Chapter 5
Climate change impacts
This chapter assesses the potential impacts of climate change and how these alter in scale and intensity with increasing warming. The IPCC ‘Impacts, Adaptation and Vulnerability’ reports look at potential impacts on a regional level as well as by different sectors, such as freshwater resources, ecosystems, coastal and ocean systems, food security, and human health. It is also necessary to estimate the extent and magnitude of climate change impacts at national and local levels. There are a number of excellent national reports and tools, such as the US National Climate Assessment and the UK Climate Impacts Programme, both of which have interactive tools to understand the potential effects of climate change within their own countries. In this chapter, the potential impacts are broken down into sectors: extreme heat and droughts, storms and floods, agriculture, ocean acidification, biodiversity, and human health.
What is dangerous climate change?
One of the most important questions for policy makers is what is dangerous climate change? Because if we are to cut global GHG emissions we need a realistic target concerning the degree of climate change with which we can cope. In February 2005, the British government convened an international science meeting at Exeter, UK, to discuss this very topic. This was a very political science meeting, as the UK government was looking for a recommendation to take to the Group of Eight (G8) meeting in Gleneagles. At that time Britain held both the chair of the G8 and the presidency of the EU, and the then Prime Minister Tony Blair wished to push forward internationally his joint agenda of climate change reduction and poverty alleviation in Africa. The meeting and a lot of supporting research at the time suggested a limit of 2°C above pre-industrial average temperature: below this threshold there seemed to be both winners and losers due to regional climate change, but above this temperature everyone seemed to lose. It has now been shown that due to the impacts of extreme weather events there are in fact no regions that benefit from a 2˚C warming. At the Paris climate change negotiation meeting in 2015 the Alliance of Small Island States (AOSIS) and some key developing countries reiterated that even a small amount of warming would be devastating for their countries. The Paris agreement set 2˚C as the key target but added the aspiration of 1.5˚C. Subsequently the IPCC special report on 1.5˚C global warming published in 2018 supported this lower target by demonstrating that there is a significant increase in regional and national climate change impacts between a 1.5˚C and 2.0˚C world.
Extreme events and society’s coping range
The single biggest problem with climate change is our inability to predict its effects on the future. Humanity can live, survive, and even flourish in extreme climates from the Arctic to the Sahara, but problems arise when the predictable extremes of local climate are exceeded. For example, heatwaves, storms, droughts, and floods in one region may be considered fairly normal weather in another. This is because each society has a coping range—a range of weather with which it can deal. Figure 24 shows the theoretical effect of combining the societal coping range with climate change. In our present climate, the coping range encompasses nearly all the variations in weather with maybe only one or two extreme events. These could be 1-in-200-year events that surpass the coping ability of that society. As the climate moves gently to its new average, if the coping range stays the same then more extreme events will occur. Hence a 1-in-200-year event may become a 1-in-50-year event. The good news is that the societal coping range is flexible and can adapt to a shifting baseline and more frequent extreme events—as long as there is strong climate science to provide clear guidance on what sort of changes are going to occur. The speed with which the societal coping range can expand depends on what aspect of society is being affected: adaptation of the individual’s behaviour can be extremely quick, while building major infrastructure can take decades to complete. One of the biggest challenges of climate change is to build flexible and resilient societies that are able to adapt to a changing future.
24. Climate change, societal coping range, and extreme events.
Extreme heat, drought, and wildfires
As global temperatures increase, heatwaves increase. As precipitation becomes more variable and concentrated into more intense rainfall events, so dry periods get longer and droughts increase. The combination of extreme heat and drought causes more wildfires.
Heatwaves are often referred to as the ‘silent killer’. They disproportionately affect the elderly, and it is sustained night-time temperatures that kill because while asleep older people are less able to regulate their body temperature. In the Lancet Countdown 2020 report, global heat-related mortality was tracked for people over 65 years of age since 1980. It showed a dramatic rise since 2010 in heat exposure of older people, driven by the combination of increasing heatwave occurrences and ageing populations. In 2019, there were a record 475 million exposure events, causing over 2.9 billion days of heatwave exposure for the elderly.
