The effects of global warming are particularly clear to people when they take on extreme forms – be it extreme heat, droughts, storms or floods. Examples include the extensive forest fires in Southern Europe in 2022, the flooding catastrophe following heavy rain in western Germany and Belgium in July 2021, the devastating wildfires in Australia in 2020 and the extreme heat in Siberia in the Arctic Circle of up to 38 °C, also in 2020.

Many extreme weather events worldwide can no longer be explained by natural variations over the decades or incidental events such as volcanic eruptions and changes in solar radiation. Instead, they can be explained by human-made climate change. Whether and to what extent that is true in each case is being investigated as part of “attribution research” using climate models.

More heat in Germany

As both an indication and result of the climate crisis the temperatures are constantly rising in Germany and have been setting records for highest values since 2000. The decade from 2011 to 2020 in Germany was already 2 °C warmer than the reference time period of 1881 to 1910. Since the begin of systematic comprehensive records in 1881, the average temperature has risen by 1.6 °C and thus more than the global average of 1.2 °C. There has also been a recent increase in the number of days seeing maximum values higher than 30 °C. Since the 1950s it has tripled from some three days a year to a current average of nine days. In 2019, for the first time in the history of weather records, 40 °C or more for three days in a row were recorded in Germany. Alongside this development the number of days with ice and frost have decreased.

Melting ice, thawing permafrost

Earth is an ocean planet. 71 percent of the earth’s surface is covered by global oceans, while glaciers and ice sheets are found on a part of the land surface. Together with permafrost ground these make up the cryosphere. Both spheres have a large influence on the climate and are undergoing massive changes due to global warming. The world’s oceans absorb around half of solar radiation and significantly curb the temperature increase. The oceans absorb carbon dioxide too. The role of the cryosphere is also relevant: Around half of the carbon stored in soil is found in the permafrost ground of the Arctic, which thus represents, similar to mires, another important climate gas “sink”.

The increase of CO₂ concentration in the atmosphere and global warming have been affecting the oceans, ice sheets and permafrost ground for decades. Ice and glaciers are shrinking all over the world and the Arctic’s permafrost ground is beginning to thaw. In warmer soils it is easier for microorganisms to decay plant and animal biomass. This leads to the release of the climate gases methane and carbon dioxide which accelerate the greenhouse gas effect – not to mention that methane influences the climate around 25 times more than CO₂ on a short time scale. The Arctic could thus go from being a store of climate gases to their source.

The seasonal ocean ice area in the Arctic has continued to shrink since the late 1970s. Compared with the time period 1979 to 1988, the average surface area of pack ice in summer between 2010 and 2019 shrunk by around 25 percent, or some two million square kilometres. It is probable that the Arctic will be ice-free in summer for the first time by the middle of the century at the latest.

Sea levels are not rising equally everywhere

The melting ice of the polar caps and the glaciers is leading to rising ocean levels and the warming of the ocean is additionally leading to the expansion of the water body. As a consequence the average global sea level has risen by around 20 centimetres since 1901. And the rise is accelerating. As the World Climate Council IPCC states in an Assessment Report from 2019, the sea level rose between the years 1901 and 1990 by an average 1.4 millimetres per year. Between 2006 to 2015 this was already 3.6 millimetres per year.

Yet the sea level is not rising equally everywhere like in a bathtub. In some regions the increase is lower, in others higher than the global average. The reasons for regional differences include elevating or sinking land masses, and currents running through the oceans which distribute water with different temperatures and salt content. Understanding these differences is crucial when it comes to estimating damage and risk to the world’s coasts and islands.

Some 680 million people currently live in direct proximity to coasts or on small islands. In 2050 it could be more than a billion. Life or even survival in these regions directly depends on the future sea level. Further, increasing water levels endanger ecosystems such as mangrove forests, seagrass meadows, mudflats, coral reefs, rocky coasts and sandy beaches. Even back country can be affected if the increase leads to groundwater salinization.

Endangered ocean ecosystems

The biodiversity of the oceans is endangered by marine heatwaves in which the temperature of the surface layer remains at an unusually high level for a long time. On the west coast of North America (2013 to 2016) and the east coast of Australia (2015/16, 2016/17 and 2020) these warm phases have led to sudden changes in the structure of ecological communities that will likely be felt for years. It resulted in a measurable loss of biodiversity and a collapse of local fish grounds and aquacultures. In addition, it limited the growth of species that build coral reefs, seaweed forests or seagrass meadows and are thus important for many animals and plants.

