Increasingly severe consequences of climate change (GMT 9)

Briefing Published 18 Feb 2015 Last modified 01 Jun 2015, 02:07 PM

Recent changes in the global climate are unprecedented over millennia and will continue. Climate change is expected increasingly to threaten natural ecosystems and biodiversity, slow economic growth, erode global food security, harm human health and increase inequality.

The risks of pervasive and irreversible impacts are expected to increase. They could, however, be reduced by further emissions abatement and adaptation measures, building on past actions in Europe and internationally. Key risks for Europe include flood events, droughts and other weather extremes that damage ecosystems and biodiversity, as well as infrastructure and human well-being.

Drivers

The evidence is clear. Climate change is real, and it is largely caused by human activities, primarily greenhouse gas emissions from fossil fuel burning, but also from other activities such as agriculture and deforestation. Through these activities, atmospheric concentrations of greenhouse gases such as carbon dioxide, methane or ozone have increased, causing the Earth to warm. Carbon dioxide concentrations have increased by about 40 % since 1750, with most of the increase since the 1970s when global energy consumption started to increase strongly.[1] Evidence from ice cores suggest that current carbon dioxide concentrations are higher than at any other time over the last 800 000 years.[2]

Recent progress in climate science allows for a clear attribution of the human contribution to changes in many components of the climate system.[1] It is extremely likely[3] that most of the observed rise in global surface temperature since the mid-20th century was caused by increases in greenhouse gas emissions and other anthropogenic activities. It is also very likely that human influence has substantially contributed to increases in upper ocean temperatures, Arctic sea-ice loss, global mean sea-level rise and changes in the frequency and intensity of temperature extremes, such as heat waves, since the mid-20th century.[1] There have been no significant long-term changes in the sun’s energy output that could have contributed to the observed climatic changes.[1]

Figure 1: Projected changes in average temperature, 2081–2100 relative to 1986–2005 for low-emission (left: RCP 2.6) and high-emission (right: RCP 8.5) scenarios.[1]

Data source: IPCC (2013)  

Trends

Observed changes

The Earth’s combined land and ocean surface temperature has warmed by 0.85 (0.65–1.06) °C between 1880 and 2012, and the number of hot days and nights[4] has increased over most land areas. Multiannual and decadal variability caused by natural factors does not contradict this long-term global warming trend. Observed warming is accompanied by significant reductions in ice and snow cover across the world – the minimum summer extent of Arctic sea ice has decreased by about 40 % since 1979.[1]

Observed changes in precipitation show strong regional variations. In many regions, including Europe and North America, increases in either the frequency or intensity of heavy precipitation events have been observed. In contrast, climate records show an increased frequency and intensity of drought events in the Mediterranean and parts of Africa.[1]

Global sea levels have risen by about 20 cm since 1901 due to thermal expansion and the melting of glaciers and ice sheets. The rate of increase has risen from 1.7 mm for 1901–2010 to 3.2 mm for 1993–2010.[1]

Projected future changes[5]

By the late 21st century (2081–2100), global mean surface temperature is expected to increase by another 2.6–4.8 °C compared to the reference period (1986–2005) if greenhouse gas emissions continue on a high trajectory (RCP 8.5; Figure 1, right). Strong emissions abatement could limit this to 0.3–1.7 °C (RCP 2.6; Figure 1, left).[1] To have a two-thirds chance of keeping the global mean surface temperature rise to below 2 °C compared to the pre-industrial period, the target of the United Nations Framework Convention on Climate Change (UNFCCC), cumulative carbon emissions since 1870 need to be kept below 1 000 gigatonnes, of which 515 gigatonnes were already emitted between 1870 and 2011.[1]

Figure 2: Projected change of global mean sea level (21st century)[1]
 

Data source: IPPC (2013)
Note: The figure shows modelled global mean sea level rise over the 21st century relative to 1986-2005, derived from a combination of the CMIP5 ensemble with process-based models, for RCP2.6 and RCP8.5.

As temperature increases, it is very likely that the number and intensity of hot extremes and heat waves will increase globally. Projected changes in precipitation vary significantly between regions. Mean precipitation is likely to decrease further in such regions as the Mediterranean and North Africa, in particular under a high-emission scenario. In contrast, more intense and frequent extreme precipitation events are very likely in most mid-latitude regions, in, for example, Europe and North America, and wet tropical regions.

