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Negative Effects Of Global Warming Essay Pdf

See also: Global warming and Effects of global warming

Climate change has brought about possibly permanent alterations to Earth's geological, biological and ecological systems.[1] These changes have led to the emergence of a not so large-scale environmental hazards to human health, such as extreme weather,[2]ozone depletion, increased danger of wildland fires,[3]loss of biodiversity,[4] stresses to food-producing systems and the global spread of infectious diseases.[5] The World Health Organization (WHO) estimates that 160,000 deaths, since 1950, are directly attributable to climate change.

To date, a neglected aspect of the climate change debate, much less research has been conducted on the impacts of climate change on health, food supply, economic growth, migration, security, societal change, and public goods, such as drinking water, than on the geophysical changes related to global warming. Human impacts can be both negative and positive. Climatic changes in Siberia, for instance, are expected to improve food production and local economic activity, at least in the short to medium term. Numerous studies suggest, however, that the current and future impacts of climate change on human society are and will continue to be overwhelmingly negative.[6][7]

The majority of the adverse effects of climate change are experienced by poor and low-income communities around the world, who have much higher levels of vulnerability to environmental determinants of health, wealth and other factors, and much lower levels of capacity available for coping with environmental change. A report on the global human impact of climate change published by the Global Humanitarian Forum in 2009, estimated more than 300,000 deaths and about $125 billion in economic losses each year, and indicating that most climate change induced mortality is due to worsening floods and droughts in developing countries.[8]

Key vulnerabilities[edit]

Most of the key vulnerabilities to climate change are related to climate phenomena that exceed thresholds for adaptation; such as extreme weather events or abrupt climate change, as well as limited access to resources (financial, technical, human, institutional) to cope. In 2007, the IPCC published a report of key vulnerabilities of industry, settlements, and society to climate change.[9] This assessment included a level of confidence for each key vulnerability:

  • Very high confidence: Interactions between climate change and urbanization: this is most notable in developing countries, where urbanization is often focused in vulnerable coastal areas.
  • High confidence:
    • Interactions between climate change and global economic growth: Stresses due to climate change are not only linked to the impacts of climate change, but also to the impacts of climate change policies. For example, these policies might affect development paths by requiring high cost fuel choices.
    • Fixed physical infrastructures that are important in meeting human needs: These include infrastructures that are susceptible to damage from extreme weather events or sea level rise, and infrastructures that are already close to being inadequate.
  • Medium confidence: Interactions with governmental and social cultural structures that already face other pressures, e.g., limited economic resources.

Health[edit]

Main article: Effects of climate change on human health

Climate change poses a wide range of risks to population health – risks that will increase in future decades, often to critical levels, if global climate change continues on its current trajectory.[10] The three main categories of health risks include: (i) direct-acting effects (e.g. due to heat waves, amplified air pollution, and physical weather disasters), (ii) impacts mediated via climate-related changes in ecological systems and relationships (e.g. crop yields, mosquito ecology, marine productivity), and (iii) the more diffuse (indirect) consequences relating to impoverishment, displacement, resource conflicts (e.g. water), and post-disaster mental health problems.

Climate change thus threatens to slow, halt or reverse international progress towards reducing child under-nutrition, deaths from diarrheal diseases and the spread of other infectious diseases. Climate change acts predominantly by exacerbating the existing, often enormous, health problems, especially in the poorer parts of the world. Current variations in weather conditions already have many adverse impacts on the health of poor people in developing nations,[11] and these too are likely to be 'multiplied' by the added stresses of climate change.

A changing climate thus affects the prerequisites of population health: clean air and water, sufficient food, natural constraints on infectious disease agents, and the adequacy and security of shelter. A warmer and more variable climate leads to higher levels of some air pollutants. It increases the rates and ranges of transmission of infectious diseases through unclean water and contaminated food, and by affecting vector organisms (such as mosquitoes) and intermediate or reservoir host species that harbour the infectious agent (such as cattle,[12]bats and rodents). Changes in temperature, rainfall and seasonality compromise agricultural production in many regions, including some of the least developed countries, thus jeopardising child health and growth and the overall health and functional capacity of adults. As warming proceeds, the severity (and perhaps frequency) of weather-related disasters will increase – and appears to have done so in a number of regions of the world over the past several decades.[13] Therefore, in summary, global warming, together with resultant changes in food and water supplies, can indirectly cause increases in a range of adverse health outcomes, including malnutrition, diarrhea, injuries, cardiovascular and respiratory diseases, and water-borne and insect-transmitted diseases.

Health equity and climate change have a major impact on human health and quality of life, and are interlinked in a number of ways. The report of the WHO Commission on Social Determinants of Health points out that disadvantaged communities are likely to shoulder a disproportionate share of the burden of climate change because of their increased exposure and vulnerability to health threats. Over 90 percent of malaria and diarrhea deaths are borne by children aged 5 years or younger, mostly in developing countries.[14] Other severely affected population groups include women, the elderly and people living in small island developing states and other coastal regions, mega-cities or mountainous areas.[15]

Psychological impacts[edit]

Further information: Effects of global warming on human health § Mental health

A 2011 article in the American Psychologist identified three classes of psychological impacts from global climate change:[16]

  • Direct - "Acute or traumatic effects of extreme weather events and a changed environment"
  • Indirect - "Threats to emotional well-being based on observation of impacts and concern or uncertainty about future risks"
  • Psychosocial – "Chronic social and community effects of heat, drought, migrations, and climate-related conflicts, and postdisaster adjustment"   A psychological impact is shown through peoples behaviours and how they act towards the actual situation. The topic of climate change is very complex and difficult for people to understand, which effects how they act upon it. It is shown by Ranney and Clark(2016)[17] that by informing people to make them understand the topic of climate science clearly, it promotes the change in behaviour towards mitigation of climate change.

Extreme weather events[edit]

Further information: Extreme weather

This trend towards more variability and fluctuation is perhaps more important, in terms of its impact on human health, than that of a gradual and long-term trend towards higher average temperature.[18] Infectious disease often accompanies extreme weather events, such as floods, earthquakes and drought.[citation needed] These local epidemics occur due to loss of infrastructure, such as hospitals and sanitation services, but also because of changes in local ecology and environment.

