Long-term variability of sea surface temperature in Taiwan Strait

Long-term variability of sea surface temperature (SST) in the Taiwan Strait was studied from the U.K. Met Office Hadley Centre climatological data set HadISST1. In 1957–2011, three epochs were identified. The first epoch of cooling SST lasted through 1976. The regime shift of 1976–1977 led to an extremely rapid warming of 2.1 °C in 22 years. Another regime shift occurred in 1998–1999, resulting in a 1.0 °C cooling by 2011. The cross-frontal gradient between the China Coastal Current and offshore Taiwan Strait waters has abruptly decreased in 1992 and remained low through 2011. The long-term warming of SST increased towards the East China Sea, where the SST warming in 1957–2011 was about three times that in the South China Sea. The long-term warming was strongly enhanced in winter, with the maximum warming of 3.8 °C in February. The wintertime amplification of long-term warming has resulted in a decrease of the north–south SST range from 5 to 4 °C and a decrease in the amplitude of seasonal cycle of SST from 11 to 8 °C.     

Statistical Projections of Ocean Climate Indices off Newfoundland and Labrador

ABSTRACT

Present global climate models (GCMs) are unable to provide reliable projections of physical oceanographic properties on the continental shelf off Newfoundland and Labrador. Here we first establish linear statistical relationships between oceanographic properties and coastal air temperature based on historical observations. We then use these relationships to project future states of oceanographic conditions under different emission scenarios, based on projected coastal air temperatures from global (Canadian Earth System Model, version 2 (CanESM2), Geophysical Fluid Dynamics Laboratory's Earth System Model, version 2M (GFDL-ESM2M)) and regional (Canadian Regional Climate Model (CRCM)) climate models. Estimates based on CanESM2 agree reasonably well with observed trends, but the trends based on two other models result in substantial underestimates. Projected trends are closer to observations under a high emission scenario than under median-level emission scenarios. Over the next 50 years, the increases in projected sea surface temperature off eastern Newfoundland (Station 27) range from 0.4° to 2.2°C. The increases in bottom ocean temperature over the Newfoundland and Labrador Shelves range from 0.4° to 2.1°C. The area of the cold intermediate layer (<0°C) on the Flemish Cap (47°N) section is projected to decrease by 9–35% of the 1981–2010 average. The decline in sea-ice extent off Newfoundland and Labrador ranges from 20 to 77% of the average (0.4–1.5?×?10⁵?km²), and the reduction in the number of icebergs at 48°N off Newfoundland ranges from 30% to nearly 100% of the norm at this latitude. Despite differences among the models and scenarios, statistical projections indicate that conditions in this region will reach or exceed their maxima (sea surface temperature, bottom ocean temperature) and reach or fall below their minima (sea-ice extent, number of icebergs) that were observed during the course of monitoring activities over the past 30–60 years, possibly as early as 2040. We note, however, that the statistical relationships based on historical data may not hold in the future because of the changing influence of input from Arctic waters and because of large uncertainties in projected air temperatures from GCMs.     

The freshwater transport of the labrador current

Abstract

A simple variant of the salt flux calculation is used to estimate the freshwater transport of the Labrador Current. A freshwater budget is then constructed for the Labrador Sea, comparing the summed inputs of fresh water with the fresh water lost in the Labrador Current. Our results indicate that Baffin Bay and Hudson Strait are the largest contributors to the freshwater flux of the Labrador Current. It is found that there is ample freshwater transport in the very low salinity waters to meet the required input of fresh water of northerly origin to the Middle Atlantic Bight.     

