due to a very extensive territory of yakutia ( 3,083,000 km ) , it is hardly possible to estimate permafrost temperatures at all of its 200 cattle burial grounds , especially because most grounds are situated in very remote and hard - to - reach places .
we used the data of weather stations located in the same administrative districts as the burial grounds to estimate the trends in local air temperatures .
the geographical coordinates ( latitude , longitude , and altitude ) and international identification indexes of all yakutia weather stations are listed at the website of russian meteorological service ( www.meteo.ru ) ; their locations are available on the interactive map at http://www.3planeta.com/googlemaps/karty-google-maps.html .
we retrieved the daily temperature data for these weather stations from the us national climatic data centre website and selected years 19612010 as the study period .
ncdc website maintains the most comprehensive archive of meteorological data collected all over the world up - to - date .
the analysis of available archive data showed that only 17 out of 26 selected district weather stations reported their daily temperature data for all years between 1961 and 2010 , whereas the data for the remaining 9 administrative districts were either incomplete or absent .
regional models of climate change in yakutia have been developed only at a very broad geographic scale .
there are only two such models : one covers all territories to the north of 65n and the other covers all territories to the south of 65n .
the first model reports the following changes in annual average temperatures relative to the baseline : 0.2c for 19711980 ; 0.8c for 19811990 ; and 0.1c for 19912000 .
the second model reports the following temperature increments : 0.12c for 19711980 ; 1.6c for 19811990 ; and 0.3c for 19912000 [ 24 .
such aggregated information was not sufficient to estimate the temperature trends in individual administrative districts .
for this purpose , we used the records of daily temperatures for those 17 districts where such data were available .
even these datasets contained several periods of missing data and these were dealt in the following way .
if , for any given year , more than 15% of daily data were missing , we excluded this year from the analysis .
if 1 month of daily data were missing , we used daily temperatures during the same month of the preceding year and calculated the annual average temperature using these  proxy data .
then , the time series of annual average temperatures between 1961 and 2010 were tested for a linear trend using least squares method .
the territory of yakutia can be subdivided into four climate - geographic zones : west part from laptev sea to the south boundaries of the republic ; central plains part ; northeast part that includes the arctic tundra and novosibirsk islands ; and south highlands part ( www.atlas-yakutia.ru ) .
the survey of cattle burial sites showed that most of them were located in the western part ( 112 sites ) and in the central plains part ( 112 sites ) , whereas the smallest numbers ( 43 sites ) were located in the east part , which is mostly occupied by mountains ( fig .
1 ) . geographic distribution of burial grounds of cattle that died ( + ) from anthrax in yakutia .
the observed trends in the average annual temperatures in different parts of yakutia in 19612010 are summarized in table 1 .
the lowest air temperatures are typical for the east part , where the number of cattle burial grounds is the smallest .
statistically significant linear temperature trends were obtained for the eight administrative districts with the highest annual average temperatures .
the smallest change was observed in viluisky district , t=0.6c ( thistoric=17.9c and tcurrent=18.5c ) .
the greatest change was observed in churapchinsky district , t=1.0c ( thistoric=17.9c and tcurrent=18.9c ) . in yakutsky district ,
it was interesting to observe that the annual warming rate in viluisky district was also minimal among all studied districts ( 0.02c / year ) , while the annual warming rate in churapchinsky district was maximal ( 0.04c / year ) .
descriptive statistics of annual and july average temperatures in 19612010 and linear trends in annual average for selected administrative districts of yakutia with the greatest numbers of anthrax cattle burial grounds another characteristic of climate warming was the relative increase in the number of  very hot days defined as the days with average daily temperature above the respective long - term average for this date , calculated over the past 50 years . the proportions of such days ( n ) were calculated for the  historic and the 
current periods : nhistoric= 34.5% and ncurrent= 52% in viluisky district ; nhistoric= 39.1% and ncurrent= 56% in yakutsky district ; nhistoric= 38.9% and ncurrent= 52% in churapchinsky district .
average daily temperatures in july 2010 were greater than the long - term average temperature of july during all 31 days of this month .
the ranges of annual average temperatures observed in different parts of yakutia are shown in fig .
the most pronounced temperature trend was observed in the administrative districts around yakutsk city ( fig .
statistical analysis confirmed a significant 0.1% level positive trend in the annual average temperatures in yakutsk .
similar results have been obtained earlier ( 24 ) : climate warming is more pronounced in central and south yakutia than in north yakutia .
the districts with the greatest increments of annual average temperatures also reported the highest numbers of outbreaks of anthrax : between 4 and 11 cases during the last 80 years . according to veterinary experts , these districts present the greatest risks of anthrax ( 14 ) . from epidemiology standpoint , thorough monitoring of anthrax cattle burial grounds
is recommended for the entire territory of yakutia , not just for several selected parts .
this monitoring should include regular surveys of cattle burial sites , checks of fences around them , inspections of land - use permits , and other documentation , detailed measurements of permafrost parameters around such sites .
the trends in permafrost temperatures may vary greatly even within a single administrative district ( 24 ) .
unfortunately , the authors could not find any information about the actual condition of siberian anthrax cattle burial sites , cropping out the remains or soil erosion .
the authors recommend thorough monitoring of activity of airborne anthrax both in the northern and southern parts of yakutia , in the conditions of climate change , especially in light of the findings obtained in central asia ( kazakhstan ) , where geographic distribution of b. anthracis was studied ( 25 ) .
statistically significant positive trends in the annual average temperatures were established in 8 administrative districts out of 17 districts of yakutia for which sufficient meteorological data were available .
these eight districts should be carefully monitored in the first place , but all regions where the outbreaks of siberian anthrax took place in the past should probably deserve equal attention of epidemiologists . gradual phaseout of these burial grounds should use modern technologies of utilization of cattle remains .
it is quite important , therefore , to estimate the threshold temperatures above which depreservation of the frozen remains becomes significant .
temperature thresholds of permafrost degradation are estimated on the basis of geomorphological indicators ( segregated frost heave mound 
detailed field surveys on the state of cattle burial grounds and the measurements of air and permafrost temperatures are needed for objective assessment of epidemiologic situation . besides
massive vaccination of domestic animals has been proven to be effective to reduce the rates of this disease among both domestic animals and people living in the russian arctic .
the authors have not received any funding or benefits from industry or elsewhere to conduct this study .
 climate warming in the arctic may increase the risk of zoonoses due to expansion of vector habitats , improved chances of vector survival during winter , and permafrost degradation . 
 monitoring of soil temperatures at siberian cryology control stations since 1970 showed correlations between air temperatures and the depth of permafrost layer that thawed during summer season . between 1900s and 1980s , the temperature of surface layer of permafrost increased by 24c ; and a further increase of 3c is expected . 
 frequent outbreaks of anthrax caused death of 1.5 million deer in russian north between 1897 and 1925 . 
 anthrax among people or cattle has been reported in 29,000 settlements of the russian north , including more than 200 yakutia settlements , which are located near the burial grounds of cattle that died from anthrax . 
 statistically significant positive trends in annual average temperatures were established in 8 out of 17 administrative districts of yakutia for which sufficient meteorological data were available . at present , it is not known whether further warming of the permafrost will lead to the release of viable anthrax organisms . nevertheless , we suggest that it would be prudent to undertake careful monitoring of permafrost conditions in all areas where an anthrax outbreak had occurred in the past . 
Materials and methods
Results
Discussion
Conclusions
Conflict of interest and funding