An explosive cocktail that threatens: the cumulative effects of climate disruption

Alobal warming is a physical phenomenon that is relatively simple to understand: by affecting the balance between incoming solar radiation and outgoing infrared radiation, anthropogenic greenhouse gases increase the Earth's energy balance, causing it to warm. What is less understood is the simultaneity of contradictory phenomena. In one part of the world, drought is occurring in one part of the world, while in other parts of the world, heavy rains are falling.

This apparent contradiction, which feeds the bed of climate sceptics of all stripes, is the result of physical phenomena interrelated in a global system. For example, by promoting the evaporation of water and increasing the capacity of the air to retain moisture, warming can lead to drought in areas that are generally dry, resulting in the maturation of forest fires and heat waves when evaporative heat transfer ceases. Opposite reactions occur in areas that are usually humid where constant evaporation leads to more precipitation, which is usually followed by flooding due to soil saturation. At the same time, as the ocean warms, evaporation increases, leading to higher wind speeds, storms, and heavy rainfall. These storm surges are in turn aggravated by the rise in sea level resulting from the increased volume of heated water molecules and the melting of land ice. To compound the problem, CO2 released into the atmosphere dissolves in the ocean, accelerating its acidification and disrupting ocean currents. It all makes sense.

Climatic factors are interrelated but their global analysis is singularly complex to carry out. All the more so as some phenomena will have more important effects in one place and not in another, masking the understanding of their globality. Therefore, a focus on one climatic hazard often masks the changes and impacts produced by other hazards, even though they are linked. This lack of perspective gives us an incomplete, even misleading assessment of climate change.

This is what a team of international researchers wanted to correct by compiling thousands of data to provide a complete picture of the interrelationship of climate risks. They identified 467 factors, many of which are able to combine with each other and intensify the multiple climate hazards to which humanity is currently vulnerable. Their study is a first and has just been published in the prestigious journal Nature Climate Change.

The scientists who conducted the study developed a table including ten climate hazards (warming, precipitation, floods, drought, heat waves, fires, sea level, storms, changes in natural land cover and ocean chemistry) that they cross-referenced with six aspects of human systems (health, food, water, infrastructure, economy and security). These six aspects are further broken down into 89 attributes of human life. The data used to develop this table come from more than 12,000 references and documents published in the scientific literature since the 1980s. Out of all the possible combinations, each documented by numerous concrete examples, researchers have revealed 467 interactions or pathways by which humanity is affected by climate hazards.

Climate change is killing; and it's already killing en masse. Whether by hyperthermia during heat waves, drowning during floods, hunger during droughts, or injuries during storms, landslides, fires and other cataclysms, climate change is increasing the number of victims year after year, all over the planet.

But, when weather patterns don't kill, they make you sick. Heart and respiratory problems caused by heat, respiratory problems developed after fires, but also as a result of moulds generated after storms, organic pollutants released by melting ice or pollens released during extended periods of vegetation flowering due to global warming.

By transforming the habitat of certain pathogens and their vectors, warming and changes in rainfall have contributed to the development of epidemics that were thought to have been forgotten: cholera, dengue fever, malaria, etc.

The authors of the study note that forest fragmentation has increased tick density near populations, triggering outbreaks of Lyme disease and encephalitis. Fires have brought fruit bats closer to cities, causing outbreaks of Hendra and Nipah viruses; drought has mobilized livestock near cities, leading to outbreaks of haemorrhagic fever; melting ice has caused voles to move around, spreading hantaviruses in their movement.

Climate risks also affect mental health. For example, depression and post-traumatic stress disorder have been reported after storms in the United States, floods in the United Kingdom and heat waves in France. Cases of existential distress have been reported during the drought in Australia, an increase in drug abuse after storms in the United States and poor mental health as a result of climate change in Canada (for example, the loss of sea ice has inhibited cultural practices such as hunting and fishing, leading to waves of depression among the Inuit).