Glacial/interglacial changes in the East Australian current

The East Australian Current (EAC) is the western boundary current of the south Pacific gyre transporting warm tropical waters to higher southern latitudes. Recent modelling shows that the partial separation of the EAC (~32°S) and the coupled formation of the Tasman Front (~34°S) are caused by a steep gradient in the zonally integrated wind stress curl. Analysis of oxygen isotope ratios (δ¹⁸O) in the planktonic foraminifer, Globigerinoides ruber, from sediment cores from the Coral Sea and Tasman Sea indicates that the EAC separation shifted northward to between 23 and 26°S during the last glacial. We suggest these results indicate a significant change in the Pacific wind stress curl during the glacial. Given recent evidence for El Niño-like conditions in the Pacific during the last glacial, with a reduction in the east–west sea surface temperature (SST) gradient, we suggest that weaker trade winds combined with more northerly, stronger westerlies were associated with a change to the wind stress curl, which repositioned the EAC separation and Tasman Front. In contrast, by ~11 ka BP, the EAC separation was forced south of 26°S. This southward shift was synchronous with a rapid warming of tropical SSTs, and the onset of a La Niña-like SST configuration across the tropical Pacific. It appears that the south Pacific trade winds strengthened accordingly, causing the EAC to readjust its flow. This readjustment of the EAC marks the onset of modern surface-ocean circulation in the southwest Pacific, but the present EAC transport was only achieved in the late Holocene, after 5 ka BP.     

A snapshot of the Labrador current inferred from ice‐floe movement in NOAA satellite imagery

Abstract

Ice floes along the Labrador Coast were tracked using visible NOAA satellite images on two consecutive days (26 and 27 April, 1984) when the ice‐pack extended beyond the Labrador Current, and winds were weak. The resulting “snapshot” of the velocity field reveals strong topographic steering of the Labrador Current, such that the current speed and width in different areas are dependent on the steepness of the continental slope, and the current deflects into and out of Hopedale Saddle. Between 55 and 58°N, the main core of the current is 60–90 km wide, with speeds of 30–55 cm s^?1. The overall circulation pattern is in good agreement with historical water mass analyses over the shelf and slope, and with estimates of the speed of the Labrador Current obtained by other methods.     

Satellite observations of labrador current undulations

Abstract

Analysis of visual images of the offshore ice margin of the Labrador Coast, taken on four consecutive days from the NOAA‐5 satellite, reveals horizontal oscillations with a mean wavelength of 75 km and amplitude of 15 km. The oscillations travel downstream, with the Labrador Current, at a speed C ≈ 0.2 m s^‐1. Oscillations of similar periods are seen in moored current meter records. An examination of available models of baro tropic and baro‐clinic instability shows that the latter mechanism could account for the generation of the observed oscillations from the shear in the Labrador Current.     

Climate Change on Newfoundland and Labrador Shelves: Results From a Regional Downscaled Ocean and Sea-Ice Model Under an A1B Forcing Scenario 2011–2069

Climate change may affect ocean and ice conditions in coastal oceans and thus have significant impacts on coastal infrastructure, marine navigation, and marine ecosystems. In this study a three-dimensional ice–ocean model is developed to examine likely changes of ocean and ice conditions over the Newfoundland and Labrador Shelves in response to climate change. The model is configured with a horizontal grid of approximately 7?km and a vertical grid of 46 levels and is run from 1979 to 2069. The projection period is 2011 to 2069 under a median emission scenario A1B used by the Intergovernmental Panel on Climate Change. For the projection period, the surface atmospheric forcing fields used are from the Canadian Regional Climate Model over the North Atlantic. The open boundary conditions come from the Canadian Global Climate Model, Version 3 (CGCM3), adjusted for the 1981–2010 mean of the Simple Ocean Data Assimilation model output. The simulated fields over the 1981–2010 period have patterns consistent with observations. Over the Newfoundland and Labrador Shelves during the projection period, the model shows general trends of warming, freshening, and decreasing ice. From 2011 to 2069, the model projects that under A1B sea surface temperature will increase by 1.4°C; bottom temperature will increase by 1.6°C; sea surface salinity will decrease by 0.7; bottom salinity will decrease by 0.3; and sea-ice extent will decrease by 70%. The sea level will rise by 0.11?m at the St. John's tide-gauge station because of oceanographic change, and the freshwater transport of the Labrador Current will double as a result of freshening. The regional ice–ocean model reproduces more realistic present climate conditions and projects considerably different future climate conditions than CGCM3.     

