Impact Of Extreme Temperatures Research Articles

Spatiotemporal distribution and lag effect of extreme temperature exposure on mortality of residents in Jiangsu, China

BackgroundWith the ever-increasing occurrence of extreme weather events as a result of global climate change, the impact of extreme temperatures on human health has become a critical area of concern. Specifically, it is imperative to investigate the impact of extreme weather conditions on the health of residents. MethodsIn this study, we analyze the daily death data from 13 prefecture-level cities in Jiangsu Province from January 2014 to September 2022, using the distributed lag nonlinear model (DLNM) to comprehensively account for factors such as relative humidity, atmospheric pressure, air pollutants, and other factors to evaluate the lag and cumulative effects of extreme low temperature and high temperature on the death of residents across different age groups. Additionally, we utilize the Geographical Detector to analyze the effects of various meteorological and environmental factors on the distribution of resident death in Jiangsu Province. This provides valuable insights that can guide health authorities in decision-making and in the protection of residents. ResultsThe experimental results indicate that both extreme low and high temperatures increase the mortality of residents. We observe that the impact of extreme low temperatures has a delayed effect, peaking after 3–5 days and lasting up to 11–21 days. In contrast, the impact of extreme high temperature is greatest on the first day, and lasts only 2–4 days. ConclusionBoth extreme high and low temperatures increase the mortality of residents, with the former being more transient and stronger and the latter being more persistent and slower. Furthermore, residents over 75 years of age are more vulnerable to the effects of extreme temperatures. Finally, we note that the spatial distribution of resident deaths is most closely associated consistent with the spatial distribution of daily mean temperature, and there is significant spatial heterogeneity in deaths among residents in Jiangsu Province.

Risk effects of meteorological factors on human brucellosis in Jilin province, China, 2005–2019

BackgroundThe impact of climate on zoonotic infectious diseases (or can be referred to as climate-sensitive zoonotic diseases) is confirmed. Yet, research on the association between brucellosis and climate is limited. We aim to understand the impact of meteorological factors on the risk of brucellosis, especially in northeastern China. MethodsMonthly incidence data for brucellosis from 2005 to 2019 in Jilin province was obtained from the China Information System for Disease Control and Prevention (CDC). Monthly meteorological data (average temperature (°C), wind velocity (m/s), relative humidity (%), sunshine hours (h), air pressure (hPa), and rainfall (mm)) in Jilin province, China, from 2005 to 2019 were collected from the China Meteorological Information Center (http://data.cma.cn/). The Spearman's correlation was used to choose among the several meteorological variables. A distributed lag non-linear model (DLNM) was used to estimate the lag and non-linearity effect of meteorological factors on the risk of brucellosis. ResultsA total of 24,921 cases of human brucellosis were reported in Jilin province from 2005 to 2019, with the peak epidemic period from April to June. Low temperature and low sunshine hours were protective factors for the brucellosis, where the minimum RR values were 0.50 (95 % CI = 0.31–0.82) for −13.7 °C with 1 month lag and 0.61 (95 % CI = 0.41–0.91) for 110.5h with 2 months lag, respectively. High temperature, high sunshine hours, and low wind velocity were risk factors for brucellosis. The maximum RR values were 2.91 (95 % CI = 1.43–5.92, lag = 1, 25.7 °C), 1.85 (95 % CI = 1.23–2.80, lag = 2, 332.6h), and 1.68 (95 % CI = 1.25–2.26, lag = 2, 1.4 m/s). The trends in the impact of extreme temperature and extreme sunshine hours on the transmission of brucellosis were generally consistent. ConclusionHigh temperature, high sunshine hours, and low wind velocity are more conducive to the transmission of brucellosis with an obvious lag effect. The results will deepen the understanding of the relationship between climate and brucellosis and provide a reference for formulating relevant public health policies.

