Climate Comparisons and Change Projections for the Northwest Atlantic from Six CMIP5 Models

Abstract

Key physical variables for the Northwest Atlantic (NWA) are examined in the “historical” and two future Representative Concentration Pathway (RCP) simulations of six Earth System Models (ESMs) available through Phase 5 of the Climate Model Intercomparison Project (CMIP5). The variables are air temperature, sea-ice concentration, surface and subsurface ocean temperature and salinity, and ocean mixed-layer depth. Comparison of the historical simulations with observations indicates that the models provide a good qualitative and approximate quantitative representation of many of the large-scale climatological features in the NWA (e.g., annual cycles and spatial patterns). However, the models represent the detailed structure of some important NWA ocean and ice features poorly, such that caution is needed in the use of their projected future changes. Monthly “climate change” fields between the bidecades 1986–2005 and 2046–2065 are described, using ensemble statistics of the changes across the six ESMs. The results point to warmer air temperatures everywhere, warmer surface ocean temperatures in most areas, reduced sea-ice extent and, in most areas, reduced surface salinities and mixed-layer depths. However, the magnitudes of the inter-model differences in the projected changes are comparable to those of the ensemble-mean changes in many cases, such that robust quantitative projections are generally not possible for the NWA.     

Projections of Extreme Rainfall in Hong Kong in the 21st Century

The possible changes in the frequency of extreme rainfall events in Hong Kong in the 21st century wereinvestigated by statistically downscaling 30 sets of the daily global climate model projections (involvinga combination of 12 models and 3 greenhouse gas emission scenarios,namely,A2,A1B,and B1) of theFourth Assessment Report of the Intergovernmental Panel on Climate Change.To cater for the intermittentand skewed character of the daily rainfall,multiple stepwise logistic regression and multiple stepwise linearregression were employed to develop the downscaling models for predicting rainfall occurrence and rainfallamount,respectively.Verification of the simulation of the 1971-2000 climate reveals that the models ingeneral have an acceptable skill in reproducing past statistics of extreme rainfall events in Hong Kong.Theprojection results suggest that,in the 21st century,the annual number of rain days in Hong Kong is expectedto decrease while the daily rainfall intensity will increase,concurrent with the expected increase in annualrainfall.Based on the multi-model scenario ensemble mean,the annual number of rain day is expected todrop from 104 days in 1980-1999 to about 77 days in 2090-2099.For extreme rainfall events,about 90% ofthe model-scenario combinations indicate an increase in the annual number of days with daily rainfall 100mm (R100) towards the end of the 21st century.The mean number of R100 is expected to increase from 3.5days in 1980-1999 to about 5.3 days in 2090-2099.The projected changes in other extreme rainfall indicesalso suggest that the rainfall in Hong Kong in the 21st century may also become more extreme with moreuneven distributions of wet and dry periods.While most of the model-emission scenarios in general projectconsistent trends in the change of rainfall extremes in the 21st century,there is a large divergence in theprojections among different model/emission scenarios.This reflects that there are still large uncertainties inmodel simulations of future extreme rainfall events.     

Projections of Climate Change over China for the 21st Century

1. IntroductionUnder the background of global warming in the20th century, it was also getting warmer of 0.2-0.7°C/100 yr over China for the last 100 years, espe-cially for the last 50 years (0.6-0.9°C/50 yr) based onthe instrumental observations (Wang and Gong, 2000;Ren et al., 2004; Zhao et al., 2004). In another way, itwas noticed that the concentration of greenhouse gasesand sulfate aerosols in the atmosphere increased by thehuman emissions. Some new evidences indicated thatthe greenho…     

Changes in Canada's Climate: Trends in Indices Based on Daily Temperature and Precipitation Data

