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Heat and cold — mean air temperature

Page Last modified 25 Nov 2021
8 min read
It is now beyond question… Europe is getting hotter. Average surface air temperature gives a clear and consistent signal of global and regional climate change. It has a direct impact on natural ecosystems, agriculture, and human health and well-being. Rising temperatures affect all types of ecosystems through shifts in species distribution and population structure and increase the risk of species extinction. These changes can impact ecosystem services, such as carbon storage, and affect crop production. Higher temperatures also naturally increase the risk of arid conditions and droughts.

Key messages

 

  • All regions in Europe have experienced warming, which is projected to continue in the future. By the end of the century, Europe as a whole and its three sub-regions are projected to experience further warming between a maximum of 1.5 °C (low-emissions scenario) and 4.5 °C (high-emissions scenario).
  • Growing degree days have increased throughout Europe. Further increases are projected throughout the century, with the largest increase in southern Europe. 
  • Heating degree days have decreased throughout Europe. The decline in heating degree days is expected to continue in the future under all scenarios, with the largest decrease in northern Europe.
  • Cooling degree days have increased in Europe. This increase is projected to continue in the future, with the largest increase in southern Europe.

 Please select an index from the blue selection bar below :

  • Mean temperature
  • Growing degree days
  • Heating degree days
  • Cooling degree days

 


Definition

The mean temperature index is a base index representing the average air temperature over different timescales (e.g. seasonally or annually). This index is based on highly comprehensive data sets for past, present and future periods obtained from both observations and model simulations.

Index factsheet (ETC/CCA Technical Paper): Mean temperature

Relevance

Changes in annual mean temperature are often used as a headline index for regional climate change assessments, as they can serve as a proxy for changes in various heat- and cold-related hazards. Furthermore, changes in seasonal mean temperature are directly relevant for many sectoral applications, such as agriculture, forest and ecosystem management, and energy consumption. In addition, an increase in mean temperature together with increases in CO2 concentrations and relative humidity can trigger climate change-induced corrosion of buildings and infrastructure.

Past and projected changes

The mean temperature index shows a warming trend throughout Europe in recent decades. This is projected to continue, with the warming rate depending on the emissions scenario. The pan-European temperature is projected to increase by between less than 1.5 °C, for the low-emissions scenario (representative concentration pathway (RCP) 2.6), and around 4.5 °C, for the high-emissions scenario (RCP8.5), by the end of the century, with respect to the reference period 1986-2005. The projected changes in annual mean temperature are similar across all three European sub-regions. Larger variations may occur in smaller regions and in individual seasons (not shown).

Further information (European Climate Data Explorer: Daily mean temperature — Monthly statistics, 2011-2099

 Annual mean temperature for the European land area and sub-regions


Annual mean temperature

 

Notes:   The black lines show the annual values for 1950-2020 from reanalysis data, and the dashed horizontal lines show the means for 1986-2005. Solid grey, blue, yellow and red lines represent the ensemble medians of model simulations for the historical period and under low-, medium- and high-emissions scenarios (RCP2.6, RCP4.5 and RCP8.5, respectively) (smoothed by a 20-year moving average). Shaded areas show the 15th and 85th percentile ranges of the model ensembles. The size of the model ensemble used for each scenario is shown by the coloured numbers in the top-right corner.

Source:  ERA5 and bias-adjusted CMIP5 data.

Current situation and projected changes in annual mean temperature in Europe

Notes:   The top panel shows the 1986-2005 mean values based on the reanalysis. The central row and bottom row show the projected values and the projected changes, respectively, of the 15th and 85th percentiles for the near and far future. The size of the model ensemble used for each scenario is reported in the time-series figure below.

Source:  ERA5 and bias-adjusted CMIP5 data.

Definition

The growing degree days index provides a measure of the accumulated heat available for vegetation growth. It is calculated from the accumulated sum over the year of daily mean temperature exceedances of a base temperature threshold. A base temperature of 5 °C is considered representative of most European crops. Other definitions of the index are possible, including variations in the base temperature, the use of an upper temperature threshold and restrictions for a given growing season.

Index factsheet (ETC/CCA Technical Paper): Growing degree days

Relevance

The growing degree days index has wide applicability in agriculture. It is used primarily to characterise plant phenology for a large variety of crops in Europe, but also to predict conditions that favour pest outbreaks and influence the insect generation cycle during the growing season.

Past and projected changes

Growing degree days have increased since the 1980s throughout Europe, particularly in southern Europe. Further increases are projected throughout the rest of the century under the medium- and high-emissions scenarios (representative concentration pathway (RCP)4.5 and RCP8.5), with the largest absolute change in southern Europe, whereas the increasing trend is projected to stabilise by the middle of the century under the low-emissions scenario (RCP2.6).