Coral reefs in particular are not only threatened by increasing warmth but also by the acidification of the oceans. The pH level of the ocean surface has reduced from typically 8.2 to 8.1 since the pre-industrial era. Although this change may seem small, the pH value scale is actually logarithmic. An increase by the value of 1 means a tenfold increase in the acid content. Thus the acid content has risen by almost 30 percent from the pre-industrial era to today. The consequences for the perfectly balanced and sensitive ecosystem are severe: The gas reacts with the seawater to create carbonic acid which adversely affects the building of chalky structures as seen in coral reefs, mussel and snail shells, and zooplankton.

Species extinction and forest loss

The climate crisis negatively affects organism diversity and has already altered marine and terrestrial ecosystems all over the world. The extensive dieback of coral reefs, which count as biodiversity hotspots alongside tropical forests, leads to unparalleled species loss. Animals and plants are also threatened elsewhere by the displacement of climate zones and extreme weather events. As stated in the Sixth Assessment Report of the World Climate Council (IPCC) it is very likely that some species have already gone extinct as a result of climate change.
 

The tropical rainforests and the temperate forests of the middle and northern latitudes absorb, alongside mires and permafrost ground, more CO₂ than they emit. They therefore represent an important store of greenhouse gases and help to reduce the effect of global warming. However, they are still threatened by extensive deforestation, the expansion of agricultural land, and human settlements. Climate change is also contributing to forest loss. Around the world trees are dying primarily as a result of drought. In Germany, according to estimates from the German Aerospace Center, the number of trees declined from January 2018 to April 2021 by an area of 500,000 hectares – i.e. almost five percent of the entire forest surface area.

In the forests in the mid and northern latitudes in Asia, Europe and North America, a lot is changing. Communities are being pushed back into higher and more northern areas, blossom and leaf building is taking place earlier, tree diseases are spreading to the north, and pests infect the trees more often. Worldwide more and more surface areas are affected by wildfires, thus making them into additional sources of CO₂.
 

Changed conditions for agriculture

Agriculture and fishery are both directly and indirectly affected by the climate crisis, which in turn impacts the population’s food supply. Global warming changes the amounts and patterns of rainfall. Droughts are occurring more frequently and for longer, storms and floods are increasing and becoming heavier, and new pests and diseases are spreading. All of these negatively affect the production as well as the quality, price and availability of food.

The south and the west of the European continent are especially affected by this negative development. In Southern Europe, global warming has influenced the harvest of almost all important cultivated plants, recently leading led to a stagnation in yields. The enduring drought in 2018 led to significant cereal harvest losses in Germany. While the yields were 16 percent less than the nationwide three-year average of the previous years, they were significantly lower in some individual federal states.

Sudden crop losses as a consequence of extreme weather events are making worldwide food supplies uncertain and are especially affecting smaller food producers, low-income households and the local population in regions at a climate disadvantage. Reduced food diversity can result in malnutrition, particularly among children, the elderly and pregnant people and especially in countries in the Global South.

New health risks

Climate change can make us ill – and in lots of ways. Heatwaves can worsen cardiovascular illnesses, change the effects of medications and lead to excess mortality. In Germany, for example, there were an estimated 8,700 deaths related to the heatwave in 2018, the year which saw the second hottest summer since records began. Increased temperatures further facilitate the spread of pathogens, since certain algae, bacteria or disease-carrying mosquitoes always survive better in warm environments. Extreme weather can also disrupt medical treatment or destroy the drinking water system – and weaken the body’s immune response.

How new dangers are arising on a regional level can also be seen in Germany, where the Robert Koch Institute named 175 districts as risk regions for ticks carrying the FSME disease in 2022. In 2012 it was still only 140. Meanwhile, new diseases are appearing in Germany that were only previously known from travelling, such as rickets transmitted by mites and lice, or the West Nile fever transmitted by mosquitoes.

A reduction in water quality and water scarcity as a result of drought periods could lead to the spread of cholera and diarrhoea in many countries. Heatwaves also facilitate dangerous algae blooms. To people in some regions of the world, harvest losses and climate change either represent an increasing threat of malnutrition or mean that they have to live with the consequences of eating food that has been contaminated by, for example, moulds.

Published: August 2022