Heatwaves and droughts, however, are relative terms, as it depends where they occur and whether a region already has adaptations in place. The 2003 heatwave in Europe killed an estimated 70,000 people. Hardest hit was France with 14,800 deaths in the first three weeks of August and deaths in Paris increasing by 140%. After the 2003 heatwave it was realized that many of these deaths were due to the very weak public health response. As a result in many countries there were sweeping policy changes, including better heatwave prediction and emergency preparations, improved building design and air conditioning for hospitals and retirement homes, increased training for health professionals, an emphasis on responsible media coverage with health recommendations, and planned regular visits to the most vulnerable members of the population. These new policies throughout Europe have prevented a significant number of deaths during subsequent heatwaves, such as 2018. One of the reasons it is so difficult to understand the impacts of climate change is because people and societies can adapt to new conditions very quickly. Figure 25 shows the 2003 European heatwave in the context of summer temperatures over the last 100 years and those predicted for the next 100 years. What is clear is that the temperature of the 2003 heatwave could be the average summer temperature in 2050, and heatwaves above this new baseline may still occur. Adaptation to heatwaves, however, takes planning, resources, and money, and so though this has been possible in much of Europe there are many areas of the world where such preparation is not happening due to poverty and lack of good governance.
25. Comparison of the 2003 heat wave with past and future summer temperatures.
Droughts are also a major killer that should be considered. A drought happens when an area undergoes a prolonged period without sufficient water supply, whether surface or underground water. A drought can last for months or years and is usually caused when an area receives consistently below average rainfall. Droughts have a substantial impact on the local ecosystem and agriculture, including drops in crop growth and yield, and loss of livestock. Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm to the local economy. Prolonged drought has caused famine, mass migrations, and humanitarian crises. From a disease point of view, droughts are much worse than floods because of a lack of fresh drinking water and stagnant pools of water bringing disease. In 2019, almost three times the global land surface area was affected by extended drought compared with the period between 1986 and 2005. One of the major concerns with climate change is that areas vulnerable to drought will have them more frequently, and areas that have never had them will start to experience them.
There has been an increase in wildfire risk in 114 out of 196 countries for the period 2016–19 as compared to the baseline period of 2001–4. Over this period there was a global increase to nearly 72,000 people per day being exposed to wildfire per year. Significant increases have occurred in Australia, Southern Hemisphere Africa, Brazil, and USA. The USA had record-breaking fire sessions in 2017, 2018, and 2020.
In Australia the 2019–20 bushfires season became known as the Black Summer. Throughout the summer, hundreds of fires burned, mainly in the south-east of the country, due to record heat and a prolonged drought. The fires burned an estimated 72,000 square miles, destroying nearly 10,000 buildings, and killing at least 450 people and 1 billion animals. Some endangered species may have been driven to extinction. With increasing incidences of extreme heat and droughts, wildfire risk will continue to grow across the world.
Storms and floods
Storms and floods are major natural hazards. Over the past two decades they have been responsible for three-quarters of the global insured losses, and over half the fatalities and economic losses from natural catastrophes. It is, therefore, essential that we know what is likely to happen in the future. There is evidence that the temperate regions, particularly in the Northern Hemisphere, have become more stormy over the past 50 years. Flood events have shown an upward trend since 2005, with almost three times the global land area flooded in 2019 (0.55–1.5% of global land surface area) compared with the period 1986–2005. This has not been driven by increases in any specific areas but by an increase in a wide range of events across the globe. The climate models suggest that the proportion of rainfall occurring as heavy rainfall has increased and will continue to do so, as will the year-to-year variability. This will increase the frequency and magnitude of flooding events.
Two-fifths of the world’s population lives under the monsoon belt, which brings life-giving rains. Monsoons are driven by the temperature contrast between continents and oceans. Moisture-laden surface air blows from the Indian Ocean to the Asian continent, and from the Atlantic Ocean into west Africa during Northern Hemisphere summers, when the land masses become much warmer than the adjacent ocean. In winter, the continents become cooler than the adjacent oceans and high pressure develops at the surface, causing surface winds to blow towards the ocean. Climate models indicate an increase in the strength of the summer monsoons as a result of global warming over the next 100 years. There are three reasons why this should occur: (1) global warming will cause temperatures on continents to rise even higher than those of the ocean in summer and this is the primary driving force of the monsoon system; (2) decreased snow cover in Tibet, which is to be expected in a warmer world, will increase this temperature difference between land and sea, increasing the strength of the Asian summer monsoon; (3) a warmer climate means the air can hold more water vapour, so the monsoon winds will be able to carry more moisture. For the Asian summer monsoon, this could mean an increase of 10–20% in average rainfall, with an interannual variability of 25–100% and a dramatic increase in the number of days with heavy rain. The most concerning finding of the models is the predicted increase in rain variability between years, which could double, making it very difficult to predict how much rainfall will occur each year—essential knowledge for farmers.
