* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download impact of climate change on the management of district heating
Climate change and agriculture wikipedia , lookup
Effects of global warming on humans wikipedia , lookup
Effects of global warming on human health wikipedia , lookup
Urban heat island wikipedia , lookup
Global warming wikipedia , lookup
Attribution of recent climate change wikipedia , lookup
Climate change feedback wikipedia , lookup
Early 2014 North American cold wave wikipedia , lookup
Climate change, industry and society wikipedia , lookup
IPCC Fourth Assessment Report wikipedia , lookup
Physical impacts of climate change wikipedia , lookup
Climate sensitivity wikipedia , lookup
General circulation model wikipedia , lookup
Solar radiation management wikipedia , lookup
Global warming hiatus wikipedia , lookup
Global Energy and Water Cycle Experiment wikipedia , lookup
IMPACT OF CLIMATE CHANGE ON THE MANAGEMENT OF DISTRICT HEATING SYSTEMS Authors : C. Déandreis (IPSL), P. Braconnot (IPSL), S. Planton (CNRMGAME).Study performed for the DALKIA company State of the knowledge on Diurnal temperature range Summary Definition This fact sheet proposes a literature review as of May 2009 on diurnal temperature range. Studies to date describe the past evolution of diurnal temperature range and give projections for the next century. The global annual mean (oceans and continents) of this temperature range has fallen by about 0.07°C per decade since 1950. This fall is the result of a more rapid rise in daily minimum temperatures (Tmin) than in daily maximum temperatures. At the global scale, the diurnal temperature range should continue to shrink over the next century due to the intensification of global warming (Meehl et al., 2007). At the regional level the trend is more variable. In particular, southern Europe, eastern China and the south-eastern United States are showing an increase in their diurnal temperature range. These contrasts are expected to become more intense over the 21st century. To date, no study has been conducted on changes in extreme values and diurnal temperature range variability. The daily temperature range or diurnal temperature range (often written DTR) corresponds to the maximum variation in temperature over a period of 24 hours in a given place. It is expressed in degrees Celsius (°C) or kelvin (K)1. It is defined as the difference between the daily maximum temperature (Tmax) and the daily minimum temperature (Tmin): DTR = Tmax - Tmin Factors influencing diurnal temperature range The analysis of diurnal temperature range first requires an examination of its two terms: Tmax and Tmin. Their respective variations are not controlled by the same physical mechanisms. Tmax is reached during daylight hours. It depends on the amount of solar radiation absorbed by the Earth’s surface. The influence of infrared radiation on Tmax is thus negligible. The level of daytime heating depends on the following factors: ❚❚ the level of insolation: this is higher in the middle of the day and in summer; ❚❚ cloud cover: clouds reflect varying amounts of solar radiation back into space depending on their thickness (very thick cloud cover will prevent any daytime heating); ❚❚ wind: it dilutes the layer of warm air near the ground into unheated air and thereby prevents its warming. Strong winds can prevent any daytime heating. Wind can also rapidly replace a cold air mass with a warm air mass, or vice versa; 1. Conversion formula °C to K: K = °C + 273.15. IMPACT OF CLIMATE CHANGE ON THE MANAGEMENT OF DISTRICT HEATING SYSTEMS ❚❚ surface albedo2: a surface such as snow has a high albedo, as it reflects almost all the solar energy hitting the surface and thereby prevents daytime heating of the air near the ground; ❚❚ atmospheric particles (or aerosols): these absorb and reflect solar radiation. Their mean effect tends to reduce maximum temperatures; ❚❚ air humidity: this can also play an important role in absorbing some near-infrared radiation; ❚❚ thermal mass: this depends on the soil type and moisture. The higher it is (very wet soil, for example), the lower the maximum temperature. The Tmin, on the other hand, is reached during the night. The surface cools through the emission of infrared radiation and lowers the temperature of the layer of air in contact with it. The level of cooling depends on: ❚❚ cloud cover: clouds reflect infrared radiation back towards the ground. Thick cloud cover prevents nocturnal cooling; ❚❚ air humidity: it absorbs some near-infrared radiation and prevents nocturnal cooling; ❚❚ wind: it dilutes the thin layer of cold air into uncooled air. The stronger the wind, the less the temperature will fall. Strong wind prevents nocturnal cooling; ❚❚ surface emissivity: the more the surface radiates (infrared), the more it cools. This is the case of snow; ❚❚ thermal mass: this depends on the soil type and moisture. The