Causes of Climate Change - part two

Michiel Haas – the Netherlands

Already visible effects of climate change 

New heat records every year since the start of the 21st century 

Ominous heat records are broken year after year. The fight against climate change has been accelerating since the Paris agreements, but is still seriously inadequate. With the current international climate plans, we are moving towards a global warming of 3.2 °C. Such temperature rise has major consequences for people and the environment.

The 21st century now accounts for 18 of the 19 hottest years of the measurement series since 1880 worldwide. The 2018 World Meteorological Organisation (1) (WMO) report confirms that 2018 was the hottest year ever - a striking 1.2 degrees Celsius above the pre-industrial period and 0.07 degrees Celsius above the previous record of 2017. 2019 is likely to surpass the heat of 2018.

The temperature of the sea surface is also the warmest ever in the measurements. The sea level continued to rise, and the surface of the polar caps was far below average for most of the year. Said report speaks of an unprecedented

global heat wave, an exceptionally small area of ​​sea ice on both poles and a rapid rise in sea level. These are largely the result of climate change but were given an extra boost by the weather phenomenon El Niño.

El Niño

El Niño, Spanish for 'the child', is a weather phenomenon that heats up the waters of the Pacific Ocean every three to seven years, with serious consequences for the weather in large parts of the world. El Niño is often accompanied by violent storms in South America and droughts in Asia and southern Africa. El Niño is not a climate change phenomenon, but due to rising temperatures, the El Niños of the last decades are heavier. The last El Niño that lasted from 2014-2016 caused the tropical forests to emit an additional 3 billion tonnes of CO2 (due to drought, forest fires and less growth of forests). That is almost one fifth of the emissions from fossil fuels and cement production in the same period. And this does have a major impact on climate change.

Warming and heat waves 

The last five years (2014-2015-2016-2017-2018) were always the hottest years since the start of our measurements. The graph below also clearly shows that it is getting warmer. In the Netherlands, it has already become 1.7 degrees Celsius warmer since the pre-industrial era. In our climate, it still feels pleasant. However, we have to deal with more and more heat waves with temperatures above 30 degrees and even heat waves above 40 degrees Celsius; which is less pleasant. A heat wave is described by the KNMI as a sequence of at least 5 summer days in De Bilt (maximum temperature 25.0 °C or higher), of which at least three are tropical (maximum temperature 30.0 °C or higher). Since 1901, 27 heat waves have been registered in De Bilt, of which more than half since 1990, namely 16 heat waves. And 11 in this century alone. The pace of the heat waves is increasing. This applies to the Dutch situation. But the temperature is also rising in other places in the world.


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Temperature rise in the world: 1990, top 2000, 2018 and the expectation for 2030, we see it getting redder, which means that the temperature rise exceeds 2.0 degrees Celsius

The European Environment Agency (EEA) writes about the climate in Europe in its four-yearly report (2). "More heat waves and problems due to warm nights in the city, not only around the Mediterranean Sea but also in and around the Netherlands and other Northern European cities."

From the past decades it can be concluded that global warming leads to increased risks of heat waves and dry episodes. In addition, the temperature on the hottest days and nights in the scenarios also rises more than the average warming. Because the temperature in cities is often several degrees higher than in rural areas (also called Urban Heat Island), the impact of these hot and dry days in cities is much greater. It is assumed that this effect means an extra 4 degrees Celsius. Measurements taken in Rotterdam during the heat wave in 2015 (3) showed that the temperatures measured in the city were up to 9.9 degrees higher than the surrounding green areas.

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Temperature rise due to the heat island effect in cities (source: Urban_heat_island.svg: TheNewPhobia derivative work: Alexchris (Urban_heat_island.svg) [Public domain], via Wikimedia Commons

Drought and forest fires

The south of Europe has in recent years increasingly had to deal with large wildfires. The rain season is mostly in winter there. So, if there is little rainfall, nature dries out due to the warming Earth in the course of spring. This change in climate around the Mediterranean Sea leads to a further drying out and an increasing risk of major forest fires. That was painfully clear again during the summer of 2017. Vast forest fires in southern Europe, especially in France, Spain, Portugal, Montenegro and Greece. In 2019, we also see an increase in forest fires in unexpected places in the northern hemisphere. Siberia, Canada and Alaska are areas where forest fires occur regularly. Forest fires cause ecological and economic damage every year in an area the size of the European Union, which is not small.

Fortunately, in southern Europe and even worldwide, the total number of forest and heathland fires and the area of ​​the burnt area has decreased in recent decades, although there are major regional differences. How can this be explained?

By giving more attention to the prevention of natural fires and increasing knowledge about how these natural fires originate and how to control or prevent them, we learn to prepare for this natural phenomenon. Partly thanks to satellite observations, we can respond faster. But also because nomads travel less and settle more often in permanent places, less nature is burned down.