One of the more contentious areas of climate change science is the study and predictions of future tropical cyclones, better known as typhoons or hurricanes. There is clear evidence that the number and intensity of hurricanes have increased over the past four decades in the North Atlantic Ocean, southern Indian Ocean, and Pacific Ocean. This is because the number and intensity of hurricanes are directly linked to the SST. As hurricanes can only start to form if the SST is above 26°C it would seem logical that in a warmer world there would be more hurricanes. Yet the actual formation of hurricanes is much rarer than the opportunities for them to occur. Only 10% of centres of falling pressure over the tropical oceans give rise to fully-fledged hurricanes. Other considerations, such as wind shear to start the rising air spinning, must be included to understand the genesis of tropical storms. In a year of high incidence, perhaps a maximum of fifty tropical storms will develop to hurricane levels. Predicting the level of a disaster is difficult, as the number of hurricanes is not the key, it is whether they make landfall, and how intense and prolonged they are once they have hit land.
When hurricanes hit in developed countries, the major effect is usually economic loss, while in developing countries it is loss of life. For example, Hurricane Katrina, which hit New Orleans in 2005, caused over 1,800 deaths and over $150 billion in damages. By contrast, Hurricane Mitch, which hit Central America in 1998, killed at least 11,000 people, made 1.5 million people homeless, and caused $6 billion in damages. And in 2013, Typhoon Haiyan, the most powerful tropical cyclone ever recorded, devastated large portions of South-East Asia, particularly the Philippines, affecting 11 million people, causing over 6,300 deaths with another 1,000 people missing, but only resulted in a reported $2.2 billion in damages.
One of the most important and mysterious elements in global climate is the periodic switching of the direction and intensity of ocean currents and winds in the Pacific. Originally known as El Niño (‘the Christ child’ in Spanish), as it usually appears at Christmas, and now more usually known as part of ENSO (El Niño–Southern Oscillation), this phenomenon typically occurs every three to seven years. It may last from several months to more than a year. ENSO is an oscillation between three climates: ‘normal’ conditions, La Niña (a cooler opposite of El Niño), and El Niño. El Niño conditions have been linked to changes in the monsoon, storm patterns, and occurrence of droughts all over the world. The 1997–8 El Niño conditions were the strongest on record and caused droughts in the southern USA, east Africa, northern India, north-east Brazil, and Australia. In Indonesia, forest fires burned out of control in the very dry conditions. In California, parts of South America, Sri Lanka, and east-central Africa, there were torrential rains and terrible floods.
The state of the ENSO has also been linked to the position and occurrence of hurricanes in the Atlantic. There is also considerable debate over whether ENSO has been affected by climate change. The El Niño conditions generally occur every two to six years, and in the past 40 years this has continued with no discernible pattern. Reconstruction of past climate using coral reefs in the western Pacific shows SST variations dating back 150 years, well beyond our historical records. The SST shows the shifts in ocean current which accompany shifts in the ENSO and reveals that there have been two major changes in the frequency and intensity of El Niño events. First was a shift at the beginning of the 20th century from a 10- to 15-year cycle to a 3- to 7-year cycle. The second was a sharp threshold in 1976 when a marked shift to more intense and frequent El Niño events occurred with a cycle of between two and four years. Climate models all agree that ENSO will continue in the future, and in the higher emission scenarios in the second half of this century, ENSO variability will become much more extreme, creating more rainfall and drought events, and influencing the number and intensity of tropical storms in unpredictable ways.
