Permafrost Thaw Accelerates in Boreal Peatlands During Late-20th Century Climate Warming

Permafrost covers 25% of the land surface in the northern hemisphere, where mean annual ground temperature is less than 0°C. A 1.4–5.8 °C warming by 2100 will likely change the sign of mean annual air and ground temperatures over much of the zones of sporadic and discontinuous permafrost in the northern hemisphere, causing widespread permafrost thaw. In this study, I examined rates of discontinuous permafrost thaw in the boreal peatlands of northern Manitoba, Canada, using a combination of tree-ring analyses to document thaw rates from 1941–1991 and direct measurements of permanent benchmarks established in 1995 and resurveyed in 2002. I used instrumented records of mean annual and seasonal air temperatures, mean winter snow depth, and duration of continuous snow pack from climate stations across northern Manitoba to analyze temporal and spatial trends in these variables and their potential impacts on thaw. Permafrost thaw in central Canadian peatlands has accelerated significantly since 1950, concurrent with a significant, late-20th-century average climate warming of +1.32 °C in this region. There were strong seasonal differences in warming in northern Manitoba, with highest rates of warming during winter (+1.39 °C to +1.66 °C) and spring (+0.56 °C to +0.78 °C) at southern climate stations where permafrost thaw was most rapid. Projecting current warming trends to year 2100, I show that trends for north-central Canada are in good agreement with general circulation models, which suggest a 4–8 °C warming at high latitudes. This magnitude of warming will begin to eliminate most of the present range of sporadic and discontinuous permafrost in central Canada by 2100.     

Reconstruction of Nineteenth Century Summer Temperatures in Norway by Proxy Data from Farmers'Diaries

Proxy data from five farmers; diaries in the Møre, Dovre and Trøndelag regions in central Norway were used for climatic reconstruction purposes. The method chosen was "simple linear regression analysis" with the start of the grain harvest (barley or oats) as predictor and summer temperature (May – August) as predictand. Overlapping periods with modern instrumental observations (starting 1858 or later) were used for calibration of the model. The model was tested on independent data by establishing the regression on one half of the overlapping period and applying the regression on the other half. The standard deviation in the residuals varied from 0.3°C to 0.7°C and the biases of the mean values from –0.3°C to +0.3°C. Climatic reconstructions were established for the early- and mid-nineteenth century summer temperature, i.e. during the last part of what has come to be regarded as the "Little Ice Age", in this article considered to end around 1880.By use of the proxy data model, huge inhomogeneities of the "classical" Trondheim series were detected, the early nineteenth century part of the series evidently being too warm. The inhomogeneity was removed by use of adjustment terms. The adjusted series indicates that in the Trondheim region the summer temperature during the last part of the "Little Ice Age" phase was about 1°C lower than the latest 60 years. This is in serious contradiction to the classical Trondheim series.     

Northern Canadian Wetlands: Net Ecosystem CO2 Exchange and Climatic Change

Northern Canadian peatlands represent a long term sink for atmospheric carbon dioxide (CO2), however there is concern they may become a net source of CO2 due to climatic change. Climatic change is expected to result in significant changes in regional hydrology in boreal and subarctic regions of Canada. A hydrologic model predicted a summer water table drop of 0.14 m in northern Canadian fens given an increase in summer temperature and rainfall of 3°C and 1 mm d-1, respectively. Moreover, surface peat temperature increased by 2.3°C. Net ecosystem exchange of CO2 was modelled using these modelled hydrologic and thermal changes with respiration:peat temperature and water table:net ecosystem production relationships developed from measurements at wetlands in northern Sweden and near Churchill, Manitoba. Model results indicate that the net atmospheric CO2 sink function of fens may be enhanced under future 2 × CO2 scenarios, while bogs may become a net source of atmospheric CO2. If the net ecosystem productivity response to the new hydrologic conditions was ignored then the model predicts a decrease in summer carbon storage for all peatland types.     