Diseases[edit]

Further information: Effects of global warming on infectious diseases

Climate change may lead to dramatic increases in prevalence of a variety of infectious diseases. Beginning in the mid-'70s, there has been an “emergence, resurgence and redistribution of infectious diseases”.[18] Reasons for this are likely multicausal, dependent on a variety of social, environmental and climatic factors, however, many argue that the “volatility of infectious disease may be one of the earliest biological expressions of climate instability”.[18] Though many infectious diseases are affected by changes in climate, vector-borne diseases, such as malaria, dengue fever and leishmaniasis, present the strongest causal relationship. Observation and research detect a shift of pests and pathogens in the distribution away from the equator and towards Earth's poles.[19]

Malaria[edit]

Increased precipitation like rain could increase the number of mosquitos indirectly by expanding larval habitat and food supply. Malaria kills approximately 300,000 children (under age 5) annually, poses an imminent threat through temperature increase .[20] Models suggest, conservatively, that risk of malaria will increase 5-15% by 2100 due to climate change.[21] In Africa alone, according to the MARA Project (Mapping Malaria Risk in Africa),[22] there is a projected increase of 16–28% in person-month exposures to malaria by 2100.[23]

Non-climatic determinants[edit]

Sociodemographic factors include, but are not limited to: patterns of human migration and travel, effectiveness of public health and medical infrastructure in controlling and treating disease, the extent of anti-malarialdrug resistance and the underlying health status of the population at hand.[24] Environmental factors include: changes in land-use (e.g. deforestation), expansion of agricultural and water development projects (which tend to increase mosquito breeding habitat), and the overall trend towards urbanization (i.e. increased concentration of human hosts). Patz and Olson argue that these changes in landscape can alter local weather more than long term climate change.[20] For example, the deforestation and cultivation of natural swamps in the African highlands has created conditions favourable for the survival of mosquito larvae, and has, in part, led to the increasing incidence of malaria.[20] The effects of these non-climatic factors complicate things and make a direct causal relationship between climate change and malaria difficult to confirm. It is highly unlikely that climate exerts an isolated effect.

Environment[edit]

Climate change may dramatically impact habitat loss, for example, arid conditions may cause the deforestation of rainforests, as has occurred in the past.[25]

Temperature[edit]

A sustained wet-bulb temperature exceeding 35° is a threshold at which the resilience of human systems is no longer able to adequately cool the skin. A study by NOAA from 2013 concluded that heat stress will reduce labor capacity considerably under current emissions scenarios.[26] There is evidence to show that high temperatures can increase mortality rates among fetuses and children[27] Although the main focus is often on the health impacts and risks of higher temperatures, it should be remembered that they also reduce learning and worker productivity, which can impact a country's economy and development.

Water[edit]

See also: Water crisis

The freshwater resources that humans rely on are highly sensitive to variations in weather and climate. In 2007, the IPCC reported with high confidence that climate change has a net negative impact on water resources and freshwater ecosystems in all regions.[28] The IPCC also found with very high confidence that arid and semi-arid areas are particularly exposed to freshwater impacts.[28]

As the climate warms, it changes the nature of global rainfall, evaporation, snow, stream flow and other factors that affect water supply and quality. Specific impacts include:

  • Warmer water temperatures affect water quality and accelerate water pollution.[29]
  • Sea level rise is projected to increase salt-water intrusion into groundwater in some regions. This reduces the amount of freshwater available for drinking and farming.[29][30]
  • In some areas, shrinking glaciers and snow deposits threaten the water supply.[31] Areas that depend on melted water runoff will likely see that runoff depleted, with less flow in the late summer and spring peaks occurring earlier.[29] This can affect the ability to irrigate crops. (This situation is particularly acute for irrigation in South America,[32] for irrigation and drinking supplies in Central Asia, and for hydropower in Norway, the Alps, and the Pacific Northwest of North America.)
  • Increased extreme weather means more water falls on hardened ground unable to absorb it, leading to flash floods instead of a replenishment of soil moisture or groundwater levels.[33]
  • Increased evaporation will reduce the effectiveness of reservoirs.
  • At the same time, human demand for water will grow for the purposes of cooling and hydration.

Displacement and migration[edit]

See also: Environmental migrant

Climate change causes displacement of people in several ways, the most obvious—and dramatic—being through the increased number and severity of weather-related disasters which destroy homes and habitats causing people to seek shelter or livelihoods elsewhere. Effects of climate change such as desertification and rising sea levels gradually erode livelihood and force communities to abandon traditional homelands for more accommodating environments. This is currently happening in areas of Africa’s Sahel, the semi-arid belt that spans the continent just below its northern deserts. Deteriorating environments triggered by climate change can also lead to increased conflict over resources which in turn can displace people.[34]

The IPCC has estimated that 150 million environmental migrants will exist by the year 2050, due mainly to the effects of coastal flooding, shoreline erosion and agricultural disruption.[35] However, the IPCC also cautions that it is extremely difficult to measure the extent of environmental migration due to the complexity of the issue and a lack of data.[9]

According to the Internal Displacement Monitoring Centre, more than 42 million people were displaced in Asia and the Pacific during 2010 and 2011, more than twice the population of Sri Lanka. This figure includes those displaced by storms, floods, and heat and cold waves. Still others were displaced drought and sea-level rise. Most of those compelled to leave their homes eventually returned when conditions improved, but an undetermined number became migrants, usually within their country, but also across national borders.[36]

Asia and the Pacific is the global area most prone to natural disasters, both in terms of the absolute number of disasters and of populations affected. It is highly exposed to climate impacts, and is home to highly vulnerable population groups, who are disproportionately poor and marginalized. A recent Asian Development Bank report highlights “environmental hot spots” that are particular risk of flooding, cyclones, typhoons, and water stress.[37]

Some Pacific Ocean island nations, such as Tuvalu, Kiribati, and the Maldives,[38] are considering the eventual possibility of evacuation, as flood defense may become economically unrealistic. Tuvalu already has an ad hoc agreement with New Zealand to allow phased relocation.[39] However, for some islanders relocation is not an option. They are not willing to leave their homes, land and families. Some simply don’t know the threat that climate change has on their island and this is mainly down to the lack of awareness that climate change even exists. In Vutia on Viti Levu, Fiji’s main island, half the respondents to a survey had not heard of climate change (Lata and Nuun 2012). Even where there is awareness many believe that it is a problem caused by developed countries and should therefore be solved by developed countries.[40]

Governments have considered various approaches to reduce migration compelled by environmental conditions in at-risk communities, including programs of social protection, livelihoods development, basic urban infrastructure development, and disaster risk management. Some experts even support migration as an appropriate way for people to cope with environmental changes. However, this is controversial because migrants – particularly low-skilled ones – are among the most vulnerable people in society and are often denied basic protections and access to services.[37]

Climate change is only one factor that may contribute to a household's decision to migrate; other factors may include poverty, population growth or employment options.[41] For this reason, it is difficult to classify environmental migrants as actual "refugees" as legally defined by the UNHCR.[42] Neither the UN Framework Convention on Climate Change nor its Kyoto Protocol, an international agreement on climate change, includes any provisions concerning specific assistance or protection for those who will be directly affected by climate change.[43]

In small islands and megadeltas, inundation as a result of sea level rise is expected to threaten vital infrastructure and human settlements.[44][45] This could lead to issues of statelessness for populations in countries such as the Maldives and Tuvalu[46] and homelessness in countries with low-lying areas such as Bangladesh.

