Available water resources, even if renewable, are limited: while 71% of the world’s surface is covered by water, only between 0.3 and 0.5% available to drink. Of the total annual water withdrawal around the world, as much as 69% is destined to agriculture, 19% to industries and 12% to municipalities. United Nations Development Programme (UNDP), around 700 million people in 43 countries suffer today from lack of water and almost one-fifth of the world’s population live in areas of physical scarcity. The situation is only bound to worsen in the future due to the increase of population and climate change reducing water availability.
The change in the water cycle induced by global warming, with reduced rainfall and increased evaporation worldwide, and other interconnected impacts of climate change, such as ice melting and shrinking glaciers (which are an important reserve of water), heavy rainfall episodes and flooding (during which water rapidly moves into the oceans and it is difficult to retain for human usage), replacement of snow with rain, and so on, pose a growing threat to water security.
It is estimated that by 2025 almost half of the world’s population will be living in water-stressed areas and as many as 1.8 billion people in countries or regions with absolute water scarcity. The most impacted area in the world is Middle East and North Africa, where physical lack of water and projected impacts of climate change are interlaced with the highly unsustainable use of the available resources.
The phenomenon of drought has to be understood in its various displays. The Inter-governmental Panel on Climate Change (IPCC) refers to four types of drought: meteorological, that is an extended period of abnormally low rainfall; agricultural, when soil moisture is low; hydrological, or an abnormal decrease of surface and groundwater; and environmental drought, a combination of the others.
In the future, IPCC estimates lands affected by extreme drought will increase by a factor of 10 to 30, from today’s 1-3% to 30% by the 2090s. The main driver is the change of the water cycle due to global warming: even if episodes of both extremely high and low rainfall are predicted to increase, in average the drying trend will prevail.
The impacts of drought on the human society are numerous. Since 1900, drought-related deaths amount to more than 11 million, and more than 2 billion people have been affected by its consequences. Reduced access to clean water is the primary or concomitant cause of most diseases and deaths. As reported by OCHA, one of the most impacted areas is the Horn of Africa: the people displaced for drought-related issues now amount to 3.7 million, while 14.3 million live in conditions of severe food insecurity.
The U.N. Convention to Combat Desertification defines the phenomenon as “land degradation in arid, semiarid and dry subhumid areas resulting from various factors, including climatic variations and human activities”. It is a global phenomenon, which affects drylands as a result of the excessive exploitation of ecosystem services and the diminishing reserves of water due to climate change. Drylands are a valuable resource: the CGIAR research programme on drylands reports they cover more than 40% of the globe and are inhabited by more than 1/3 of the world’s population. The process of desertification destroys each year 12 million ha of productive land, where 20 million tons of grain could have been harvested. Furthermore, desertification may affect also non-drylands with dust storms, downstream flooding and climate change.
Desertification is particularly threatening in Africa, where two-thirds of land is desert of drylands. While this land is used for agriculture and food production, almost three-fourths of it is degrading. Frequent and severe periods of drought have been affecting the continent in recent years, and particularly the Horn of Africa and the Sahel.
Two-thirds of the African continent is desert or drylands and it is estimated that nearly three-fourths of those desert and drylands are degrading. 485 million people are already suffering the impacts of this process of desertification, which makes sterile lands previously used for agriculture and food production and triggers processes of displacement and migration.
The world population is expected to increase to almost 10 billion in 2050 and 11.2 billion in 2100. More than half of this growth will occur in sub-Saharan Africa, where already a quarter of the population is undernourished. As reported by the WRI, taking into account the increase of population and the shifting diets, the world would need to produce 69 percent more food calories in 2050 compared to 2006.
In this context, climate change is a further threat to food security. Unusually high or low temperatures and extreme weather events such as drought, floods and tropical storms cause huge damage to agriculture.
Indeed, FAO calculated that in developing countries the agricultural sector absorbs 25% of all the economic damages produced by climate-related disasters. In the long term, the rise of sea level, the increase of average temperatures and the change of the water cycle induced by global warming will impact food production at global level.