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Forest fires in southern Europe and also in Siberia and Canada cause great damage and even deaths (photo: Peter J. Wilson on Shutterstock)

More extreme weather 

Due to the warming Earth and especially the warmer seawater, which is the engine of the showers, we more often face more extreme weather. Meteorologist Jennifer Faber from Buienradar (4) says: "If global warming continues, weather events will become more and more extreme. Not only for Europe but also for the Netherlands. We must bear in mind that we will get heavier or more showers."

In recent years, we have noticed that showers can be more intense, more precipitation in a shorter time, often locally, accompanied by strong winds and gusts of wind. Hailstorms can hit suddenly, with large hailstones. In particular, heavy rainfall within a short time is increasing with around 12 percent per degree of warming and that is already noticeable.


Due to the increasing rainfall and urbanisation with associated canalisation of rivers and the pavement of surfaces, rivers have had a harder time draining all the water properly. For the Netherlands as a delta country, our large rivers, such as the Rhine, have to drain more rainwater in the winter, while less melt water in the summer due to further evaporation. The expectation is that the Rhine, now a combined rain and melt water river, will become more like a rain river. A rain river has high drainage in the winter and low drainage in the summer. The Maas has always been a rain river. For both rivers, high water levels are not only more frequent, but they also have higher water levels. The Netherlands has already prepared for this situation by creating extra space in the river floodplains. Many other countries have not yet taken these precautions.

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A flooded river due to heavy rainfall (source: Lisa S. via Shutterstock)

Sea level rise

 There is much talk about a sea level rise. But what exactly does that mean?

The relative sea level rise at a certain place on Earth is the sum of the increase in the height of the sea level (absolute sea level rise) and the local soil movement. In the Netherlands, we have a subsidence of a few centimetres per century, due to the subsidence of the soil and due to the after-ice effects of the last ice age. In some places, the subsidence is much faster, think of Gouda for example.

An absolute rise in sea level is caused by changes in the total amount of water in the oceans (for example due to melting of glaciers or land ice) and in the change in volume due to temperature changes. Hot water expands, cold water shrinks. The largest contribution is currently made by the increase in volume due to the temperature rise of the ocean water.

Sea level off the Dutch coast has risen steadily in 125 years by around 23 cm, or a change of 1.9 mm per year. This corresponds broadly to the worldwide rise in sea level of around 22 cm over the same period. Since 1993, the global sea level rise has been accelerating.

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A global sea level rise of 1.2 to 1.5 mm per year is estimated for the period 1901-1990. The IPCC (2013) achieves a global sea level rise of probably 3.2 mm per year for the period between 1993 and 2010. The IPCC provides a lower limit of 2.8 and an upper limit of 3.6 mm per year for this estimate.

Drought and hunger 

Our part of Europe is also sometimes drier than normal, although that is not yet certainly due to climate change. We do not see any increase in dry periods compared to the past, but we do see that the drought can be more extreme. Droughts in the Netherlands also pose a risk of forest fires, although their scale and intensity will not be comparable to the scenes that occur every year in southern Europe. In our country, however, there are other problems in the event of persistent drought. Such as the sinking of old dikes, with the risk of flooding. Ultimately, salinization can occur, damage to crops and, in the longer term, a threat to the drinking water and food supplies.

Globally, we see an increase in drought in areas such as the Middle East, India, Central Africa (Sahel zone) and Southern Africa. With failed harvests and a possible doubling of the number of people with hunger as a result.

Wars and climate change refugees 

Climate change is of course never the only cause of a war, but it can contribute to its origin. The war in Syria was partly caused by the drought in the northeast of the country. Leo Meyer, climate consultant and former climate researcher at the Netherlands Environmental Assessment Agency (PBL), talks about this in The State of Climate 2015 (5): "It is difficult to prove that a climate event has contributed to the emergence of conflicts, and it is even more difficult to attribute a regional climate event to global warming."

But in the case of Syria, scientists succeeded quite well. The area is generally fairly fertile and is inhabited by many farmers who farm there. From 2007 to 2010, however, three dry years followed each other, causing harvests to fail. The scientists calculated that the chance that those three dry years fall within the natural variation of the climate was negligibly small. "It must have been climate change," says Meyer. The drought caused farmers to leave their land and move to the city. Some cities gained up to 50 percent more residents. "If you arrange it properly, you can manage such an influx," says Meyer. “But Assad did nothing at all. As a result, dissatisfaction grew, resulting in conflicts.” It makes it clear once again that there is never one cause behind a war, but that all kinds of forces work together.

Of course, Syria is not the only place where we are dealing with climate refugees. According to the United Nations (UN), there are currently 140 million people displaced by climate change. Many of them are Africans, but also people


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from India and Bangladesh.

Syrian refugees demanding access to the EU (source: Kostas Koutsaftikis /




  1. WMO Statement on the State of the Global Climate in 2016

  1. Climate change, impacts and vulnerability in Europe 2016 – European Environment Agency

  1. Bomen en planten moeten de stad koel houden – Cor Speksnijder


  1. De staat van het klimaat 2015 – Stichting HIER klimaatbureau (Climate Agency)

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