Effect of temperature on production of CH4 and CO2 from Peat in a Natural and Flooded Boreal Forest Wetland

Flooding of a small boreal forest wetland (979) in northwestern Ontario, caused the formation of peat islands, which resulted in an approximate 10 °C increase in peat temperatures at a depth of 50 cm. Peat collected from the flooded wetland and a natural unflooded wetland was incubated anaerobically at temperatures of 4 °C, 15 °C, and 20 to 25 °C. Flooding of the wetland greatly increased CH4 production rates by increasing the ratio of CH4:CO2 produced from 979 peat (40% : 60%) compared to 632 peat (20% : 80%), at both preflood and postflood temperatures, likely due to the altered hydrological and geochemical conditions within the peat mats due to flooding. CH4 and CO2 production rates approximately tripled for every 10 °C temperature increase and may have been linked to to the metabolic rate of the methanogens or the fermentors independent of the substrate quality. Methane production rates from deep peat deposits within the islands were also significant and responded well to temperature increases despite peat 14C ages of 1000 years. Due to the large quantity of carbon stored within natural wetlands, artificial reservoirs may act as a significant and long term source of CH4 to the atmosphere.     

Changes in the Wetlands of Andalusia (Doñana Natural Park, SW Spain) at the End of the Little Ice Age

The Little Ice Age is a climatic period still insufficiently known. This ignorance is more marked in the case of Andalusia (southern Spain), where only recent works throw any light on the topic. Our studies, primarily from the perspective of botany and changes in the plant landscape, reveal the effects that this period had in these latitudes, and in particular on the Doñana Natural Park (SW Spain). This work shows an aridization in climatic conditions coinciding with the end of the Little Ice Age. The results corroborate the most recent theses on this period in Spain. Furthermore, the effects on the marsh areas studied lead us to conclude that the interpretation of the Little Ice Age in these southern latitudes should be different to that normally given for more northerly latitudes – much better known and more studied than the Mediterranean regions.     

Evidence for climatic conditions between CA. 900-1300 A.D. in the southern canadian rockies

Available evidence for climatic conditions in the southern Canadian Rockies around the period of the Early Medieval Warm Period is presented and reviewed. Treelines appear to have been above present levels during the 14th–17th centuries and there is limited evidence of higher treelines ca. 1000¹⁴C yr B.P. (ca. 1000 A.D.). During the 13th century at least three glaciers were advancing over mature forest in valley floor sites, 0.5–1.0 km upvalley of Little Ice Age maximum positions attained in the 18th and 19th centuries. Tree-ring width chronologies from treeline sites show suppressed growth in the early 12th century and for several periods in the 12th–14th centuries. The only tree-ring chronology presently spanning the 900–1300 A.D. interval has generally wider ringwidths between 950 and 1100 A.D. suggesting conditions were more favourable at that time. Forested sites overrun by glaciers in the 12th–14th centuries have only been deglaciated within the present century.     

Permafrost Degradation and Ecological Changes Associated with a WarmingClimate in Central Alaska

Studies from 1994–1998 on the TananaFlats in central Alaska reveal that permafrostdegradation is widespread and rapid, causing largeshifts in ecosystems from birch forests to fens andbogs. Fine-grained soils under the birch forest areice-rich and thaw settlement typically is 1–2.5 mafter the permafrost thaws. The collapsed areas arerapidly colonized by aquatic herbaceous plants,leading to the development of a thick, floatingorganic mat. Based on field sampling of soils,permafrost and vegetation, and the construction of aGIS database, we estimate that 17% of the study area(263,964 ha) is unfrozen with no previous permafrost,48% has stable permafrost, 31% is partiallydegraded, and 4% has totally degraded. For thatportion that currently has, or recently had,permafrost (83% of area), 42% has been affected bythermokarst development. Based on airphoto analysis,birch forests have decreased 35% and fens haveincreased 29% from 1949 to 1995. Overall, the areawith totally degraded permafrost (collapse-scar fensand bogs) has increased from 39 to 47% in 46 y. Based on rates of change from airphoto analysis andradiocarbon dating, we estimate 83% of thedegradation occurred before 1949. Evidence indicatesthis permafrost degradation began in the mid-1700s andis associated with periods of relatively warm climateduring the mid-late 1700s and 1900s. If currentconditions persist, the remaining lowland birchforests will be eliminated by the end of the nextcentury.     