The impact of extreme temperature on labor wage: Evidence from Chinese manufacturing firms

Labor wage is a common focus of welfare economics and public policy, but little is known about its response to climate factors. With random year-to-year variation in temperature based on county-level data while using comprehensive and nationwide manufacturing data in China, this paper identifies the effect of extreme temperatures on firm-level labor wage. The result shows an inverted U-shape relationship between temperature and firm-level labor wage. We find that extremely high and low temperatures affect labor wage through different channels. Specifically, extremely cold temperatures lower labor wage by reducing the average wage from the intensive margin, whereas the negative impact of high temperatures on labor wage is mainly driven by the decrease in the number of employees from the extensive margin aspect. The temperature effect is more pronounced for labor-intensive firms, firms with employees with lower education levels, and low-tech firms. Areas with a hot climate are more sensitive to extremely cold temperatures but are not affected by extremely high temperatures because of the adaptation to climate change. We also find that the high-temperature subsidy policy has not achieved the expected goal of protecting workers’ welfare during this period. Our results suggest that China should raise public awareness of the danger of extreme temperatures and take various adaptive measures to deal with extreme temperatures.

The Impact of Extreme Temperatures on Grain Production in the Huaihe River Basin

The Huaihe River Basin is an important major grain producing area in China, maintaining the stability of grain output is of great significance to food security. However, with global warming, the frequency of extreme temperature events has increased, and the frequent meteorological disasters have brought great challenges to the stable supply of food production. In this paper, the impact of extreme temperature on grain production in the Huaihe River Basin was analyzed by using the daily temperature and agricultural production related data of 28 prefecture-level cities in the Huaihe River Ecological Economic Belt from 2001 to 2020. The following conclusions are drawn: 1) The influence coefficient of extreme high temperature on grain production in the Huaihe River Basin is -0.021, extreme low temperature has no significant impact on food production. 2) The effects of extreme temperature on food production in different regions in the river basin were heterogeneous, but the overall impact was negative. The influence coefficients of extremely high temperature days on the eastern region and Midwest region were -0.035 and -0.052, respectively, while the influence coefficients of extremely low temperature days on the eastern region were -0.413. The results showed that the increase in the number of extremely high temperature days would reduce production in the eastern region andMidwest region of the basin, while the northern region was not significantly affected by extreme heat. The increase in the number of extremely low temperature days will reduce grain production in the eastern region, and the impact on the Midwest region and the northern region will not be significant. Based on the above conclusions, three suggestions are put forward to maintain the safety of food production in the Huaihe River Basin: 1) enhance the ability to detect climate change in the basin; 2) Protect the stability of grain cultivated land in the river basin; 3) Innovative breeding of climate-resilient food crop seeds.

Impact of extreme temperatures on the performance evaluation of China's work-related injury insurance system.

With the influence of climate change resulting in more extreme days, a rise in the number of work-related injuries could be expected. The literature has addressed the performance evaluation of a work-related injury insurance (WII) system via a two-stage structure with input/output correlation as well as the impact of extreme temperatures under different scenarios. This article thus evaluates the performance of a system comprised of operational and service sub-systems under three scenarios of extreme temperatures and proposes a hybrid two-stage dynamic data envelopment analysis (DEA) model with nondiscretionary variables for measuring integrated WII efficiency under the three scenarios. The results are as follows: (1) the poor performance of the operational and service sub-systems leads to the integrated WII system's low efficiency for 30 provinces in China during 2010-2019, except for Zhejiang, Hainan, and Qinghai. (2) Extreme temperatures must be considered when measuring WII efficiency and its stage efficiencies, or otherwise WII efficiency and operational efficiency will be underestimated in 19 provinces. (3) The negative impacts of extreme temperatures on the efficiency of the integrated WII system should be taken notice of, especially for Sichuan.

Impact of extreme temperatures on emergency hospital admissions by age and socio-economic deprivation in England

Climate change poses an unprecedented challenge to population health and health systems’ resilience, with increasing fluctuations in extreme temperatures through pressures on hospital capacity. While earlier studies have estimated morbidity attributable to hot or cold weather across cities, we provide the first large-scale, population-wide assessment of extreme temperatures on inequalities in excess emergency hospital admissions in England. We used the universe of emergency hospital admissions between 2001 and 2012 combined with meteorological data to exploit daily variation in temperature experienced by hospitals (N = 29,371,084). We used a distributed lag model with multiple fixed-effects, controlling for seasonal factors, to examine hospitalisation effects across temperature-sensitive diseases, and further heterogeneous impacts across age and deprivation. We identified larger hospitalisation impacts associated with extreme cold temperatures than with extreme hot temperatures. The less extreme temperatures produce admission patterns like their extreme counterparts, but at lower magnitudes. Results also showed an increase in admissions with extreme temperatures that were more prominent among older and socioeconomically-deprived populations - particularly across admissions for metabolic diseases and injuries.

