According to data from Slovenian Environment Agency (ARSO), from 1961 the average temperature in Slovenia has increased by 2°C. This change is much more complex than it might seem, because it implies many negative consequences that will be felt throughout the country, such as extended drought periods, followed by floods, rainy winters without snow, and heat waves, which will inevitably lead to increase in mortality rates among the most vulnerable groups of the population, such as the elderly and those with serious health conditions. We talked about the impacts of temperature increase and other climate change-related issues with Mojca Dolinar, responsable for climate analysis in Slovenian Environment Agency.

Pod črto: In Slovenia, last September has been pleasantly warm, and the increase in the average temperature is probably seen by many as a positive thing. Would people take more seriously the warnings about the consequences of climate change if we were heading into a new ice age?

Mojca Dolinar: The effects of climate change can also include the temperature decrease. The Gulf Stream is responsible for a powerful heat transfer from the Equator to the North Pole. Climate models suggest that if the Gulf Stream stopped, because of variations in salinity and temperature of the sea water, the temperatures in Atlantic and Northern Europe would considerably decrease. As ironic as it may sound, global warming could lead to the onset of a new ice age in some parts of Europe.

It is not easy to explain the effect of climate change because the climate system is very complex and the consequences of global warming are not the same everywhere. Some regions will continue to warm, some others will cool. In some areas precipitation rates will decrease, while in other areas will increase. If the highest temperature recorded today was 27°C instead of expected 25°, it doesn’t make a lot of difference, but if annual average temperature rises by 2°C, that’s a big change.

Can you explain this a little better?

According to our measurements, from 1961 the average temperature in Slovenia has increased by 2°, going from 10°C to 12 °C. Slovenia is warming faster than the global average, as during the same period the average global temperature has increased by 1°C. However, a two-degree increase in average temperature doesn’t mean the same thing in Ljubljana and in the Gorizia region, because these are two very different areas.

It probably doesn’t mean that the weather in Ljubljana, situated inland, will become more pleasant, similar to the weather in Slovenian coast?

Unfortunately no. A two-degree increase in average temperature provokes considerable changes in precipitation regime. In some areas precipitation will decrease, while in other areas it will increase. The low rainfall areas will become even drier. Climate models also suggest that extreme wheather phenomena will become more intense due to temperature increase: heavy rainfalls and floods, droughts, hurricanes, and in Slovenia mostly storms, heat waves, and hailstorms. Of course, extreme weather events were happening also in the past, well before the intensification of greehouse effect. However, due to increase in temperature and in atmosferic energy, extreme weather events are becoming more frequent and intense.

Why does temperature increase provoke intensification of extreme wheather events?

Warm air is able to hold more water vapour than cold air. This means that in the atmosphere must evaporate larger quantity of water before the vapour begins to condensate. As a result, the time interval between two consecutive rain events becomes longer and rainfalls become more intense. Long time intervals between two precipitation events can cause droughts, which are often followed by severe floods. Furthermore, we can expect significant changes in annual precipitation trend. All climate scenarios for Slovenia predict an increase of precipitation during the winter months.

But that doesn’t mean more snow?

No, due to temperature increase, rainfalls are likely to prevail. The snow-covered area has drastically decreased compared with the 1960s and 1970s. It’s snowing less, mainly in the middle mountains, and this trend is expected to continue. We will witness more and more frequently the situation where a lot of snow falls in a short period of time, and then it all melts down within a few days.

Bad news for winter tourism?

Not only for winter tourism. Nowadays, on our mountains the snow cover lasts until spring, or until the beginning of summer, before it starts to melt, and it is an important water resource that feeds our rivers. In the future, winters will become more rainy and we will need to collect raiwater in order to use it in the following months, for example for the production of hydropower or for irrigation.

Experts often warn of rise in diseases as one of the effects of global warming. Our region is also exposed to his risk?

Various studies have demonstrated that climate change brought back certain infectious diseases that have been eradicated. Malaria, for example, re-emerged in nordic countries, while West Nile virus came to our region. Due to favourable weather conditions, the number of generations that insects can produce in a year increases. The consequences of climate change will be felt most acutely in the summer.

Why?

