Land

V. Romanovsky¹, R. Armstrong², A. Shiklomanov³, D. Walker⁴, and G. Jia⁵

¹Geophyiscal Institute, University of Alaska Fairbanks, Fairbanks, AK
²CIRES/NSIDC, University of Colorado, Boulder, CO
³University of New Hampshire, Durham, NH
⁴Institute of Arctic Biology, University of Alaska–Fairbanks, Fairbanks, Alaska
⁵RCE/TEA, Chinese Academy of Science, Beijing, China

Summary

Land-based observations, while widely ranging, reflect the effects of a general warming trend. For instance, there was an increase in the relative greenness of the Arctic region, consistent with warming soil and air temperatures, earlier snow melt, and the expansion of shrubs and tree line to the north. Permafrost continues to warm, however the rate of warming in the 2000s is significantly slower than in the 1990s. There is a continued tendency for a decrease in the snow cover of the Northern Hemisphere in the months of April through October. Glaciers are shrinking in most of the world. The amount of river discharge to the Arctic Ocean is increasing.

Vegetation

Evidence of widespread changes in vegetation in northern latitudes comes from trends in terrestrial greennessas detected by the Normalized Difference Vegetation Index (NDVI) derived from the NOAA AVHRR satellites (Myneni et al. 1997; Zhou et al. 2001; Lucht et al. 2002; Jia et al. 2003; Goetz et al. 2005; Bunn et al. 2007). During the 1981–2005 period of observation, about 6% of the circumpolar tundra area experienced an increase in NDVI and about 1% experienced a decrease (Fig.L1; Bunn et al. 2007). The positive trends in NDVI in tundra areas have been strongest in North America. For example, in the tundra region south of 70°N (the region of the Arctic with a consistent AVHRR record from 1982 to 2005) the rate of change in NDVI is +0.58% yr^–1 over the North American Arctic compared to +0.34% yr^–1 over the Eurasian Arctic (Jia et al. 2007). Forested areas experienced a slight decline over the same period: NDVI declined in 6% of the forested area versus an increase in 4% of the area.

Figure L1. Spatial distribution of trends in May to Aug photosynthetic activity across the northern high latitudes from 1981 through 2005. Significant positive trends in photosynthetic activity are shown in green, and negative trends are shown in rust. (From Bunn et al. 2007.)

Vegetation responds relatively quickly to warming temperatures by growing more vigorously and densely. Over a longer time span, changing climate alters vegetation type. Land cover on much of the Alaska North Slope, for example, is transitioning from tundra to shrubs (Wang and Overland 2004). Recent vegetation dynamics observations across the Arctic also indicate that, in general, shrubs have become more abundant and taller. A study in northern Alaska (Tape et al. 2006) showed that both larger and smaller shrub species have increased in size, abundance and extent over the last 50 years. As well as increasing in size and filling in empty patches, the shrubs were colonizing new areas (Figure L2).

Figure L2. Large shrubs have colonized a river terrace that was virtually free of large shrubs in 1949. The new shrubs are more than 2 m high. In the foreground are poplar trees. Photo from the Chandler River located at 68° 25.14' N, 161° 15.24' W: 7/4/1948 and 7/29/2001. (Tape et al. 2006).

Changes in land cover, vegetation density, and other factors are reflected in NDVI. Overall, increasing NDVI is consistent with warming soil and air temperatures, earlier snow melt, and the expansion of shrubs and tree line to the north.

Permafrost

Observations show a general increase in permafrost temperatures during the last several decades in Alaska (Osterkamp and Romanovsky 1999; Romanovsky et al. 2002; Osterkamp 2003; Romanovsky et al. 2007a), northwest Canada (Couture et al. 2003; Smith et al. 2005), Siberia (Pavlov 1994; Oberman and Mazhitova 2001; Romanovsky et al. 2007b; Pavlov and Moskalenko 2002), and northern Europe (Isaksen et al. 2000; Harris and Haeberli 2003). Permafrost temperature records uninterrupted for more than 25 yr have been obtained by the University of Alaska Fairbanks along the International Geosphere-Biosphere Programme Alaskan transect, which spans the entire continuous permafrost zone in the Alaskan Arctic. All of the observatories show a substantial warming during the last 20 yr (Fig. L3). The detailed characteristic of the warming varies between locations, but is typically from 0.5° to 2°C at the depth of zero seasonal temperature variations in permafrost (Osterkamp 2005). These data also indicate that the increase in permafrost temperatures is not monotonic. During the observational period, relative cooling has occurred in the mid-1980s, in the early 1990s, and then again in the early 2000s. As a result, permafrost temperatures at 20-m depth experienced stabilization and even a slight cooling during these periods. Permafrost temperature was relatively stable on the North Slope of Alaska during 2000–07. However, 2007 data show a noticeable increase in the temperature at 20-m depth by 0.2°C at the two northernmost sites of Deadhorse and West Dock. Permafrost temperature did not change significantly at the other North Slope sites. This may indicate a new wave of permafrost warming similar to the warming that started in 1994 (Fig.L2), which also started at the Deadhorse and West Dock sites and only later appeared at the interior sites.