The extensive literature review conducted by the authors of the study also reveals that climate risks are implicated in prenatal and postnatal health problems. Children born to pregnant women exposed to floods are reported to have increased bed-wetting, aggression towards other children and lower than average birth weight. Similarly, exposure to smoke from fires at critical stages of pregnancy may have affected brain development and resulted in premature delivery, low head circumference, low birth weight and fetal death or reduced survival. Finally, the salinity of drinking water caused by saltwater intrusion, aggravated by rising sea levels, is often linked to gestational hypertension, creating serious health problems for both mother and fetus.

Crop yields are affected directly and indirectly by exceeding the physiological thresholds of crops. Direct physical losses are caused by storms (for example, about 35 % of bean production was lost due to Hurricane Mitch in Honduras in 1998), rainfall, floods (more than 7,600 ha of agricultural land was destroyed by floods in Vietnam in 2009), sea level rise (agricultural land was lost through salt water intrusion in Bangladesh), fires and drought (in Russia in 2010, about 33% of cereal production was lost through both fires and drought).

But that's not all. Indirect losses due to hazards beyond the physiological tolerances of the crops were caused by warming (e.g. wheat yield loss of 3 to 10 % per 1°C increase in China), drought (a yield decrease of about 36 % during the 2003 drought in Italy), heat waves (a single day above 38°C reduced annual yields in the United States by 5 %), natural land cover changes (crop yields around the world have been reduced by natural land cover changes, increasing evaporation and reducing soil moisture).

Quantitative but also qualitative losses: Climatic hazards have also had an impact on crop quality by modifying the nutrient content and increasing the risk of contamination. For example, the protein content of some cereals has decreased due to drought and heat waves, while flooding and thawing of permafrost due to warming has led to soil contamination and food spoilage, making plant material unfit for consumption.

The authors of the study note that climatic hazards have an impact on animals used for food. Livestock mortality has been associated with warming (e.g. bluetongue was positively correlated with rising temperatures in Europe), drought (in 2000, three-quarters of livestock died due to drought in Kenya), flooding (livestock losses totalled more than 236,000 head in the major floods in Bangladesh in 1987 and 1988) and changes in land cover reducing the amount of pasture. Fish stocks have declined as a result of warming, both directly (warmer temperatures have exceeded the temperature tolerance of some species such as cod and high water temperatures have reduced oxygen levels, with serious implications for salmonid reproduction) and indirectly (warmer temperatures have altered food webs by reducing primary productivity).

Climatic vagaries also have repercussions on the habitat of the various animal species dedicated to food. Fire runoff has increased the heavy metal content of lakes and rivers, rainfall has increased the sediment and nutrient load of lagoons, rising sea levels have altered the dynamics of lagoons, chemical changes in the oceans have led to coral bleaching which has reduced the amount of fish. Coral quality has also been affected. Warming has increased the methylation of mercury and promoted the growth of pathogens involved in food poisoning. Floods, storms and fires have also been linked to increased heavy metal runoff, leading to the accumulation of mercury in fish and increasing the risk of poisoning in humans.

The scientists who conducted this study found that the quantity and quality of freshwater was severely affected by climate hazards. Drought, warming and heat waves have dried up wells and reduced water levels in reservoirs, leading to water shortages and mandatory restrictions. Drought, for example, led to temporary shortages of drinking water for more than 200,000 people in Puerto Rico in 1997-1998 and 33 million in China in 2001. Declining water supply has also been attributed to changes in land cover, including the spread of invasive plant species that have increased evapotranspiration, as has desertification, which has led to losses in water storage in areas such as the Sahel. Mountainous regions are not spared as warming is leading to a decrease in snow accumulation and retreat of glaciers, resulting in lower water tables and shortages of drinking water.

Major infrastructures, particularly those in the electricity, transport and construction sectors are seriously affected by climate change. Heat waves cause overheated power lines to collapse, reducing the efficiency of electricity conduction and hydroelectric production. Dry soil acts as an insulator that causes underground cables to overheat and melt. Power outages due to heat waves have affected millions of people around the world. For example, large-scale power outages affected 670 million people in India in 2012, 35 million in Saudi Arabia in 2010, 500,000 in South Australia in 2009, 200,000 in Buenos Aires in 2014, and 50 million in the northeastern United States and Canada in 2003.