Coasts
As we have seen, the IPCC reports that sea level could rise by between 50 cm and 130 cm by 2100 compared with pre-industrial times. This prediction is of major concern to all those living in coastal areas, as rising sea levels will reduce the effectiveness of coastal defences against storms and floods, and increase the instability of cliffs and beaches. In the developed world, the response to this danger has been to add another few feet to the height of sea walls around property on the coast, the abandoning of some poorer quality agricultural land to the sea (as it is no longer worth the expense of protecting it), and the enhancement of legal protection for coastal wetlands, being nature’s best defence against the sea. Globally, there are some nations based on small islands and river deltas that face a much more urgent situation (see Figure 26).
26. Areas most at risk from sea-level rise.
For small island nations, such as the Maldives in the Indian Ocean and the Marshall Islands in the Pacific, a 1 m rise in sea level would flood up to 75% of the dry land, making the islands uninhabitable. Interestingly, it is also these countries, which rely mainly on tourism, that have some of the highest fossil-fuel emissions per head of population. Other major concentrations of population at risk are those that live alongside river deltas, as in, for example, Bangladesh, Egypt, Nigeria, and Thailand. A World Bank report concluded that human activities on the deltas, such as dams and fresh-water extraction, were causing these areas to sink much faster than any predicted rise in sea level, increasing their vulnerability to storms and floods.
In the case of Bangladesh, over three-quarters of the country is within the deltaic region formed by the confluence of the Ganges, Brahmaputra, and Meghna rivers. Over half the country lies less than 5 m above sea level, so flooding is a common occurrence. During the summer monsoon a quarter of the country is flooded. Yet these floods, like those of the Nile, bring with them life as well as destruction. The water irrigates and the silt fertilizes the land. The fertile Bengal delta supports one of the world’s most dense populations, over 110 million people in 140,000 square kilometres (km2). Every year, the Bengal delta should receive over 1 billion tonnes of sediment and 1,000 cubic kilometres (km3) of fresh water. This sediment load balances the erosion of the delta by both natural processes and human activity. However, the Ganges, Brahmaputra, and Meghna have been dammed for irrigation and power generation, preventing the movement of silt downriver. The reduced sediment input is causing the delta to subside. Exacerbating this is the rapid extraction of fresh water.
Since the 1980s, 100,000 tube wells and 20,000 deep wells have been sunk, increasing the fresh-water extraction six-fold. These wells are essential to improving the quality of life for people in this region, but they have produced a subsidence rate of up to 2.5 cm per year, one of the highest rates in the world. Using estimates of subsidence rate and global warming sea-level rise, the World Bank has estimated that by the end of the 21st century, the relative sea level in Bangladesh could rise by as much as 1.8 m. In a worst-case scenario, they estimated that this would result in a loss of up to 16% of land, supporting 13% of the population, and producing 12% of the current GDP. Unfortunately, this scenario does not take any account of the devastation of the mangrove forest and the associated fisheries. Moreover, increased landward intrusions of salt water would further damage water quality and agriculture.
Many major cities around the world are vulnerable to flooding because they were built close to rivers or the coast in order to facilitate trade via the oceans. Examples of current cities most at risk include, in Asia: Dhaka (20.3 million people today), Shanghai (17.5 million), Guangzhou (13 million), Shenzen (12.5 million), Jakarta (10.8 million), Bangkok (10.5 million), Hong Kong (8.4 million), Ho Chi Minh City (8.3 million), and Osaka (5.2 million); in North America: New York (18.8 million), Boston (4.9 million), Miami (2.7 million), and New Orleans (0.4 million); in South America: Guayaquil (2.9 million) and Rio de Janeiro (1.8 million); in Africa: Abidjan (3.7 million) and Alexandria (3.0 million); and in Europe: London (8.9 million) and The Hague (2.5 million).