ABSTRACT

Trends in indices based on daily temperature and precipitation are examined for two periods: 1948–2016 for all stations in Canada and 1900–2016 for stations in the south of Canada. These indices, a number of which reflect extreme events, are considered to be impact relevant. The results show changes consistent with warming, with larger trends associated with cold temperatures. The number of summer days (when daily maximum temperature >25°C) has increased at most locations south of 65°N, and the number of hot days (daily maximum temperature >30°C) and hot nights (daily minimum temperature >22°C) have increased at a few stations in the most southerly regions. Very warm temperatures in both summer and winter (represented by the 95th percentile of their daily maximum and minimum temperatures, respectively) have increased across the country, with stronger trends in winter. Warming is more pronounced for cold temperatures. The frost-free season has become longer with fewer frost days, consecutive frost days, and ice days. Very cold temperatures in both winter and summer (represented by the 5th percentile of their daily maximum and minimum temperatures, respectively) have increased substantially across the country, again with stronger trends in the winter. Changes in other temperature indices are consistent with warming. The growing season is now longer, and the number of growing degree-days has increased. The number of heating degree-days has decreased across the country, while the number of cooling degree-days has increased at many stations south of 55°N. The frequency of annual and spring freeze–thaw days shows an increase in the interior provinces and a decrease in the remainder of the country. Changes in precipitation indices are less spatially coherent. An increase in the number of days with rainfall and heavy rainfall is found at several locations in the south. A decrease in the number of days with snowfall and heavy snowfall is observed in the western provinces, while an increase is found in the north. There is no evidence of significant changes in the annual highest 1-day rainfall and 1-day snowfall. The maximum number of consecutive dry days has decreased, mainly in the south.     

一个地球系统模式模拟的气候变化对海洋碳循环的影响

使用维多利亚大学的地球系统模式进行模拟,选取1800-2500年间较高的CO₂浓度情景（RCP8.5）,分析由于CO₂增加引起的气候变化对海洋碳循环的影响。当气候敏感度为3.0 K时,相对于无气候变化,到2100年,由于大气CO₂增加造成的气候变化导致海表面温度升高2.7 K,北大西洋深水流量减少4.5 Sv,海洋对人为碳的年吸收减少0.8 Pg C;比较人为溶解无机碳在海洋中的垂直累积分布,发现气候变化对海洋吸收大气CO₂的影响在北大西洋区域最明显。1800-2500年,相对于不考虑气候变化的情景,模式模拟的气候变化导致整个海洋对人为碳的累积吸收总量减少23.1%,其中北大西洋减少32.0%。此外,比较不同气候敏感度（0～4.5 K,间隔为0.5 K）的模拟结果发现,气候敏感度越高,气候变化对海洋吸收CO₂能力的抑制作用越明显。     

北京1960—2008年气候变暖及极端气温指数变化特征

应用均一化逐日气象观测资料,分析了北京地区1960—2008年气候变暖及主要极端气温指数的统计特征。结果表明：近49年来北京年平均气温增温速率约为0.39℃/10a,最高、最低气温变化具有明显的非对称性。霜冻日数和气温年较差呈现下降趋势,暖夜指数及热浪指数呈现上升趋势,除气温年较差外,其他极端气温指数的气候变率均在加大。北京年平均气温及极端气温指数主要存在21年、15～17年及准10年周期特征。年平均气温与极端气温指数之间存在较强相关性,气候变暖突变发生前后某些极端气温指数发生频率表现出明显差异。自1980年起,北京市区极端最高气温及其增温率明显高于近郊和远郊,高温日数市区多于近郊,近郊多于远郊;近、远郊极端最低气温温差高于城、近郊温差。     

Projection of Extreme Temperatures in Hong Kong in the 21st Century

The possible changes in the frequency of extreme temperature events in Hong Kong in the 21st century were investigated by statistically downscaling 26 sets of the daily global climate model projections (a combination of 11 models and 3 greenhouse gas emission scenarios, namely A2, A1B, and B1) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The models’ performance in simulating the past climate during 1971–2000 has also been verified and discussed. The verification revealed that the models in general have an acceptable skill in reproducing past statistics of extreme temperature events. Moreover, the models are more skillful in simulating the past climate of the hot nights and cold days than that of the very hot days. The projection results suggested that, in the 21st century, the frequency of occurrence of extremely high temperature events in Hong Kong would increase significantly while that of the extremely low temperature events is expected to drop significantly. Based on the multi-model scenario ensemble mean, the average annual numbers of very hot days and hot nights in Hong Kong are expected to increase significantly from 9 days and 16 nights in 1980–1999 to 89 days and 137 nights respectively in 2090–2099. On the other hand, the average annual number of cold days will drop from 17 days in 1980–1999 to about 1 day in 2090–2099. About 65 percent of the model-scenario combinations indicate that there will be on average less than one cold day in 2090–2099. While all the model-emission scenarios in general have projected consistent trends in the change of temperature extremes in the 21st century, there is a large divergence in the projections between difierent model/emission scenarios. This reflects that there are still large uncertainties in the model simulation of the future climate of extreme temperature events.     