higher it is (very wet soil, for example), the lower the minimum temperature. From these observations regarding Tmax and Tmin, we see that cloud cover tends to reduce the diurnal temperature range (lower levels of nocturnal cooling and daytime heating). But this range will be wide on sunny, windless days. Other factors may influence the diurnal temperature range (DTR): ❚❚ Liquid water vs. continental surface: the more continental the region, the wider the DTR will be. On the contrary, the presence of oceanic masses reduces this range, since water acts as a temperature regulator. The presence of lakes or groundwater (see thermal mass above) is enough to reduce this temperature range; ❚❚ latitude: the closer a place is to the equator, the more the solar energy provided varies between day and night; 2. The surface albedo is the ratio of incident radiation to reflected radiation. INVULNERABLe | DALKIA State of knowledge > PAGE 2 ❚❚ relief: the DTR increases at higher altitudes. Atmospheric density decreases as the altitude increases. Thus, in the daytime, the atmospheric layer reflects less incident solar radiation back into space (the Tmax increases more easily). On the other hand, at night, infrared radiation is trapped less by greenhouse gases (very cold nights). Table 1 summarises the impact of these different factors on the Tmax, Tmin, and DTR. Factors Tmax Tmin DTR Clouds Wind Albedo Emissivity Latitude Liquid water* Relief ∕ + ∕ + + ∕ + ∕ + - + + TABLE 1 Impact of different factors on maximum, minimum and diurnal temperature range variations. *Oceans, lakes, groundwater, etc. Recent changes in diurnal temperature range Uncertainties associated with studies of diurnal temperature range are generally high, as they include both uncertainties about the estimation of maximum temperatures and those about minimum temperatures. These uncertainties are all the greater when the zone studied is small (regional versus global). However, several studies have revealed significant trends from a statistical point of view, at least at the global level. Annual trends: Figure 1 presents the evolution of annual anomalies for the maximum temperature, minimum temperature and DTR, relative to the period 1961-19903. Analysis of maximum and minimum land surface temperatures logged daily over the 1950-2004 period shows that the maximum temperature range observed over the course of a day is noticeably decreasing (-0.0666°C per decade). Globally, we are seeing a warming of both minimum and maximum 3. The annual mean maximum temperature anomaly corresponds to the difference between the annual mean maximum temperature and its mean value calculated for the reference period 1961-1990. This definition also applies to the minimum temperature anomaly and the diurnal temperature range anomaly. The analysis of anomalies (rather than gross values) is preferred in climatology as it makes it possible to study the trend of a variable without the mean bias of the models. a) 1950-2004 a) 1950 - 2004 a) 1950 - 2004 b) 1979 b) 1979-2004 - 2004 b) 1979 - 2004 FIGURE 1 Evolution of global annual mean anomaly (oceans and continents) of the maximum temperature (top), minimum temperature (middle) and diurnal temperature range (bottom) for the period 1950-2004 relative to the reference 1961-1990 (from Vose et al., 2005). temperatures. However, minimum temperatures are rising around 1.5 times faster than maximum temperatures (0.204°C compared to 0.141°C per decade). Over this period, the decrease in diurnal temperature range is comparable to mean warming. For the period 1979-2004, the temperature range measured over the course of a day stabilises. For this period, the Tmax and Tmin trends are very similar (0.287°C compared to 0.295°C per decade). The trend (-0.001°C per decade) is not statistically significant at the 5% level over this period (Tmax and Tmin trends too similar). No suitable data sets exist to extend this study to the beginning of the 20th century. Geographical distribution: The planispheres in Figure 2 represent the regional diurnal temperature range anomalies for the period 1950-2004 and for the period 1979-2004. The anomalies were calculated relative to the period 1961-1990. For the period 1950-2004 (Figure 2.a), we see that the decrease in the temperature range over the course of a FIGURE 2 Trend of DTR anomalies for the periods 1950-2004 (a) and 1979-2004 (b). Grid resolution 5x5 (from Vose et al., 2005). day concerns all parts of the world, with the exception of a few regions (north-eastern Canada, southern Argentina, south-eastern Australia). These findings from the study by Vose et al. (2005) have been confirmed by several regional studies (Bonsal et al. 2001; Wibig and Glowicki, 2002; Kruger and Shongwe, 2004, for Canada, Poland and South Africa respectively). However, for the period 1979-2004 (Figure 2.b), the trend of the diurnal temperature range is far more