John Houghton observes, “Talking in terms of changes in global average surface temperature . . . however, tells us little about the actual impacts of global warming on human communities.”1 What affects individuals and communities most are the day-to-day variations in climate in the specific regions where they live. The impacts of climate change, in fact, pose serious, wide-ranging threats to human societies and natural ecosystems around the world. The larger and faster the changes in climate are, the more difficult it will be for human and natural systems to adapt.2
In the present chapter we proceed from a physical explanation of climate change to its concrete consequences for human communities and ecosystems. We examine here the impacts of climate change that are already present as well as scenarios for the immediate future. Some of the major impacts of climate change discussed here are extreme weather events; droughts and desertification; reduction of snow cover, including the melting of glaciers; sea-level rise; ocean acidification with consequences for marine life; and the loss of biodiversity.
extreme Weather events
Extreme weather is probably the most tangible among the impacts of anthropogenic global warming and associated climate change. It appears that the exceptionally stable weather that characterized
1 John Houghton, “Sustainable Climate and the Future of Energy,” in creation in crisis: christian Perspectives on Sustainability, ed. Robert S. White (London:
SPCK, 2009), 15. See also National Research Council, Monitoring climate change impacts: Metrics at the intersection of the human and earth Systems (Washington, DC: The National Academies Press, 2010), 1.
2 The National Academy of Sciences, understanding and responding to climate change: highlights of national Academies (Washington, DC: National Academies Press, 2008), 16.
the Holocene epoch is under increasing threat from human-induced climate change. As we have seen earlier, it was the uniquely equable climate of the interglacial period of the Holocene that made agricul-ture possible and in its wake enabled the rise of various civilizations in different parts of the world. When stable weather patterns go awry, the very foundations of our present livelihoods and societies find them-selves on a shaky ground, as communities and nations are discovering in many parts of the globe.
The link between climate change and extreme weather is imme-diately perceived, in a rather intuitive way, by the people who live closest to the Earth, attentive to the intricate rhythms of nature.
These include subsistence farmers, forest dwellers, indigenous com-munities, fisher folk, and others. With every passing year those who live in intimate contact with the Earth—as opposed to those who live in the air-conditioned and artificially lit indoor spaces of corporate boardrooms—realize that nature’s balance is tilting and that seasons and weather patterns are changing.
The scientific community has also been closely studying the phe-nomena of extreme weather patterns and its link to anthropogenic climate change during the last few decades. It had been cautious until very recently to attribute individual natural calamities or freak weather patterns directly to human-induced climate change for lack of sufficient and credible data. It is, in fact, difficult to attribute a natural calamity like hurricane Katrina, which struck New Orleans in 2005, to climate change, in spite of evidence showing that warming of the ocean surface can lead to more intense tropical storms.3 The weather system is extremely complex; it is conditioned by so many factors and variables. So the scientists have been cautious to directly attribute extreme weather, unlike other impacts of climate change like desertification, melting of glaciers, sea-level rise, or biodiversity loss, to global warming and associated climate change.
Now it appears that the situation has changed. After decades of painstaking research and gathering data, the scientific community has begun to present its verdict on the link between anthropogenic global warming and extreme weather events. A high point in this process was the publication of a special report on the relationship between climate change and extreme weather events in 2012 by the scientists
3 See Richard A. Anthens et al., “Hurricanes and Global Warming—Potential Linking Consequences,” Bulletin of the American Meteorological Society 87 (2006): 623–28; Greg J. Holland and Peter J. Webster, “Heightened Tropical Cyclone Activity in the North Atlantic: Natural Variability or Climate Trend?,”
Philosophical transactions of the royal Society 365 (2007): 2695–716.
of the IPCC.4 The document is an authoritative synthesis of scientific literature in the field during the last decade or so, and it sheds light on how human-induced climate change is leading to extreme weather events, a trend only destined to accelerate in the future. We shall rely on this important study as well as other pertinent sources in exploring the link between extreme weather and human-induced climate change.