Impact of extreme temperatures on production of different rice types: A county‐level analysis for China

AbstractThe response of China's rice yield to climate change is crucial for ensuring food security for China and the globe. However, previous studies have focused on the impact of climate change on a specific rice type or rice as a whole. For the first time, this study combines a new set of the early, middle, and late rice production data and daily weather data at the county level to comprehensively estimate the heterogeneous yield response to extreme temperatures in China. Along with the projections of future temperature and precipitation, we also forecast the potential yield losses when exposed to higher future warming trends. The results show that holding current growing regions and calendars fixed, the yield of popular middle and late rice types will drop by 5.7% ± 1.5% and 11% ± 4.5% under the most extreme scenario compared to no climate change scenarios by the end of this century (2070–2090 average). These results imply that recent structural changes in favor of producing these popular types of rice may satisfy the demand for high‐quality rice but may also increase the risks of climate change to the food supply in China. Therefore, more efforts should be concentrated on incorporating this type of heterogeneity in climatic impacts into national and regional plans for the agricultural adaptation.

Impact of Extreme Temperature and Soil Water Stress on the Growth and Yield of Soybean (Glycine max (L.) Merrill)

Climate change is a major environmental stressor that would adversely affect tropical agriculture, which is largely rain-fed. Associated with climate change is an increasing trend in temperature and decline in rainfall, leading to prolonged and repeated droughts. The purpose of this study was to determine the effect of climate variables such as temperature, relative humidity, vapor pressure deficit (VPD), and soil water on the phenology, biomass, and grain yield of soybean crops. A greenhouse experiment was set in a split plot design with three average environmental conditions as the main plots: E1 (36 °C, RH = 55%), E2 (34 °C, RH = 57%) and E3 (33 °C, RH = 44%). Additionally, there were three water treatments: W1 (near saturation), W2 (Field capacity), and W3 (soil water deficit) and two soybean varieties (Afayak and Jenguma). These treatments were replicated nine times. The results showed that high temperatures (E1) accelerated the crop development, particularly at flowering. Additionally, increased atmospheric demand for water under a high temperature environment resulted in high evapotranspiration, leading to high transpiration which probably reduced photosynthetic activity of the plants and thereby contributing to biomass and grain yield loss. Biomass and yield were drastically reduced for the combined effect of high temperature (E1) and drought (W3) as compared to combined effect of ambient temperature (E3) and well-watered condition (W1). Increasing temperatures and erratic rainfall distributions associated with climate change poses a potential threat to the soybean production in Ghana.

Growth Recovery and Phenological Responses of Juvenile Beech (Fagus sylvatica L.) Exposed to Spring Warming and Late Spring Frost

Global change increases the risk of extreme climatic events. The impact of extreme temperature may depend on the tree species and also on the provenance. Ten provenances of Fagus sylvatica L. were grown in a common garden environment in Belgium and subjected to different temperature treatments. Half of the one year old seedlings were submitted to a high thermal stress in the spring of the first year, and all plants were exposed to a late spring frost in the second year. The high-temperature treated plants displayed reduced growth in the first year, which was fully compensated (recovery with exact compensation) in the second year for radial growth and in the third year for height growth. Frost in the spring of the second year damaged part of the saplings and reduced their growth. The frost damaged plants regained the pre-stress growth rate one year later (recovery without compensation). The high temperature treatment in the first year and the frost damage in the second year clearly influenced the phenological responses in the year of the event and in the succeeding year. Little population differentiation was observed among the provenances for growth and for phenological responses. Yet, a southern provenance, a non-autochthonous provenance (original German provenance that was planted in Belgium about a century ago) and a more continental provenance flushed earlier than the local Atlantic provenances in the year of the frost event, resulting in more frost damage. Some caution should therefore be taken when translocating provenances as an anticipation of the predicted climate warming.

The impact of extreme temperatures on human mortality in the most populated cities of Romania.