Consider the case of London. At the moment, London is protected from flooding by the Thames Barrier. The Thames Barrier was built in response to the catastrophic floods of 1953, and was finally ready for use in 1982 (it was officially opened on 8 May 1984). The Thames Barrier protects 150 km2 of London and property worth at least £1.5 trillion. Because of the foresight of previous scientific advisors to the UK government, it was built to withstand a 1-in-2,000-year flood. With the increased sea level due to climate change, this protection by 2030 will drop to a 1-in-1,000-year event. By 2020 the Barrier had closed 193 times in its 38-year history; and over 40% of these closures have occurred in the last 10 years. The UK economy is the sixth largest in the world, with approximately £1.4 trillion per year generated through London. London is also one of the three main centres, along with New York and Tokyo, for 24-hour share-trading. If London were disabled by a major flood then not only would this hit the economy of the UK, but potentially it could disrupt global trade. Hence the UK Environment Agency has put in place plans to guard against a significant sea-level rise in the future, including plans for a new barrier between Essex and Kent to guard against a possible 4 m rise in sea level. But most other cities around the world do not have the resources to plan for this sort of protection.
The Lancet Countdown 2020 report estimates that without intervention, between 145 million and 565 million people could be affected and displaced as a result of future sea-level rise.
Agriculture
One of the major worries concerning climate change is the effect it will have on agriculture, both globally and regionally. The main question is whether the world can feed itself with an extra 2 billion people on the planet by 2050 and a rapidly changing climate. Figure 27 shows the drop in cereal grain yields that has already occurred. Modelling suggests that in higher latitudes agricultural productivity may increase due to the longer growing season and reduced frost damage—but some of this will be offset by more frequent crop damage due to extreme weather events. Agriculture production will however reduce significantly in the tropics and sub-tropics due to much hotter temperatures and more variable rainfall.
27. Changes in cereal grain yields between 1980 and 2020.
Higher temperatures and humidity will also be a challenge for many societies that rely heavily on subsistence agriculture, as higher air temperatures and humidity make working outside more difficult and increase the likelihood of hyperthermia. This will impact on the health of anyone who has to work outside regularly, including construction and farm workers. Across the globe already a potential 278 billion work hours were lost in 2019 due to extreme conditions—92 billion hours greater than in 2000. Seven countries (Cambodia, India, China, Indonesia, Nigeria, Brazil, and the USA) together represent approximately 60% of the global hours lost in 2019, with India experiencing by far the greatest loss. In the first six countries, the impact on work hours lost fell mainly on agricultural workers.
Estimating the overall impact of climate change on agriculture is difficult as agricultural production has very little to do with feeding the world’s population and much more to do with trade and economics. This is why the European Union has stockpiles of food, while many underdeveloped countries export cash crops (such as sugar, cocoa, coffee, tea, and rubber) but cannot adequately feed their own populations. A classic example is the west African state of Benin, where cotton farmers can obtain cotton yields four to eight times per hectare greater than their US competitors in Texas. However, because the USA subsidizes its farmers, this means that US cotton is cheaper than that coming from Benin. Currently, US cotton farmers receive over $4 billion in subsidies, almost twice the total GDP of Benin. In 2002, Brazil filed a case with the World Trade Organization (WTO) against the USA for unfair subsidies and distortion of trade. They won their case in 2005; however, 15 years later, the USA is still discussing what changes should be made to their farming subsidies. So even if climate change makes Texan cotton yields even lower, it does not change the biased market forces still illegally in operation.
Markets can reinforce the difference between agricultural impacts in developed and developing countries. Variations in supply and demand could mean that agricultural exporters may gain in monetary terms even if the supplies fall, because when a product becomes scarce, the price rises. The other completely unknown factor is the extent to which a country’s agriculture can be adapted. For example, in climate change models it is assumed that production levels in developing countries will fall to a greater degree than those in developed countries because their estimated capability to adapt is less than that of developed countries. But this is just another assumption that has no analogue in the past, and as these effects on agriculture will occur over the next century, many developing countries may catch up with the developed world in terms of adaptability.
One example of the real regional problems that climate change could cause is the case of coffee growing in Uganda. Here, the total area suitable for growing Robusta coffee would be dramatically reduced, to 10% of the present area, by a temperature increase of 2°C. Only higher areas of land would remain suitable for coffee growing, the rest would become too hot. But no one can tell whether these remaining areas would make more or less money for the country, because if other coffee growing areas around the world are similarly affected, the price of coffee beans will increase due to scarcity. This demonstrates the vulnerability to the effects of global warming of many developing countries whose economies often rely heavily on one or two agricultural products, as it is very difficult to predict the changes that global warming will cause in terms of crop yield and its cash equivalent. Hence one major adaptation to global warming should be the broadening of the economic and agricultural base of the most threatened countries. This, of course, is much harder to accomplish in practice than on paper, and it is clear that the USA, EU, and China agricultural subsidies and the current one-sided world trade agreements have a greater effect on global agricultural production and the ability of countries to feed themselves than climate change will ever have. Solutions look to be even further away with the failure of the WTO negotiations.