The World Bank predicts that a “severe hit” will spur conflict and migration across the Middle East, Central Asia, and Africa.[47]

Security[edit]

Main article: Climate security

Climate change has the potential to exacerbate existing tensions or create new ones — serving as a threat multiplier. It can be a catalyst for violent conflict and a threat to international security.[48][49] A meta-analysis of over 50 quantitative studies that examine the link between climate and conflict found that "for each 1 standard deviation (1σ) change in climate toward warmer temperatures or more extreme rainfall, median estimates indicate that the frequency of interpersonal violence rises 4% and the frequency of intergroup conflict rises 14%".[50][51] The IPCC has suggested that the disruption of environmental migration may serve to exacerbate conflicts,[52] though they are less confident of the role of increased resource scarcity.[9] Of course, climate change does not always lead to violence, and conflicts are often caused by multiple interconnected factors.[53]

A variety of experts have warned that climate change may lead to increased conflict. The Military Advisory Board, a panel of retired U.S. generals and admirals, predicted that global warming will serve as a "threat multiplier" in already volatile regions.[54] The Center for Strategic and International Studies and the Center for a New American Security, two Washington think tanks, have reported that flooding "has the potential to challenge regional and even national identities," leading to "armed conflict over resources." They indicate that the greatest threat would come from "large-scale migrations of people — both inside nations and across existing national borders."[55] However, other researchers have been more skeptical: One study found no statistically meaningful relationship between climate and conflict using data from Europe between the years 1000 and 2000.[56]

The link between climate change and security is a concern for authorities across the world, including United Nations Security Council and the G77 group of developing nations. Climate change's impact as a security threat is expected to hit developing nations particularly hard. In Britain, Foreign SecretaryMargaret Beckett has argued that "An unstable climate will exacerbate some of the core drivers of conflict, such as migratory pressures and competition for resources."[57] The links between the human impact of climate change and the threat of violence and armed conflict are particularly important because multiple destabilizing conditions are affected simultaneously.

Experts have suggested links to climate change in several major conflicts:

Additionally, researchers studying ancient climate patterns (paleoclimatology) have shown that long-term fluctuations of war frequency and population changes have followed cycles of temperature change since the preindustrial era.[68] A 2016 study finds that "drought can contribute to sustaining conflict, especially for agriculturally dependent groups and politically excluded groups in very poor countries. These results suggest a reciprocal nature–society interaction in which violent conflict and environmental shock constitute a vicious circle, each phenomenon increasing the group’s vulnerability to the other."[69]

Social impacts[edit]

See also: Climate change and gender

The consequences of climate change and poverty are not distributed uniformly within communities. Individual and social factors such as gender, age, education, ethnicity, geography and language lead to differential vulnerability and capacity to adapt to the effects of climate change. Climate change effects such as hunger, poverty and diseases like diarrhea and malaria, disproportionately impact children; about 90 percent of malaria and diarrhea deaths are among young children. Children are also 14–44 percent more likely to die from environmental factors,[70] again leaving them the most vulnerable.Those in urban areas will be affected by lower air quality and overcrowding, and will struggle the most to better their situation.[14]

Social effects of extreme weather[edit]

See also: List of costliest Atlantic hurricanes and Physical impacts of climate change

As the World Meteorological Organization explains, "recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions."[71] Pielke et al. (2008) normalized mainland U.S. hurricane damage from 1900 to 2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 has the second most damage among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane, with $157 billion of normalized damage.[72]

The American Insurance Journal predicted that "catastrophe losses should be expected to double roughly every 10 years because of increases in construction costs, increases in the number of structures and changes in their characteristics."[73] The Association of British Insurers has stated that limiting carbon emissions would avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s. The cost is also increasing partly because of building in exposed areas such as coasts and floodplains. The ABI claims that reduction of the vulnerability to some inevitable effects of climate change, for example through more resilient buildings and improved flood defences, could also result in considerable cost-savings in the longterm.[74]

Human settlement[edit]

Further information: Current sea level rise

A major challenge for human settlements is sea-level rise, indicated by ongoing observation and research of rapid declines in ice-mass balance from both Greenland and Antarctica. Estimates for 2100 are at least twice as large as previously estimated by IPCC AR4, with an upper limit of about two meters.[75] Depending on regional changes, increased precipitation patterns can cause more flooding or extended drought stresses water resources.

Coasts and low-lying areas[edit]

For historical reasons to do with trade, many of the world's largest and most prosperous cities are on the coast. In developing countries, the poorest often live on floodplains, because it is the only available space, or fertile agricultural land. These settlements often lack infrastructure such as dykes and early warning systems. Poorer communities also tend to lack the insurance, savings, or access to credit needed to recover from disasters.

In a journal paper, Nicholls and Tol (2006) considered the effects of sea level rise:[76]

The most vulnerable future worlds to sea-level rise appear to be the A2 and B2 [IPCC] scenarios, which primarily reflects differences in the socio-economic situation (coastal population, Gross Domestic Product (GDP) and GDP/capita), rather than the magnitude of sea-level rise. Small islands and deltaic settings stand out as being more vulnerable as shown in many earlier analyses. Collectively, these results suggest that human societies will have more choice in how they respond to sea-level rise than is often assumed. However, this conclusion needs to be tempered by recognition that we still do not understand these choices and significant impacts remain possible.

The IPCC reported that socioeconomic impacts of climate change in coastal and low-lying areas would be overwhelmingly adverse. The following impacts were projected with very high confidence:[77]

  • Coastal and low-lying areas would be exposed to increasing risks including coastal erosion due to climate change and sea level rise.
  • By the 2080s, millions of people would experience floods every year due to sea level rise. The numbers affected were projected to be largest in the densely populated and low-lying mega-deltas of Asia and Africa; and smaller islands were judged to be especially vulnerable.

A study in the April 2007 issue of Environment and Urbanization reports that 634 million people live in coastal areas within 30 feet (9.1 m) of sea level.[78] The study also reported that about two thirds of the world's cities with over five million people are located in these low-lying coastal areas.