Temperature variations and rice yields in China: historical contributions and future trends

Temperature is the principal factor that determines rice growth, development and ultimately grain yield. In this study, normal growing-degree-days (NGDD) and killing growing-degree-days (KGDD) were used to capture the different effects of normal and extreme temperatures on rice yields, respectively. Based on these indexes, we assessed the contributions of temperature variations to county-level rice yields across China during the historical period (1980–2008), and estimated the potential exposure of rice to extreme temperature stress in the near future (2021–2050). The results showed that historical temperature variations had measurable impacts on rice yields with a distinct spatial pattern: for different regions, such variations had contributed much to the increased rice yields in Northeast China (Region I) (0.59 % yield year^?1) and some portions of the Yunnan-Guizhou Plateau (Region II) (0.34 % yield year^?1), but seriously hindered the improvements of rice yields in the Sichuan Basin (SB) (?0.29 % yield year^?1) and the southern cultivation areas (Region IV) (?0.17 % yield year^?1); for the entire country, half of the contributions were positive and the other half were negative, resulting in a balance pattern with an average of 0.01 % yield year^?1. Under the RCP8.5 scenario, climate warming during 2021–2050 would substantially reduce cold stress but increase heat stress in the rice planting areas across China. For the future period, Region I, II and eastern China would be continually exposed to more severe cold stress than the other regions; Region III (including SB and the mid-lower reaches of Yangtze River (MLRYR)) would be the hot spot of heat stress.     

Assessment of surface air warming in northeast China, with emphasis on the impacts of urbanization

Based on homogenized land surface air temperature (SAT) data (derived from China Homogenized Historical Temperature (CHHT) 1.0), the warming trends over Northeast China are detected in this paper, and the impacts of urban heat islands (UHIs) evaluated. Results show that this region is undergoing rapid warming: the trends of annual mean minimum temperature (MMIT), mean temperature (MT), and mean maximum temperature (MMAT) are 0.40 C decade^?1, 0.32 C decade^?1, and 0.23 C decade^?1, respectively. Regional average temperature series built with these networks including and excluding “typical urban stations” are compared for the periods of 1954–2005. Although impacts of UHIs on the absolute annual and seasonal temperature are identified, UHI contributions to the long-term trends are less than 10% of the regional total warming during the period. The large warming trend during the period is due to a regime shift in around 1988, which accounted for about 51% of the regional warming.     

Understanding Madden-Julian-Induced sea surface temperature variations in the North Western Australian Basin

The strongest large-scale intraseasonal (30–110 day) sea surface temperature (SST) variations in austral summer in the tropics are found in the eastern Indian Ocean between Australia and Indonesia (North-Western Australian Basin, or NWAB). TMI and Argo observations indicate that the temperature signal (std. ~0.4 °C) is most prominent within the top 20 m. This temperature signal appears as a standing oscillation with a 40–50 day timescale within the NWAB, associated with ~40 Wm^?2 net heat fluxes (primarily shortwave and latent) and ~0.02 Nm^?2 wind stress perturbations. This signal is largely related to the Madden-Julian Oscillation. A slab ocean model with climatological observed mixed-layer depth and an ocean general circulation model both accurately reproduce the observed intraseasonal SST oscillations in the NWAB. Both indicate that most of the intraseasonal SST variations in the NWAB in austral winter are related to surface heat flux forcing, and that intraseasonal SST variations are largest in austral summer because the mixed-layer is shallow (~20 m) and thus more responsive during that season. The general circulation model indicates that entrainment cooling plays little role in intraseasonal SST variations. The larger intraseasonal SST variations in the NWAB as compared to the widely-studied thermocline-ridge of the Indian Ocean region is explained by the larger convective and air-sea heat flux perturbations in the NWAB.     

The influence of the ocean on the chemistry of precipitation in Nova Scotia*

Abstract

Between the fall of 1977 and December 1980, over 800 samples of precipitation were collected at 9 rural locations across Nova Scotia.

Average pH was 4.61, and an average conductivity of 25 μS cm^?1 confirmed the low ionic strength of rain and snow. Of all ions, chloride was the most abundant at 76 μeq L^?1 (2.7 mg L^?1). Oceanic origins were perceived as the source for chloride as well as for Na, Mg, 51 % of K, 21% of Ca, and 21% of SO₄, and the sea collectively accounted for 66% of all ions inNova Scotian precipitation. In contrast, the dominating ions in New York, New Hampshire, Ontario and Norway were H⁺ and SO₄.