Figure L3. (top) Location of the long-term University of Alaska permafrost observatories in northern Alaska. West Dock is at Prudhoe Bay. (bottom) Changes in permafrost temperatures at 20-m depth during the last 25 to 30 yr (updated from Osterkamp 2003).

Snow extent

Northern Hemisphere snow cover extent has a mean maximum of approximately 47 million km², typically occurring in February. The minimum usually occurs in August and is less than about 1 million km², most of which is snow on glaciers and perennial snow fields. As a result, snow cover is the land surface characteristic responsible for the largest annual and interannual differences in land surface albedo. Snow covers a much smaller area in the Southern Hemisphere, approximately 2% of the global total, and plays a relatively small role in global climate. A time series of snow extent in the Northern Hemisphere, beginning in 1978 and derived from two sources, is presented in Fig. L4. There is a consistent decreasing trend in snow cover in the months of April through October, with the strongest seasonal signal occurring between April and August. Data derived from NOAA snow charts (Robinson and Frei 2000; Frei and Robinson 1999; Ramsay 1998; NOAA/NESDIS/ OSDPD/SSD 2006) indicate a statistically significant decreasing trend of –2.1% decade^–1 (Brodzik et al. 2006). Snow cover data derived from passive microwave imagery (Armstrong and Brodzik 2001; Armstrong et al. 2005a,b) show a decreasing trend of –0.7% decade^–1, although it is not significant at the 90% level. Both time series show similar inter-annual variability and consistently indicate Northern Hemisphere maximum extents exceeding 40 million km². The western United States is among the regions with the strongest decreasing trends, supporting Groisman et al. (2004) and Mote et al. (2005) results using in situ observations. Shallow snow cover at low elevations in temperate regions is the most sensitive to temperature fluctuations and hence most likely to decline with increasing temperatures (Lemke et al. 2007, 343–346).

Figure L4. (top) Time series of Northern Hemisphere snow covered area derived from passive microwave (purple/green) and NOAA snow charts (orange), and (bottom) snow covered area departures from monthly means, 1978–2007. (Click for larger images).

For the Northern Hemisphere winter of 2006–07, the microwave data indicate negative departures from the long-term mean (1978–2007) for every month except October and February, with an average negative departure for the winter months (November through April) of approximately 0.7 million km². For the calendar year of 2007, the NOAA data indicate an average snow cover extent of 24.0 million km², which is 1.5 million km² less than the 38-yr average and represents the third least extensive snow extent for the period of record.

Glaciers

Glaciers and ice caps, excluding those adjacent to the large ice sheets of Greenland and Antarctica, can be found on all continents except Australia and have an estimated total area between 512 and 540 × 103 km². The complicated and uncertain processes that control how fast glaciers move make it difficult to use changes in the areal extent of glaciers as a straightforward indicator of changes in climatic conditions. Mass balance measurements, or the difference between the accumulation and ablation, are a more direct method to determine the year-to-year "health" of a glacier. Changes in mass balance correspond to changes in glacier volume. These measurements are typically obtained from less than about 0.2% of the world's glaciers. Researchers have measured mass balance on more than 300 glaciers since 1946, with a continuous record for about 40 glaciers since the early 1960s (e.g., Cogley 2005; Kaser et al. 2006). These results indicate that in most regions of the world, glaciers are shrinking in mass. From 1961 to 2005, the thickness of "small" glaciers decreased approximately 12 m, or the equivalent of more than 9,000 km³ of ice (Dyurgerov and Meier 2005; online at http://nsidc.org/sotc/glacier_balance.html). Recent mass loss of glaciers, ice caps, and ice sheets is estimated to be 0.58 mm Sea Level Equivalent (SLE) per year between 1961 and 2005 and 0.98 mm SLE per year between 1993 and 2005 (Dyurgerov and Meier 2005; online at http://nsidc.org/sotc/sea_level.html). In contrast to the two major ice sheets, Greenland and Antarctica, the network of small glaciers and ice caps, although making up only about 4% of the total land ice area or about 760,000 km³, may have provided as much as 60% of the total glacier contribution to sea level change since the 1990s. This acceleration of glacier melt may cause 0.1 to 0.25 m of additional sea level rise by 2100 (Meier et al. 2007). The greatest mass losses per unit area are found in Patagonia, Alaska, and northwest United States/southwest Canada. However, because of the corresponding large areas, the biggest contributions in total to sea level rise come from Alaska, the Arctic, and the Asian high mountains.