Energy sector[edit]

Oil, coal and natural gas[edit]

Oil and natural gas infrastructure is vulnerable to the effects of climate change and the increased risk[citation needed] of disasters such as storm, cyclones, flooding and long-term increases in sea level. Minimising these risks by building in less disaster prone areas, can be expensive and impossible in countries with coastal locations or island states. All thermal power stations depend on water to cool them. Not only is there increased demand for fresh water, but climate change can increase the likelihood of drought and fresh water shortages. Another impact for thermal power plants, is that increasing the temperatures in which they operate reduces their efficiency and hence their output. The source of oil often comes from areas prone to high natural disaster risks; such as tropical storms, hurricanes, cyclones, and floods. An example is Hurricane Katrina's impact on oil extraction in the Gulf of Mexico, as it destroyed 126 oil and gas platforms and damaged 183 more.[79]

However, previously pristine arctic areas will now be available for resource extraction[80]

Nuclear[edit]

Climate change, along with extreme weather and natural disasters can affect nuclear power plants in a similar way to those using oil, coal, and natural gas. However, the impact of water shortages on nuclear power plants cooled by rivers will be greater than on other thermal power plants. This is because old reactor designs with water-cooled cores must run at lower internal temperatures and thus, paradoxically, must dump more heat to the environment to produce a given amount of electricity. This situation has forced some nuclear reactors to be shut down and will do so again unless the cooling systems of these plants are enhanced to provide more capacity. Nuclear power supply was diminished by low river flow rates and droughts, which meant rivers had reached the maximum temperatures for cooling. Such shutdowns happened in France during the 2003 and 2006 heat waves. During the heat waves, 17 reactors had to limit output or shut down. 77% of French electricity is produced by nuclear power; and in 2009 a similar situation created a 8GW shortage, and forced the French government to import electricity. Other Cases have been reported from Germany, where extreme temperatures have reduced nuclear power production 9 times due to high temperatures between 1979 and 2007. In particular:

Similar events have happened elsewhere in Europe during those same hot summers. Many scientists agree that if global warming continues, this disruption is likely to increase.[79]

Hydroelectricity[edit]

Changes in the amount of river flow will correlate with the amount of energy produced by a dam. Lower river flows because of drought, climate change, or upstream dams and diversions, will reduce the amount of live storage in a reservoir; therefore reducing the amount of water that can be used for hydroelectricity. The result of diminished river flow can be a power shortage in areas that depend heavily on hydroelectric power. The risk of flow shortage may increase as a result of climate change. Studies from the Colorado River in the United States suggests that modest climate changes (such as a 2 degree change in Celsius that could result in a 10% decline in precipitation), might reduce river run-off by up to 40%. Brazil in particular, is vulnerable due to its having reliance on hydroelectricity as increasing temperatures, lower water flow, and alterations in the rainfall regime, could reduce total energy production by 7% annually by the end of the century.[79]

Cost[edit]

The scientific evidence for links between global warming and the increasing cost of natural disasters due to weather events[81] is weak, but, nevertheless, prominent mainstream environmental spokesmen such as Barack Obama and Al Gore have emphasized the possible connection.[82] For the most part increased costs due to events such as Hurricane Sandy[83] are due to increased exposure to loss resulting from building insured facilities in vulnerable locations.[84] This information has been denounced by Paul Krugman[85] and ThinkProgress as climate change denial.[86]

Insurance[edit]

An industry directly affected by the risks of climate change is the insurance industry.[87] According to a 2005 report from the Association of British Insurers, limiting carbon emissions could avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s.[88] A June 2004 report by the Association of British Insurers declared "Climate change is not a remote issue for future generations to deal with; it is, in various forms here already, impacting on insurers' businesses now."[89] The report noted that weather-related risks for households and property were already increasing by 2–4% per year due to the changing weather conditions, and claims for storm and flood damages in the UK had doubled to over £6 billion over the period from 1998–2003 compared to the previous five years. The results are rising insurance premiums, and the risk that in some areas flood insurance will become unaffordable for those in the lower income brackets.

Financial institutions, including the world's two largest insurance companies: Munich Re and Swiss Re, warned in a 2002 study that "the increasing frequency of severe climatic events, coupled with social trends could cost almost 150 billion US$ each year in the next decade".[90] These costs would burden customers, taxpayers, and the insurance industry, with increased costs related to insurance and disaster relief.

In the United States, insurance losses have also greatly increased. It has been shown that a 1% climb in annual precipitation can increase catastrophe loss by as much as 2.8%.[91] Gross increases are mostly attributed to increased population and property values in vulnerable coastal areas; though there was also an increase in frequency of weather-related events like heavy rainfalls since the 1950s.[92]

Transport[edit]

Roads, airport runways, railway lines and pipelines, (including oil pipelines, sewers, water mains etc.) may require increased maintenance and renewal as they become subject to greater temperature variation. Regions already adversely affected include areas of permafrost, which are subject to high levels of subsidence, resulting in buckling roads, sunken foundations, and severely cracked runways.[93]

See also[edit]

References[edit]

  1. ^America's Climate Choices. Washington, D.C.: The National Academies Press. 2011. p. 15. ISBN 978-0-309-14585-5.  
  2. ^MPIBGC/PH (2013). "Extreme meteorological events and global warming: a vicious cycle?". Max Planck Research. 
  3. ^Tang, Ying, S. Zhong, L. Luo, X. Bian, W.E. Heilman, J. Winkler. "The Potential Impact of Regional Climate Change on Fire Weather in the United States". Annals of the Association of American Geographers. 105 (1): 1–21. doi:10.1080/00045608.2014.968892. 
  4. ^Sahney, S., Benton, M.J. and Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land"(PDF). Biology Letters. 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC 2936204. PMID 20106856. 
  5. ^A. J. McMichael (2003). A. McMichael; D. Campbell-Lendrum; C. Corvalan; K. Ebi; A. Githeko; J. Scheraga; A. Woodward, eds. "Global Climate Change and Health: An Old Story Writ Large". World Health Organization. Geneva. 
  6. ^"Ghfgeneva.org"(PDF). Archived from the original(PDF) on 10 April 2011. 
  7. ^"Oxfam GB - leading UK charity fighting global poverty"(PDF). Oxfam GB. 
  8. ^"Yale Environment 360: Study Claims 300,000 Deaths Attributable to Global Warming Each Year". 
  9. ^ abcWilbanks, T.J.; et al. (2007). "Industry, settlement and society. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change Parry et al. (eds.)". Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A. Retrieved 20 May 2009. . PDF version with page numbers.
  10. ^A.J. McMichael; R. Woodruff; S. Hales (2006). "Climate Change and Human Health: Present and Future Risks". Lancet. 367 (9513): 859–69. doi:10.1016/S0140-6736(06)68079-3. PMID 16530580. 
  11. ^http://www.wmo.int/pages/publications/bulletin_en/documents/57_4_short_en.pdfWMO
  12. ^Lunde, T.M.; Lindtjørn, B. (2013). "Cattle and climate in Africa: How climate variability has influenced national cattle holdings from 1961–2008". PeerJ. 1 (1): e55. doi:10.7717/peerj.55. 
  13. ^Munich Climate-Insurance Initiative (2013). "Climate Change and Rising Weather Related Disasters". 
  14. ^ ab"WHO - The global burden of disease: 2004 update". 
  15. ^"- Human Development Reports"(PDF). Archived from the original(PDF) on 29 April 2011. 
  16. ^Doherty, Thomas J.; Clayton, Susan (2011). "The psychological impacts of global climate change". PsycNET. 66 (4): 265–276. doi:10.1037/a0023141. 
  17. ^Ranney, Michael Andrew; Clark, Dav (2016-01-01). "Climate Change Conceptual Change: Scientific Information Can Transform Attitudes". Topics in Cognitive Science. 8 (1): 49–75. doi:10.1111/tops.12187. ISSN 1756-8765. 
  18. ^ abcP. Epstein (2002). "Climate Change and Infectious Disease: Stormy Weather Ahead?". Epidemiology. 13 (4): 373–375. doi:10.1097/00001648-200207000-00001. 
  19. ^Daniel P. Bebber; Mark A. T. Ramotowski; Sarah J. Gurr (2013). "Crop pests and pathogens move polewards in a warming world". Nature Climate Change. 3: 985–988. Bibcode:2013NatCC...3..985B. doi:10.1038/nclimate1990. 
  20. ^ abcJ. Patz; S. Olson (2006). "Malaria Risk and Temperature: Influences from Global Climate Change and Local Land Use Practices". Proceedings of the National Academy of Sciences. 103 (15): 5635–5636. Bibcode:2006PNAS..103.5635P. doi:10.1073/pnas.0601493103. PMC 1458623. PMID 16595623. 
  21. ^S. Bhattacharya; C. Sharma; R. Dhiman; A. Mitra (2006). "Climate Change and Malaria in India". Current Science. 90 (3): 369–375. 
  22. ^"Nigeria: Duration of the Malaria Transmission Season"(PDF). mara.org.za. MARA/ARMA (Mapping Malaria Risk in Africa / Atlas du Risque de la Malaria en Afrique). July 2001. Archived from the original(PDF) on 2005-12-10. Retrieved 24 January 2007. 
  23. ^J. Patz; D. Campbell-Lendrum; T. Holloway; J. Foley (2005). "Impact of Regional Climate Change on Human Health". Nature. 438 (7066): 310–317. Bibcode:2005Natur.438..310P. doi:10.1038/nature04188. 
  24. ^J. Patz; A.K. Githeko; J.P. McCarty; S. Hussein; U. Confalonieri; N. de Wet (2003). A. McMichael; D. Campbell-Lendrum; C. Corvalan; K. Ebi; A. Githeko; J. Scheraga; A. Woodward, eds. "Climate Change and Infectious Diseases". Climate Change and Human Health: Risks and Responses. Geneva: World Health Organization. 
  25. ^Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica"(PDF). Geology. 38 (12): 1079–1082.
Flooding in the U.S. Midwest, June 2008

