The United Nations Climate Change Conference is underway in Paris. Among other topics, the participants debate on how to decrease global temperature by 2ºC. Meanwhile, Kraków scientists published a report on the impact of climate change on the city as well as its surroundings.
Global warming is a hot topic. Every year, several hundred reports on climate change are being published. Scientists universally agree that not only climate change is happening, but also that we, the humans, are responsible for that. Despite that, many don't believe the researchers. Ignoring the result of studies and political disputes prevents world leaders from reaching an agreement that would enable them to effectively combat CO2 emission, deforestation and other detrimental processes.
According to Intergovernmental Panel on Climate Change's Fifth Assessment Report from 2013, the average global air temperature in the years 2016–2035 may increase by about 0.3 to 0.7ºC compared to the period of 1986–2005. Additionally, it may increase by 1.5ºC until the end of the 21st century compared to the period of 1850–1900. "Inhabitants of urban areas are particularly vulnerable to an increase in heat stress, since cities generate additional heat – we're not only talking about car and electronic devices, but also the physical properties of urban environment," explained Dr hab. Anita Bokwa from the Department of Climatology of the JU Institute of Geography and Spatial Management, coordinator of a project named Urban climate in Central European cities and global climate change. "One of the results of high-density housing and predominance of built environment is higher temperature in cities. We call this an urban heat island."
25ºC and counting
The framework of the project included conducting a series of analyses in Kraków, Vienna, Brno, Bratislava and Szeged. Apart from Szeged, all the other cities are located in area with diverse topography. It's an element of the environment which can greatly influence the local climate of urbanised areas – and Kraków is an example of negative influence.
"We measured the heat stress by comparing the average number of hot days, i.e. days when the temperature was equal to or higher than 25ºC. We investigated the highest and lowest average daily air temperature, relative humidity and wind force. We then checked the times when maximum temperature ≥ 25ºC," Dr hab. Anita Bokwa said. Using a variety of methods, a series of maps was created to illustrate potential changes. "We have shown the average annual number of hot days in those cities in the years 2021–2050 and 2071–2100, compared to the period of 1971–2000, depending on which clime change scenario proves to be true. The scenarios differ from each other in the level of greenhouse gases, and consequently, their concentration in atmosphere."
Currently, the average annual number of hot days in Kraków is 20.3 (data from 1971–2000). How will this change because of global warming? The researchers' predictions about this process vary from scenario to scenario. These scenarios, called Representative Concentration Pathways, show various possibilities of global warming effect: from the least severe (RCP2.6 – 40.6 days in 2071–2100) to the most severe (RCP8.5 – 65 days in 2071–2100). Aside from urbanised areas, places with low geographical positions are the most vulnerable. However, the number of hot days in the centres of the cities will be the highest. According to the estimates in scenario RCP8.5, the average annual number of hot days in the centre of Kraków will reach 104.5.
Although the increase of hot days in Kraków is of considerable scale, it cannot compare to Szeged (about 500 kilometres south of Kraków), where – according to the most pessimistic scenario – it may reach 159.1 days.
Original text: www.nauka.uj.edu.pl