River discharge

Overall, the twenty-first century to date is characterized by an increased level of river discharge to the Arctic Ocean (www.R-ArcticNet.sr.unh.edu). The mean 2000–06 discharge from six of the largest Eurasian rivers (North Dvina, Pechora, Ob, Yenisei, Lena, and Kolyma) was 127 km³ (7%) higher than long-term mean over the period 1936–99 (Fig. L5). The largest Siberian rivers, Yenisey and Lena, provided more than 70% of this increase. Preliminary 2007 estimates of annual discharge to the Arctic Ocean from the Russian rivers have been made using near-real-time data (http://RIMS.unh.edu). These estimates indicate a relatively high annual discharge for the six largest Eurasian rivers, possibly achieving a new historical maximum in 2007 for total discharge to the Arctic Ocean over the 1936–2007 observational period. The mean annual discharge to the ocean over 2000–06 from the five largest North American rivers was about 6% (30 km³) greater than the long-term mean over 1973–99. The historical annual maximum was observed for the summary discharge in 2005 (Fig. L5). However, the relatively short discharge time series for North America (37 yr) and the significant unmonitored land area does not support conclusions with the same reliability as for Eurasia.

Figure L5. Total annual discharge to the Arctic Ocean from the six largest rivers in the Eurasian pan-Arctic for the observational period 1936–2006 (updated from Peterson et al. 2002) (red line) and from the five largest North American pan-Arctic rivers over 1973–2006 (purple line). The least squares linear trend lines are shown as dashed blue.

References

Armstrong, R. L., and M. J. Brodzik, 2001: Recent Northern Hemisphere snow extent: A comparison of data derived from visible and microwave sensors. Geophys. Res. Lett., 28, 3673–3676.

—, —, K. Knowles, and M. Savoie, 2005a: Global monthly EASE-Grid snow water equivalent climatology. National Snow and Ice Data Center, Boulder, CO, digital media. [Available online at http://nsidc. org/data/nsidc-0271.html.]

—, B. Raup, S. J. S. Khalsa, R. Barry, J. Kargel, C. Helm, and H. Kiefer, 2005b: GLIMS glacier database. National Snow and Ice Data Center, Boulder, CO, digital media. [Available online at http://nsidc.org/ data/nsidc-0272.html.]

Brodzik, M. J., R. L. Armstrong, E. C. Weatherhead, M. H. Savoie, K. W. Knowles, and D. A. Robinson, 2006: Regional trend analysis of satellite-derived snow extent and global temperature anomalies. Eos, Trans. Amer. Geophys. Union, 87 (Fall Meeting Suppl.), Abstract U33A-0011.

Bunn, A. G., S. J. Goetz, J. S. Kimball, and K. Zhang, 2007: Northern high-latitude ecosystems respond to climate change. Eos, Trans. Amer. Geophys. Union, 88, 333–334.

Cogley, G. J., 2005: Mass and energy balances of glaciers and ice sheets. Encyclopedia of Hydrological Sciences, M. Anderson, Ed., John Wiley and Sons , 2555–2573.

Couture, R., S. Smith, S. D. Robinson, M. M. Burgess, and S. Solomon, 2003: On the hazards to infraAMERICAN METEOROLOGICAL SOCIETY july 2008 | S169 structure in the Canadian North associated with thawing of permafrost. Proc. Geohazards (2003), Third Canadian Conf. on Geotechnique and Natural Hazards, Edmonton, Alberta, Canada, The Canadian Geotechnical Society, 97–104.

Dyurgerov, M. B., and M. F. Meier, 2005: Glaciers and the changing earth system: A 2004 snapshot. Institute of Arctic and Alpine Research, University of Colorado Occasional Paper 58, 117 pp.

Frei, A., and D. A. Robinson, 1999: Northern Hemisphere snow extent: Regional variability 1972–1994. Int. J. Climatol., 19, 1535–1560.

Goetz, S. J., A. G. Bunn, G. J. Friske, and R. A. Houghton, 2005: Satellite-observed photosynthetic trends across boreal North America associated with climate and fire disturbance. Proc. Natl. Acad. Sci. USA, 102, 13 521–13 525.

Groisman, P. Ya., R. W. Knight, T. R. Karl, D. R. Easterling, B. Sun, and J. H. Lawrimore, 2004: Contemporary changes of the hydrological cycle over the contiguous United States, trends derived from in situ observations. J. Hydrometeor., 5, 64–85.

—, —, D. R. Easterling, T. R. Karl, G. C. Hegerl, and V. N. Razuvaev, 2005: Trends in intense precipitation in the climate record. J. Climate, 18, 1326–1350.

Harris, C., and Coauthors, 2003: Warming permafrost in European mountains. Global Planet. Change, 39, 215–225.