In Nova Scotia, chloride concentrations in rain (mg L^?1) are a function of distance D (km) from the coast and may be described by the equation Cl [mg L^?1] = 4.5D^?0.42. It indicates that Cl concentrations are reduced by about 50% within 0.5 km of the coast, and 80% within 5 km. The continental North American chloride data examined are also consistent with the relationship.

The shape of the chloride curve is similar to curves others have developed from rain and lake water chemistry observations in Holland and the United Kingdom, although those, and other European data, indicate that the marine influence is less pronounced in northeastern North America.

The marine influence of precipitation chemistry on Nova Scotia has a maximum seasonal amplitude during the winter.     

Coupled North Atlantic slope water forcing on Gulf of Maine temperatures over the past millennium

To investigate ocean variability during the last millennium in the Western Gulf of Maine (GOM), we collected a 142-year-old living bivalve (Arctica islandica L.) in 2004, and three fossil A. islandica shells (calibrated ¹⁴C_AMS = 1030 ± 78 ad; 1320 ± 45 ad; 1357 ± 40 ad) for stable isotope and growth increment analysis. A statistically significant relationship exists between modern GOM temperature records [shell isotope-derived (30 m) (r = ?0.79; P < 0.007), Prince 5 (50 m) (r = ?0.72; P < 0.019), Boothbay Harbor SST (r = ?0.76; P < 0.011)], and Labrador Current (LC) transport data from the Eastern Newfoundland Slope during 1993–2003. In all cases, as LC transport increased, GOM water temperatures decreased the following year. Decadal trends in the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) influence GOM water temperatures in the most recent period, with water temperatures decreasing during NAO and AMO negative modes most likely linked to LC transport and Gulf Stream interaction. Mean shell-derived isotopic changes (δ¹⁸O_c) during the last 1,000 years were +0.47‰ and likely reflect a 1–2°C cooling from 1000 ad to present. Based on these results, we suggest that observed cooling in the GOM during the last millennium was due to increased transport and/or cooling of the LC, and decreased Gulf Stream influence on the GOM.     

Holocene vegetation and hydrology variations and their associations with climate changes: a multi-proxy analysis of a sediment core from an alpine basin in the middle Tianshan Mountains

We in this paper present a multi-proxy study of a 186-cm-long lacustrine sediment core (i.e., BY Core) obtained from the Youerdusi Basin in the middle Tianshan Mountains in an attempt to disentangle the causal associations among climate changes, ecological responses and hydrological variations. Palynological, assemblages and the associated biome scores indicate that the upper limit of the forest zone was closer to the Youerdusi Basin with a larger wetland extent in the Youerdusi Basin during the early part (i.e., from ~ 10.5 to ~ 5.8 cal. kyr BP) of the data-covering period (i.e., from ~ 10.5 to ~ 2.4 cal. kyr BP). The upper limit of the forest zone was farther away from the Youerdusi Basin with a smaller wetland extent in the Youerdusi Basin during the late part (i.e., from ~ 5.8 to ~ 2.4 cal. kyr BP). The changes of taiga biome score and the AP% ratio indicate a persistent cooling trend during the data-covering period which is well corroborated by various proxy data from nearby sites and the cooling trend is chronologically consistent with the trend of Northern Hemisphere temperature anomalies that was interpreted to be a delayed response to the summer solar irradiance at 50° N. The tundra biome score and the associated percentages of Cyperaceae in the Youerdusi Basin show two major stages of wetland extent variation. The wetland extent variation in the Youerdusi Basin might have been controlled by precipitation and/or by glacier-melting potential that was in turn controlled by both temperature and the extent of remained ice cover in higher elevations. The δ¹³C_org values obtained from the BY Core indicate a wetting trend during the data-covering period which is reasonably corroborated by various proxy data from nearby sites. We infer that the wetting trend was causally associated with the Holocene increasing trend of the North Atlantic Ocean SST (sea surface temperature) and also with the Holocene increasing trend of the westerlies’ intensity.