Global ocean temperature in the upper 100 m is projected to increase by 0.6–2.0 °C by 2100, depending on the emissions scenario. Arctic sea-ice cover will continue to shrink, and, under a high emissions scenario (RCP 8.5), the Arctic Ocean in September is likely to be almost ice-free before mid-century.

Global mean sea-level rise is projected to accelerate further, with an additional rise by 2081–2100 of 0.26–0.55 m (RCP 2.6) or 0.52–0.98 m (RCP 8.5; Figure 2; 1). The rise will not stop in 2100, and even modest sustained warming of 2 °C above pre-industrial levels is estimated to lead to sea-level rise of at least 4 m over of the following 2 000 years.[6][7]

Implications[8]

Drawing on a larger scientific knowledge base than ever before, the IPCC has concluded that continued global warming will increase the likelihood of severe, pervasive and irreversible consequences in most world regions.[9] However, risk reduction is possible through climate-change mitigation and adaptation (for details of the European context see SOER2015). Mitigation is the only option for reducing the risk of large-scale climate change. Action taken now and in the next few decades will determine the severity of consequences in the second half of the 21st century and beyond, while the co-benefits of mitigation action, such as reductions in air pollution, could be felt immediately.

Climate change mitigation and adaptation are also linked to other aspects of sustainable development, in particular the protection of biodiversity and food and energy security (GMT 8). A recent study, for example, suggests that with rising populations (GMT 1) and projected consumption levels (GMT 2, 5 and 6), there will not be enough land to simultaneously conserve all remaining natural ecosystems, halt forest loss and switch to 100 % renewable energy.[10]

Natural ecosystems and their services

The IPCC estimates that an increase in global temperature of up to 2 °C compared to preindustrial levels carries moderate risks in terms of global aggregate impacts on ecosystems. Unique and threatened systems including the Arctic sea-ice ecosystem, coral reefs and the Amazon forest, however, are at very high risk of severe consequences even at this level of warming. Under scenarios of stronger warming, a large share of terrestrial and freshwater species is very likely to face an increased risk of extinction, with associated extensive further losses of biodiversity and ecosystem services.

Marine ecosystems such as coral reefs are projected to face substantial risks due to the combined effects of ocean warming, ocean acidification and local stressors – pollution and eutrophication (GMT 10) – in particular for medium- and high-emission scenarios. Moreover, a global redistribution of marine species is expected, with decreases in the catch potential of fisheries at tropical latitudes and associated implications for livelihoods.

Human well-being and economic activities

Throughout the 21st century, climate change is projected to slow the rate of economic growth, increase inequality, erode food security and increase the displacement of people, particularly in low-income developing countries (GMT 1). Risks are unevenly distributed and are greater for disadvantaged people regardless of their country's level of development. With continued sea-level rise, low-lying areas, developing countries, in particular, are very likely to increasingly experience severe impacts through coastal flooding and coastal erosion. Indeed, flood losses in 136 major coastal cities around the globe could total USD 1 trillion or more annually by 2050 unless protection is upgraded.[11]

Estimated impacts of climate changes on crop yields since 1960 show some regionally limited gains but mostly losses. Projections suggest increasingly negative impacts on global agricultural production throughout this century (see Figure 3). Global temperature increases of 4 °C or more towards the end of the 21st century, combined with increased food demand, would pose significant risks for global food security. Agricultural productivity is particularly threatened in semi-arid regions where most currently irrigated areas are projected to face increased water needs. Increases in carbon dioxide concentrations also impact plant growth directly – while elevated carbon dioxide levels can increase plant photosynthesis, they decrease food quality by inhibiting nitrogen uptake.[12]

Impacts from climate change-related extreme events are projected to increase further with warming. Increased urban flood damage from extreme precipitation is a key climate-related risk in most world regions, including in Europe. Increased drought stress and associated water restrictions and wildfires are expected in southern Europe, Australia, and parts of Africa, Asia and North America. In many of these regions, increased risks to drinking-water quality are projected even when conventional water treatment is applied.

Increases in human health impacts due to extreme heat events and the spread of disease are expected in many regions, including Europe.[13][14][SOER2015]

Figure 3: Projected change in global aggregate crop yields due to climate change (2010–2109)[9]

Data source: IPPC (2014)
Note: Changes in crop yields are relative to late 20th century levels. The projections consider both low-emission and high-emission scenarios, tropical and temperate regions, and adaptation and no-adaptation cases. Data for each time frame sums up to 100 %.