Uncertainty in Predicting the Effect of Climatic Change on the Carbon Cycling of Canadian Peatlands

Northern peatlands play an important role globally in the cycling of C, through the exchange of CO2 with the atmosphere, the emission of CH4, the production and export of dissolved organic carbon (DOC) and the storage of C. Under 2 × CO2 GCM scenarios, most Canadian peatlands will be exposed to increases in mean annual temperature ranging between 2 and 6° C and increases in mean annual precipitation of 0 to 15 %, with the most pronounced changes occurring during the winter. The increase in CO2 uptake by plants, through warmer temperatures and elevated atmospheric CO2, is likely to be offset by increased soil respiration rates in response to warmer soils and lowered water tables. CH4 emissions are likely to decrease in most peatlands because of lowered water tables, except where the peat surface adjusts to fluctuating water tables, and in permafrost, where the collapse of dry plateau and palsa will lead to increase CH4 emission. There likely will be little change in DOC production, but DOC export to water bodies will decrease as runoff decreases. The storage of C in peatlands is sensitive to all C cycle components and is difficult to predict. The challenge is to develop quantitative models capable of making these predictions for different peatlands. We present some qualitative responses, with levels of uncertainty. There will be, however, as much variation in response to climatic change within a peatland as there will be among peatland regions.     

Yangtze Delta floods and droughts of the last millennium: Abrupt changes and long term memory

Summary Climate variability and flood events in the Yangtze Delta, which is a low-lying terrain prone to flood hazards, storm tides and typhoons, are studied in terms of a trend and detrended fluctuation analysis of historical records. The data used in this paper were extracted from historical records such as local annuals and chronologies from 1000–1950 and supplemented by instrumental observations since 1950. The historical data includes frequencies of floods, droughts and maritime events on a decadal basis. Flood magnitudes increase during the transition from the medieval warm interval into the early Little Ice Age. Fluctuating climate changes of the Little Ice Age, which are characterised by arid climate events, are followed by wet and cold climate conditions with frequent flood hazards. For trend analysis, the Mann-Kendall test is applied to determine the changing trends of flood and drought frequency. Flood frequency during 1000–1950 shows a negative trend before 1600 A.D. and a positive trend thereafter; drought frequency increases after 1300. The detrended fluctuation analysis of the flood and drought frequencies reveals power law scaling up to centuries; this is related to long-term memory and is similar to the river Nile floods.     

National Inventories of Terrestrial Carbon Sources and Sinks: The U.K. Experience

The U.K. has extensive databases on soils, land cover and historic land use change which have made it possible to construct a comprehensive inventory of the principal terrestrial sources and sinks of carbon for approximately the year 1990, using methods that are consistent with, and at least as accurate as, the revised 1996 guidelines recommended by IPCC where available – and including categories which are not currently considered under the UN Framework Convention on Climate Change. This country inventory highlights issues concerning methodology, uncertainty, double counting, the importance of soils and the relative magnitude of sources and sinks which are reported to the UNFCCC relative to other sources and sinks. The carbon sinks (negative values in MtC a^-1) for categories reported to the UNFCCC, based on the IPCC categories, were estimated to be: forest trees and litter (–2.1), U.K. forest products (–0.5, ignoring imports and exports), non-forest biomass (–0.3), forest soils (–0.1) and soils on set-aside land (–0.4). The carbon sources (positive values) reported under the UNFCCC were estimated to be: losses of soil organic carbon resulting from cultivation of semi-natural land (6.2) and from urbanization (1.6), drainage of peatlands (0.3) and fenlands (0.5), and peat extraction (0.2). A range of other sources and sinks not covered by the IPCC guidelines were also quantified, namely, the accumulation of carbon in undrained peatlands (–0.7, ignoring methane emission), sediment accretion in coastal marshes (–0.1), the possible U.K. share of the CO₂ and N fertilization carbon sink (–2.0) and riverine organic and particulate carbon export to the sea (1.4, which may be assumed to be a source if most of this carbon is released as CO₂ in the sea). All sinks totalled –6.2 and sources 10.2, giving a net flux to the atmosphere in 1990 of 4.0 MtC a^-1. Uncertainties associated with categories, mostly based on best guesses, ranged from ±15% for forest biomass and litter to ±60% for CO₂ and N fertilization.     