     

Extraordinary blowing snow transport events in East Antarctica

In the convergence slope/coastal areas of Antarctica, a large fraction of snow is continuously eroded and exported by wind to the atmosphere and into the ocean. Snow transport observations from instruments and satellite images were acquired at the wind convergence zone of Terra Nova Bay (East Antarctica) throughout 2006 and 2007. Snow transport features are well-distinguished in satellite images and can extend vertically up to 200 m as first-order quantitatively estimated by driftometer sensor FlowCapt?. Maximum snow transportation occurs in the fall and winter seasons. Snow transportation (drift/blowing) was recorded for ~80% of the time, and 20% of time recorded, the flux is >10^?2 kg m^?2 s^?1 with particle density increasing with height. Cumulative snow transportation is ~4 orders of magnitude higher than snow precipitation at the site. An increase in wind speed and transportation (~30%) was observed in 2007, which is in agreement with a reduction in observed snow accumulation. Extensive presence of ablation surface (blue ice and wind crust) upwind and downwind of the measurement site suggest that the combine processes of blowing snow sublimation and snow transport remove up to 50% of the precipitation in the coastal and slope convergence area. These phenomena represent a major negative effect on the snow accumulation, and they are not sufficiently taken into account in studies of surface mass balance. The observed wind-driven ablation explains the inconsistency between atmospheric model precipitation and measured snow accumulation value.     

Decadal fingerprints of freshwater discharge around Greenland in a multi-model ensemble

The recent increase in the rate of the Greenland ice sheet melting has raised with urgency the question of the impact of such a melting on the climate. As former model projections, based on a coarse representation of the melting, show very different sensitivity to this melting, it seems necessary to consider a multi-model ensemble to tackle this question. Here we use five coupled climate models and one ocean-only model to evaluate the impact of 0.1 Sv (1 Sv = 10⁶ m³/s) of freshwater equally distributed around the coast of Greenland during the historical era 1965–2004. The ocean-only model helps to discriminate between oceanic and coupled responses. In this idealized framework, we find similar fingerprints in the fourth decade of hosing among the models, with a general weakening of the Atlantic Meridional Overturning Circulation (AMOC). Initially, the additional freshwater spreads along the main currents of the subpolar gyre. Part of the anomaly crosses the Atlantic eastward and enters into the Canary Current constituting a freshwater leakage tapping the subpolar gyre system. As a consequence, we show that the AMOC weakening is smaller if the leakage is larger. We argue that the magnitude of the freshwater leakage is related to the asymmetry between the subpolar-subtropical gyres in the control simulations, which may ultimately be a primary cause for the diversity of AMOC responses to the hosing in the multi-model ensemble. Another important fingerprint concerns a warming in the Nordic Seas in response to the re-emergence of Atlantic subsurface waters capped by the freshwater in the subpolar gyre. This subsurface heat anomaly reaches the Arctic where it emerges and induces a positive upper ocean salinity anomaly by introducing more Atlantic waters. We found similar climatic impacts in all the coupled ocean–atmosphere models with an atmospheric cooling of the North Atlantic except in the region around the Nordic Seas and a slight warming south of the equator in the Atlantic. This meridional gradient of temperature is associated with a southward shift of the tropical rains. The free surface models also show similar sea-level fingerprints notably with a comma-shape of high sea-level rise following the Canary Current.     

Declining Oxygen on the British Columbia Continental Shelf

The first thorough examination of oxygen concentrations in Canadian waters of the Pacific Ocean reveals several patterns in space and time. Sub-surface concentrations of oxygen tend to be lower in shelf waters than in deep-sea waters on the same isopycnal and lower in southern waters of the continental shelf than farther north. The lowest near-bottom concentration was 0.7 ml L^?1 (31 μmol kg^?1) in mid-shelf waters in summer off southwest Vancouver Island in the Juan de Fuca Eddy region. Oxygen concentration there declined at a rate of 0.019 ml L^?1 y^?1 (0.83 μmol kg^?1 y^?1) from 1979 to 2011. This decline is attributed mainly to changes in oxygen concentrations on the same density surfaces, rather than to changes in the depth of constant-density surfaces. A numerical simulation of ocean currents and nutrient concentrations in and surrounding the Juan de Fuca Eddy in summer reveals persistent upwelling into the centre of this eddy and slow bottom currents within the eddy. Upwelled water at bottom of the Juan de Fuca Eddy has water properties associated with the California Undercurrent on the 26.6 sigma-t surface at 200 m depth, where oxygen concentration is typically 2.0 ml L^?1 (87 μmol kg^?1) and declined at a rate of 0.025 ml L^?1 y^?1 (1.1 μmol kg^?1 y^?1) from 1981 to 2011, mainly as a result of changes on constant-density surfaces rather than to uplifting isopycnals. We propose that upwelling advects deep, oxygen-poor water onto the continental shelf bottom, and the slow bottom currents allow time for oxidation of organic material in bottom waters to further reduce the oxygen concentration.

