Global warming until now

Global warming continues. Eight of the ten warmest years in recorded history have occurred since 2000, although the rate at which global average temperature increases has slowed down significantly over the last decade, compared to the average increase between 1975 and 2008. Recent publications show that this is due to natural variations that are well understood. For instance, the last decade started with a strong El Niño in 1998, increasing global temperature with approximately 0.25°C, and ended with a significant La Niña in 2008, lowering temperature with approximately 0.15°C (4).

The observed climate variations in the 20th century can be explained by a combination of natural and human causes. There are three distinct natural causes of climate variations: volcanic eruptions, variations in solar activity and El Niño (5):

1. Strong volcanic eruptions, such as those of Mt. Pinatubo in the Philippines in 1991, expel enormous quantities of dust high into the air. This dust remains in the atmosphere for several years and reflects sunlight back into space. As a result, the Earth’s surface becomes cooler.
2. The second natural factor, solar activity, is not constant and, consequently, the quantity of energy which reaches the Earth from the Sun varies slightly over time. This will in turn affect the temperature on Earth.
3. The third natural factor is El Niño. The temperature of the seawater in an area to the west of Peru is abnormally high once every 3–7 years, which causes changes in the ocean circulation patterns. This change eventually leads to abnormal global weather patterns and affects the average global temperature.

From 1950 until the mid-1990s these three natural factors had a net cooling effect on the climate. Nevertheless, the average global temperature has increased considerably since the 1980s, mainly due to the emission of greenhouse gases (5).

Humans are also influencing the climate in another manner. Aerosols have a predominantly cooling effect and mask some of the warming effect of the rising concentrations of greenhouse gases. However, there are also aerosols which have a warming effect (mainly soot); these absorb heat and then emit this to their surroundings. With increasingly stringent air pollution control measures, the predominantly cooling effect of aerosols has decreased over the course of time (5).

Air temperature changes until now

During 1900-2005 yearly averaged temperature has risen by 1.7⁰C in the Netherlands (1). Until now, temperature rise in the Netherlands has been faster than the global average (3).

In Western Europe, the observed temperature rise over the last decades appears much higher than the global average, by about a factor of two. In winter and spring, higher temperatures are caused by changes in atmospheric circulation, tending to more westerlies in the observations than was calculated by the models. In spring and summer, there is an increase in the amount of solar radiation that reaches the ground, partly due to lower aerosol concentrations. This is underrepresented by state-of-the-art climate models (4).

The relatively strong temperature rise in the Netherlands in recent decades is mainly due to changes in the prevailing wind direction (5,22). The direction of the wind is correlated to developments in high and low pressure areas above the North Atlantic Ocean, the so-called North Atlantic Oscillation (NAO): the changes in air pressure differences between Iceland and the Azores. This determines airflow patterns above the North Sea and the European mainland. … In particular, the late winter / early spring period has been noticeably warmer since the 1980s due to the increase in southwesterly winds. It is still not clear whether this increase in ‘warm’ winds in this season is correlated with a human effect on the climate (5,22).

The extremely dry and hot summer of 2003

In central and northwestern Europe the summer of 2003 was the hottest in more than 500 years. The average summer temperature in Europe was almost 2⁰C higher than the long-year average of 17.5⁰C over the period 1901–1995. The central part of Europe and, in particular, the Alps had the largest temperature aberration: more than 5⁰C above normal. Up until then the warmest European summer had been that of 1757 when it was particularly warm in southern Scandinavia, eastern Europe and western Russia (5).

In the Netherlands, it was less extreme. The Dutch summer of 2003 was, with an average temperature of 18.6⁰C, about as warm as the summer of 1947, which was the warmest summer of the 20th century in the Netherlands (5).

Precipitation changes until now

Annual and seasonal precipitation

Changes in the annual precipitation amounts, the precipitation amounts in the winter and summer halves of the year, the number of days per year with a precipitation amount greater than 20 or 30 mm, and the 5-d annual maximum precipitation amount were determined both for the period 1951–2009 using the data from 240 stations and the period 1910–2009 with the data from 102 stations. Significant increases were found for all six indices (11). For the period 1910-2009 the following significant changes in precipitation amounts and intensity were found (11):

• 25% increase in mean annual precipitation;
• 35% increase in mean winter precipitation;
• 16% increase in mean summer precipitation, with a relatively strong increase since the beginning of the 1980s;
• almost doubling of the average number of exceedances of the 30 mm threshold. Most of these exceedances occur during the summer half-year, in particular a relatively strong increase after 1980;
• a sharp contrast was found between coastal regions with a significant increase in mean summer precipitation and the east and southeast of the country with little change in mean summer precipitation.