The impact of extreme weather conditions on humans is one of the most important topics in biometeorology studies. The main objective of this study is to analyze the relationship between temperature-related weather conditions and natural mortality in the five most populated cities of Romania, namely, Bucharest, Cluj-Napoca, Constanța, Iași, and Timișoara. The results of this study aim to bridge a gap in national research. In the present paper, we used daily natural mortality data and daily minimum and maximum air temperatures. The distributed lag nonlinear model (DLNM) allowed us to identify weather conditions associated with natural mortality. The most important results are as follows: (i) a higher daily mortality is related to a high frequency of heat stress conditions; (ii) a higher maximum temperature increases the relative risk (RR) of natural mortality; (iii) the maximum number of fatalities is recorded on the first day of high-temperature events; and (iv) individuals much more easily adapt to cold stress conditions. The main conclusion in this study is that the inhabitants of the most populated cities in Romania are more sensitive to high-temperature stress than to low-temperature stress.

Impact of Extreme Temperatures on Emergency Hospital Admissions by Age and Socio-Economic Deprivation in England

Climate change poses an unprecedented challenge to population health and health systems' resilience. While earlier studies have estimated morbidity attributable to hot or cold weather across cities, we provide the first large-scale, population-wide assessment of extreme temperatures on inequalities in excess emergency hospital admissions in England. We used a panel dataset of emergency hospital admissions across hospitals between 2001-2012 in England combined with meteorological data to exploit daily variation in temperature experienced by hospitals and a 30-day lag period. We used a distributed lag model with multiple fixed-effects controlling for seasonal factors, to examine interaction effects across diseases with age and indicators of deprivation. We assessed hospital impacts across age groups and levels of deprivation for six disease categories identified as being the most weather-sensitive. Our results showed an increase in emergency hospital admissions with extreme temperatures that were more prominent among older and socially-deprived populations. We estimated larger hospitalisation impacts associated with extreme cold temperatures than with extreme hot temperatures, net of secular trends and local variation.

Trends in extreme temperature indices over Lagos, Nigeria

There is the need to understand the trend and impact of extreme temperature on coastal cities because they are generally susceptible to extreme precipitation events. This study explores the trend in extreme temperature for Lagos State, Nigeria. The indices for daily minimum and maximum temperature data was calculated for the period 1991–2015 using the RClimDex software. The result showed that both minimum value of daily minimum temperature (TNn) and cool days (TX10p) showed negative trends among the indices considered. Significant trends were observed in warm nights (TN90p), warm days (TX90p) and mean of maximum temperature (Tmax-mean). Warm nights were found to be increasing while cold nights are either unchanged or decreasing. This study reveals that there are evidences of increase in warming of Lagos State.

Impact of Extreme Temperatures on Ambulance Dispatches Due to Cardiovascular Causes in North-West Spain.

Introduction and objectives. The increase in mortality and hospital admissions associated with high and low temperatures is well established. However, less is known about the influence of extreme ambient temperature conditions on cardiovascular ambulance dispatches. This study seeks to evaluate the effects of minimum and maximum daily temperatures on cardiovascular morbidity in the cities of Vigo and A Coruña in North-West Spain, using emergency medical calls during the period 2005–2017. Methods. For the purposes of analysis, we employed a quasi-Poisson time series regression model, within a distributed non-linear lag model by exposure variable and city. The relative risks of cold- and heat-related calls were estimated for each city and temperature model. Results. A total of 70,537 calls were evaluated, most of which were associated with low maximum and minimum temperatures on cold days in both cities. At maximum temperatures, significant cold-related effects were observed at lags of 3–6 days in Vigo and 5–11 days in A Coruña. At minimum temperatures, cold-related effects registered a similar pattern in both cities, with significant relative risks at lags of 4 to 12 days in A Coruña. Heat-related effects did not display a clearly significant pattern. Conclusions. An increase in cardiovascular morbidity is observed with moderately low temperatures without extremes being required to establish an effect. Public health prevention plans and warning systems should consider including moderate temperature range in the prevention of cardiovascular morbidity.

Heat and cold waves at the South of the Russian Far East in 1999-2017

Threshold values of 3% and 97% percentiles of annual distribution of mean daily temperature are used to determine the cold and heat waves, respectively, for weather stations in the southern part of the Russian Far East for the period from December 1999 to 2017. Cold waves are identified mainly in December and January. The coldest winter seasons with the longest cold waves, up to 11 days, were observed in 2000/2001 and 2012/2013; the maximum total excess of negative temperatures over the threshold value was 116°C in weather station Poliny Osipenko. Heat waves were registered mainly in July. The hottest summer was in 2011, when heat wave was observed during July and August, with the longest wave at the northern Nikolaevsk-on-Amur; the maximum total excess of positive temperatures over the threshold was 74°C in Poliny Osipenko. There was no clear trend in the inter-annual dynamics of mean temperatures of winter and summer, but temperature variations can reach ±6°C and ±4, respectively. Climate extremes vary significantly during the study period, but usually rarely go beyond two standard deviations. Taking into account the possible impact of extreme temperatures on human health, their effect on the increase of mortality in Khabarovsk is discussed.