RÉSUMÉ?[Traduit par la rédaction] Le premier examen approfondi des concentrations d'oxygène dans les eaux canadiennes de l'océan Pacifique révèle plusieurs configurations dans le temps et dans l'espace. Les concentrations d'oxygène sous la surface ont tendance à être plus faibles dans les eaux de la plate-forme continentale que dans les eaux de l'océan profond sur la même isopycne et plus faibles dans les eaux du sud de la plate-forme que plus loin au nord. La concentration la plus faible près du fond était de 0.7 ml L^?1 (31 μmol kg^?1) dans les eaux du milieu de la plate-forme en été au large du sud-ouest de l’île de Vancouver dans la région du remous de Juan de Fuca. Les concentrations en oxygène à cet endroit ont diminué au rythme de 0.019 ml L^?1 a^?1 (0.83 μmol kg^?1 a^?1) entre 1979 et 2011. Cette diminution est principalement attribuée aux changements dans les concentrations d'oxygène sur les surfaces d’égale densité plutôt qu'aux changements dans la profondeur des surfaces de densité constante. Une simulation numérique des courants océaniques et des concentrations de nutrients dans le remous de Juan de Fuca et dans les régions avoisinantes en été révèle des remontées d'eau froide persistantes vers le centre de ce remous et des courants de fond lents à l'intérieur du remous. L'eau qui a remonté au fond du remous de Juan de Fuca a des propriétés liées au sous-courant de Californie sur la surface sigma–t 26.6 à une profondeur de 200 m, où la concentration en oxygène est normalement de 2.0 ml L^?1 (87 μmol kg^?1), et a diminué au taux de 0.025 ml L^?1 a^?1 (1.1 μmol kg^?1 a^?1) de 1981 à 2011, principalement à cause des changements sur les surfaces de densité constante plutôt que du soulèvement des isopycnes. Nous pausons l'hypothèse que les remontées d'eau advectent des eaux profondes pauvres en oxygène au bas de la plate-forme continentale et que les lents courants de fond donnent le temps à l'oxydation de la matière organique dans les eaux de fond, ce qui réduit davantage la concentration de l'oxygène.     

A decade of cloud‐to‐ground lightning in Canada: 1999–2008. Part 1: Flash density and occurrence

Abstract

Flash density and occurrence features for more than 23.5 million cloud‐to‐ground (CG) lightning flashes detected by the Canadian Lightning Detection Network (CLDN) from 1999 to 2008 are analyzed on 20 × 20 km equal area squares over Canada. This study was done to update an analysis performed in 2002 with just three years of data. Flashes were detected throughout the year, and distinct geographic differences in flash density and lightning occurrence were observed. The shape and locations of large scale patterns of lightning occurrence remained almost the same, although some details were different. Flash density maxima occurred at the same locations as found previously: the Swan Hills and Foothills of Alberta, southeastern Saskatchewan, southwestern Manitoba and southwestern Ontario. A region of greater lightning occurrence but relatively low flash density south of Nova Scotia occurred at the same location as reported previously. New areas of higher flash density occurred along the US border with northwestern Ontario and southern Quebec. These appear to be northward extensions of higher flash density seen in the previous study. The greatest average CG flash density was 2.8 flash km^?2 y^?1 in southwestern Ontario, where the greatest single‐year flash density (10.3 flash km^?2 y^?1) also occurred. Prominent flash density minima occurred east of the Continental Divide in Alberta and over the Niagara Escarpment in southern Ontario.