heterogeneous. We even see an increase in this range in several regions, including the south-eastern United States, many parts of Europe and south-eastern China. Physical causes of the decrease in DTR The physical causes of this decrease in diurnal temperature range are still uncertain. In particular, few studies have been carried out on this subject. In addition, they have often been conducted using limited sets of data. The results presented below are therefore to be approached with caution; they are likely to evolve rapidly in response to forthcoming studies on this subject. INVULNERABLe | DALKIA State of knowledge > PAGE 3 IMPACT OF CLIMATE CHANGE ON THE MANAGEMENT OF DISTRICT HEATING SYSTEMS The decrease in diurnal temperature range has been linked to the increase in anthropogenic pollutant emissions (greenhouse gases and aerosols). An aerosol is a suspension of particles in the atmosphere, which reflect the incident solar radiation. They thereby reduce the diurnal surface temperature (Tmax). The increase in the number of these aerosols due to human activity has long been an argument for the decrease in diurnal temperature range. However, one study (Stone and Weaver, 2002) shows that the effect of aerosols is negligible (their direct effect being offset by their water vapour feedback). The decrease is this temperature range is therefore only the result of the increase in atmospheric greenhouse gas concentrations. Stone and Weaver (2003) also showed that the diurnal temperature range is more sensitive to climate change feedback than to the direct effect of increasing greenhouse gas concentrations (a rise in Tmin caused by the increasing greenhouse effect). In a statistical study, they show that increasing cloud cover and soil moisture are the main causes of the decrease in the diurnal temperature range for most of the cases studied. The increase in cloud cover (higher impact of low rain clouds) causes a reduction in solar energy reaching the surface (reduction in Tmax) and captures the infrared energy emitted from the surface overnight (increase in Tmin). The increase in soil moisture permits faster cooling of the surface during the daytime through evaporation and also moderates temperatures during the daytime by increasing the heat capacity of the ground. There is one exception to this rule: winter at midlatitudes when snow covers the ground. It thus insulates the surface (preventing the effect of soil moisture) and increases its reflective properties (which reduces the impact of the reflection of solar radiation by clouds). The question of the effect of land use change has also been raised (Stone and Weaver, 2003). It seems that this factor may have a considerable impact on diurnal temperature range at the local and regional scales. To date, there are no explanatory elements in the literature about the stabilisation of diurnal temperature range from 1979. INVULNERABLe | DALKIA State of knowledge > PAGE 4 Model performance – validation over the historical period The observed change in diurnal temperature range is greater than the change simulated by most models (-0.08°C compared to -0.02°C per decade for the period 1950-1993). The study by Stone and Weaver (2002) shows that in the northern hemisphere, their model underestimates the trend of the diurnal temperature range mainly due to an overestimation of the Tmax in summer and autumn and an underestimation of the Tmin in spring and winter. In the southern hemisphere, the conclusions are more uncertain due to a lack of data (few monitoring stations). In this study, the model/observation variations concerning the trend of the diurnal temperature range were mainly attributed to the misrepresentation of the increase in cloud cover by models. Diurnal temperature range and future climate change The maximum temperature range measured in the course of a day should continue to decrease in the future due to the intensification of global warming (Figure 3.a). However, this decrease does not concern all parts of the world. The southern United States, Latin America, South Africa, southern Europe, eastern China and southern Australia will all see a considerable increase in their diurnal temperature range. Changes in this temperature range (positive or negative) could be as much as 0.5°C by the end of the century in certain regions (results consistent between the models used in this study). As with historical trends, future changes in the diurnal temperature range are closely linked to the evolution of total cloud cover (Figure 3.b). This range decreases over regions where cloud cover becomes denser, and increases in regions where cloud cover diminishes. Where Europe is concerned, there is a strong contrast between southern Europe (considerable growth in diurnal temperature range) and northern Europe (decrease in this range). The results are consistent between models for the extreme south and north of the