A warm and wet little climatic optimum and a cold and dry little ice age in the southern rocky mountains,U.S.A.

The zenith of Anasazi Pueblo Indian occupation in the northern Colorado Plateau region of the southwestern U.S.A. coincides with the Little Climatic Optimum or Medieval Warm Period (A.D. 900–1300), and its demise coincides with the commencement of the Little Ice Age. Indexes of winter (jet-stream derived) and summer (monsoon derived) precipitation and growing season length were developed for the La Plata Mountains region of southwestern Colorado. The results show that during the height of the Little Climatic Optimum (A.D. 1000–1100) the region was characterized by a relatively long growing season and by a potential dry farming zone or elevational belt (currently located between 2,000 m and 2,300 m elevation) that was twice as wide as present and could support Anasazi upland dry farming down to at least 1,600 m, an elevation that is quite impossible to dry farm today because of insufficient soil moisture. This expanded dry-farm belt is attributable to a more vigorous circulation regime characterized by both greater winter and summer precipitation than that of today. Between A.D. 1100 and 1300 the potential dry-farm belt narrowed and finally disappeared with the onset of a period of markedly colder and drier conditions than currently exist. Finally, when the Little Ice Age terminated in the mid A.D. 1800s and warmer, wetter conditions returned to the region, another group of farmers (modern Anglos) were able to dry farm the area.The U.S. Government right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

On the Use of the Jesuit Order Private Correspondence Records in Climate Reconstructions: A Case Study from Castille (Spain) for 1634–1648 A.D.

This work analyses the climatic information content of more than 1000 letters belonging to the private correspondence of the Jesuit order during the period 1634–1648. The information obtained mainly originates in Castille, and it was codified to obtain quantitative indices representative of the evolution of the thermal and rainfall anomalies. The results show that intense rainfall and cold air waves predominated during the study period, in accordance with other results on the climatic evolution of the Iberian Peninsula during the Little Ice Age.     

Secular trends in high northern latitude temperature reconstructions based on tree rings

Boreal tree-ring records from high latitude North America, Scandinavia and Russia provide baseline data reflecting long-term trends in Arctic annual temperature. Reconstructions from 1682–1968 indicate the latter part and termination of the Little Ice Age and that the northern regions are now warmer by comparison. The resulting high-resolution, extended temperature time series allows examination of underlying causes of climatic change not possible using only the instrumental record. The recent recorded data for the Arctic show recovery from the cooling in the 1950's–1960's. The overall evaluation confirms that the high northern latitudes are now in an anomalously warm state relative to the past three centuries.     

Determining Effects of Area Burned and Fire Severity on Carbon Cycling and Emissions in Siberia