The increase in mean winter precipitation over the period 1951–2009 is partly explained by changes in the pattern of atmospheric circulation in this period which brings more humid maritime air over the Netherlands (11). The increase in mean summer precipitation is much more a local trend, which is probably related to changes in the sea surface temperature (12,13). An increase in the mean sea surface temperature during summer of 1.2–1.5°C was found during the period 1951–2006, being about twice as large as the global mean temperature change (12).

During 1951–2009, apart from the spring months, the coastal area has consistently become wetter compared with the inland area. An analysis of daily precipitation data for the period 1951–2009 showed that, overall, both mean and extreme precipitations have increased on seasonal and annual scales over the last 59 years and especially in the last 30 years for the entire country, changes being largest along the West coast. Sea surface temperature was shown to have a larger influence on precipitation in The Netherlands than other factors such as elevation and urbanization (13). The adjacent North Sea is a shallow coastal sea (20–200m deep) and therefore cools or warms relatively fast (on time scales of weeks to months). Temperatures over sea are higher from August onward and enhance coastal precipitation until December when the atmosphere is on average too stable for frequent convective showers to occur (14). From April to July coastal precipitation is suppressed by relatively cold sea water temperatures (13).

Precipitation extremes

Observations show a strong increase in the intensity and likelihood of local precipitation extremes similar to the event observed on 28 July 2014, when a number of thunderstorms moved across the Netherlands and precipitation totals in excess of 130 mm fell in just a few hours. Uncertainty margins are large, however, due to natural variability. Climate model simulations show that a fraction of this increase can be attributed to global warming; the remainder is due either to natural variability or to an underestimation of the trend in models. These simulations show that it is difficult to attribute extreme precipitation events to anthropogenic climate change (20).

The results from an analysis of the maxima of long-term (1901–2013) daily precipitation records from a densely sampled Central European station network, spanning Austria, Switzerland, Germany and the Netherlands, support the expected tendency of increasing extreme precipitation intensity with continuing global warming. The increase is approximately 6-8% per degree Celcius, both for short- and long-duration events (21).

Wind climate changes until now

Since 1962 the number of storms per year has decreased. To what extent this decrease is correlated with rising temperatures is not clear (5). A northward shift in mean storm track position since about 1950 is consistent in studies on wind climate in northwestern Europe over the last decades (18). This northeast shift together with the trend pattern of decreasing cyclone activity for southern mid- latitudes and increasing trends north of 55 - 60°N after around 1950 seems consistent with scenario simulations to 2100 under increasing greenhouse gas concentrations (19).

The analysis of 101 years of storm loss estimates in the Netherlands revealed multidecadal variability with a dominant multi-annual cycle of about 50 years and stability over a 100 year time scale. The Netherlands has experienced a downward trend in windstorm losses in the past two decades to a record low level slightly below the previous minimum of 50 years ago. The current minimum in aggregate losses is driven by the reduced rate of occurrence of damaging storms (10).

Results of analyses of long-term changes in wind climate in different parts of Europe generally conflict due to significant differences in data and methods between investigations, such as (10):

• the basic observation variable (loss data, wind speed, surface pressures);
• the metric of storminess (reported societal losses, wind percentiles, rate of change of surface pressure, proxies such as ‘gale-days’);
• the study region;
• the length of the historical period (from the past 20 years to many hundreds of years).

Global warming in the 21st century

Claims that global warming has stopped since 1998 are at odds with long-term observations, which show comparable variations on similar timescales. It is expected that, in the longer term, warming will continue. According to several solar physicists, the sun may enter a stage of very low activity. Global temperature increase due to human influence might be tempered by 0.2°C in the coming decades, but long-term projections of global warming in IPCC 2007 remain unchanged (4).

A doubling of the CO2-concentration since the pre-industrial era is most likely to lead to an average global increase of 3⁰C. There is a chance that this number will be lower, and that future human induced global warming will happen slower than anticipated by the IPCC. In that case, negative impacts will be smaller than is generally assumed for policy responses. However, the odds that the increase will be higher than 3⁰C, are greater, due to several mechanisms in the climate system that may accelerate global warming. Therefore, the chance of underestimation of the future increase in global temperature is larger than of overestimation (4).

Air temperature changes in the Netherlands in the 21st century

The Royal Netherlands Meteorological Institute has drawn up four scenarios of climate change for 2050 and 2100 with respect to 1991-2020: one set for low emissions of greenhouse gasses (dry and wet climate) and one set for high emissions of greenhouse gasses (dry and wet climate) (23).

The projected precipitation changes for 2050 and 2100 compared with 1991-2020 are summarized in the tables below.

