Costs of climate change today
It is important to understand how already the present warming of 1°C  is able to cause weather catastrophies and thousands of casualties (in the Arktic, Alaska and Canada warming has, however, already reached up to 4°C [2,3]). Until now climate change resulted in the following three phenomena: 1. Radiation reaching the soil has increased, 2. Globally it has become warmer (1°C) and 3. The humidity of the atmosphere has increased. These three phenomena have resulted in a number of physical/climatological consequences, which have negatively affected us:
Heat waves and droughts
Due to an increased radiation reaching the soil and the warming of the atmosphere by 1°C, droughts and heat waves became more frequent and more intense. Temperature did not just rise by 1°C, but due to the higher concentration of greenhouse gases radiation reaching the soil intensified and at the same time more extreme weather events occured (see below), which together resulted locally in much higher temperture increases than 1°C. Notably, the present warming of 1°C refers to the average warming in the atmonsphere. The earths surface heats up much more due to increased (infrared) radiation than 1°C. This causes drying of the soil and may result in a deficit of humidity in the air above, which in turn can cause weather conditions, in which the dry, hot air is isolated by the atmosphere for several days or weeks . This happend during the great heat waves in 2003 and 2010 . In 2003, the average temperature near the earths surface was up to 15°C higher than in preceeding years . In 2003, this heat wave alone cost 70 000 fatalities across Europe  and damages of 12.3 bil. Euro . Further heat waves occured in 2015, 2017 und 2018 . And also the year 2019 seems to become an exceptionally warm year .
One may think, heat waves and other extreme weather events occur also naturally. This may be true for single weather events. However, when considering the frequency of such extreme events on a global scale (see. figure above), there is a clear trend: Weather catastrophies occur more and more frequently and this increase reflects increasing temperature (figure above). In Germany, for example, the number of days with 30°C or more per year has tripled since 1950 .
In Europe, the heat wave of 2018 was accompanied by droughts and wildfires in Sweden, Norway, Latvia, Germany, Great Britain and Irland . For Germany alone, damages to agriculture amounted to 770 bil. Euro . Germany provided 340 mio. Euro for farmers. Harves losses reached 50%, damages were 3.9 bil. Euro, there were about 100 fatalities [10,13]. Furthermore, wildfires in several European countries caused additional damages. The Association of German Forest Owners estimated damages of 5.4 bil. Euro, caused by wildfires, dried trees and bark beetles (which develops more rapidly at higher temperatures) . Navigation on river Rhine had partly to be stopped due to low tide, which endangered the coal supply to coal power plants. The picture looked similar in North America aus: In 2018, the campfires in California caused the highest damages due to fire of all times. These campfires caused about 100 deaths and damages of about 21.7 bil. US$ .
Extreme rainfall, floodings and storms
The global increase of the humidity (atmosphere) has particularly negative implications for us. This increase is results from the following: Due to the warming of the oceans more water evaporates, hence increasing humidty of the atmosphere. At the same time warmer air can also hold more moisture than cold air (about twice as much per temperature increase by 10°C [15,16]). This means, over the oceans humidity increases. Over continents the situation differs. On one hand, land masses heat up more than oceans , and on the other hand, heating results in a stronger dissication of the soil [16,17]. Hence the air is not as humid as the air above the oceans. It depends on the regional situation, what results from this difference of humidity and temperature (e.g. the distance to oceans, the dominating wind direction, etc.). In some regions, there has been more precipitation and in other regions less (e.g. when the wind direction is continental), but in any case weather events have been becoming more extreme. Implications of this have evaluated e.g. by Munich Re on a global scale. The company Munich Re is a reinsurance company, which ensures e.g. against damages by weather catastrophies. This is the reason why Munich Re has a particular interest to assess damages related to weather events and their increase due to climate change as accurately as possible. Munich Re points in particular to the following extreme weather events related to climate change (all of which have increased in frequency and intensity): Wildfires/campfires, hail, heat waves, extreme storms (incl. tropical stroms, i.e. cyklones, typhoons, hurricanes), extreme rainfall, flooding . According to Munich Re 17 of the 18 warmes years since 1901 were in the period from 2001 to 2017  (at the time when their article was published the year 2018 was not yet included, otherwise it would probably have been included).