Further information (European Climate Data Explorer): Biologically effective degree days, 2011-2099

Annual growing degree days for the European land area and sub-regions 


 Annual growing degree days for the European land area and sub-regions

Notes:   The black lines show the annual values for 1950-2020 from reanalysis data, and the dashed horizontal lines show the means for 1986-2005. Solid grey, blue, yellow and red lines represent the ensemble medians of model simulations for the historical period and under low-, medium- and high-emissions scenarios (RCP2.6, RCP4.5 and RCP8.5, respectively) (smoothed by a 20-year moving average). Shaded areas show the 15th and 85th percentile ranges of the model ensembles. The size of the model ensemble used for each scenario is shown by the coloured numbers in the top-right corner.

Source:  ERA5 and bias-adjusted CMIP5 data.

Current situation and projected changes in annual growing degree days in Europe

Notes:   The top panel shows the 1986-2005 mean values based on the reanalysis. The central row and bottom row show the projected values and the projected changes, respectively, of the 15th and 85th percentiles for the near and far future. The size of the model ensemble used for each scenario is reported in the time-series figure above.

Source:  ERA5 and bias-adjusted CMIP5 data.

Definition

The heating degree days index is a proxy for the energy required for heating buildings. It is computed from the cumulated daily deviation of the outdoor air temperature from a base temperature threshold from October to March. The base temperature threshold, period considered and calculation methodology can vary according to the local climate and applications. A base temperature of 15.5 °C is here considered representative of the pan-European scale, and daily minimum, mean and maximum temperature values are used as input variables.

Index factsheet (ETC/CCA Technical Paper): Heating degree days

Relevance

The heating degree days index is relevant mainly for energy-related applications and complements the information provided by the cooling degree days index. A decrease in heating degree days could result in a significant reduction in energy consumption for heating in Europe.

Past and projected changes

Heating degree days have decreased throughout Europe since the 1980s. The largest decrease has been in northern Europe where the absolute value is highest. The decline in heating degree days is expected to continue under all emissions scenarios. The decline could reach about 40 % by the end of the 21st century under the high-emissions scenario (representative concentration pathway (RCP)8.5), whereas the initial declining trend is projected to stabilise from the middle of the century under the low-emissions scenario (RCP2.6).


Annual heating degree days for the European land area and sub-regions

Heating degree days

Current situation and projected changes in annual heating degree days in Europe

 

Notes:   The black lines show the annual values for 1950-2020 from reanalysis data, and the dashed horizontal lines show the means for 1986-2005. Solid grey, blue, yellow and red lines represent the ensemble medians of model simulations for the historical period and under low-, medium- and high-emissions scenarios (RCP2.6, RCP4.5 and RCP8.5, respectively) (smoothed by a 20-year moving average). Shaded areas show the 15th and 85th percentile ranges of the model ensembles. The size of the model ensemble used for each scenario is shown by the coloured numbers in the top-right corner.

Source:  ERA5 and bias-adjusted CMIP5 data.


Definition

The cooling degree days index is a proxy for the energy demand for cooling buildings. It is computed from the cumulated daily deviation of the outdoor air temperature from a given base temperature threshold from April to September. The base temperature threshold, period considered and calculation methodology of this index can vary according to the local climate and applications. A base temperature of 22 °C is here considered representative for assessing the energy demand at the pan-European scale, and daily minimum, mean and maximum temperature values are used as input essential climate variables.

Index factsheet (ETC/CCA Technical Paper): Cooling degree days

Relevance

The cooling degree days index is widely applicable in the energy sector. A significant increase in the number of cooling degree days can increase Europe’s energy use and lead to higher costs and higher impacts on the peak capacity of supply networks (EEA, 2019Adaptation challenges and opportunities for the European energy system: Building a climate-resilient low-carbon energy system).

Past and projected changes

Cooling degree days have increased in Europe since the 1980s, with the largest increase observed in southern Europe. This increase is projected to continue, with a small increase, a doubling and approximately a quadrupling of cooling degree days in Europe projected under the low-, medium- and high-emissions scenarios (representative concentration pathway (RCP)2.6, RCP4.5 and RCP8.5), respectively, during the 21st century. The largest increase is projected for southern Europe, whereas only small increases are projected for northern Europe.

Annual cooling degree days for European land area and sub-regions 

Cooling degree days


 


Notes:   The top panel shows the 1986-2005 mean values based on the reanalysis. The central row and bottom row show the projectedvalues and the projectedchanges, respectively, of the 15th and 85th percentiles for the near and far future. The size of the model ensemble used for each scenario is reported in the time-series figure above.

Source:  ERA5 and bias-adjusted CMIP5 data.

 

 

 

Chapters of the Europe's changing climate hazards report

  1. Heat and cold

  2. Wet and dry

  3. Wind

  4. Snow and ice

  5. Coastal

  6. Open ocean

                                                                               

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