Anthropogenic greenhouse gas emissions, as we saw in Chapter 3, are upsetting the atmosphere’s balance and, with it, upsetting the bal-ance of nature. Changes in global climate due to global warming can naturally lead to changes in extreme weather and climate events. In fact, raising the Earth’s temperature is like turning up the heat under a saucepan. Global warming pumps more energy into weather systems, making them more turbulent and unpredictable.5 As the IPCC’s special report states: “A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of extreme weather and climate events, and can result in unprecedented extreme weather and climate events.”6 The scientists of the IPCC conclude from analysis of data of the past few years that “observed changes in climate extremes reflect the influence of anthropogenic climate change in addition to natural climate variability.”7 Thus, for the recent past scientists are able to infer that most of the observed weather extremes are linked to anthropogenic influences.8
However, when it comes to the link between human-induced cli-mate change and extreme weather patterns in the future, the scientists are much more forthright. The reason is obvious: both greenhouse gas emissions and the global average surface temperature are destined to
4 See IPCC, Managing the risks of extreme events and disasters to Advance climate change Adaptation: Special report of the iPcc, ed. C. B. Field et al.
(Cambridge: Cambridge University Press, 2012).
5 Alastair McIntosh, hell and high Water: climate change, hope and the hu-man condition (Edinburgh: Birlinn, 2009), 41. See also Kirstin Dow and Thomas E. Downing, the Atlas of climate change: Mapping the World’s greatest chal-lenge (London: Earthscan, 2006), 26–27.
6 IPCC, Managing the risks of extreme events and disasters to Advance climate change Adaptation, 7.
7 Ibid., 7. See also Dim Coumou and Stefan Rahmstorf, “A Decade of Weather Extremes,” nature climate change 2 (2012): 491.
8 The Fifth Assessment Report of the IPCC of 2013 offers further confirmation in this regard. The report notes, for example, that since about 1950 the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale. See IPCC, climate change 2013: the Physical Science Basis: contribution of Working group i to the fifth Assessment report of the intergovernmental Panel on climate change, ed. T. F. Stocker et al. (Cam-bridge: Cambridge University Press, 2013), 5.
rise steeply in the decades to come. From the analysis of past data and with the help of climate models scientists are able to make confident projections about the effects of human activities on weather patterns worldwide in the decades to come.
According to the scientists, it is virtually certain that increases in the frequency of warm daily temperature extremes and decreases in cold extremes will occur throughout the twenty-first century on a global scale. It is also very likely that heat waves will increase in length, fre-quency, and/or intensity of warm spells over most land areas. In fact, a “one in twenty years” hottest-day phenomenon is likely to become a “one in two years” event by the end of the twenty-first century in most regions except in the high latitudes of the Northern Hemisphere, where it is likely to become a “one in five years” occurrence.9 The typical European summer of the 2040s will be even warmer than the extreme summer of 2003. As Robert Henson observes, a heat wave does not have to bring the warmest temperatures ever observed to have catastrophic effects. A long string of hot days combined with unusually steamy nights will suffice.10 The 2013 Fifth Assessment of the IPCC states:
It is virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas on daily and seasonal timescales as global mean temperatures increase. It is very likely that heat waves will occur with a higher frequency and duration. Occasional cold winter extremes will continue to occur.11 The scientists are also able to predict with high confidence that changes in heat waves, glacial retreat, and permafrost degradation will affect high-mountain phenomena like landslides and outburst floods from glacial lakes. Landslides in some regions will also be driven by changes in rainfall patterns.12
There is growing evidence that human-induced climate change has begun to directly influence rainfall patterns and the planet’s
9 IPCC, Managing the risks of extreme events and disasters to Advance climate change Adaptation, 13. See also The National Academy of Sciences, ecological impacts of climate change (Washington, DC: The National Academies Press, 2009), 7.