Changes in temperature, ocean acidification, sea level rise, drought and extreme weather events impact negatively on world’s biodiversity, in particular in areas where it is more vulnerable: this imply threat over vegetal and animal species and biomes’ changes (swift from one type of ecosystem to another, for example from tropical forest to savanna).
A research realized by the Jet Propulsion Laboratory, Caltech, under a NASA contract, identified among the most vulnerable areas: Himalayas and Tibetan Plateau, Madagascar, the Mediterranean region, Southern South America, Great Lakes and Great Plains area in North America as well as northern and southern taiga and boreal forests.
Biodiversity loss provoke by climate change makes it even more urgent to protect areas of high biodiversity. The IPCCC report Latin America as one of the largest areas of biodiversity concentration where the impacts of climate change are expected to increase biodiversity loss. The Yasuni National Park, in the ecuadorian amazonian forest is an example of biodiversity hotspot to be protected. It is one of the more diverse ecosystems in the world.
Ecological sensitivity and climate change
IUCN Red List – species susceptibility to climate change impacts
Regional implications of climate change on biodiversity
Yasuni Park’s biodiversity
IPCC estimates that, between 1901 and 2010, sea levels have risen about 20 cm worldwide, with strong local disparities. Since the 1990s this trend has accelerated dramatically, with an annual average rate of 3.2 mm. The IPCC estimates that, at current emissions level, average sea level rise will be 24-30 cm by 2065 and 40-36 cm by 2100. Even if emissions were stopped today, the impacts would continue to be felt for centuries.
The immediate causes of the sea-level rise are both ice melting and water thermal expansion, due to global warming. Many coastal areas are at risk of erosion, flood and salinisation of the groundwater. At least eight small islands in the Pacific Ocean have already disappeared, maybe more. An analysis by Climate Central found that, at current emission levels, by the end of the century up to 650 million people could live in land below the sea level or regularly flooded. Among the most vulnerable areas there are poor and densely populated countries, especially in Asia, such as Bangladesh, and the small Pacific islands. Eight of the world’s 10 largest cities are near a coast, according to the U.S. Atlas of the Oceans, and thus are potentially at risk.
One of the impacts of climate change is the increase in number and severity of extreme weather events. While it is difficult to directly link a single episode to climate change, observed trends, theoretical understanding of the climate system and numerical modeling demonstrate that global warming is increasing the risk of these types of events today. Indeed, rising temperatures, increases in the amount of water vapour in the atmosphere and changes in atmospheric circulation directly influence heat waves and extreme precipitation events. The statistical trend shows that the number and intensity of extreme events has been increasing in recent years.
The economic and social impacts are huge. According to FAO, natural disasters caused about USD 1500 billion damages in 10 years and killed 1.5 million people. The numbers are rising: now, about USD 250-300 billion damages are caused each year.
The most impacted areas are in the global South. According to German Watch, of the ten most affected countries between 1995 and 2014, nine were in the low income or lower-middle income group.
According to the IPCC, each of the last three decades has been successively warmer than any other decade since 1850. It was calculated that, since the industrial revolution, land and ocean in average warmed +0.85°C.
The link between the current global warming and human emissions is scientifically certain: paleoclimatology, that is the study of Earth’s climate in the past, proved that there never was a similar rapid increase in carbon concentration in such a short time. CO2 atmospheric concentration in the last 10.000 years was comparatively stable, well under 300 ppm. Only in the last two centuries it began growing, with a steep increase after theSecond World War. In this moment, concentration levels are the highest in the last 800.000 years.
The IPCC has elaborated 4 “Representative Concentration Pathways” (RCP) that show to what point, with different emission levels and relative carbon concentration in the atmosphere, average temperatures are going to increase. In the business-as- usual scenario (RCP 8.5), we are going towards an average +3.7°C increase.
The warming is not uniform: temperatures have already gone up about twice their average in some areas and as much as four times in some Arctic regions. The impacts are enormous, and affect ecosystems at global level.