The Russian boreal forest contains about 25% of the global terrestrial biomass, and even a higher percentage of the carbon stored in litter and soils. Fire burns large areas annually, much of it in low-severity surface fires – but data on fire area and impacts or extent of varying fire severity are poor. Changes in land use, cover, and disturbance patterns such as those predicted by global climate change models, have the potential to greatly alter current fire regimes in boreal forests and to significantly impact global carbon budgets. The extent and global importance of fires in the boreal zone have often been greatly underestimated. For the 1998 fire season we estimate from remote sensing data that about 13.3 million ha burned in Siberia. This is about 5 times higher than estimates from the Russian Aerial Forest Protection Service (Avialesookhrana) for the same period. We estimate that fires in the Russian boreal forest in 1998 constituted some 14–20% of average annual global carbon emissions from forest fires. Average annual emissions from boreal zone forests may be equivalent to 23–39% of regional fossil fuel emissions in Canada and Russia, respectively. But the lack of accurate data and models introduces large potential errors into these estimates. Improved monitoring and understanding of the landscape extent and severity of fires and effects of fire on carbon storage, air chemistry, vegetation dynamics and structure, and forest health and productivity are essential to provide inputs into global and regional models of carbon cycling and atmospheric chemistry.     

Variability of Sea-Ice Extent in Baffin Bay over the Last Millennium

Comparison of an ice core glaciochemical time-series developed from thePenny Ice Cap (PIC), Baffin Island and monthly sea-ice extent reveals astatisticallysignificant inverse relationship between changes in Baffin Bay spring sea-iceextent andPenny Ice Cap sea-salt concentrations for the period 1901–1990 AD.Empiricalorthogonal function analysis demonstrates the joint behavior between changesin PICsea-salt concentrations, sea-ice extent, and changes in North Atlanticatmosphericcirculation. Our results suggest that sea-salt concentrations in snowpreserved on thePIC reflect local to regional springtime sea-ice coverage. The PIC sea-saltrecord/sea-ice relationship is further supported by decadal and century scalecomparisonwith other paleoclimate records of eastern Arctic climate change over the last700 years. Our sea-salt record suggests that, while the turn of the century wascharacterized bygenerally milder sea-ice conditions in Baffin Bay, the last few decades ofsea-ice extentlie within Little Ice Age variability and correspond to instrumental recordsof lowertemperatures in the Eastern Canadian Arctic over the past three decades.     

Modelling climate change effects on the spatial distribution of mountain permafrost at three sites in northwest Canada

Spatial models of present-day mountain permafrost probability were perturbed to examine potential climate change impacts. Mean annual air temperature (MAAT) changes were simulated by adjusting elevation in the models, and cloud cover changes were examined by altering the partitioning of direct beam and diffuse radiation within the calculation for potential incoming solar radiation (PISR). The effects of changes in MAAT on equilibrium permafrost distribution proved to be more important than those due to cloud cover. Under a ?2 K scenario (approximating Little Ice Age conditions), permafrost expanded into an additional 22?C43% of the study areas as zonal boundaries descended by 155?C290 m K^???1. Under warming scenarios, permafrost probabilities progressively declined and zonal boundaries rose in elevation. A MAAT change of +5 K, caused two of the areas to become essentially permafrost-free. The absolute values of these predictions were affected up to ±10% when lapse rates were altered by ±1.5 K km^???1 but patterns and trends were maintained. A higher proportion of diffuse radiation (greater cloud cover) produced increases in permafrost extent of only 2?C4% while decreases in the diffuse radiation fraction had an equal but opposite effect. Notwithstanding the small change in overall extent, permafrost probabilities on steep south-facing slopes were significantly impacted by the altered partitioning. Combined temperature and PISR partitioning scenarios produced essentially additive results, but the impact of changes in the latter declined as MAAT increased. The modelling illustrated that mountain permafrost in the discontinuous zone is sensitive spatially to long-term climate change and identified those areas where changes may already be underway following recent atmospheric warming.     

Diurnal variations in methane emissions from West Siberia peatlands in summer

New data on the diurnal variability of methane emission in summer (2013-2014) from West Siberia peatland ecosystems are presented. It is demonstrated that diurnal variations in methane emission differ much depending on a peatland ecosystem under study. Diurnal variations in methane emission in the fens and hollows of the ridge-hollow complex (RHC) are revealed as well as their reproducibility in 2013-2014. The maximum emission is registered in the daytime, and the minimum is observed at night. There is no diurnal variation in methane emission in ryams (pine bogs) and ridges of RHC. It is revealed that in the upper layer of peat (at the depth up to 10 cm for hollows and at the depth of 2 and 5 cm for fens) the contribution of temperature variability to methane emission variations in fens and hollows is 15-20%. The multiple linear regression with peat temperature at several depths allows explaining 44-54% of the variability of methane flux from peatlands. No significant correlation between methane fluxes and the temperature of peat and air was identified in the diurnal cycle in ryams and ridges.     