Ocean acidification
Direct measurements of the ocean’s chemistry have shown that the pH of the oceans is getting lower; that is, they are getting more acidic (see Figure 28). This is because CO2 in the atmosphere dissolves in the surface water of the ocean. This process is controlled by two main factors: the amount of CO2 in the atmosphere and the temperature of the ocean. The oceans have already absorbed about a third of the CO2 resulting from human activities, which has led to a steady decrease in ocean pH levels. With increasing atmospheric CO2 in the future, the amount of dissolved CO2 in the ocean will continue to increase. Some marine organisms, such as corals, foraminifera, coccoliths, and shellfish, have shells composed of calcium carbonate, which dissolves in acid. Laboratory and field experiments show that under high CO2 levels the more acidic waters cause some marine species to develop misshapen shells and have lower growth rates, although the effect varies among species. Acidification also alters the cycling of nutrients and many other elements and compounds in the ocean, and it is likely to shift the competitive advantage among species, and have impacts on marine ecosystems and the food web. This is a major worry as fishing is still an important source of food, with about 95 million tonnes of fish caught by commercial fishing and another 50 million tonnes produced by fish farms per year.
28. Ocean acidification.
Biodiversity
The current loss of biodiversity around the world is due to human activity, including deforestation, agriculture, urbanization, and mineral exploitation. Extinction rates are currently 100–1,000 times higher than the background natural rate and climate change will exacerbate this decline. The IPCC impact report lists the following species as those most at risk from climate change: the mountain gorilla in Africa; amphibians that live in the cloud forests of the neotropics; the spectacled bear of the Andes; forest birds of Tanzania; the ‘resplendent quetzal’ bird in Central America; the Bengal tiger, and other species found only in the Sundarban wetlands; rainfall-sensitive plants found only in the Cape Floral Kingdom of South Africa; and polar bears and penguins near the poles. The primary reason for the threat to these species is that they are unable to migrate in response to climate change because of their particular geographical location or the encroachment of human activity, especially farming and urbanization. An example of the former is the cloud forests of the neotropics: as climate changes, this particular climatic zone will migrate up the mountainside—to the point where there is no more mountain to climb.
One example of an ecosystem under threat is the coral reefs. Coral reefs are a valuable economic resource for fisheries, recreation, tourism, and coastal protection. Some estimate that the global cost of losing the coral reefs runs into hundreds of billions of dollars each year. In addition, reefs are one of the largest global stores of marine biodiversity. The last few years have seen unprecedented declines in the health of coral reefs. An estimated 50% of the hard corals on Australia’s Great Barrier Reef have been lost in the past few years from bleaching events, which are caused by extreme water temperatures. The Great Barrier Reef is the world’s largest coral reef system, composed of over 2,900 individual reefs and 900 islands stretching for over 1,400 miles. In other regions, as much as 70% of the coral has died in a single season. There has also been an upsurge in the variety, incidence, and virulence of coral disease in recent years, with major die-offs in Florida and much of the Caribbean region. In addition, increasing atmospheric CO2 concentrations could decrease the calcification rates of the reef-building corals, resulting in weaker skeletons, reduced growth rates, and increased vulnerability to erosion. Model results suggest these effects would be most severe at the current margins of coral reef distribution.
On a more theoretical note, the biologist Chris Thomas and colleagues published a study in Nature investigating the possible increase in extinction rates over the next 50 years in key regions such as Mexico, Amazonia, and Australia. The theoretical models suggest that a 2˚C warming by 2050 could condemn to extinction one-quarter of all species they studied. This study has been criticized as there are many assumptions in their models which may or may not be true: for example, they assume we know the full climatic range in which each species can persist and the precise relationship between shrinking habitat and extinction rates. So these results should be seen only as the likely direction of extinction rates, not necessarily the exact magnitude. However, this and many other scientific studies demonstrate the huge threat to regional and global biodiversity and illustrate the sensitivity of biological systems to the amount and rate of warming that will occur in the future.