This article is primarily about effects during the 21st century. For longer-term effects, see Long-term effects of global warming. See also Effects of global warming on humans.

The effects of global warming are the environmental and social changes caused (directly or indirectly) by human emissions of greenhouse gases. There is a scientific consensus that climate change is occurring, and that human activities are the primary driver.[1] Many impacts of climate change have already been observed, including glacier retreat,[2] changes in the timing of seasonal events[2] (e.g., earlier flowering of plants),[3] and changes in agricultural productivity.[2]

Future effects of climate change will vary depending on climate change policies[4] and social development.[5] The two main policies to address climate change are reducing human greenhouse gas emissions (climate change mitigation) and adapting to the impacts of climate change.[6]Geoengineering is another policy option.[6]

Near-term climate change policies could significantly affect long-term climate change impacts.[4][7] Stringent mitigation policies might be able to limit global warming (in 2100) to around 2 °C or below, relative to pre-industrial levels.[8] Without mitigation, increased energy demand and extensive use of fossil fuels[9] might lead to global warming of around 4 °C.[10][11] Higher magnitudes of global warming would be more difficult to adapt to,[12] and would increase the risk of negative impacts.[13]

Definitions

See also: attribution of recent climate change

In this article, "climate change" means a change in climate that persists over a sustained period of time.[14][15] The World Meteorological Organization defines this time period as 30 years.[14] Examples of climate change include increases in global surface temperature (global warming), changes in rainfall patterns, and changes in the frequency of extreme weather events. Changes in climate may be due to natural causes, e.g., changes in the sun's output, or due to human activities, e.g., changing the composition of the atmosphere.[16] Any human-induced changes in climate will occur against a background of natural climatic variations[16] and of variations in human activity such as population growth on shores or in arid areas which increase or decrease climate vulnerability.[17]

Also, the term "anthropogenic forcing" refers to the influence exerted on a habitat or chemical environment by humans, as opposed to a natural process.[18]

Temperature changes

This article breaks down some of the impacts of climate change according to different levels of future global warming. This way of describing impacts has, for instance, been used in the IPCC (Intergovernmental Panel on Climate Change) Assessment Reports on climate change.[20] The instrumental temperature record shows global warming of around 0.6 °C during the 20th century.[21] In a study carried out by David R. Easterling et al., trends were observed over a period of time. “It is clear from the observed record that there has been an increase in the global mean temperature of about 0.6℃ since the start of the 20th century and that this increase is associated with a stronger warming in daily minimum temperatures than in maximums leading to a reduction in the diurnal temperature range.”[22]

SRES emissions scenarios

The future level of global warming is uncertain, but a wide range of estimates (projections) have been made.[23] The IPCC's "SRES" scenarios have been frequently used to make projections of future climate change.[24]:22–24 The SRES scenarios are "baseline" (or "reference") scenarios, which means that they do not take into account any current or future measures to limit GHG emissions (e.g., the UNFCCC's Kyoto Protocol and the Cancún agreements).[25] Emissions projections of the SRES scenarios are broadly comparable in range to the baseline emissions scenarios that have been developed by the scientific community.[23][26]

In the IPCC Fourth Assessment Report, changes in future global mean temperature were projected using the six SRES "marker" emissions scenarios.[27] Emissions projections for the six SRES "marker" scenarios are representative of the full set of forty SRES scenarios.[28] For the lowest emissions SRES marker scenario ("B1" – see the SRES article for details on this scenario), the best estimate for global mean temperature is an increase of 1.8 °C (3.2 °F)[27] by the end of the 21st century. This projection is relative to global temperatures at the end of the 20th century.[29] The "likely" range (greater than 66% probability, based on expert judgement)[30] for the SRES B1 marker scenario is 1.1–2.9 °C (2.0–5.2 °F).[27] For the highest emissions SRES marker scenario (A1FI), the best estimate for global mean temperature increase is 4.0 °C (7.2 °F), with a "likely" range of 2.4–6.4 °C (4.3–11.5 °F).[27]

The range in temperature projections partly reflects (1) the choice of emissions scenario, and (2) the "climate sensitivity".[24]:22–24 For (1), different scenarios make different assumptions of future social and economic development (e.g., economic growth, population level, energy policies), which in turn affects projections of greenhouse gas (GHG) emissions.[24]:22–24 The projected magnitude of warming by 2100 is closely related to the level of cumulative emissions over the 21st century (i.e. total emissions between 2000–2100).[31] The higher the cumulative emissions over this time period, the greater the level of warming is projected to occur.[31]

(2) reflects uncertainty in the response of the climate system to past and future GHG emissions, which is measured by the climate sensitivity.[24]:22–24 Higher estimates of climate sensitivity lead to greater projected warming, while lower estimates of climate sensitivity lead to less projected warming.[32]