秋季区域海冰面积异常与冬季大气环流及东亚区域气候的关系

利用北极海冰面积资料和NCEP／NCAR再分析逐月高度场、风场资料以及中国160站气温资料，探讨秋季区域海冰异常与冬季大气环流及区域气候的关系，结果表明，秋季东西伯利亚海海冰的年际变化与北半球冬季大气环流及东亚冬季风有着密切的关系，秋季该海区海冰偏多（偏少），相应冬季东亚冬季风偏强（偏弱）；进一步分析发现秋季该海区海冰面积偏大（偏小），相应冬季中国大部地区气温明显偏低（偏高）。     

Past and Future Changes in the Climate of Hong Kong

Over the years, the Hong Kong Observatory has carried out scientific studies to evaluate the observed climate trends and project the future climate in Hong Kong. Analysis of the meteorological observations at the observatory's headquarters in Tsim Sha Tsui since 1885 reveals that the temperature rise in Hong Kong during the past 124 years is in accord with the global rising trend. The accelerated rising trend in the mean temperature in last few decades may be attributed to the anthropogenic influences, especially urbanization. A similar increasing trend is also observed for rainfall. Other observations such as increasing cloud amount and decreasing total global solar radiation are all consistent with the global trend. Studies of past occurrences of extreme temperature and rainfall have also been carried out. The results indicate that cold episodes have become rarer while very hot days and heavy rain events are becoming more frequent. The observatory also makes use of the data from the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) and employs statistical downscaling techniques to carry out projections of temperature and precipitation in the 21st century. It is found that the rise in temperature in Hong Kong will be slightly higher than the global mean in the 21st century. The annual rainfall in Hong Kong is also expected to rise by the end of the 21st century, so is its year-to-year variability.     

冬季喀拉海、巴伦支海海冰面积变化对后期北太平洋海温的影响

采用Ｗａｌｓｈ的１９５３～１９９０年逐月北极海冰密集度资料、１９５３～１９８７年北半球海表温度资料、１９４６～１９８９年月平均５００ｈＰａ高度场以及１９８０～１９８９年８５０ｈＰａ高度场、风场和温度场资料,研究了冬季北极关键区（喀拉海、巴伦支海海区）海冰面积变化对后期北太平洋海表温度的影响。研究结果表明：冬季喀拉海、巴伦支海海冰可以影响初夏北太平洋中部海温。冬季该海区海冰偏多,则冬、春季节亚洲大陆冷空气活动偏北,春季白令海海冰偏少、阿留申低涡减弱西移,引导偏北的大陆冷空气南下,在热力和动力共同作用下,使北太平洋中部海温偏低;相反,冬季喀拉海、巴伦支海海冰偏少时,则冬、春季节亚洲大陆冷空气活动偏南,冷空气在东亚地区向南爆发,同时,白令海海冰偏多、阿留申低涡加深东移,北太平洋中部西风偏强且位置偏北,东太平洋副热带高压位置也偏北,使北太平洋中部海温受到来自低纬度地区暖湿气流的影响,海温将偏高。     

不同排放情景下贵州21世纪气候变化预估

利用IPCCAR4提供的模式预估结果,分析了不同排放情景下21世纪贵州气候变化特征,结果表明：21世纪由于人类排放的增加,贵州省将继续变暖、变湿。到21世纪后期（2071--2099年）贵州省温度比常年高2～3,2℃,降水比常年多3．8％-5．8％。且在SRESA．2（高排放）、A1B（中排放）、B1（低排放）情景下贵州省年平均温度（降水）整体变化幅度分别为4．0℃／100a（136mm／100a）、3．6℃／100a（96mm／100a）、2．1℃／100a（61mm／100a）,体现了排放量越高,增温（增湿）越显著的特征。从季节特征来看,不同情景下冬季温度的增加趋势都大于其它季节;冬季降水预估没有明显的变化趋势,其余季节基本上以上升趋势为主。其中在A1B、B1排放情景下21世纪前期（2011--2040年）降水有减少趋势,在A2情景下降水无明显变化趋势。     

Reducing Uncertainties in Climate Projections with Emergent Constraints:Concepts,Examples and Prospects

Models disagree on a significant number of responses to climate change, such as climate feedback, regional changes,or the strength of equilibrium climate sensitivity. Emergent constraints aim to reduce these uncertainties by finding links between the inter-model spread in an observable predictor and climate projections. In this paper, the concepts underlying this framework are recalled with an emphasis on the statistical inference used for narrowing uncertainties, and a review of emergent constr...     