Resilience Analysis and Cascading Failure Modeling of Power Systems under Extreme Temperatures

In this paper, we propose an AC power flow based cascading failure model that explicitly considers external weather conditions, extreme temperatures in particular, and evaluates the impact of extreme temperature on the initiation and propagation of cascading blackouts. Based on this model, careful analysis is performed on the resilience of the power system under extreme temperatures. Specifically, load and dynamic line rating changes are modeled due to temperature disturbance, the probabilities for transmission line and generator outages are evaluated, and the timing for each type of events is carefully calculated to decide the actual event sequence. It should be emphasized that the correlated events, in the advent of external temperature changes, could together contribute to voltage instability. Besides, we model undervoltage load shedding and operator re-dispatch as control strategies for preventing the propagation of cascading failures. The effectiveness of the proposed model is verified by simulation results on the RTS-96 3-area system and it is found that temperature disturbances can lead to correlated load change and line/generator tripping, which together will greatly increase the risk of cascading and voltage instability. Critical temperature change, critical area with temperature disturbance, identification of most vulnerable buses, and comparison of different control strategies are also carefully investigated.

Regulation of glutathione-dependent antioxidant defense system of grass carp Ctenopharyngodon idella under the combined stress of mercury and temperature.

In this study, we investigated the combined effects of temperatures fluencies and mercury (Hg) on glutathione-dependent antioxidant system in fish, by measuring the oxidative stress indicator (LPO, lipid peroxidation) and the parameters involved in the glutathione-related antioxidant defense system (GPx, glutathione peroxidase; GR, glutathione reductase; GST, glutathione S-transferase; GSH, reduced glutathione), as well as the expression of related genes in grass carp, Ctenopharyngodon idella. Fish (45.37 ± 3.58g) were exposed to 10 test groups, e.g., 15°C with/without Hg, 20°C with/without Hg, 25°C with/without Hg, 30°C with/without Hg, 35°C with/without Hg for 4weeks. Three-way ANOVA was used to analyze the correlation between the measured parameters and experimental conditions (water temperature, Hg exposure, exposure time, and their interactions.). Our results show that there is no interaction between mercury and low temperature, but the combined effect at high temperature has been confirmed, which indicated the glutathione-dependent enzyme system in grass carp has a complex regulatory mechanism with temperature fluctuations. In the actual field monitoring, it is necessary to consider the impact of extreme temperature on the toxicity of pollutants in the aquatic ecosystem.

Exposure to suboptimal ambient temperature during specific gestational periods and adverse outcomes in mice.

Exposure to suboptimal ambient temperature during pregnancy has been reported as a potential teratogen of fetal development. However, limited animal evidence is available regarding the impact of extreme temperatures on maternal pregnancy and the subsequent adverse pregnancy outcomes. Our objective in this study is to investigate the relationship between temperature and maternal stress during pregnancy in mice. This study used the Naval Medical Research Institute (NMRI) mice during the second and third pregnant weeks with the gestational day (GD) (GD 6.5-14.5 and GD 14.5-17.5). Mice were exposed to suboptimal ambient temperature (1 °C, 5 °C, 10 °C, 15 °C, 40 °C, 42 °C, 44 °C, 46 °C, and 48 °C for the experimental group and 23 °C for the control group) 1 h per day, 7 days a weekin each trimester. Measurements of placental development (placental weight [PW] and placental diameter [PD]) and fetal growth (fetal weight [FW] and crown-to-rump length [CRL]) between experimental and control groups were compared using analysis of variance (ANOVA). Data on the occurrence of preterm birth (PTB) and abnormalities were also collected. The results showed that exposure to both cold and heat stress in the second and third weeks of pregnancy caused significant decreases in measurements of placental development (PW and PD) and fetal growth (FW and CRL). For all temperature exposures, 15 °C was identified as the optimal temperature in the development of the embryo. Most PTB occurrences were observed in high-temperature stress groups, with the highest PTB number seen in the exposure group at 48 °C, whereas PTB occurred only at 1 °C among cold stress groups. In the selected exposure experiments, an approximate U-shaped relation was observed between temperature and number of abnormality occurrence. The highest percentage of these anomalies occurred at temperatures of 1 °C and 48 °C, while no abnormalities were observed at 15 °C and in the control group. Our findings strengthened the evidence that exposure to suboptimal ambient temperatures may trigger adverse pregnancy outcomes and worsen embryo and fetal development in mice.

