Ongoing climatic change in Northern Eurasia: justification for expedient research

A brief overview of the ongoing climatic and environmental changes in Northern Eurasia serves as an editorial introduction to this, the second, special Northern Eurasia Earth Science Partnership Initiative (NEESPI) focus issue of Environmental Research Letters. Climatic changes in Northern Eurasia over the last hundred years are reflected in numerous atmospheric and terrestrial variables. Many of these are noticeably significant above the confidence level for 'weather' or other (fire regime, ecosystem change) noise and thus should be further investigated in order to adapt to their impacts. In this focus issue, we introduce assorted studies of different aspects of contemporary change in Northern Eurasia. Most of these have been presented at one of the NEESPI workshops (for more information see neespi.org) and/or American Geophysical Union and European Geosciences Union NEESPI open sessions during the past year. These studies are diverse, representing the diversity of climates and ecosystems across Northern Eurasia. Some of these are focused on smaller spatial scales and/or address only specific aspects of the global change implications across the subcontinent. But the feeling (and observational evidence) that these changes have already been quite rapid and can have global implications inspires us to bring this suite of papers to the readers' attention. See the PDF for the full text of the editorial. Focus on Climatic and Environmental Change in Northern Eurasia Contents Preface Northern Eurasia Earth Science Partnership Initiative Pavel Groisman and Amber J Soja Editorial Siberia integrated regional study: Multidisciplinary investigations of interrelation between Siberia environment dynamics and global climate change E P Gordov and E A Vaganov Studies of the energy and water cycles in Northern Eurasia Comparison and evaluation of gridded radiation products across northern Eurasia T J Troy and E F Wood Reanalysis data underestimate significant changes in growing season weather in Kazakhstan C K Wright, K M de Beurs, Z K Akhmadieva, P Y Groisman and G M Henebry Climate change in Inner Mongolia from 1955 to 2005—trends at regional, biome and local scales N Lu, B Wilske, J Ni, R John and J Chen Application of the Snowmelt Runoff model in the Kuban river basin using MODIS satellite images M V Georgievsky Record Russian river discharge in 2007 and the limits of analysis A I Shiklomanov and R B Lammers Paleoclimatic reconstructions for the south of Valdai Hills (European Russia) as paleo-analogs of possible regional vegetation changes under global warming E Novenko, A Olchev, O Desherevskaya and I Zuganova Diagnosis of the record discharge of Arctic-draining Eurasian rivers in 2007 Michael A Rawlins, Mark C Serreze, Ronny Schroeder, Xiangdong Zhang and Kyle C McDonald Studies of the cryosphere in Northern Eurasia Groundwater storage changes in arctic permafrost watersheds from GRACE and in situ measurements Reginald R Muskett and Vladimir E Romanovsky Changes in snow cover over Northern Eurasia in the last few decades O N Bulygina, V N Razuvaev and N N Korshunova Modeling sub-sea permafrost in the East Siberian Arctic Shelf: the Dmitry Laptev Strait D Nicolsky and N Shakhova Snow cover basal ice layer changes over Northern Eurasia since 1966 Olga N Bulygina, Pavel Ya Groisman, Vyacheslav N Razuvaev and Vladimir F Radionov Snow cover and permafrost evolution in Siberia as simulated by the MGO regional climate model in the 20th and 21st centuries I M Shkolnik, E D Nadyozhina, T V Pavlova, E K Molkentin and A A Semioshina Studies of the biosphere in Northern Eurasia The influence of regional surface soil moisture anomalies on forest fires in Siberia observed from satellites A Bartsch, H Balzter and C George Change and persistence in land surface phenologies of the Don and Dnieper river basins V Kovalskyy and G M Henebry Effects of climatic changes on carbon dioxide and water vapor fluxes in boreal forest ecosystems of European part of Russia A Olchev, E Novenko, O Desherevskaya, K Krasnorutskaya and J Kurbatova The effects of climate, permafrost and fire on vegetation change in Siberia in a changing climate N M Tchebakova, E Parfenova and A J Soja An image-based inventory of the spatial structure of West Siberian wetlands A Peregon, S Maksyutov and Y Yamagata Modeling of the carbon dioxide fluxes in European Russia peat bogs J Kurbatova, C Li, F Tatarinov, A Varlagin, N Shalukhina and A Olchev Feedbacks of windthrow for Norway spruce and Scots pine stands under changing climate O Panferov, C Doering, E Rauch, A Sogachev and B Ahrends Reconstruction and prediction of climate and vegetation change in the Holocene in the Altai–Sayan mountains, Central Asia N M Tchebakova, T A Blyakharchuk and E I Parfenova Simulating the effects of soil organic nitrogen and grazing on arctic tundra vegetation dynamics on the Yamal Peninsula, Russia Qin Yu, Howard Epstein and Donald Walker Possible decline of the carbon sink in the Mongolian Plateau during the 21st century Y Lu, Q Zhuang, G Zhou, A Sirin, J Melillo and D Kicklighter The frequency of forest fires in Scots pine stands of Tuva, Russia G A Ivanova, V A Ivanov, E A Kukavskaya and A J Soja Lateral extension in Sphagnum mires along the southern margin of