Over the next several millennia, projections suggest that global warming could be irreversible.[33] Even if emissions were drastically reduced, global temperatures would remain close to their highest level for at least 1,000 years (see the later section on irreversibilities).[34][35]

Projected warming in context

Global surface temperature for the past 5.3 million years as inferred from cores of ocean sediments taken all around the global ocean. The last 800,000 years are expanded in the lower half of the figure (image credit: NASA).[36]

Scientists have used various "proxy" data to assess past changes in Earth's climate (paleoclimate).[37] Sources of proxy data include historical records (such as farmers' logs), tree rings, corals, fossil pollen, ice cores, and ocean and lake sediments.[37] Analysis of these data suggest that recent warming is unusual in the past 400 years, possibly longer.[38] By the end of the 21st century, temperatures may increase to a level not experienced since the mid-Pliocene, around 3 million years ago.[39] At that time, models suggest that mean global temperatures were about 2–3 °C warmer than pre-industrial temperatures.[39] Even a 2 °C rise above the pre-industrial level would be outside the range of temperatures experienced by human civilization.[36][40]

Physical impacts

Main article: Physical impacts of climate change

Seven of these indicators would be expected to increase in a warming world and observations show that they are, in fact, increasing. Three would be expected to decrease and they are, in fact, decreasing.[41]

A broad range of evidence shows that the climate system has warmed.[43] Evidence of global warming is shown in the graphs opposite. Some of the graphs show a positive trend, e.g., increasing temperature over land and the ocean, and sea level rise. Other graphs show a negative trend, e.g., decreased snow cover in the Northern Hemisphere, and declining Arctic sea ice extent. Evidence of warming is also apparent in living (biological) systems.[44]

Human activities have contributed to a number of the observed changes in climate.[45] This contribution has principally been through the burning of fossil fuels, which has led to an increase in the concentration of GHGs in the atmosphere.[46] Another human influence on the climate are sulfur dioxide emissions, which are a precursor to the formation of sulfate aerosols in the atmosphere.[47]

Human-induced warming could lead to large-scale, irreversible, and/or abrupt changes in physical systems.[48][49] An example of this is the melting of ice sheets, which contributes to sea level rise.[50] The probability of warming having unforeseen consequences increases with the rate, magnitude, and duration of climate change.[51]

Effects on weather

Observations show that there have been changes in weather.[52] As climate changes, the probabilities of certain types of weather events are affected.

Changes have been observed in the amount, intensity, frequency, and type of precipitation.[24]:18 Widespread increases in heavy precipitation have occurred, even in places where total rain amounts have decreased. With medium confidence (see footnote 1), IPCC (2012)[55] concluded that human influences had contributed to an increase in heavy precipitation events at the global scale.

Projections of future changes in precipitation show overall increases in the global average, but with substantial shifts in where and how precipitation falls.[24]:24 Projections suggest a reduction in rainfall in the subtropics, and an increase in precipitation in subpolar latitudes and some equatorial regions.[54] In other words, regions which are dry at present will in general become even drier, while regions that are currently wet will in general become even wetter.[54] This projection does not apply to every locale, and in some cases can be modified by local conditions.[54]

Extreme weather

See also: Extreme weather and Tropical cyclone § Global warming

Over most land areas since the 1950s, it is very likely that there have been fewer or warmer cold days and nights.[56] Hot days and nights have also very likely become warmer or more frequent.[56] Human activities have very likely contributed to these trends.[56] There may have been changes in other climate extremes (e.g., floods, droughts and tropical cyclones) but these changes are more difficult to identify.[56]

Projections suggest changes in the frequency and intensity of some extreme weather events.[56] Confidence in projections varies over time.[56]

Near-term projections (2016–2035)

Some changes (e.g., more frequent hot days) will probably be evident in the near term, while other near-term changes (e.g., more intense droughts and tropical cyclones) are more uncertain.[56]

Long-term projections (2081–2100)

Future climate change will be associated with more very hot days and fewer very cold days.[56] The frequency, length and intensity of heat waves will very likely increase over most land areas.[56] Higher growth in anthropogenic GHG emissions will be associated with larger increases in the frequency and severity of temperature extremes.[57]

Assuming high growth in GHG emissions (IPCC scenario RCP8.5), presently dry regions may be affected by an increase in the risk of drought and reductions in soil moisture.[58] Over most of the mid-latitude land masses and wet tropical regions, extreme precipitation events will very likely become more intense and frequent.[56]

Tropical cyclones

At the global scale, the frequency of tropical cyclones will probably decrease or be unchanged.[59] Global mean tropical cyclone maximum wind speed and precipitation rates will likely increase.[59] Changes in tropical cyclones will probably vary by region, but these variations are uncertain.[59]

Effects of climate extremes

The impacts of extreme events on the environment and human society will vary. Some impacts will be beneficial—e.g., fewer cold extremes will probably lead to fewer cold deaths.[60] Overall, however, impacts will probably be mostly negative.[61][62] A rise in temperature will cause the glaciers to melt, when water heats up, it expands, both of these factors contribute to a rise in sea levels which will put people living in lowland areas, for example The Netherlands in danger.

Cryosphere

See also: Retreat of glaciers since 1850

The cryosphere is made up of areas of the Earth which are covered by snow or ice.[63] Observed changes in the cryosphere include declines in Arctic sea ice extent,[64] the widespread retreat of alpine glaciers,[65] and reduced snow cover in the Northern Hemisphere.[66]

Solomon et al. (2007)[67] assessed the potential impacts of climate change on summertime Arctic sea ice extent. Assuming high growth in greenhouse gas emissions (SRES A2), some models projected that Arctic sea ice in the summer could largely disappear by the end of the 21st century.[67] More recent projections suggest that the Arctic summers could be ice-free (defined as ice extent less than 1 million square km) as early as 2025–2030.[68]

During the 21st century, glaciers[69] and snow cover are projected to continue their widespread retreat.[70] In the western mountains of North America, increasing temperatures and changes in precipitation are projected to lead to reduced snowpack.[71] Snowpack is the seasonal accumulation of slow-melting snow.[72] The melting of the Greenland and West Antarctic ice sheets could contribute to sea level rise, especially over long time-scales (see the section on Greenland and West Antarctic Ice sheets).[50]

Changes in the cryosphere are projected to have social impacts.[73] For example, in some regions, glacier retreat could increase the risk of reductions in seasonal water availability.[74] Barnett et al. (2005)[75] estimated that more than one-sixth of the world's population rely on glaciers and snowpack for their water supply.