Isaksen, K., D. Vonder Mühll, H. Gubler, T. Kohl, and J. L. Sollid, 2000: Ground surface temperature reconstruction based on data from a deep borehole in permafrost at Janssonhaugen, Svalbard. Ann. Glaciol., 31, 287–294.

Jia, G. J., H. E. Epstein, and D. A. Walker, 2007: Trends in vegetation greenness in the Arctic from 1982-2005. Eos, Trans. Amer. Geophys. Union, 88 (Fall Meeting Suppl.), Abstract B21-0041.

Jia, G. J., H. E. Epstein, and D. A. Walker, 2003: Greening of arctic Alaska, 1981–2001. Geophys. Res. Lett., 30, 2067, doi:10.1029/2003GL018268.

Kaser, G., J. G. Cogley, M. B. Dyurgerov, M. F. Meier, and A. Ohmura, 2006: Mass balance of glaciers and ice caps: Consensus estimates for 1961–2004. Geophys. Res. Lett., 33, L19501, doi:10.1029/2006GL027511.

Lemke, P., and Coauthors, 2007: Observations: Changes in Snow, Ice and Frozen Ground. Climate Change 2007: The Physical Science Basis, S. Solomon.

Lucht, W., and Coauthors, 2002: Climatic control of the high-latitude vegetation greening trend and Pinatubo effect. Science, 296, 1687–1689.

Myneni, R. B., C. D. Keeling, C. J. Tucker, G. Asrar, and R. R. Nemani, 1997: Increased plant growth in the northern high latitudes from 1981 to 1991. Nature, 38, 698–702.

Mote, P. W., A. F. Hamlet, M. P. Clark, and D. P. Lettenmaier, 2005: Declining mountain snowpack in western North America. Bull. Amer. Meteor. Soc., 86, 39–49.

Oberman, N. G., and G. G. Mazhitova, 2001: Permafrost dynamics in the north-east of European Russia at the end of the 20th century. Norw. J. Geogr., 55, 241–244.

Osterkamp, T. E., 2003: A thermal history of permafrost in Alaska. Permafrost: Proceedings of the 8th International Conference on Permafrost, Zurich, Switzerland, 21-25 July 2003, M. Phillips, S. M. Springman, and L. U. Arenson, Eds., Vol. 2, A. A. Balkema, 863–868.

—, 2005. The recent warming of permafrost in Alaska. Global Planet. Change, 49, 187–202.

—, and V. E. Romanovsky, 1999: Evidence for warming and thawing of discontinuous permafrost in Alaska. Permafrost Periglacial Processes, 10, 17–37.

Pavlov, A. V., 1994: Current changes of climate and permafrost in the Arctic and Sub-Arctic of Russia. Permafrost Periglacial Processes, 5, 101–110.

—, and N. G. Moskalenko, 2002: The thermal regime of soils in the north of Western Siberia. Permafrost Periglacial Processes, 13, 43–51.

Ramsay, B. H., 1998: The Interactive Multisensor Snow and Ice Mapping System. Hydrol. Processes, 12, 1537–1546.

Romanovsky, V. E., M. Burgess, S. Smith, K. Yoshikawa, and J. Brown, 2002: Permafrost temperature records: Indicators of climate change. Eos, Trans. Amer. Geophys. Union, 83, 589.

—, S. Gruber, A. Instanes, H. Jin, S. S. Marchenko, S. L. Smith, D. Trombotto, and K. M. Walter, 2007a: S176 | july 2008 Frozen ground. Global Outlook for Ice and Snow, United Nations Publications, 181–200.

—, T. S. Sazonova, V. T. Balobaev, N. I. Shender, and D. O. Sergueev, 2007b: Past and recent changes in permafrost and air temperatures in Eastern Siberia. Global Planet. Change, 56, 399–413.

Robinson, D. A., and A. Frei, 2000: Seasonal variability of northern hemisphere snow extent using visible satellite data. Prof. Geogr., 51, 307–314.

Smith, S. L., M. M. Burgess, D. Riseborough, and F. M. Nixon, 2005: Recent trends from Canadian permafrost thermal monitoring network sites. Permafrost Periglacial Processes, 16, 19–30.

Tape, K., M. Sturm, and C. Racine, 2006: The evidence for shrub expansion in Northern Alaska and the Pan-Arctic. Global Change Biology, 12, 686-702.

Wang, M., and J. Overland, 2004: Detecting Arctic climate change using Köppen climate classification. Climatic Change, 67, 43–62.

Zhou, L., C. J. Tucker, R. K. Kaufmann, D. Slayback, N. V. Shabanov, I. Fung, and R. B. Myneni, 2001: Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999. J. Geophys. Res., 106 (D17), 20 069–20 083.

October 6, 2008

About the Report Card

Printable Handout :: Full Arctic Report Card (PDF)
 NOAA Arctic Theme Page