Climate Crisis

Causes of Climate Change

The temperature on Earth is influenced by the greenhouse effect: greenhouse gases in the atmosphere reflect heat from the Earth's surface back to Earth, raising the global mean temperature to 15°C instead of chilly -18°C.
However, the concentration of the greenhouse gas CO₂ has increased by more than 50% since the beginning of the industrial revolution in 1850 and was at a new record of 417ppm in 2022 [1]. The increase in CO₂ concentration in the last 60 years is thus 100 times greater than the increase during the natural warming at the end of the last cold period 11,000-17,000 years ago [1].
As a result, the earth’s mean temperature is rising at an alarming rate. The global mean temperature in 2011-2020 was 1.09°C higher than in 1850-1900 [2]. In 2024, the global average temperature exceeded pre-industrial levels by 1.55°C for the first time [7]. If this trend continues, the 1.5-degree target of the Paris Agreement will be missed .In the last 100,000 years, similar temperatures only occurred during the Atlantic period around 6500 years ago. However, the temperature increase during the Atlantic period was caused by a different level of solar radiation and happened much slower than today [2]. Today, humans are the main drivers of climate change: By using fossil fuels and producing emissions from agriculture and industry, humans already contributed 1.07°C to global warming; natural drivers influenced the climate by only -0.1°C to 0.1°C [2]. This is why we now speak of an anthropogenic climate change.

Tipping Points

Tipping points are critical thresholds in the climate system. If tipping points are reached, drastic and irreversible climate changes can occur, which can even intensify climate change. Many possible tipping points are known, e.g.:

• Ice-Albedo-Effect: If the sea ice melts, the darker ocean surface below is exposed. Less heat radiation is reflected there than on the lighter ice surface, causing surface temperatures to rise. This in turn causes more sea ice to melt. Arctic sea ice is already at its lowest level in 1000 years, and it is assumed that the Arctic will be ice-free in summers by 2050 [2].
• Melting of permafrost: Permafrost soils are soils that are permanently frozen. When they melt, more organic material is decomposed, releasing methane and CO₂. It is assumed that permafrost soils will melt to a depth of 3m by 2100 [3,4].
• Ocean acidification: The ocean is a CO₂ sink and has absorbed 20-30% of atmospheric CO₂ since 1980 [3]. Due to the rapid uptake, the CO₂ cannot be transferred to deeper ocean layers, resulting in ocean acidification. This has far-reaching consequences for marine ecosystems [5]. In addition, an acidified ocean can absorb less CO₂ and the increasing ocean temperature could even contribute to CO₂ being released again. This could even increase the global temperature rise [6].

Effects

The effects of climate change are very diverse and vary greatly from region to region. But in principle, the following impacts can be expected:

• Increase in the frequency, severity and duration of extreme events such as droughts, storms, heavy precipitation events, floods and heat waves. This also affects ecosystems on land and in water. With a warming of 2°C, 18% of all terrestrial life could become extinct [2]. A decrease in biodiversity also endangers our livelihoods. Particularly in areas that are already at risk, extreme events can lead to considerable damage to infrastructures and even make them uninhabitable [2]. This primarily affects people, who contribute relatively little to climate change.
• Threats to food production and access to clean drinking water: Food production is increasingly threatened by higher temperatures, an increase in extreme events and pest infestations. In addition, the availability of drinking water will decrease, especially after the melting of glaciers [2]. Here, too, the Global South is particularly affected.
• Health risk: Heat waves and increased occurrence of smog in cities as well as the spread of diseases will endanger our health [2].

What can we do?