Oceans

Main article: Effects of global warming on oceans

The role of the oceans in global warming is complex. The oceans serve as a sink for carbon dioxide, taking up much that would otherwise remain in the atmosphere, but increased levels of CO
2 have led to ocean acidification. Furthermore, as the temperature of the oceans increases, they become less able to absorb excess CO
2. The ocean have also acted as a sink in absorbing extra heat from the atmosphere.[76]:4 The increase in ocean heat content is much larger than any other store of energy in the Earth’s heat balance over the two periods 1961 to 2003 and 1993 to 2003, and accounts for more than 90% of the possible increase in heat content of the Earth system during these periods.[77]

Global warming is projected to have a number of effects on the oceans. Ongoing effects include rising sea levels due to thermal expansion and melting of glaciers and ice sheets, and warming of the ocean surface, leading to increased temperature stratification. Other possible effects include large-scale changes in ocean circulation.

Acidification

Main article: Ocean acidification

About one-third of the carbon dioxide emitted by human activity has already been taken up by the oceans.[79] As carbon dioxide dissolves in sea water, carbonic acid is formed, which has the effect of acidifying the ocean, measured as a change in pH. The uptake of human carbon emissions since the year 1750 has led to an average decrease in pH of 0.1 units.[80] Projections using the SRES emissions scenarios suggest a further reduction in average global surface ocean pH of between 0.14 and 0.35 units over the 21st century.

The effects of ocean acidification on the marine biosphere have yet to be documented.[80] Laboratory experiments suggest beneficial effects for a few species, with potentially highly detrimental effects for a substantial number of species.[79] With medium confidence, Fischlin et al. (2007)[81] projected that future ocean acidification and climate change would impair a wide range of planktonic and shallow benthic marine organisms that use aragonite to make their shells or skeletons, such as corals and marine snails (pteropods), with significant impacts particularly in the Southern Ocean.

Oxygen depletion

The amount of oxygen dissolved in the oceans may decline, with adverse consequences for ocean life.[82][83]

Sea level rise

Main article: Current sea level rise

See also: Future sea level

There is strong evidence that global sea level rose gradually over the 20th century.[85] With high confidence, Bindoff et al. (2007)[86] concluded that between the mid-19th and mid-20th centuries, the rate of sea level rise increased. Authors of the IPCC Fourth Assessment Synthesis Report (IPCC AR4 SYR, 2007)[21] reported that between the years 1961 and 2003, global average sea level rose at an average rate of 1.8 mm per year (mm/yr), with a range of 1.3–2.3 mm/yr. Between 1993 and 2003, the rate increased above the previous period to 3.1 mm/yr (range of 2.4–3.8 mm/yr). Authors of IPCC AR4 SYR (2007)[21] were uncertain whether the increase in rate from 1993 to 2003 was due to natural variations in sea level over the time period, or whether it reflected an increase in the underlying long-term trend.

There are two main factors that have contributed to observed sea level rise.[85] The first is thermal expansion: as ocean water warms, it expands.[87] The second is from the contribution of land-based ice due to increased melting. The major store of water on land is found in glaciers and ice sheets. Anthropogenic forces very likely (greater than 90% probability, based on expert judgement)[30] contributed to sea level rise during the latter half of the 20th century.[45]

There is a widespread consensus that substantial long-term sea level rise will continue for centuries to come.[88] In their Fourth Assessment Report, the IPCC[89] projected sea level rise to the end of the 21st century using the SRES emissions scenarios. Across the six SRES marker scenarios, sea level was projected to rise by 18 to 59 cm (7.1 to 23.2 in), relative to sea level at the end of the 20th century.[90] Thermal expansion is the largest component in these projections, contributing 70–75% of the central estimate for all scenarios.[91] Due to a lack of scientific understanding, this sea level rise estimate does not include all of the possible contributions of ice sheets (see the section on Greenland and West Antarctic Ice sheets).

An assessment of the scientific literature on climate change was published in 2010 by the US National Research Council (US NRC, 2010).[92] NRC (2010)[92] described the projections in AR4 (i.e. those cited in the above paragraph) as "conservative", and summarized the results of more recent studies. Cited studies suggested a great deal of uncertainty in projections.[92] A range of projections suggested possible sea level rise by the end of the 21st century of between 0.56 and 2 m, relative to sea levels at the end of the 20th century.[92]

Ocean temperature rise

From 1961 to 2003, the global ocean temperature has risen by 0.10 °C from the surface to a depth of 700 m. There is variability both year-to-year and over longer time scales, with global ocean heat content observations showing high rates of warming for 1991–2003, but some cooling from 2003 to 2007.[93] The temperature of the Antarctic Southern Ocean rose by 0.17 °C (0.31 °F) between the 1950s and the 1980s, nearly twice the rate for the world's oceans as a whole.[94] As well as having effects on ecosystems (e.g. by melting sea ice, affecting algae that grow on its underside), warming reduces the ocean's ability to absorb CO
2.[citation needed] It is likely (greater than 66% probability, based on expert judgement)[30] that anthropogenic forcing contributed to the general warming observed in the upper several hundred metres of the ocean during the latter half of the 20th century.[45]

Regions

Main article: Regional effects of global warming

Regional effects of global warming vary in nature. Some are the result of a generalised global change, such as rising temperature, resulting in local effects, such as melting ice. In other cases, a change may be related to a change in a particular ocean current or weather system. In such cases, the regional effect may be disproportionate and will not necessarily follow the global trend.

There are three major ways in which global warming will make changes to regional climate: melting or forming ice, changing the hydrological cycle (of evaporation and precipitation) and changing currents in the oceans and air flows in the atmosphere. The coast can also be considered a region, and will suffer severe impacts from sea level rise.

Observed impacts

With very high confidence, Rosenzweig et al. (2007)[44] concluded that physical and biological systems on all continents and in most oceans had been affected by recent climate changes, particularly regional temperature increases. Impacts include earlier leafing of trees and plants over many regions; movements of species to higher latitudes and altitudes in the Northern Hemisphere; changes in bird migrations in Europe, North America and Australia; and shifting of the oceans' plankton and fish from cold- to warm-adapted communities.[96]

The human influence on the climate can be seen in the geographical pattern of observed warming, with greater temperature increases over land and in polar regions rather than over the oceans.[97]:6 Using models, it is possible to identify the human "signal" of global warming over both land and ocean areas.[97]:6

Projected impacts

Projections of future climate changes at the regional scale do not hold as high a level of scientific confidence as projections made at the global scale.[97]:9 It is, however, expected that future warming will follow a similar geographical pattern to that seen already, with greatest warming over land and high northern latitudes, and least over the Southern Ocean and parts of the North Atlantic Ocean.[98] Nearly all land areas will very likely warm more than the global average.[99]

The Arctic, Africa, small islands and Asianmegadeltas are regions that are likely to be especially affected by climate change.[100]Low-latitude, less-developed areas are at most risk of experiencing negative impacts due to climate change.[101]Developed countries are also vulnerable to climate change.[102] For example, developed countries will be negatively affected by increases in the severity and frequency of some extreme weather events, such as heat waves.[102] In all regions, some people can be particularly at risk from climate change, such as the poor, young children and the elderly.[100][101][103]

Social systems

Main articles: Effects of climate change on humans and Climate change, industry and society