the boreal region, Western Siberia A Peregon, M Uchida and Y Yamagata Evaluating the sensitivity of Eurasian forest biomass to climate change using a dynamic vegetation model J K Shuman and H H Shugart Studies of socioeconomic processes in Northern Eurasia Comparing patterns of ecosystem service consumption and perceptions of range management between ethnic herders in Inner Mongolia and Mongolia L Zhen, B Ochirbat, Y Lv, Y J Wei, X L Liu, J Q Chen, Z J Yao and F Li Land cover/land use change in semi-arid Inner Mongolia: 1992–2004 Ranjeet John, Jiquan Chen, Nan Lu and Burkhard Wilske Spatial and temporal patterns of greenness on the Yamal Peninsula, Russia: interactions of ecological and social factors affecting the Arctic normalized difference vegetation index D A Walker, M O Leibman, H E Epstein, B C Forbes, U S Bhatt, M K Raynolds, J C Comiso, A A Gubarkov, A V Khomutov, G J Jia, E Kaarlejarvi, J O Kaplan, T Kumpula, P Kuss, G Matyshak, N G Moskalenko, P Orekhov, V E Romanovsky, N G Ukraientseva and Q Yu Methods of surface monitoring from space A bio-optical algorithm for the remote estimation of the chlorophyll-a concentration in case 2 waters Anatoly A Gitelson, Daniela Gurlin, Wesley J Moses and Tadd Barrow Estimation of chlorophyll-a concentration in case II waters using MODIS and MERIS data—successes and challenges W J Moses, A A Gitelson, S Berdnikov and V Povazhnyy Dual scale trend analysis for evaluating climatic and anthropogenic effects on the vegetated land surface in Russia and Kazakhstan K M de Beurs, C K Wright and G M Henebry Satellite microwave remote sensing of North Eurasian inundation dynamics: development of coarse-resolution products and comparison with high-resolution synthetic aperture radar data R Schroeder, M A Rawlins, K C McDonald, E Podest, R Zimmermann and M Kueppers

as estimated by the Surface Radiation Budget project is positive only for a short period of the year. But, in July this quantity exceeded values in the Sahara or the desert Southwest US (figure 2).
Temperature change across Northern Eurasia has accelerated, especially in Siberia and the continental interior (figure 3). The latitudinal expanse of mountain systems across the Eurasian interior (Himalayas, Karakorum, Caucasus, Tian Shan, and others) serves to block the moisture influx from tropical oceans to Northern Eurasia (Kuznetsova 1983). This blocking terrain and the large size of Eurasia leads to a larger (compared to North America) dependence of the water budget of Northern Eurasia from the water vapor transfer that originates from the North Atlantic via the westerlies. The intensity of the latter depends strongly upon the meridional gradients of the surface air temperature field. The pattern of ongoing global warming (stronger warming in high latitudes compared to the tropics) gradually reduces these gradients and this process has accelerated in recent decades (figure 4). As a result, we have already witnessed a gradual increase in the frequency and extent of dry conditions and forest fire risk across Northern Asia (Mescherskaya and Blazhevich 1997, Zhai et al 2004, Soja et al 2007, Groisman et al 2007, 2009, Elizbarashvili et al 2009. Changes of global concern in the Artic North of the Eurasian coast, the Arctic Ocean is rapidly advancing towards perennial ice-free conditions and has already lost nearly half of its end-of-summer extent since the late 1970s (Serreze et al 2007). The sea ice thickness has also been noticeably reduced (Frolov et al 2009). This development changes  regional albedo and dramatically affects the cold season heat fluxes from the ocean to the atmosphere. Thus, Northern Eurasia and, particularly, its Arctic are being affected by global and regional factors that are contributing to these observed changes and the positive feedbacks to this forcing may further exacerbate the situation. This dramatic retreat of the Arctic sea ice is causing: (a) rampant coastal erosion of the Arctic shelf (up to 10 m yr −1 ; Ogorodov 2003); (b) release of carbon (both methane and CO 2 ) stored on the frozen shelf and coast (Shakhova et al 2009); and (c) an additional source of heat and moisture in early winter. Figure 5 depicts the land and ocean cover composite for July-September 2008 based on Terra-MODIS RGB with 250 m resolution in the Arctic. It shows the areas of the Arctic Ocean that remain ice-free during these three months in 2008, which are substantial and much larger than just 20-25 years ago. As a result, we observe a significant increase of maximum snow depth across the northern part of Russia (Bulygina et al 2009), an unusual behavior of the hemispheric snow cover in October (it is not shrinking with warming against all odds due to an additional source of moisture to the Arctic atmosphere). Impact on the World Ocean thermohaline circulation due to changes in the fresh water inflow into the Arctic Ocean was a concern of the Arctic Fresh Water Budget Initiative (Vörösmarty et al 2004) because being a small fraction of the World Ocean (less than 4%), the Arctic Ocean drainage is disproportionally high (about 10%). Furthermore, observations and pilot projections predict that the discharge and heat influx from major Siberian rivers into the Arctic Ocean has increased (Shiklomanov et al 2007, Lammers et al 2007 and will further increase (Kattsov et al 2007).

