Both internal fluctuations and external forces are causes of climate change.
The concentration of greenhouse gases in the atmosphere has been increasing ever since the beginning of industrialization at the end of the 18th century, so for more than 200 years. In the case of carbon dioxide, the main cause is the burning of carbon-based energy sources that have been created over the course of the Earth’s history (“fossil fuels”) – primarily coal, oil, and natural gas. When it comes to methane, the main sources include intensive agriculture practices (particularly livestock farming) and the use of fossil fuels (including leaks from natural gas wells and pipelines). Nitrous oxide, otherwise known as laughing gas, is also released mainly in agriculture (such as through the use of large amounts of artificial fertilizers).³
The acidity of liquids is specified by a pH value – the lower the pH value is, the more acidic the liquid. The pH value of near-surface seawater is currently around 8.1 on average worldwide, having already fallen by around 0.1 compared to the preindustrial era. While this change might sound insignificant, it translates to a 26 percent increase in acidity (because the pH scale is logarithmic). Among other things, this development threatens numerous calcifying marine organisms, such as corals, mussels, and crabs.
In Germany, one of the consequences of climate change is the increase in heavy rains. Having said that, the number of consecutive days with no precipitation is also going up, especially in summer. Both are leading to an increase in hydroclimatic extremes that pose a threat, such as droughts and floods. Scientists predict that this trend will continue into the future. According to data from Germany’s National Meteorological Service, the number of days with low soil moisture has already increased significantly since 1961. Germany’s northeast and the Rhine-Main region are being hit particularly hard by the increasing dryness of the soil.
The mean surface temperature of the North Sea in the German Bight increased by about 1.3 degrees Celsius on average between 1969 and 2017. An increase in water temperatures since 1982 of around 1.6 degrees Celsius has been measured off the German Baltic coast. The exact values vary, sometimes considerably, depending on location and water depth.
If emissions go unchecked, the rise in the global average temperature could exceed four degrees Celsius by the end of the century. At the 2015 UN Climate Change Conference in Paris, delegates decided that the global temperature increase should be limited to “well below two degrees Celsius” compared to preindustrial levels – and even to 1.5 degrees, if possible. However, we could exceed this limit in just over a decade if the current warming trend continues.
Even though doing so certainly poses a great challenge, it is within our power to rapidly and drastically curb greenhouse gas emissions, as numerous studies and also practical experience show. Many of the technologies needed for this exist, and some of them are already financially competitive within the current political structures.
In the 1950s, Germany experienced, on an annual average, around three “hot days,” which is what meteorologists call those days when the temperature rises to 30 degrees Celsius or higher. Between 1991 and 2019, the number of “hot days” had already increased to 8.8 days per year on average. In contrast, the average number of “below-freezing days,” i.e., days when the temperature remains below 0 degrees Celsius all day, decreased from 28 to 19 days per year during the same period. In winter 2019/2020, Hamburg, for example, did not experience a single below-freezing day – a first since record-keeping began.
Even seemingly low levels of global warming can have serious consequences. For example, if Earth heats up by 1.5 degrees Celsius compared to preindustrial levels, 70 to 90 percent of the world’s coral reefs will likely die. At two degrees, practically all of them will die (98 to 99 percent).