In particular strong storms (such as hurricanes) have produce enormous damages recently. The most ‘expensive’ storm was hurricane Katrina in 2005, which claimed 1322 lives and caused damages of 125 bil. US$ . Five federal states of the US were affected. Further storms and weather catastropies since the year 2000 are summarised in the following tables:
|Hurricane Katrina, USA||2005||1 322||125 bil. US$||Most ‘expensive’ storm ever|
|Cyklone Nargis, Myanmar||2008||140 000||4 bil. US$|
|Flooding, Pakistan||2010||1760||9.5 bil. US$||Largest weather catastrophy in Pakistan|
|Hurricane Sandy, USA||2012||210||68.5 bil. US$||Second most ‘expensive’ storm ever|
|Typhoon Haiyan, Asia||2013||6 334||10.5 bil. US$|
Especially over the Atlantic storms have become more frequent. The mechanisms leading to tropical storms are partly quite well understood . Since tropical storms need a minimum temperature to develop, and since the temperature has increased, such storms now occur already in areas further north (or south in the southern hemisphere) than previously . This is seen as a very clear sign that climate change affects tropical storms.
Storms or extrem weather conditions cause not only damages by strong wind and rainfall. In particular in temperate zones also hail can cause substatial damages. Recently, a study in collabortion with Munich Re demonstrated that the frequency of hail events has increased in Europe, based on data from the last 37 years . Small hail grains (up to 2 cm) usually cause harvest losses, since plants are damaged, or damages of cars . Larger hail grains are a threat for humans and animals and they can cause substantial damages of faces of buildings, windows or roofs verursachen. In 2019, a single hail storm in Bavaria, Germany, caused damages of about ca. 190 mio. Euro. 20 000 cars were dented, windows, solar installations, roller blinds and faces of buildings destroyed .
Melting polar ice, melting glaciers
As warm water occupies a larger volume compated to cold water, warming by 1°C causes a change of volume of the oceans equivalent to 50 cm elevation of the sea. . Additionally, warming by 1°C significantly reduced the ice sheet of the poles and Greenland. Melting of ice masses doesn’t happen immediately, since they are massive. It takes a couple of years to melt these ice sheets. However, once all ice has melted that is going to melt due the 1°C warming, the level of the sea is expected to rise by 7 m, in particular considering metling of all ice of Greenland . One may wonder, how it is possible that a mere 1°C cause such an effect. Considering why the ice sheets at the poles end somewhere towards the south may help to understand this. In simple terms, the ice sheets stop where the temperature changes from below zero to above zero. When moving from the poles towards the equator, the temperature gradually increases. Once it surpasses zero degrees, ice cannot persist. When moving from the poles towards the equator, 1°C temperature change corresponds to about 440 km (i.e. about 2° degrees latitude ). Hence when the temperature rises by 1°C, the ice sheets retreat at the Arctic by 440 km. That is a considerable amount of melting water. Of course this is a very simplified calculation. Measured data have demonstrated the following: From 1979 to 2017 the ice masses of the Antarctic retreated by about 150 000 cubic kilometers . That corresponds to an ice cube of 390 km edge length. It is expected that the arctic will be ice free in summer staring between 2020 to 2050 [29,30].
Until the sea level rise of 7 m caused by 1°C warming is reached (i.e. until all ice that will melt due to this warming has melted), a number of coastal cities (such as Miami, New York, Amsterdam, etc.) will need to invest massively, in order not to drown (but note that temperature will continue to rise). Corresponding construction planning has indeed already started . In other words, even if we would immediately stop any greenhouse gas emissions completely and if there would be no further warming, more ice will melt and rise the sea level, endangering these coastal cities.
The present warming, however, does not only melt polar ice sheets, but nearly all of the 150 000 – 200 000 glaciers world-wide . Melting water from glaciers further contributes to sea level rise (to about 27% ). Locally, glaciers are often also important sources for drinking water, which is threatened due to melting . Caused by the increasing melting of glaciers there is also a higher risk of mudslides and avalanches . In Peru, since 1941 slides of melting glaciers caused 30 000 fatalities in the region Cordillera Blanca . In total there were 30 of such events. Often, the danger of slides by melting glaciers is underestimated, since below melting galciers melt water lakes form, invisible below the surface. When glaciers melt further or when triggered by an earthquake glaciers can then suddenly slide down, burying villages.
In summary, one can see that we are already paying a price for climate change. The incidence of extreme droughts and extreme weather events has increased, with hundreds and thousands of lives lost and millions and billions of lives each time. Damages are often borne by private individuals (human lives, damage to property) or they are covered by taxpayers’ money or price increases (e.g. rising food prices ). That means, we usually all pay for it. However, we often do not perceive such damage as a consequence of climate change, but as a natural disaster. Only when extreme weather events become more and more frequent, as in recent decades, or when we remember how winters were 30 years ago, when there was still plenty of snow, we may realize that there is a trend.
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