Progress in the Development and Application of Climate Ocean Models and Ocean-Atmosphere Coupled Models in China

A review is presented about the development and application of climate ocean models and oceanatmosphere coupled models developed in China as well as a review of climate variability and climate change studies performed with these models. While the history of model development is briefly reviewed, emphasis has been put on the achievements made in the last five years. Advances in model development are described along with a summary on scientific issues addressed by using these models. The focus of the review is the climate ocean models and the associated coupled models, including both global and regional models, developed at the Institute of Atmospheric Physics, Chinese Academy of Sciences. The progress of either coupled model development made by other institutions or climate modeling using internationally developed models also is reviewed.     

淮河流域夏季降水异常与若干气候因子的关系

基于旋转经验正交函数分解 (REOF) 方法探讨淮河流域1961—2010年夏季降水与厄尔尼诺/南方涛动 (ENSO)、北大西洋涛动 (NAO)、印度洋偶极子 (IOD)、太平洋年代际振荡 (PDO) 之间的关系,并进一步分析各气候因子不同位相单独以及联合对淮河流域夏季降水的影响。结果表明:淮河流域夏季降水与ENSO,PDO,NAO,IOD等气候因子具有较稳定的相关性,其中,PDO和IOD是影响淮河流域夏季降水的关键因子,且PDO与夏季降水呈显著负相关关系;各气候因子的冷暖位相单独及联合对淮河流域夏季降水的影响不同,PDO的冷期以及NAO,IOD冷位相使流域北部的夏季降水量呈显著增加趋势,PDO分别联合ENSO,NAO和IOD的冷、暖位相对流域北部地区和淮河上游地区的夏季降水影响显著。     

The response of currents in Trinity Bay,Newfoundland, to local wind forcing

Abstract

Analysis of current measurements taken between June and October 1984 at four moorings in Trinity Bay, Newfoundland, is discussed. The alongshore component of current exhibits baroclinic fluctuations coherent with the along‐bay component of wind stress at periods between 3 and 7 days. A two‐layer model of internal Kelvin waves propagating around the perimeter of an elongated bay and forced by a spatially uniform wind stress is presented. The observations support several features of the model response to wind forcing. Along the side of the bay on which Kelvin waves are incoming, the amplitude of the response increases into the bay and decreases with increasing frequency. Along the outgoing side of the bay the amplitude of the response generally shows a maximum at a frequency between 0.2 and 0.3 cpd. The phase lag between current and wind is consistent with a forced response. An example is given of upwelling and downwelling on opposite sides of the bay in agreement with the model behaviour.     

Ocean acidification and climate change: synergies and challenges of addressing both under the UNFCCC

Ocean acidification and climate change are linked by their common driver: CO₂. Climate change is the consequence of a range of GHG emissions, but ocean acidification on a global scale is caused solely by increased concentrations of atmospheric CO₂. Reducing CO₂ emissions is therefore the most effective way to mitigate ocean acidification. Acting to prevent further ocean acidification by reducing CO₂ emissions will also provide simultaneous benefits by alleviating future climate change. Although it is possible that reducing CO₂ emissions to a level low enough to address ocean acidification will simultaneously address climate change, the reverse is unfortunately not necessarily true. Despite the ocean's integral role in the climate system and the potentially wide-ranging impacts on marine life and humans, the problem of ocean acidification is largely absent from most policy discussions pertaining to CO₂ emissions. The linkages between ocean acidification, climate change and the United Nations Framework Convention on Climate Change (UNFCCC) are identified and possible scenarios for developing common solutions to reduce and adapt to ocean acidification and climate change are offered. Areas where the UNFCCC is currently lacking capacity to effectively tackle rising ocean acidity are also highlighted.     

Reappraisal of Asian Summer Monsoon Indices and the Long-Term Variation of Monsoon

The Webster and Yang monsoon index (WYI)-the zonal wind shear between 850 and 200 hPa was calculated and modified on the basis of NCEP/NCAR reanalysis data. After analyzing the circulation and divergence fields of 150-100 and 200 hPa, however, we found that the 200-hPa level could not reflect the real change of the upper-tropospheric circulation of Asian summer monsoon, especially the characteristics and variation of the tropical easterly jet which is the most important feature of the upper-tropospheric circulation. The zonal wind shear U850-U(150 100) is much larger than U850-U200, and thus it can reflect the strength of monsoon more appropriately. In addition, divergence is the largest at 150 hPa rather than 200 hPa, so 150 hPa in the upper-troposphere can reflect the coupling of the monsoon system. Therefore, WYI is redefined as DHI, i.e., IDH=U850* - U(150 100)*, which is able to characterize the variability of not only the intensity of the center of zonal wind shear in Asia, but also the monsoon system in the upper and lower troposphere. DHI is superior to WYI in featuring the long-term variation of Asian summer monsoon as it indicates there is obvious interdecadal variation in the Asian summer monsoon and the climate abrupt change occurred in 1980. The Asian summer monsoon was stronger before 1980 and it weakened after then due to the weakening of the easterly in the layer of 150-100 hPa, while easterly at 200 hPa did not weaken significantly. After the climate jump year in general, easterly in the upper troposphere weakened in Asia, indicating the weakening of summer monsoon; the land-sea pressure difference and thermal difference reduced, resulting in the weakening of monsoon; the corresponding upper divergence as well as the water vapor transport decreased in Indian Peninsula, central Indo-China Peninsula, North China, and Northeast China, indicating the weakening of summer monsoon as well. The difference between NCEP/NCAR and ERA-40 reanalysis data in studying the intensity and long-term variation of Asian summer monsoon is also compared in the end for reference.     

