the combined case of winter atmosphere warming due to positive amplitudes of the so-called Arctic Dipole Anomaly and summer inﬂow of warm air masses from the Nordic Seas.

GREENLAND ICE LOSS CONTINUES TO ACCELERATE: OBSERVED BY GPS AND GRACE

Shfaqat Abbas Khan and John Wahr

Greenland’s main outlet glaciers have more than doubled their contribution to global sea level rise over the last decade. Recent work has shown that Greenland’s mass loss is still increasing.

Here we show that the ice loss, which has been well-documented over southern portions of Greenland, is now spreading up along the northwest coast, with this acceleration likely starting in late 2005.

In addition to showing that the northwest ice sheet margin is now losing mass, the uplift results from both the GPS measurements and the GRACE predictions show rapid acceleration in southeast Greenland in late 2003, followed by a moderate deceleration in 2006. Because that latter deceleration is weak, southeast Greenland still appears to be losing ice mass at a much higher rate than it was prior to fall 2003.

PERMAFROST THAWING AND LONG TERM GREENHOUSE GAS PRODUCTION RATES IN NORTHEAST GREENLAND

Bo ElberlingBirger Ulf Hansen and Carsten S. Jacobsen3

The part of the soil that thaws in the summer, the active layer, has become about 10 cm thicker the last decade in Zackenberg in Northeast Greenland. Consequently, the top permafrost has been thawing and this will inﬂuence the water balance, the element cycling and not the least the microbial-driven production of greenhouse gas which potential can end up in the atmosphere. The spatial variation of the top permafrost characteristics in terms of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) production rates from two contrasting sites provides insight into processes controlling subsurface greenhouse production following permafrost thawing.

Results from Zackenberg suggest that top permafrost characteristics cannot be predicted based on nowadays vegetation cover and that top permafrost layers typically have a greater potential release of carbon dioxide, methane and nitrous oxide production rates than bottom layers of the active layer.

Preliminary results of microbial community composition indicate that top permafrost from both well and poorly-drained sites consists of an active microbial community, which is in line with observed production of both CO2, CH4 and N2O immediately upon initial thawing.

This study suggests that with additional thawing of 20-30 cm within the next 100 years at a typical tundra site in Zackenberg, today top permafrost layers may be exposed and at the end of the growing season produce as much CO2 per day as the current net CO2 ﬂux from the surface.

PERMAFROST METHANE EMISSION AS A DETECTOR OF THE FUTURE REGIONAL ARCTIC CLIMATE CHANGE

Ivan Sudakov 1 and Sergey Vakulenko 2

St. Petersburg State University, St. Petersburg, 199000, Russia St. Petersburg State University of Technology and Design, St. Petersburg, 199000, Russia

Thawing permafrost and the resulting decomposition of previously frozen organic carbon to methane is one of the most signiﬁcant potential feedbacks from terrestrial ecosystems to the atmosphere in a changing climate. Methane emissions from tundra permafrost lakes can produce a signiﬁcant positive feedback of climate change. In this abstract a new approach to modeling of methane emission from permafrost lakes is proposed. Here we focus our attention on a contribution of the Central Yakutia lakes into methane emission and methane concentration growth. In a new macroscopic approach we use mesoscale data (for example, an averaged radius of lakes). It does not require in situ measurements and can be calculated using remote sensing data. In addition, the proposed method makes it possible to estimate the coeﬃcient of positive feedback of the permafrost-climate system and to predict methane ﬂ ux into the atmosphere. This project is described only the test’s estimate, which we can receive on the basis of observational data and mathematical assumptions. As a result, we see that the methane emission can precede both gradually and catastrophically.