극한 기온이 사망자 수에 미치는 영향: 2019년 장래인구추계 평가

극한 기온이 사망자 수에 미치는 영향: 2019년 장래인구추계 평가

Spatiotemporal patterns of surface temperature over western Odisha and eastern Chhattisgarh

Extreme temperature indices are a matter of serious concern to human as well as ecological activities. They are directly or indirectly affect the health, agriculture and socioeconomic progress. Regional-scale heat wave analysis is highly important for obtaining firsthand information about the impact of extreme temperature. This study examines the trends and variability in frequency, and intensity of warm/cold days/nights to assess the impact of climate change over ten districts of western Odisha and five districts of neighboring Chhattisgarh. Though this region is industrialized, its population is highly vulnerable socioeconomic conditions within India. This study examines daily maximum and minimum temperature during the summer months (i.e., March, April and May) for 30 years (i.e., 1988–2017) over this region, using the ERA-Interim data sets at horizontal resolution of 12 km. Results suggest that the daily maximum, minimum and mean temperature over the study region increase at the rate of 0.006 °C, 0.012 °C and 0.017 °C per year, respectively. Alarmingly, frequency and intensity of warm night have increased, whereas frequency and intensity of cold nights have decreased over the years. Raigarh in Chhattisgarh has the highest increasing trend of warm night frequency (0.13 times/year) followed by Jharsuguda, Sundargarh and Sambalpur in Odisha. In addition, Sundargarh has the highest increasing trend of warm day (night) intensity ~ 0.065 days/year (~ 0.07 days/year) followed by Jharsuguda, Sambalpur, Raigarh and Janjgir Champa. The frequency of cold days in all districts shows negative trends with highest (− 0.06 times/year) in Sambalpur. Three-day trend values, highest over Sundargarh, for the warm (cold) nights are ~ 0.05 days/year (~ − 0.05 days/year). Evidently, numbers of warm nights have increased, and those of cold nights have decreased over this region.

The association between ambient temperature and the risk of preterm birth in China

BackgroundWith the gradual increase of global warming, the impact of extreme temperatures on health has become a focus of attention, however, its relationship with preterm birth remains unclear. ObjectivesTo investigate the association between exposure to extreme temperatures and preterm birth. MethodsTemperature exposures and birth outcomes of 1,020,471 pregnant women from 132 cities in China were investigated. The pregnancy process was divided into different pregnancy periods. Study areas were divided into three categories (cold, medium, and hot areas) according to the local average temperature by cluster analysis. Average temperature data for each province used in the cluster analysis came from the China Statistical Yearbook 2013. Logistic regression was used to compare the effects of exposure to hot and cold conditions on the outcomes of pregnancy in different periods and regions. ResultsA total of 1,020,471 singleton births were included, of which 73,240(7.2%) were preterm births. Compared with moderate temperatures (5th to 95th percentile), heat exposure (>95th percentile) in different periods of pregnancy increased the risk of preterm birth in hot areas. The most obvious increase was during the 3 months before pregnancy (odds ratio (OR)=1.229, 95% confidence interval (CI): 1.166–1.295). In contrast to heat exposure, cold exposure (<5th percentile) in hot areas reduced the risk of preterm birth; the protective effect was most pronounced in the 3 months before pregnancy (OR=0.784, 95% CI: 0.734–0.832). In medium and cold areas cold exposure also reduced the risk of preterm birth. The effect of exposure to extreme ambient temperatures throughout the entire pregnancy on preterm birth was similar to those of the periods above. ConclusionsAcute and chronic exposure to extreme temperatures may affect the risk of preterm birth. Extreme heat is a risk factor for preterm birth and extreme cold is a protective factor.