It is expected that the chance of extremely cold winters will decrease less quickly than would be expected on the basis of the average temperature increase. This is because the cold extremes are strongly dependent on the wind direction (easterly wind). In concrete terms this means, for example, that in the future the famous ‘Elfstedentocht’ skating tour is less likely but still possible (5).

Future cold spells in Western Europe are projected to become about 5°C warmer (and remain above freezing point), thus having a significant climatic impact. This conclusion is based on research in which a cold spell (CS) is defined as a non-interrupted sequence of days in which the 5-day average temperature falls below a threshold value Tcold (9).

In much of the North Sea region the number of tropical nights at the end of this century may rise by about 10 days under an intermediate (RCP4.5) and by more than 20 days under a high-end (RCP8.5) scenario of climate change, with tropical nights hardly ever occurring in this region under the present-day climate. Similarly, cold spells are projected to become shorter in the North Sea region, by about 3 days for the intermediate (RCP4.5) and about 4-6 days for the high-end (RCP8.5) scenario. Warm spells are projected to become markedly longer in the North Sea region, by about 30 days for the intermediate and by 60-120 days for the high-end scenario (15). 

Precipitation changes in the 21st century

The Royal Netherlands Meteorological Institute has drawn up four scenarios of climate change for 2050 and 2100 with respect to 1991-2020: one set for low emissions of greenhouse gasses (dry and wet climate) and one set for high emissions of greenhouse gasses (dry and wet climate) (23). The projected precipitation changes for 2050 and 2100 compared with 1991-2020 are summarized in the tables below.

Extreme downpour in the summer will increase whereas the total number of rainy days in the summer will probably decrease. In the most extreme scenario of the Royal Netherlands Meteorological Institute an average summer will be as dry as the one of 1976, which was the driest of several decades. 

In their 5th Assessment Report the IPCC presented a precipitation decrease at the end of the 21st century for April through September up to 10% for England, Belgium, the Netherlands and northern Germany, under the intermediate RCP4.5 scenario of climate change. These projected changes, however, do not exceed natural climate variability across the region. For October through March a precipitation increase up to 10% was projected for this North Sea region; these projected changes do exceed natural climate variability across the region (16).

Wind climate changes in the 21st century

According to the Royal Netherlands Meteorological Institute, changes in the wind climate in the 21st century will be small with respect to natural variability (1). For Dutch policy on flood protection it is considered unlikely that the storm regime along the Dutch North Sea coast and the associated maximum storm surges will change significantly in the 21st century (2). Some researchers, however, conclude that more North Sea storms might be generated leading to increases in storm surges along the North Sea coast, especially in the Netherlands, Germany and Denmark (6,7).

A review of recent scientific literature shows that the projected changes in wind extremes (speed and direction) for the North Sea region are
 typically within the range of natural variability and can even have opposite signs for different scenarios either simulated by different climate models or for different future periods (17). 

Projected precipitation changes for 2050 and 2085, according to the scenarios of the Royal Netherlands Meteorological Institute, are summarized in the table below. G and W refer to moderate and warm scenarios, respectively, in which L and H indicate lower and upper values, and the upper values assume changes in air circulation.

Indicator G G+ W W+ Change in air circulation No Yes No Yes Highest daily-averaged wind speed 2050 compared with 1981-2010 -3% -1.4% -3% 0% Highest daily-averaged wind speed 2085 compared with 1981-2010 -2% -0.9% -1.8% +2%

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for the Netherlands.

1. Royal Netherlands Meteorological Institute (KNMI) (2014)
2. Ministry of Housing, Spatial Planning and the Environment (2009)
3. Platform Communication on Climate Change (2009)
4. Netherlands Environmental Assessment Agency et al. (2009)
5. Bresser (2006)
6. Woth et al. (2005), in: Alcamo et al. (2007)
7. Beniston et al. (2007), in: Alcamo et al. (2007)
8. PBL Netherlands Environmental Assessment Agency (2011)
9. De Vries et al. (2012)
10. Cusack (2013)
11. Buishand et al. (2013)
12. Lenderink et al. (2009), in: Buishand et al. (2013)
13. Daniels et al. (2014)
14. Attema and Lenderink (2013), in: Daniels et al. (2014)
15. Sillmann et al. (2013), in: May et al. (2016)
16. IPCC (2013), in: May et al. (2016)
17. May et al. (2016)
18. Feser et al. (2015a), in: Stendel et al. (2016)
19. Ulbrich et al. (2009); Feser et al. (2015a), both in: Stendel et al. (2016)
20. Eden et al. (2018)
21. Zeder and Fischer (2020)
22. Hoogeveen and Hoogeveen (2023)
23. Royal Netherlands Meteorological Institute (KNMI) (2023)