On 15 September it turned 30 degrees and more in many places in Belgium. According to data from the European Copernicus climate portal, this was very exceptional in the past, something that only happened every 30 years. VITO researchers calculated the current probability of reaching such high temperatures in Belgium. It appears that this has already risen to once every 8 years. 

Greater chance of very hot September months

In 2013 and 2016 such warm September days have already occurred in Belgium over the past 40 years. As a result of the climate change that is in full swing, panting due to the heat in September is no longer exceptional. According to climate models from the IPCC (Intergovernmental Panel on Climate Change), global warming is continuing and by 2050 we would already be hitting 30 degrees in September every 5 years. By the end of the century, very warm September temperatures will become the new normal. We will reach 30 degrees in 1 year out of 2 if we do not reduce global greenhouse gas emissions (RCP8.5). If we do make efforts to reduce greenhouse gas concentrations, we can still limit warm September days to a little less than once every 3 years (RCP4.5).

Graph: Annual probability rate on hot September days of 30°C or more

It is clear: hot late summer days will inevitably increase due to climate change. So we will have to adapt our society to this with smart measures to make the high temperatures bearable, especially for vulnerable groups. After all, in our temperate regions, climate change is mainly felt through extremes, such as heat, which we will have to endure more often. At the same time, by reducing greenhouse gas emissions, we can limit the increasing heat.

Greater chance of long heat waves

Last summer's heatwave in our country is also in line with the climate change that is unfolding. In Uccle last summer, with 12 days, one of the longest heat waves ever measured was observed. This was felt throughout the country, for which, according to data from the European Copernicus Climate Portal, the heat wave was on average 11 wave days long and the temperature reached high peaks, up to 34.5 degrees on average across Belgian territory. Such long heat waves only occurred twice in the last 40 years, once in 2003 and another time in 2018. VITO calculated that the chance of such a long heat wave was rather small in the 1980s: less than once every 15 years, an 11-day long heat wave could occur. However, climate change means that a long heat wave is no longer that exceptional today. Once again, IPCC climate models point to more heat extremes and now a long heat wave can already occur once every 6 years.

Graph: Annual probability rate on a heat wave of 11 days or more

The likelihood of such heat waves also increases considerably in the near future due to the global warming that will continue. By 2050, we expect heat waves of this magnitude to occur more than once every four years. By the end of this century, this will be more than every 2 years if we do not reduce greenhouse gas emissions (RCP8.5) or every 3 years if we reduce emissions slightly (RCP4.5). In addition, the heat wave will be even less bearable, averaging 36.3 degrees in the best-case scenario and 38.7 degrees in a more pessimistic scenario. A heat wave such as last summer's with a maximum of 34.5 degrees would be a rather milder heat wave.

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