Storms flood roads, railways and destroy bridges, ports and dikes. The floods have paralysed several national transportation networks, disrupted rail services, closed freight traffic and stranded city dwellers. The heat waves caused deformation of railways, melting of roads, melting of asphalt and cracking of concrete roads and bridge joints due to thermal expansion. The heat waves have grounded aircraft because warm air is less dense than cold air, requiring extra speed that aircraft may not be able to reach on short runways.

The direct and indirect impacts on buildings are among the most spectacular. Floods and storms have damaged or destroyed millions of houses (about 12.8 million in Bangladesh, 8.7 million in China, 1.8 million in Pakistan, 450,000 in Jakarta, 425,000 in the United States, 45,000 in France, 30,000 in Australia and 30,000 in Jamaica). Fires caused by extreme droughts and heat destroy homes by the thousands, as we are currently seeing with the fires in California. Glacial lake outbursts due to retreating glaciers and landslides sweep away entire areas.

The loss of beaches and coastal infrastructure worldwide is the result of sea-level rise, storms, ocean swells and associated flooding, erosion and collapse. The loss of coastal land due to storms and sea-level rise affects entire islands, some of which have simply disappeared. The loss of natural cover in coral reefs and wetlands has reduced coastal protection, intensifying the effects of storms and tsunamis on infrastructure in a vicious circle.

All economic sectors are affected by climate change: economic losses, reduced labour productivity, jobs and incomes. Economic losses are often more dramatic after extreme events because they include immediate costs such as those associated with property damage. Extreme events also have indirect costs, which can have long-term impacts. Indirectly, weather-related hazards raise commodity prices. For example, the heat waves, droughts and fires in Russia in the summer of 2010 reduced local cereal production by a third, eventually doubling world wheat prices. The storms affect, through their knock-on effect, access to insurance and the price of insurance. For example, Hurricane Andrew caused the insolvency of 12 insurance companies and many companies are now refusing to issue new policies for properties less than one kilometre from the ocean on the east coast of the United States.

Climatic hazards affect availability and capacity to work. Heat waves have reduced labour productivity, as has been observed in Australia, where absenteeism has increased during heat waves, and in India and Vietnam, where heat waves have resulted in longer working days to compensate for rest periods during peak hours of the day. Storms and floods disrupt the functioning of industries, resulting in immediate job losses.

Climate change is often linked to increased conflict and violence and the disruption of the social fabric. Climatic hazards force hundreds of millions of people to leave their homes for different reasons and durations. For example, hundreds of thousands of people have been displaced as a result of floods in China and Pakistan and storms in Central America, the United States and Bangladesh, to name but a few.

Recurrent climatic hazards also lead to permanent displacement; in Bangladesh, recurrent floods have forced some rural residents to settle in urban squats. Researchers have identified several cases of planned migration of coastal communities due to melting permafrost, recurrent flooding and coastal erosion caused by sea-level rise and storms. Many cases of mass migration occur as a result of droughts, natural land cover changes and extreme precipitation events.

Climate hazards contribute to increased conflict over access to resources and can be a catalyst for violence. Drought, for example, regularly triggers conflicts over rights and access to water. Ocean chemistry is linked to changes in the distribution of commercial fish stocks, and the discovery of new resources revealed by melting sea ice generates geopolitical tensions over their use, tensions that are accentuated by the increased military presence in the Arctic region. Changes in rainfall and drought have led to a shortage of pastoral and agricultural land, triggering sectarian and intercommunal violence in the Horn of Africa, higher food prices are associated with violence throughout Africa, and food shortages have facilitated the recruitment of rebels in Burundi. Drought has also been an influential factor in migration to urban areas, exacerbating unemployment and political instability that have contributed to bloodshed in Syria and Somalia. The likelihood of civil conflict almost doubled during the El Niño years compared to the La Niña years. After 1950, warming or a change in precipitation patterns increased the risk of interpersonal violence by 4 % and inter-group conflict by 14 % globally.