Ecosystem changes of global concern in Northern Eurasia
The largest reservoir of terrestrial carbon resides in the boreal forest zone, primarily in permafrost, wetlands and soil, and 3/4 of the boreal forests are in Russia (Alexeyev and Birdsey 1998, Apps et al 1993, Zoltai and Martikainen 1996. There is an additional carbon reservoir held on the previously frozen Arctic shelf, which is becoming increasingly threatened by warming. Continuous climate warming, coupled with associated permafrost thawing ( Additionally, as regards the function of human interaction with ecosystems, the value that is placed on the environment and government management of resources can exert a strong influence in determining ecosystem health, structure and function (Zhen et al 2009). Walker et al (2009) investigated reasons for greening on the Yamal Peninsula and found a positive feedback between climate and permafrost degradation and attributed these to a complicated interaction between warming, reindeer herding, gas-field infrastructure and sea ice melt. The accurate quantification of these feedbacks directly affects our ability to project the rate of future global change, and in some cases, the magnitude and even the sign of these feedbacks are associated with significant uncertainties, while some feedbacks are likely still unidentified. At the same time, we must carefully consider the data products that are available for research, as highlighted by Wright et al (2009) andSoja et al (2009).
Biospheric models project that further changes in Northern Eurasian energy and water budgets coupled with permafrost thaw will result in substantial northward and altitudinal shifts in major ecozones, particularly in continental Siberia. In various climate change scenarios, significant decreases in taiga, tundra, and forest-tundra and increases in steppe, forest-steppe, and temperate forests are predicted (Vygodskaya et al 2007, Tchebakova et al 2009b, 2009c. This shift will affect the surface albedo (i.e. low in dark coniferous forest, high in snow-covered steppe) and moisture balance of these ecosystems in ways that are largely undefined, and these interactions will feedback to the climate system by altering patterns of precipitation, cloud cover, solar radiation and hydrologic balances. Randerson et al (2006) investigated the cumulative impact of future boreal forest fires on climate warming. They concluded a net negative climate forcing, but highlighted the uncertainty in fire severity (directly related to fire weather) and the unresolved question of the impact of changes in extensive Siberian larch forests (distinct, light, needle-leafed deciduous species underlain with permafrost).  . Climate-induced increases in fire regimes (frequency, area burned and severity) can act as a catalyst by which ecosystems move quickly towards a new equilibrium with the climate system (i.e. forest to steppe).

Conclusion
The need for expedient research in Northern Eurasia in response to recent climatic and environmental change is compelling for the following reasons.
• The changes in this part of the Earth are already among the largest, and are accelerating. • We are facing a non-linearity in environmental and climatic change in Northern Eurasia due to: (a) a dramatic retreat in Arctic sea ice; (b) the impact on the World Ocean thermohaline circulation due to changes inthe fresh water inflow into the Arctic Ocean; (c) feedbacks to the global carbon and hydrological cycles due to permafrost thaw, wetland transformation, land cover change and ecosystem shifts; and (d) identified and unidentified feedbacks to the climate system through alterations in the solar energy balance (i.e. aerosols on snow/ice, albedo change due to changes in vegetation, cloud cover, latent and sensible heat fluxes), in the distribution of aerosols and trace gases (biogenic and biomass burning) and in cloud cover and patterns of precipitation. • This region is large enough and has the carbon store necessary to feedback to regional and global climate.
The text and figures provided in this focus issue and editorial serve to illustrate and provide support for this argument.