See also: Climate change and gender

The impacts of climate change can be thought of in terms of sensitivity and vulnerability. "Sensitivity" is the degree to which a particular system or sector might be affected, positively or negatively, by climate change and/or climate variability. "Vulnerability" is the degree to which a particular system or sector might be adversely affected by climate change.[104]

The sensitivity of human society to climate change varies. Sectors sensitive to climate change include water resources, coastal zones, human settlements, and human health. Industries sensitive to climate change include agriculture, fisheries, forestry, energy, construction, insurance, financial services, tourism, and recreation.[105][106]

Food supply

Main article: Climate change and agriculture

See also: Food security, Food vs fuel, and 2007–2008 world food price crisis

Climate change will impact agriculture and food production around the world due to: the effects of elevated CO2 in the atmosphere, higher temperatures, altered precipitation and transpiration regimes, increased frequency of extreme events, and modified weed, pest, and pathogen pressure.[107] In general, low-latitude areas are at most risk of having decreased crop yields.[108]

As of 2007, the effects of regional climate change on agriculture have been small.[44] Changes in crop phenology provide important evidence of the response to recent regional climate change.[109] Phenology is the study of natural phenomena that recur periodically, and how these phenomena relate to climate and seasonal changes.[110] A significant advance in phenology has been observed for agriculture and forestry in large parts of the Northern Hemisphere.[44]

Projections

With low to medium confidence, Schneider et al. (2007)[20] projected that for about a 1 to 3 °C increase in global mean temperature (by the years 2090–2100, relative to average temperatures in the years 1990–2000), there would be productivity decreases for some cereals in low latitudes, and productivity increases in high latitudes. With medium confidence, global production potential was projected to:[20]

  • increase up to around 3 °C,
  • very likely decrease above about 3 °C.

Most of the studies on global agriculture assessed by Schneider et al. (2007)[108] had not incorporated a number of critical factors, including changes in extreme events, or the spread of pests and diseases. Studies had also not considered the development of specific practices or technologies to aid adaptation to climate change.[108]

The graphs opposite show the projected effects of climate change on selected crop yields.[112] Actual changes in yields may be above or below these central estimates.[112]

The projections above can be expressed relative to pre-industrial (1750) temperatures.[113] 0.6 °C of warming is estimated to have occurred between 1750 and 1990–2000. Add 0.6 °C to the above projections to convert them from a 1990–2000 to pre-industrial baseline.

Food security

Easterling et al. (2007)[114] assessed studies that made quantitative projections of climate change impacts on food security. It was noted that these projections were highly uncertain and had limitations. However, the assessed studies suggested a number of fairly robust findings. The first was that climate change would likely increase the number of people at risk of hunger compared with reference scenarios with no climate change. Climate change impacts depended strongly on projected future social and economic development. Additionally, the magnitude of climate change impacts was projected to be smaller compared to the impact of social and economic development. In 2006, the global estimate for the number of people undernourished was 820 million.[115] Under the SRES A1, B1, and B2 scenarios (see the SRES article for information on each scenario group), projections for the year 2080 showed a reduction in the number of people undernourished of about 560–700 million people, with a global total of undernourished people of 100–240 million in 2080. By contrast, the SRES A2 scenario showed only a small decrease in the risk of hunger from 2006 levels. The smaller reduction under A2 was attributed to the higher projected future population level in this scenario.

Droughts and agriculture

Some evidence suggests that droughts have been occurring more frequently because of global warming and they are expected to become more frequent and intense in Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia.[116] However, other research suggests that there has been little change in drought over the past 60 years.[117] Their impacts are aggravated because of increased water demand, population growth, urban expansion, and environmental protection efforts in many areas.[118] Droughts result in crop failures and the loss of pasture grazing land for livestock.[119]

Health

Main article: Effects of global warming on human health

Human beings are exposed to climate change through changing weather patterns (temperature, precipitation, sea-level rise and more frequent extreme events) and indirectly through changes in water, air and food quality and changes in ecosystems, agriculture, industry and settlements and the economy (Confalonieri et al., 2007:393).[60] According to an assessment of the scientific literature by Confalonieri et al. (2007:393),[60] the effects of climate change to date have been small, but are projected to progressively increase in all countries and regions.

A study by the World Health Organization (WHO, 2009)[120] estimated the effect of climate change on human health. Not all of the effects of climate change were included in their estimates, for example, the effects of more frequent and extreme storms were excluded. Climate change was estimated to have been responsible for 3% of diarrhoea, 3% of malaria, and 3.8% of dengue fever deaths worldwide in 2004. Total attributable mortality was about 0.2% of deaths in 2004; of these, 85% were child deaths.

Projections

With high confidence, authors of the IPCC AR4 Synthesis report[121]:48 projected that climate change would bring some benefits in temperate areas, such as fewer deaths from cold exposure, and some mixed effects such as changes in range and transmission potential of malaria in Africa. Benefits were projected to be outweighed by negative health effects of rising temperatures, especially in developing countries.

With very high confidence, Confalonieri et al. (2007)[60]:393

A summary of climate change impacts
Projected global warming in 2100 for a range of emission scenarios

Global mean surface temperature change since 1880, relative to the 1951–1980 mean. Source: NASA GISS

The graph above shows the average of a set of temperature simulations for the 20th century (black line), followed by projected temperatures for the 21st century based on three greenhouse gas emissions scenarios (colored lines).[19]

This set of graphs show changes in climate indicators over several decades. Each of the different colored lines in each panel represents an independently analyzed set of data. The data come from many different technologies including weather stations, satellites, weather balloons, ships and buoys.[42]
A map of the change in thickness of mountain glaciers since 1970. Thinning in orange and red, thickening in blue.
A map that shows ice concentration on 16 September 2012, along with the extent of the previous record low (yellow line) and the mid-September median extent (black line) setting a new record low that was 18 percent smaller than the previous record and nearly 50 percent smaller than the long-term (1979–2000) average.
This map shows changes in the amount of aragonite dissolved in ocean surface waters between the 1880s and the most recent decade (2003–2012).[78] Historical modeling suggests that since the 1880s, increased CO2 has led to lower aragonite saturation levels (less availability of minerals) in the oceans around the world.[78] The largest decreases in aragonite saturation have occurred in tropical waters.[78] However, decreases in cold areas may be of greater concern because colder waters typically have lower aragonite levels to begin with.[78]
Trends in global average absolute sea level, 1870–2008.[84]
Global ocean heat content from 1955–2012

Temperatures across the world in the 1880s (left) and the 1980s (right), as compared to average temperatures from 1951 to 1980.[95]

Projected changes in average temperatures across the world in the 2050s under three greenhouse gas (GHG) emissions scenarios.[19]

Graph of net crop production worldwide and in selected tropical countries. Raw data from the United Nations. [2]
Projected changes in crop yields at different latitudes with global warming. This graph is based on several studies.[111]
Projected changes in yields of selected crops with global warming. This graph is based on several studies.[111]

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