Researchers have also found unprecedented correlations: cases of violence, increased gender inequality and the breakdown of social order are, in their view, linked to climate change. High temperatures can increase anger and excitement, affecting how people react to provocation, which can aggravate interpersonal violence and violent crime during heat waves. In the United States, for example, a 0.5°C warming has increased rape rates by 0.20, robberies by 0.84, burglaries by 8.16 and robberies by 10.65 per 100,000 people. The breakdown of law and order during extreme rains and storms was linked to violent interpersonal behaviour, including assault and rape. Hydro-meteorological disasters have also been associated with an increase in cases of domestic violence; for example, after the 1993 flood in the midwestern United States, a significant increase in cases of battered women was reported. The relative role of climatic hazards in human conflict is currently the subject of several academic research studies.

The study of Nature reveals humanity's great vulnerability to climatic hazards. Researchers point out that " Given that different hazards can impact many aspects of human systems and may require different types and costs of adaptation, the simultaneous exposure of future societies to multiple climate hazards is a potential concern. "

The highlighting of the concomitant occurrence of several climatic risks is one of the originalities of this study. Until now, scientists have focused on analysing a risk without really taking into account the involvement of other factors and without a multifactorial analysis of the impacts. It is perfectly possible to identify and measure a heat wave, but less well known to measure the induced effects of such a phenomenon. However, one of the essential characteristics revealed by this study is that our greenhouse gas emissions trigger domino effects on a large scale. When the global climate system gets out of control, it is difficult to grasp the multiplicity of impacts that are produced. Yet they are all a threat to humans. On a more or less large scale, but an omnipresent threat on the entire planet. A threat that is all the greater when the effects become cumulative.

Globally, Europe, North America and South America are expected to experience the greatest intensification of drought. Fires are expected to intensify in Australia, but decrease over the southern Sahara. Floods are expected to increase in South America, South-East Asia and northern Russia. The duration of deadly heat waves is expected to increase in most tropical regions, while the intensity of storms is expected to increase in the pantropics. Precipitation is expected to increase in the tropics and high latitudes, but decrease in mid-latitudes. Water scarcity will worsen in many parts of Africa and the Americas.

But when researchers combine the 10 climate hazards with the 89 effects on human life, they reveal a world in turmoil. One of their scenarios calculates a world where we do not change our greenhouse gas emissions. Business as usual, we continue on the current trajectory. In this case, half of the human population will be subject to three climate risks simultaneously (up to six for some coastal regions). By the end of the century, the effects on human lives will have reached a maximum intensity.

This scenario is shown in the following animation:

All regions are concerned and all nations affected, regardless of their state of development. There will be nuances in the nature of the impacts: poor countries will pay a very heavy price in human lives, while in rich countries it is the economic dimensions that will be devastated.

Some parts of the world will be more exposed than others. When the cumulative patterns of change of all hazards are combined, the greatest co-occurrence of change is projected in the tropics, usually isolated in coastal regions. The coastal areas of South-East Asia, East and West Africa, the Atlantic coast of South and Central America will be exposed simultaneously to the most significant changes in up to six climate hazards if greenhouse gases continue to increase during the 21st century. A city such as Marseilles, for example, will experience a combination of heat waves, floods, fires, rising sea levels, shortages of drinking water and changes in the nature of sea water; an accumulation of extreme hazards. Other metropolises in the world such as Los Angeles, Rio or Sydney will, with different f actors, be subject to similar risk intensities.

The multitude of climate risks that could simultaneously impact a given society highlights the diversity of adaptations that will be required. A considerable burden on the economy and well-being will be imposed by climate change triggered by greenhouse gas emissions. Ongoing climate change poses a threat to humanity, a threat that will be greatly exacerbated if we do not change our focus. Indeed, some of our contemporaries still believe that climate change is a hoax or that environmental measures are a luxury for the wealthy, preferring their lives in the short term rather than the medium-term lives of future generations. It is high time for change.