Protecting biodiversity has other major benefits for human society. In 2020, the world was brought to a standstill by the Covid-19 pandemic. One of the reasons that Covid-19 is such a complex, severe, and even fatal respiratory disease is that it is a zoonotic virus, a virus that has jumped from another animal and mutated to infect humans. Hence the virus has a genetic signature unknown to our immune systems, delaying our ability to develop antibodies that can fight the infection. It seems increasingly likely that it is the illegal trade in endangered animals such as bats and pangolins through inhumane ‘wet markets’ in China and South-East Asia that allowed its transmission between species. The extremely high risks of such zoonotic virus outbreaks were indicated by previous outbreaks, such as avian influenza related to the H5N1 virus in 1996 and the SARS outbreak in 2002‒3. Both times, Chinese wet markets were temporally banned and then allowed to continue. Hence there is a real need to protect and respect biodiversity and wildlife to prevent these zoonotic diseases occurring again. The Chinese and other governments need to promote cultural change, along with gradual regulatory restrictions to protect wildlife and consequently humans too.
Human health
The potential health impacts of climate change are immense, and managing those impacts will be an enormous challenge. Climate change will increase deaths from heatwaves, droughts, wildfires, storms, and floods. Higher temperatures and variable precipitation threaten food production. This is due to reduced productivity because of the increased risks to people working outside regularly, such as construction and farm workers. It has been suggested that the overall death rate may drop in some countries since many elderly people die from cold weather so warmer winters would reduce this cause of death. However, this view has shown to be incorrect, as recent research has demonstrated that better housing, improved health care, higher incomes, and greater awareness of the risks of cold have been responsible for the reduction in winter deaths in the UK since 1950, while in the USA summer-heat-related deaths have been four times higher than deaths from cold for the past three decades. Hence in many societies adaptation to cold climates and improved protection for the most vulnerable members of society means that warmer winters will have little or no effect in reducing the death rate.
The 2009 University College London’s report in the Lancet journal, ‘Managing the Health Effects of Climate Change’, identified the two major areas that could affect the health of billions of people: water and food. The most important threat to human health is lack of access to fresh drinking water. At present there are still 1 billion people who do not have regular access to clean, safe drinking water. Not only does the lack of water cause major health problems from dehydration, but a large number of diseases and parasites are present in dirty water. The rising worldwide human population, particularly those concentrated in urban areas, is putting a great strain on water resources. The impacts of climate change—including changes in temperature, precipitation, and sea levels—are expected to have varying consequences for the availability of fresh water around the world. For example, changes in river run-off will affect the yields of rivers and reservoirs, and thus the recharging of groundwater supplies. An increase in the rate of evaporation will also affect water supplies and contribute to the salination of irrigated agricultural lands. Rising sea levels may result in saline intrusion in coastal aquifers. Currently, approximately 2 billion people, one-quarter of the world’s population, live in countries that are water-stressed. It has been suggested that if nothing is done to mitigate climate change then up to 50% of the world population could live in countries experiencing water-stress by 2050. Of these people, 80% will be in developing countries.
Climate change is likely to have the greatest impact in countries with a high ratio of relative use to available supply. Regions with abundant water supplies will get more than they want with increased flooding. As suggested above, computer models predict much heavier rains and thus major flood problems for Europe, whilst, paradoxically, countries that currently have little water (e.g. those relying on desalination) may be relatively unaffected. It will be countries in between, with no history or infrastructure for dealing with water shortages, that will be the most affected. In central Asia, and northern and southern Africa there will be even less rainfall, and water quality will become increasingly degraded through higher temperatures and pollutant run-off. Add to this the predicted increase in year-to-year variability in rainfall, and droughts will become more common. Hence it is those countries that have been identified as most at risk which need to start planning now to conserve their water supplies and/or to deal with the increased risks of flooding; because it is the lack of infrastructure to deal with drought and floods rather than the lack or abundance of water which causes the threat to human health.