Tree-ring reconstructed rainfall over the southeastern U.S.A. during the medieval warm period and little ice age

A 1053-year reconstruction of spring rainfall (March-June) was developed for the southeastern United States, based on three tree-ring reconstructions of statewide rainfall from North Carolina, South Carolina, and Georgia. This regional reconstruction is highly correlated with the instrumental record of spring rainfall (r = +0.80; 1887–1982), and accurately reproduces the decade-scale departures in spring rainfall amount and variance witnessed over the Southeast during the past century. No large-magnitude centuries-long trends in spring rainfall amounts were reconstructed over the past 1053 years, but large changes in the interannual variability of spring rainfall were reconstructed during portions of the Medieval Warm Period (MWP), Little Ice Age (LIA), and the 20th century. Dry conditions persisted at the end of the 12th century, but appear to have been exceeded by a reconstructed drought in the mid-18th century. High interannual variability, including five extremely wet years were reconstructed for a 20-yr period during the late 16th and early 17th centuries, and may reflect amplified atmospheric circulation over eastern North America during what appears to have been one of the most widespread cold episodes of the Little Ice Age.     

Siberian CO2 efflux in winter as a CO2 source and cause of seasonality in atmospheric CO2

Over three years, we found a consistent CO₂ efflux from forest tundra of the Russian North throughout the year, including a large (89 g C m^–2 yr^–1) efflux during winter. Our results provide one explanation for the observations that the highest atmospheric CO₂ concentration and greatest seasonal amplitude occur at high latitudes rather than over the mid-latitudes, where fossil fuel sources are large, and where high summer productivity offset by winter respiration should give large seasonal oscillations in atmospheric CO₂. Winter respiration probably contributed substantially to the boreal winter CO₂ efflux. Respiration is an exothermic process that produces enough heat to warm soils and promote further decomposition. We suggest that, as a result of this positive feedback, small changes in surface heat flux, associated with human activities in the North or with regional or global warming, could release large quantities of organic carbon that are presently stored in permafrost.     

Effects of Climate Change on Carbon Storage in Boreal Forests of China: A Local Perspective

The BIOME3 model was used to simulate the distribution patterns and carbon storage of the horizontal, zonal boreal forests in northeast and northwest China using a mapping system for vegetation patterns combined with carbon density estimates from vegetation and soils. The BIOME3 prediction is in reasonable good agreement with the potential distribution of Chinese boreal forests. The effects of changing atmospheric CO₂ concentration had a nonlinear effect on boreal forest distribution, with 3.5–10.8% reduced areas for both increasing and decreasing CO₂. In contrast, the increased climate together with and without changing CO₂ concentration showed dramatic changes in geographic patterns, with 70% reduction in area and disappearance of almost boreal forests in northeast China. The baseline carbon storage in boreal forests of China is 4.60 PgC (median estimate) based on the vegetation area of actual boreal forest distribution. If taking the large area of agricultural crops into account, the median value of potential carbon storage is 6.92 PgC. The increasing (340–500 ppmv) and decreasing CO₂ concentration (340–200 ppmv) led to decrease of carbon storage, 0.33 PgC and 1.01 PgC respectively compared to BIOME3 potential prediction under present climate and CO₂ conditions. Both climate change alone and climate change with CO₂ enrichment (340–500 ppmv) reduced largely the carbon stored in vegetation and soils by ca. 6.5 PgC. The effect of climate change is more significant than the direct physiological effect of CO₂ concentration on the boreal forests of China, showing a large reduction in both distribution area and carbon storage.