Lightning activity is seen to be highly influenced by the length of the season, proximity to cold water bodies and elevation. The diurnal heating and cooling cycle exerted the main control over lightning occurrence over most land areas; however, storm translation and transient dynamic features complicated the time pattern of lightning production. A large portion of the southern Prairie Provinces experienced more than 50% of flashes between 22:30 and 10:30 local solar time. The duration of lightning over a 20 × 20 km square at most locations in Canada is 5–10 h y^?1, although the duration exceeded 15 h y^?1 over extreme southwestern Ontario. Lightning occurred on 15–30 days each year, on average, over most of the interior of the country. The greatest number of days with lightning in a single year was 47 in the Alberta foothills and 50 in southwestern Ontario. Beginning and ending dates of the lightning season show that the season length decreases from north to south; however, there are considerable east‐west differences between regions. The season is nearly year‐round in the Pacific coastal region, southern Nova Scotia, southern Newfoundland and offshore.     

Forecasting the effects of global warming on radial growth of subalpine trees at the upper and lower distribution limits in central Japan

Effects of global warming on radial growth were examined for the subalpine tree species Abies veitchii (1600–2200 m?a.s.l.), A. mariesii (2000–2500 m?a.s.l.) and Betula ermanii (1600–2500 m?a.s.l.) in central Japan, by using dendrochronological techniques. Chronologies of tree-ring widths were examined for the three species and of maximum latewood densities for the two Abies species at their upper and lower distribution limits (total 10 chronologies). We developed multiple regression models to reproduce these chronologies from the monthly mean temperature and sum of precipitation. Of the 10 chronologies, growth-climate relations could not be modeled for tree-ring width chronologies of the three species at their lower distribution limits because of low correlation. Annual mean temperature and annual sum of precipitation will increase about 3 °C and 100 mm, respectively, by 2100 in central Japan, according to 18 climatic change scenarios (6 general circulation models ×3 greenhouse gasses emission scenarios). We predicted tree-ring widths and maximum latewood densities by substituting 18 climatic change scenarios into the growth-climate models. Maximum latewood densities and tree-ring widths of A. mariesii at the upper and lower distribution limits increased by 2100. The rates of the increase tended to be greater for scenarios with more greenhouse gas emission. By contrast, maximum latewood densities of A. veitchii and tree-ring widths of B. ermanii were unchanged by 2100, irrespective of the three greenhouse gas emission scenarios. This study showed that radial growth of the three species responds differently to global warming and their responses are predictable by dendrochronological models.     

Higher precision estimates of regional polar warming by ensemble regression of climate model projections

This study presents projections of twenty-first century wintertime surface temperature changes over the high-latitude regions based on the third Coupled Model Inter-comparison Project (CMIP3) multi-model ensemble. The state-dependence of the climate change response on the present day mean state is captured using a simple yet robust ensemble linear regression model. The ensemble regression approach gives different and more precise estimated mean responses compared to the ensemble mean approach. Over the Arctic in January, ensemble regression gives less warming than the ensemble mean along the boundary between sea ice and open ocean (sea ice edge). Most notably, the results show 3?°C less warming over the Barents Sea (~7?°C compared to ~10?°C). In addition, the ensemble regression method gives projections that are 30?% more precise over the Sea of Okhostk, Bering Sea and Labrador Sea. For the Antarctic in winter (July) the ensemble regression method gives 2?°C more warming over the Southern Ocean close to the Greenwich Meridian (~7?°C compared to ~5?°C). Projection uncertainty was almost half that of the ensemble mean uncertainty over the Southern Ocean between 30° W to 90° E and 30?% less over the northern Antarctic Peninsula. The ensemble regression model avoids the need for explicit ad hoc weighting of models and exploits the whole ensemble to objectively identify overly influential outlier models. Bootstrap resampling shows that maximum precision over the Southern Ocean can be obtained with ensembles having as few as only six climate models.     

Future climate in the Pacific Northwest

Climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and twentieth century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1°C to 0.6°C (0.2°F to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1% to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of twenty-first century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as twentieth century values (20 cm, 8^″) or as large as 1.3 m (50^″).