Food security rests on three main pillars: (1) food availability—is enough being produced? (2) Access—can people afford it? And (3) stability—is there always food available? According to the UN World Food Programme, we currently produce enough food to feed 10 billion people, easily enough to cover the predicted increase in population this century. But there are 821 million people on the brink of starvation today, up by 25 million in just five years. This is because they simply do not have enough money to buy food. Climate change threatens food availability and stability as it affects the production of food and other agricultural goods. Extreme weather events must also be considered. With an increasingly globalized economy very few countries are self-sufficient in basic food and hence food imports are very important. The cost of basic food items can be strongly influenced by global demand, national agricultural subsidies and export bans, and natural disasters, but the biggest influence is food speculation on the global markets. In 2008‒9, there was a 60% rise in the price of food and in 2011–12 there was a 40% jump in price, both linked to food speculation. So the inability of many people to afford basic food, leading to malnutrition and starvation, can be linked directly to speculation on food prices on the global markets in London, New York, and Tokyo.
Another threat to human health is the transmission of infectious diseases, which is directly affected by climatic factors. Climate change will particularly influence vector-borne diseases, that is, diseases that are carried by another organism—for example, malaria, which is carried by mosquitoes. Infective agents and their vector organisms are sensitive to factors such as temperature, surface-water temperature, humidity, wind, soil moisture, and changes in forest distribution. It is, therefore, projected that climate change and altered weather patterns would affect the range (both altitude and latitude), intensity, and seasonality of many vector-borne and other infectious diseases. For example, there is a strong correlation between increased SST and sea level, and the severity of the cholera epidemics in Bangladesh. With predicted future climate change and consequent rise in Bangladesh’s relative sea level, cholera epidemics could become more common.
In general, then, increased warmth and moisture caused by climate change will enhance transmission of diseases. But while the potential transmission of many of these diseases increases in response to climate change, we should remember that our capacity to control the diseases will also change. New or improved vaccination can be expected; some vector species can be constrained by the use of pesticides. Nevertheless, there are uncertainties and risks here, too: for example, long-term pesticide use encourages the breeding of resistant strains, while killing many natural predators of pests.
The most important vector-borne disease is malaria, with currently 500 million infected people worldwide. Plasmodium vivax, which is carried by the Anopheles mosquito, is the organism that causes malaria. The main climate factors that have a bearing on the malarial transmission potential of the mosquito population are temperature and precipitation. Assessments of the potential impact of global climate change on the incidence of malaria suggest a widespread increase of risk because of the expansion of the areas suitable for malaria transmission. Already in the past five years, the area suitable for malaria transmission in highland areas was 39% higher in Africa and 150% higher in east Asia compared to the 1950s. Mathematical models mapping out the temperature zones suitable for mosquitoes suggest that by the 2080s the potential exposure of people could increase by 2–4% (260–320 million people). The predicted increase is most pronounced at the borders of endemic malarial areas and at higher altitudes within malarial areas. The changes in malaria risk must be interpreted on the basis of local environmental conditions, the effects of socioeconomic development, and malaria control programmes or capabilities. Climate change will also provide excellent conditions for Anopheles mosquitoes to breed in southern England, continental Europe, and the northern USA.
It should, however, be noted that the occurrence of many tropical diseases is related to development. As recently as the 1940s, malaria was endemic in Finland, Poland, Russia, and thirty-six states in the USA including Washington, Oregon, Idaho, Montana, North Dakota, New York, Pennsylvania, and New Jersey. So although climate change has the potential to increase the range of many of these tropical diseases, the experience of Europe and the USA suggests that combating malaria is strongly linked to development and resources: development to ensure efficient monitoring of the disease and resources to secure a strong effort to eradicate the mosquitoes and their breeding grounds.
The impacts of climate change will increase significantly as the temperature of the planet rises. Climate change will affect the return period and severity of heatwaves, droughts, wildfires, storms, and floods. Coastal cities and towns will be especially vulnerable as sea levels rise, increasing the impacts of floods and storm surges. Water and food security as well as public health will become the most important problems facing all countries. Climate change threatens global biodiversity and the wellbeing of billions of people. In Table 4 I have tried to summarize the potential impacts of climate change. Though many colleagues are planning on how to deal with a 4˚C world, my simple advice is, let us not go there.