漠河极端气温气候特征及其变化

采用相关系数法和对比分析法,分析了1963-2000年38年间中国最北部的漠河极端最低气温和极端最高气温的气候特征及其气候变化.结果表明:漠河是中国最冷的地方,不仅在中国气象史上创下了-52.3℃的极端最低气温最低极值,且每年极端最低气温都在-38℃以下;年极端最高气温为38.0℃;极端气温年较差很大,最小为73.1℃,最大为87.0℃,1980年代后明显变小;极端最低气温总体变化不明显,但1990年代上升显著,10年间平均升高1.6℃;极端最高气温总体变化显著,为升降交替变化,1970年代显著升高,10年问平均升高了1.6℃;1980年代明显下降,10年间平均下降了1.1℃;1990年代上升,10年间平均上升0.7℃;年极端最低气温出现在11月、12月、1月和2月,1月最多,占52%;年极端最高气温出现在5-9月,7月最多,占47%;日极端最低气温多出现在4-7时;日极端最高气温多出现在14-16时;特别值得一提的是:漠河1963-2000年间1-12月的月极端最低气温都曾经出现过零下的记录.     

我国近海和邻近海的海洋环境对最近全球气候变化的响应

鉴于全球气候变暖对海洋环境和海洋生态及对经济和社会可持续发展影响的严重性,作者首先利用ERA-40再分析的风场资料以及HadISST 和SODA等海洋高分辨率再分析资料,分析了近50年来全球气候变化对中国近海(包括渤海、黄海、东海和南海)和邻近海(主要是热带和副热带西太平洋)海面附近的风力、海表纬向和经向风应力和海表温度的影响.分析结果表明: 由于受全球气候变暖的影响,1976年之后中国近海和邻近海上空的冬、夏季风变弱,从而引起中国近海冬、夏季海表风应力减弱(尤其是经向风应力),而海表水温明显上升; 并且,冬、夏季海表风应力的减弱和海水温度的上升在中国东海反映尤其明显,这些为中国近海赤潮的频繁发生提供了有利的海洋环境.此外,从中国近海上空环流散度分布的变化可见,中国近海上空从1976年之后大气环流辐散增强,这不利于中国近海上升流的形成,从而会对沿岸水域营养盐的输送产生影响.     

Evaluation of Linear and Non-Linear Downscaling Methods in Terms of Daily Variability and Climate Indices: Surface Temperature in Southern Ontario and Quebec,Canada

We downscaled atmospheric reanalysis data using linear regression and Bayesian neural network (BNN) ensembles to obtain daily maximum and minimum temperatures at ten weather stations in southern Quebec and Ontario, Canada. Performance of the linear and non-linear downscaling models was evaluated using four different sets of predictors, not only in terms of their ability to reproduce the magnitude of day-to-day variability (i.e., “weather,” mean absolute error between the daily values of the predictand(s) and the downscaled data) but also in terms of their ability to reproduce longer time scale variability (i.e., “climate,” indices of agreement between the predictand's observed annual climate indices and the corresponding downscaled values). The climate indices used were the 90th percentile of the daily maximum temperature, 10th percentile of the daily minimum temperature, number of frost days, heat wave duration, growing season length, and intra-annual temperature range.

Our results show that the non-linear models usually outperform their linear counterparts in the magnitude of daily variability and, to a greater extent, in annual climate variability. In particular, the best model simulating weather and climate was a BNN ensemble using stepwise selection from 20 reanalysis predictors, followed by a BNN ensemble using the three leading principal components from the aforementioned predictors. Finally, we showed that, on average, the first three indices presented higher skills than the growing season length, number of frost days, and the heat wave duration.