Do you remember last April? In April the average temperature was nearly 4°C above the historical average, and for us it was a pleasant thing. But if that happens during the month of July, or rather if the average temperature during the summer rises by 4°C, it would be very difficult to tolerate, because we are not used to extreme heat. All climate models predict by 2050 an increase in the frequency and intensity of heat waves.

Can we expect heat waves to be more intense in urban areas?

From 1961 until today, in Ljubljana the average temperature has increased by about 0,5°C, reaching the national average temperature. This increase is due to city characteristics. In simple terms, the factors that most affect temperature increase in urban areas are buildings and infrastructure. The atmosphere absorbs only a small amount of solar energy, allowing sunlight to reach the ground. White surfaces reflect back most of the light, while dark surfaces absorb light and radiate it, but on different wavelenght, and than the atmosphere re-radiate it as heat. Such energy transformation occurs more frequently in cities where there are many dark surfaces, like asphalt, concrete, vehicle sheet metal. These materials absorb more heat than vegetation, and retain it for a long period of time – that’s way in some cities it’s hot even at night – , thus contributing to increasing heat burden.

And consequently, there is a growing use of air conditioning?

It is almost impossible to imagine life in a city without room temperature regulation systems. Some studies have shown that we often use more energy for cooling than for heating indoor spaces. The air conditioners are problematic because they transfer the heat from indoor spaces to external environment, thus contributing to temperature increase in cities.

However, temperature trend in urban areas also depends on other factors. Let’s take the example of Ljubljana, which is situated in a valley, and this affects considerably urban microclimate. In the valleys there is low airflow and, as a result, the temperature is higher. However, if we observe trends in average annual temperature, we will notice that during the 1970s in Ljubljana autumns and winters have been colder than in previous decades. In the 1980s temperatures had begun to rise significantly. What do you think why?

Maybe because of pollution? We have noticed this change during our research. EDJNet’s analysis has shown that in Ljubljana, during the 1970s, there has been a decrease in average temperature.

Because of very specific kind of pollution. In the 1960s and 1970s, countries all over the world have been experiencing the consequences of accelerated industrial growth, which has been very dirty. At the time, industries were releasing large amounts of pollutants, causing fog which is very important factor that influences the global energy balance because it acts as a barrier against the sun’s rays. The higher the concentration of fine dust, the more likely it is that fog will form in conditions of low humidity, especially in the valleys. Sulphur oxides occur as crystals and reflect large amount of sunlight falling on them. In Ljubljana, at that time, both fog and high concentration of aerosols were very frequent, and this has caused the temperature decrease. The same situation has occured in many other cities around the world and that is way some scientists have been warning about the arrival of a new ice age. However, during the 1980s sulphur dioxide emissions have declined and temperatures have begun to rise. That period is now know as global cooling period.

These examples are often cited by climate change negationists who are trying to belittle human impact on the environment, by claiming that global warming is caused by natural fluctuations within the climate system that occur independently of human action…

The climate system is very complex and anyone can refer to certain historical periods, climate events or natural phenomena as an example that presumably demonstrates the groundlessness of alarm over global warming and of actions aimed at reducing greenhouse gas emissions. We have already experienced many extreme weather events. Examples of mild winters in areas characterised by a rigid climate have also occurred in the past. It’s clear that increase in global average temperature does not necessarily mean that every summer will be hotter than the one before. Nevertheless, in the 21th century summers are often hotter, or much hotter than normal, with temperatures exceeding normal range of climate variability. Temperature rise exceeded values predicted by climate models which don’t take into account greenhouse gas emissions from human activities. Also the frequency and intensity of extreme climate events can’t be explained only by natural cycles.

The greenhouse gas emissions from human activities are an important factor in the global climate system and they affect climate in different ways. I previously mentioned the impact of seawater temperature and salinity on the flow of the Gulf Stream. Another important factor is ice.

Ice?

Ice is a very important element that has a significant impact on Earth’s energy balance. The Arctic and Greenland ice sheets are melting rapidly. Ice reflects large amount of sunlight received which is not converted into heat. If the ice disappeared, it would leave behind a dark surface capable of absorbing light, similar to asphalt which can retain heat for very long periods of time. The melting of ice sheets is speeding up global warming. The same goes for melting of sea ice because water holds heat longer. Numerous similar mechanisms have been identified so far which contribute to the intensification of the greenhouse effect.

