30th September 2021

Hot city. Are we facing unbearable summers?

On a global level, cities are heating up. This is due to the increasing mass of concrete, steel, asphalt and car exhaust, which adds to the effects of global warming – at the expense of nature. Some sustainability experts warn that in 50 years’ time, different populated regions could get as hot as in the desert. Dr. Andrew Ferrone, Head of Meteorological Service at the Administration of Technical Agricultural Services of the Ministry of Agriculture, Viticulture and Rural Development, knows the answer.

1. Mr. Ferrone, what do you say to climate change skeptics?

In its latest report the Intergovernmental Panel on Climate Change (IPCC) has concluded, “It is unequivocal that human influence has warmed the atmosphere, ocean and land.”

234 top climate scientists from all over the world wrote this report and it was open for comments to all scientists. All the 195 Member Governments of the IPCC finally approve the summary of policy makers. This process implies that the IPCC is conservative by design, and despite this, the conclusion above is very clear. All of the scientists and the governments thus agree that humans caused global warming since 1850 and any doubt about the reality of climate change as well as its cause has no valid basis anymore.

2. Canada has suffered an unprecedented heat wave this year. Will it get unbearably hot here in Luxembourg too and if so, what temperatures can we expect here over the next few decades?

The World Weather attribution project has concluded that the Western North American extreme heat was virtually impossible without human-caused climate change. In addition, the IPCC concluded that in Europe the frequency and intensity of hot extremes have increased in recent decades and will continue to increase regardless of the evolution of future human greenhouse gas emissions. Indeed the effect of global reductions of emissions in the next decades will only start to affect temperatures in around 20 years in a discernable way, although other effects, such as reductions in air pollution will happen much faster.

In the country of Luxembourg, we have observed that the annual temperature averages in the period 1991-2020 were 1.6°C higher than in the pre-industrial period (1861-1890), compared to the 1.0°C that have been globally observed over a similar period. This is in line as the land surface is warming faster than the global average. We can expect this warming trend to continue until the 2040s. If at that point in time, global CO2 emissions are falling towards net-zero we could expect a gradual stabilization of temperatures.

3. Why do big cities seem to be particularly affected by the climate crisis?

Urban centers and cities are warmer[1] than the surrounding rural areas due to what scientists call the urban heat island effect.

This effect results from several factors, including the heat-absorbing properties of many of the building materials used in cities as well as city geometry, which reduces ventilation between buildings or can trap heat. Additionally heat generated directly from human activities, and the limited amount of vegetation contribute to the heat islands.

This implies that cities amplify the increase in heat stress due to global warming. The IPCC assessed for example that the Brussels area has warmed by 0.6°C more from 1950 to 2018 than the surrounding rural areas, but also that cities exacerbate the effect of extreme climate events, such as heatwaves, with more hot days and warm nights adding to heat stress.

[1] source: https://www.ipcc.ch/report/ar6/wg1/downloads/factsheets/IPCC_AR6_WGI_Regional_Fact_Sheet_Europe.pdf


4. How can we adapt cities to climate change and how do we make them more heat resilient?

The best way to adapt cities to climate change is to try to reduce the factors that contribute to the heat island effect described above. Changes in city geometry or building materials are nearly impossible in existing cities, but can have a big impact when considered in the planning of new urbanization or the makeover of existing parts of the city.

Moreover, the insulation of buildings can also help to reduce the heat from human activities. In this way, the housing or the offices are heated and not the whole city area, which has the advantage that it also helps to reduce the emissions of greenhouse gases.

Finally, the inclusion of water areas and/or vegetation in new projects or their addition, when possible, to existing cities can strongly reduce the heat island effect. A greener city furthermore has the advantage that the vegetation can absorb carbon dioxide from the air and thus increase the sink that is necessary to stabilize global temperatures.


5. Building houses demands a huge amount of energy. How important is the building sector in stabilizing temperatures at 1.5°C°?

In 2016[2], the global greenhouse gas emissions related to the energy used in buildings (17.5%) and the production of cement (3%) accounted for a bit more than one fifth of the total human –made emissions. This show the importance of the building sector when emissions need to be reduced to net-zero by 2050 in order to limit global warming to 1.5°C. The insulation and efficient use of energy in buildings (both residential and commercial) together with a carbon neutral way of producing the energy can contribute strongly to achieving this goal.

[2] Source: https://ourworldindata.org/emissions-by-sector

6. Can white surface (in particular roofs) reduce the urban heat island effect?

White surface have a higher albedo than darker surfaces, which means that the surface reflects more of the incoming solar radiation and less of it is absorbed and transformed into heat. This means that for example white squares heat up less than darker squares, even though the reflection dazzles persons on the square.

The effect of adding vegetation to a square, in particular trees which give shadow and absorb CO2 from the atmosphere, reduces local temperature much more than the change of color. A combination of both options can help to reduce locally the heat island effect.

These effects have however a very local effect only. Painting roofs or streets in white colors would not be sufficient to counteract the increase in global temperatures due to human-made greenhouse gases.


7. Do you have five practical tips for everyday life on how we can counteract heat waves?

The best way to counteract heat waves is to implement strong emissions reductions in the next decade and to reduce CO2 emissions to net zero around 2050 in order to limit global warming to 1.5°C. Indeed the IPCC[3] assessed that a heat wave that would statistically occur once per 50 years in pre-industrial times, is now already occurring in nearly 5 years, and would occur in nearly 14 years out of 50 if global warming has reached 2°C compared to around 8.5 times at 1.5°C.

However, even with the most ambitious global emissions reductions, Luxembourg will continue to face more frequent and more intense heat waves. When a heat wave hits the country, it is important to follow the recommendations[4] given by the Ministry of health.

[3] Source: Based on Figure SPM.6 of the SPM: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf

Source: sante.public.lu/fr/publications/a/attention-canicule-fr-de-pt/canicule-depliant-fr.pdf


Five recommendations from the Ministry of health when a heat wave hits the country

1. Drink at least 1.5l of water per day;

2. Try to avoid exposing to sunshine if possible;

3. Avoid physical activities during the hottest part of day (the peak temperatures usually occur around typically 5 pm in summer in Luxembourg);

4. Try to refresh by taking showers;

5. Attend to elderly and vulnerable persons of your surrounding and make sure they drink enough mineral water.

About the blog:

There is an urgent need for rapid transition to Global Environmental Sustainability. Thanks to changemakers, progress is possible. "Why does it matter?" is a bi-monthly series that takes a quick look at the forefront of today's trends around  sustainability. From May 2021 on, we aim to elucidate this important topic through the eyes of our experts. 

Your contribution counts too! From June on, don't miss out our experts' practical tips for your daily life.