region. Over China, we also see significant regional disparities between the Tibetan Plateau (decrease in diurnal temperature range) and eastern China (growth in this range). However, the model response is less reliable in this part of the world. a) Diurnal temperature range (°C) b) Total cloud fraction (%)*) Figure 10.10. Change of diurnal temperature range (a) and of total cloud fraction (b) between the periods 2080-2099 and 1980-1999. Results obtained from all models of the fourth IPCC report for the A1B scenario. Above the stippled areas, the result is consistent between the models (model mean exceeds standard deviation). Figure from IPCC, Third Assessment Report, chapter 10. * Cloud fraction is the fraction of a model grid that is covered with clouds, as opposed to the clear sky fraction (cloud free). It is expressed as a percentage. FIGURE 3 To date, no detailed study has been conducted to explain these contrasts, but in Europe, changes in cloud cover should play an important role, as suggested in Figure 3. Further comments (in relation to the project) This literature review raises three points of interest in the study of the vulnerability indicator defined in the fact sheet related to this case study and entitled “Vulnerability indicator: development and analysis”: 1) Europe and China can be divided into two zones in which the diurnal temperature range shows trends with opposite signs (north versus south for Europe, and east versus west for China). It will be important to take this contrast into account when analysing the vulnerability indicator concerning the diurnal temperature range. An analysis of this contrast will undoubtedly be necessary to understand the regional evolution of our climate indicator in the future. 2) All of the studies that were used to produce this fact sheet deal with changes in the mean value of the diurnal temperature range. However, in the context of the INVULNERABLe project, studying the mean 767 alone is not enough. It must be supplemented by the analysis of extremes (95th quantile, for example), the study of the signal variability, and of its annual cycle, etc. Such studies do not yet exist in the literature. 3) Within the framework of the INVULNERABLe project research, we mainly focus on wide diurnal temperature ranges, and more specifically on the probability of seeing abnormally high diurnal temperature ranges in relation to those currently recorded. The decrease in the mean global diurnal temperature range (DTR) does not systematically result in a reduction in the frequency of abnormally high values. Indeed: ❚❚ the trend of the mean is not proportional to that of extremes. If the mean diurnal temperature range decreases, the probability of observing high DTR values does not necessarily diminish. It is therefore important to study more specifically the form of the DTR distribution and its future evolution (see point 3); ❚❚ The global mean is not representative of regional disparities. Indeed, we see an increase in the diurnal temperature range in some of our target regions (eastern China, southern Europe). INVULNERABLe | DALKIA State of knowledge > PAGE 5 IMPACT OF CLIMATE CHANGE ON THE MANAGEMENT OF DISTRICT HEATING SYSTEMS Bibliography: Bonsal, B.R., X. Zhang, L.A. Vincent et W.D. Hogg, 2001b : Characteristics of daily and extreme temperatures over Canada. J. Climate 14: 1959-1976. Dai, A., K. E. Trenberth, and T. R. Karl, 1999: Effects of clouds, soil moisture, precipitation, and water vapour on diurnal temperature range, J. Clim., 12, 2451–2473. Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper, I.G. Watterson, A.J. Weaver and Z.-C. Zhao, 2007: Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Kruger, A.C. and S. Shongwe, 2004: Temperature trends in South Africa: 1960–2003. Int. J. Climatol., 24, 1929-1945. Stone D., A. J. Weaver, 2002: Daily Maximum and Minimum Temperature Trends in a Climate Model, Geophys. Res. Lett., 29 (9), 1356, doi:10.1029/2001GL014556. INVULNERABLe | DALKIA State of knowledge > PAGE 6 Stone, D. A., and A. J. Weaver, 2003: Factors contributing to diurnal temperature range trends in 20th and 21st century simulations of the CCCma coupled model, Clim. Dyn., 20, 435-445.. Trenberth, K.E., P.D. Jones, P. Ambenje, R. Bojariu, D. Easterling, A. Klein Tank, D. Parker, F. Rahimzadeh, J.A. Renwick, M. Rusticucci, B. Soden and P. Zhai, 2007: Observations: Surface and Atmospheric Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Vose R. S., D. R. Easterling, B. Gleason, 2005: Maximum and minimum temperature trends for the globe: An update through 2004, Geophys. Res. Lett., 32, L23822, doi:10.1029/2005GL024379.. Wibig J, Glowicki B, 2002: Trends in minimum and maximum temperature in Poland. Clim Res 20:123– 133 INVULNERABLe | DALKIA State of knowledge > PAGE 7 IMPACT OF CLIMATE CHANGE ON THE MANAGEMENT OF DISTRICT HEATING SYSTEMS INVULNERABLe | DALKIA State of knowledge > PAGE 8