What factors need to be taken into consideration when elaborating climate models and constructing climate change scenarios?

We use climate models to predict different scenarios for the 21th century, including the melting of glaciers, ecological responses in the ocean, changes in vegetation cover, contribution of human activities to greenhouse gas emissions, and different factors of socio-economic development. We must be aware that the climate system has long memory. The greenhouse gases – which are the primary cause of climate change – have long lifetimes, they can stay in the atmoshere for 50-200 years. All the gases emitted since the industrial revolution are still present in the atmosphere, which means that current greenhouse gases will influence climate for a very long period of time, even if all emissions stopped tomorrow.

These considerations suggest that there is nothing left to be done. And yet, in the past few years, many environmental organisations have completely changed their communication strategies. Instead of issuing alarming warnings, they highlight good practices and different models for change…

I also think that’s the best approach. Let’s return to the subject of your investigation, namely the temperature increase in urban areas. Cities are warming, and they will continue to warm. The temperature increase largely depends on the dimentions of the city, its geographical position and some other factors we cannot influence. But fortunately we can take various actions aimed at reducing the negative effects of temperature increase.

Such as planning of green areas?

Isolated trees, meadows, tree avenues and green roofs don’t have a big impact on the environment. We need to take into consideration the entire local ecosystem where green spaces and water spaces interweave. If urban green spaces are sufficiently large – like Tivoli park and Castle hill in Ljubljana – they can affect airflow and make the wind blow. The psychosocial effects of green spaces are also very important because rivers, parks and trees, besides offering great escape from the summer heat, improve the quality of life in cities.

How much does traffic contribute to climate change?

The means of transport are big polluters, even though vehicle exhaust particles remain on the ground and don’t have a big impact on global warming. Transport contributes mostly indirectly to temperature increases in urban areas. Cars require big infrastructure, which retains heat for a long period of time, like streets, parking lots, garages. Asphalt can also retain heat for a long time. There are many good reasons to reduce traffic, but the temperature increase can also be limited by reducing the numer of parking lots and by using materials that absorb less heat. Some cities have tried to tackle this problem by painting roofs white, and the same could be done with asphalt.

I forgot to mention before another measure aimed at reducing the negative effects of heat waves, that is energy requalification of buildings. Ljubljana has a district heating network and more and more citizens are heating their homes using gas. The problem is that the buildings connected to the district heating network hold large amount of heat, and city doesn’t have centralised and sustainable cooling system.

Earlier you mentioned floods, as one of the consequences of temperature increase, which over the past few years have hit several times both Ljubljana and Maribor. How can cities protect themselves from floods?

Flooding is a major threat to Ljubljana, because the city is situated in a valley where the water from all direction flows. The risk of flooding emerges when heavy and intense precipitation hits the Polhov Gradec Dolomites, which are the main orographic barrier in the area of Ljubljana. The volume of torrential streams, in particular Gradiška and Mali Graben, increases rapidly and water comes down to the Ljubljana marshes. In the past excess water drained fast thanks to high permeability of soil. Today water can’t be drained because of the presence of numerous illegal constructions and it often reaches the city. The effects of floods can be mitigated through water flow regulation new forms of urban drainage and well coordinated action with neighbour cities. However, what emerged during last big floods was a lack of real collaboration. In general, lack of collaboration is the main obstacle in fighting climate change.

The reason for such lack perhaps lies in the fact that climate change affects many different sectors?

It is often difficult to determine who is responsible for what. We elaborate climate change scenarios, but we are not policy makers. Municipal service companies are responsible for the maintenance of green and water spaces, whose creation is entrusted to urbanists and landscape architects. The issues related to energy requalification of buildings and to greenhouse gas emission reduction fall within the competence of other sectors, even thought all those aspects are closely interconnected. It is very rare to see climatologists, biologists, architects and engineers collaborating on the same project and interchanging experience. We comfort ourselves with the fact that in Slovenia there are no big cities and that not even Ljubljana has so far experienced devastating effects of global warming. However, climate models predict that, by 2050, Slovenian citizens will experience various effects of climate change, and adaption will be needed, but it won’t be possibile without systematic action at the national level.