References and footnotes

[1] IPCC (2013), 'Summary for Policymakers'. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Stocker, T.F., Qin, D., Plattner, G-K., Tignor, M., Allen, S. K., Boschung, J., Nauels, A., Xia, Y., Bex, V. and Midgley, P.M. (Eds.) Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK.

[2] NAS and RS (2014), 'Climate Change, Evidence and Causes', National Academy of Sciences of the United States of America (NAS), Washington, DC 20001, USA, Royal Society (RS), London, UK.

[3] In analogy with IPCC terminology, extremely likely refers to 95–100 % probability, very likely refers to 90–100 % likelihood, and likely refers to 66–100 % likelihood.

[4] Hot days and hot nights occur when maximum and minimum temperatures, respectively, exceed the 90th percentile with respect to the 1961–1990 baseline climate.

[5] Projections of changes in the climate systems as given here utilise a new set of emissions scenarios, the representative concentration pathways (RCPs).[15] These are four scenarios for levels of atmospheric greenhouse gases in the years up to 2100. They vary from a scenario in which greenhouse gas concentrations moderately increase between now and 2100 (RCP 2.6), to scenarios with greater levels of greenhouse gas concentrations (RCP 4.5 and RCP 6); all the way to a scenario in which greenhouse gas concentrations increase very greatly (RCP 8.5 – the scenario to which greenhouse gas emissions are currently heading if no further abatement measures are taken). The RCPs were developed to aid climate modelling, and underpinning the Fifth Assessment Reportof the IPCC. A full description of the comprehensive set of multi-model estimates, as well as further details on the projected trajectories for the various climate components are found in the Fifth Assessment Report of the IPCC.[16] While the focus of this fiche is on describing the potential situation by the end of the 21st century, projections for the coming decades and mid-21st century show similar spatial patterns (i.e. the same parts of the globe being affected by the same effects) but with smaller magnitude.

[6] Foster, G.L., and Rohling, E.J. (2013), 'Relationship between sea level and climate forcing by CO2 on geological timescales', PNAS 110(4), 1209–1214.

[7] Levermann, A., Clark, P.U., Marzeion, B., Milne, G.A., Pollard, D., Radic, V., and Robinson, A. (2013), 'The multimillennial sea-level commitment of global warming', PNAS 110(34), 13745–13750.

[8] Unless stated otherwise, the implications here are based on the findings of the Working Group II contribution to the Fifth Assessment Report of the IPCC.[9]

[9] IPCC (2014), 'Summary for Policymakers'. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK.

[10] Kraxner, F., Nordström, E-M., Havlík, P., Gusti, M., Mosnier, A., Frank, S., Valin, H., Fritz, S., Fuss, S., Kindermann, G., McCallum, I., Khabarov, N., Böttcher, H., See, L., Aoki, K., Schmid, E., Máthé, L., and Obersteiner, M. (2013), 'Global bioenergy scenarios – future forest development, land-use implications, and trade-offs', Biomass and Bioenergy 57, 86–96.

[11] Hallegatte, S., Green, C., Nicholls, R.J., and Corfee-Morlot, J. (2013), Future flood losses in major coastal cities. Nature Climate Change 3(9), 802–806.

[12] Bloom, A., Burger, M., Kimball, B.A., and Pinter, P.J. (2014), 'Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat', Nature Climate Change 4, 477–480.

[13] Bouzid, M., Colón-González, F.J., Lung, T., Lake, I.R., and Hunter, P.R. (2014), 'Climate change and the emergence of vector-borne diseases in Europe: case study of dengue fever', BMC Public Health 14:781.

[14] EEA (2012), Climate change, impacts and vulnerability in Europe 2012 — an indicator-based report, EEA Report 12/2012, European Environment Agency, Copenhagen, Denmark.

[15] Van Vuuren, D.P., Edmonds, J., Kainuma, M., Riahi, K., Thomson, A., Hibbard, K., Hurtt, G.C., Kram, T., Krey, V., Lamarque, J-F., Masui, T., Meinshausen, M., Nakicenovic, N., Smith, S.J., and Rose, S.K. (2011), 'The representative concentration pathways: an overview', Climatic Change 109(1-2), 5–31.

[16] IPCC (2013), 'Climate Change 2013: The Physical Science Basis'. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.Stocker, T.F., Qin, D., