The 1.5C temperature increase is a global threshold and areas that are warming faster are not off-track from this goal; scientists have expected for decades that polar regions would warm more than areas closer to the equator.

In Kiruna, a mining town in northern Sweden, average yearly temperatures were 3C higher in the 21s​t​ century (up to December 31s​t,​ 2017) compared to the 20t​h​ century yearly average.

In Granada, Cordoba and Malaga, all Andalusian cities, the average yearly temperature in the 21st​ century was at least 1.5C higher than in the 20t​h​ century.

In Bucharest, capital of Romania, temperatures increased by 1.4C. The increase relative to pre-industrial levels, a period often ​considered to be 1850–1900, is likely higher.

By contrast, cities on the Atlantic shore saw the least amount of warming.

These findings are the result of an analysis of over 100 million data points made available by the European Centre for Medium-Range Weather Forecasts (ECMWF), an international organisation which computes so-called "re-analyses" of weather data, based on a variety of sources such as weather stations, weather balloons, buoys and satellite observations.

This is the first time reanalysis data is made easily accessible on this scale.

Such data is well-suited to study weather patterns over periods spanning over a century, because it harmonises inputs from thousands of data sources and makes comparisons in time and space possible.

While absolute values might differ from data collected at weather stations directly, especially because cities suffer from the "heat island effect", meaning that temperatures within the cities can be up to 10C higher than in their surrounding countryside, the overall trends are the same.

Looking at daily data, EDJNet was able to show how the number of hot and cold days varied over the last 117 years. In Split for instance, the second-largest city in Croatia, the number of days where the average temperature reached 27C went from six per year in the 20th​ century to 14 per year in the 21s​t​.

Conversely, the number of cold days decreased in most cities. In the Latvian capital Riga, the number of days where the average temperature was below -1C went from 75 per year in the last century to 57 in the 21st​. Such detailed information allows for a precise assessment of the local impact of temperature change.

Longer droughts, more heatwaves

Even limited to a couple of degrees or less, temperature increases can have severe consequences, said Mojca Dolinar, head of the department of climatology at the Slovenian Environment Agency, a government body.

A hotter atmosphere can absorb more water before releasing it in the form of rain, he explained. This implies that periods between rainy episodes become longer and droughts more severe.

On the other hand, rainfall, because of the higher concentration of water in the atmosphere, tends to be more concentrated, leading to more severe floods.

Higher temperatures, especially heatwaves, were responsible for several thousands deaths since 2000. The 2003 heatwave resulted in over ​70,000 extra deaths in the western half of the European continent.

Despite the enactment of national heat plans in several countries, a ​review of the link between heat and mortality in nine European cities showed that, although excess mortality decreased in Paris, Rome and Athens since 2003, higher temperatures still cause excess deaths, not only in southern cities.

Nordic cities are more vulnerable to heat stress than those already facing heat regularly. In Madrid, for instance, mortality (relative to non-hot days) increases when the average daily temperature exceeds 21C, against 19C in Stockholm.

Excess mortality caused by the so-called "Lucifer" 2017 heatwave, during which temperatures rose above 40C in the Balkans, Italy and Spain, and by the 2018 heatwave in Northern Europe has yet to be analysed by national health authorities or by academics.

Too hot for school

Heatwaves are most deadly but higher temperatures affect European in other ways. Researchers have shown that pupils perform less well, especially in mathematics, when the daily average temperature rises ​above 22C.

In 415 of the 539 cities analysed by EDJNet, the number of school days per year with an average daily temperature over 22C increased in the 21s​t​ century, relative to the 20t​h​.

In Seville, for instance, pupils suffered from an average of 12 school days over 22C per year in the 20th​ century. This number doubled to 24 per year in the 21s​t​ century. The consequences of a hotter environment on the academic performance of European pupils have not yet been assessed.

Crime

Criminologists have ​known since the 1980s that, in the United States at least, violent crime increases with temperature.

In Europe, despite rising temperatures, no national crime agency or academic tried to replicate the analysis.

Rail and road transport are also affected by rising temperatures, as tarmac softens the roads to the point that some of them need to be closed during especially hot days. Rail transit within cities (overground trains and trams) can suffer from rail buckling as the metal of the rail expands and becomes unstable. This can cause delays and, as ​happened in Washington D.C. underground in 2012, derailments.

Despite the wide array of effects higher temperatures have had on European cities, it is hard to see concerted, concrete adaptation efforts being carried out locally.

Some ​national climate change plans conflate the fight against climate change with adaptation to higher temperatures.

Climate change can only be contained by keeping hydrocarbon in the ground and capturing carbon from the atmosphere (neither option has produced any result so far), whereas adaptation to higher temperatures means ensuring that human settlements remain habitable under a changing climate.

National plans are ​often limited to regulatory instruments, such as incitative taxation for renewable energy.

When it comes to creating green spaces to limit the heat island effect and, therefore, mortality from heatwaves, to upgrading the local transport network to make it more resilient to heat or to installing cooling devices in classrooms, cities are on their own.

In the coming weeks EDJNet will publish a series of stories on the local impact of the rising in temperatures in specific European cities, and investigate if and what kind of measures local authorities and other stakeholders are preparing for mitigating the adverse effects of increasing temperatures.

For each city, a report on the temperature increase, and its consequences, is available in nine languages. You can browse all available city reports.

The European Data Journalism Network (EDJNet) is a platform for data-driven news on European affairs brought to you in up to 12 languages by a consortium of media and data journalists from all over Europe, which includes EUobserver.