10 Robert Henson, the rough guide to climate change (London: Rough Guides Ltd., 2006), 43, 52.
11 IPCC, climate change 2013: the Physical Science Basis, 20.
12 IPCC, Managing the risks of extreme events and disasters to Advance climate change Adaptation, 15.
fundamental hydrological cycle. The physical basis underlying the link between global warming and precipitation changes is simple and direct. Rainfall patterns form part of the natural hydrological cycle of the Earth, sustained by the process of evaporation. “Heated by the sun’s radiation, the ocean and land surface evaporate water, which then moves around with winds in the atmosphere, condenses to form clouds, and falls back to the Earth’s surface as rain or snow, with the flow to the oceans via rivers completing the global hydrological (water) cycle.”13 One of the major impacts of present human-induced global warming and associated climate change is precisely an undue interference with the hydrological cycle of the planet, leading to drastic changes in precipitation patterns. Increased warming leads to greater evaporation of surface moisture, leading to extra water vapor in the atmosphere. It is estimated that the water-holding capacity of air increases by about 7 percent for every 1°C of warming.14 This is a nonlinear relationship, meaning the effect gets stronger for each additional degree of warming. As the climate warms, water-holding capacity increases with higher temperatures, and consequently the water vapor amounts in the atmosphere rise as well. This moisture then gets carried around by atmospheric winds, and the convergence of increased water vapor leads to more intense precipitation and risk of heavy rain and snow events.15
In the context of current phase of human-induced global warming, climate models and empirical evidence point to an increase in rainfall.
Warmer climates, owing to increased water vapor, can lead to more intense precipitation events, even when the total annual rainfall is
13 K. E. Trenberth, “Changes in Precipitation with Climate Change,” climate research 47 (2011): 123.
14 The calculation is done based on the well-known Clausius-Clapeyron equa-tion, according to which increased temperature causes increased atmospheric water vapor concentrations; hence, changes in water vapor transport and the hydrologic cycle can be expected. The typical values are about 7 percent change for 1°C change in temperature. See Trenberth, “Changes in Precipitation with Climate Change,” 124; S. Solomon et al., “Irreversible Climate Change due to Carbon Dioxide Emissions,” Proceedings of the national Academy of Sciences 106 (2009): 1706.
15 Trenberth, “Changes in Precipitation with Climate Change,” 123–25; K. E.
Trenberth, “Precipitation in a Changing Climate: More Floods and Droughts in the Future,” GEWEX News (May 19, 2009): 8; Henson, the rough guide to climate change, 57. The recent melting of the Arctic has led to more extreme winter weather in the Northern Hemisphere in recent years. See Nicola Jones,
“Arctic Melt Leads to Extreme Weather Extremes,” nature climate change 2 (2012): 221.
reduced slightly, and with prospects for even stronger events when the overall rainfall amounts increase. It is also estimated that pre-cipitation will generally increase in areas with already high amounts of precipitation and generally decrease in areas with low amounts of rainfall.16 Apart from the general patterns the character of rainfall also appears to be changing. During the last three decades, increases in heavy rains are found to be occurring in most places, even when mean precipitation is not increasing. At the global level the number of very wet days has increased during the past fifty years, even in places where mean precipitation amounts are not increasing.17 As for future prospects, it is projected that there will be more rain at high latitudes, less rain in the dry subtropics, and uncertain but probably substantial changes in tropical areas.18 The 2013 IPCC report warns that “extreme precipitation events over most of the mid-latitude land masses and over wet tropical regions will very likely become more intense and more frequent by the end of this century, as global mean surface temperature increases.”19
The changes in rainfall patterns due to global warming can lead to the risk of increased storms and floods, both of which have significant socioeconomic impacts. Floods are associated with extremes in rainfall that usually come with tropical storms, thunderstorms, orographic rainfall, and widespread extratropical cyclones. When it comes to floods, it is the character of the precipitation that really counts. Several areas around the globe in recent decades have seen rain concentrated in short, intense bursts that produce flash floods or in multi-day torrents that can cause near-biblical floods across entire regions.20 Floods also have a huge human cost. Deaths as a result of flooding and cyclones are humankind’s worst natural disasters, accounting for nearly two-thirds of lives lost from all forms of natural disasters.
Moreover, the disease and famine that follow floods often cause even
16 See The Royal Society, climate change: A Summary of the Science (Septem-ber 2010), para. 44; Tren(Septem-berth, “Changes in Precipitation with Climate Change,”
131.
17 Trenberth, “Changes in Precipitation with Climate Change,” 128; Trenberth,
“Precipitation in a Changing Climate,” 8.
18 The National Academy of Sciences, Advancing the Science of climate change (Washington, DC: The National Academies Press, 2010), 48; IPCC, Managing the risks of extreme events and disasters to Advance climate change Adaptation, 13; Nicholas Stern, the economics of climate change (Cambridge: Cambridge University Press, 2007), 74.
19 IPCC, climate change 2013: the Physical Science Basis, 23.
20 Henson, the rough guide to climate change, 55–61.
more deaths than the floods themselves. Conservative estimates sug-gest that 80 million people worldwide will be at risk of flooding in the coming decades, 80 percent of them in the lower-income countries of Asia, like Bangladesh.21
In the context of climate change, scientists predict that it is likely that the average maximum wind speed of tropical cyclones (also known as typhoons or hurricanes) will increase throughout the coming century, although increases may not occur in all ocean basins. Signifi-cantly, “the observed increases in water vapor affect both the green-house effect, thus providing a positive feedback to climate change, and the hydrological cycle, by providing more atmospheric moisture for all storms to feed upon.”22 Heavy rainfalls associated with tropical cyclones are likely to increase with continued warming. However, it is also likely that overall there will be either a decrease or essentially no change in the number of tropical cyclones.23
Another impact of climate change, ironically the opposite of exces-sive precipitation, is drought, which exacerbates the phenomenon of desertification around the globe.
Droughts and Desertification
Drought may be defined as a recurring extreme climatic event over land characterized by below-normal rainfall over a period that can last from months to years.24 Drought is probably the most conspicu-ous effect of anthropogenic global warming and associated climate change that could harm millions of people in the coming decades.
The specter of extended or permanent drought over large parts of currently habitable or arable land, which may be irreversible over centuries, can also threaten food security and cause massive displace-ment of people.25
21 Nick Spencer and Robert White, christianity, climate change, and Sustain-able living (London: SPCK, 2007), 37; McIntosh, hell and high Water, 41.
22 Trenberth, “Changes in Precipitation with Climate Change,” 126.
23 See IPCC, Managing the risks of extreme events and disasters to Advance climate change Adaptation, 13; The National Academy of Sciences, Advancing the Science of climate change, 49–50.
24 See Aiguo Dai, “Drought Under Global Warming: A Review,” climate change 2 (2011): 45.
25 See Millennium Ecosystem Assessment, ecosystems and human Well-being:
desertification Synthesis (Washington, DC: World Resources Institute, 2005), ii;
Joseph Romm, “The Next Dust Bowl,” nature 478 (2011): 450–51.
In the current stage of climate science, attributing an increase in the severity of droughts to climate change is fraught with difficulties.
This is so because drought is caused not only by climate change but also by other factors like ocean currents, urbanization, deforestation, changes in agriculture, and other climatic uncertainties. Recent studies of past climates through tree rings and other proxy data demonstrate that drought is itself a normal part of climatic variations. These studies have revealed that large-scale droughts have occurred several times during the past 500–1,000 years over many parts of the world, including North America, Mexico, Asia, Africa, and Australia. These historical droughts are linked to tropical sea-surface temperature variations, the La Niña and El Niño events in the Pacific, and other natural factors.26 More recent events like the Dust Bowl drought of the 1930s over the Great Plains in North America, or the even more recent drought around Lake Chad in Africa, appear to be the result of a combination of many factors. The story of Lake Chad is a clear example of what can happen when climate change and land use inter-sect. Once the sixth largest fresh-water lake in the world, Lake Chad has shriveled by 95 percent over the last forty years, a victim of the 1970s and 1980s droughts as well as intensive irrigation.27
However, the intensity and frequency of droughts in recent decades appear to be linked with anthropogenic global warming. Climate scientists have noted marked global aridity changes since 1950, cor-responding with the rapid increases in global surface temperatures and atmospheric CO2 and other greenhouse gases:
From 1950 to 2008, most land areas have warmed up by 1–3°C, with the largest warming over northern Asia and northern North America. During the same period, precipitation decreased over most of Africa, southern Europe, South and East Asia, eastern Australia, Central America, central Pacific coasts of North America and some parts of South America.28
A string of recent studies have clearly attributed the increasing aridity and decreasing rainfall in the Sahel region of Africa to anthropogenic climate change.29 On the global scale some of the long-term records
A string of recent studies have clearly attributed the increasing aridity and decreasing rainfall in the Sahel region of Africa to anthropogenic climate change.29 On the global scale some of the long-term records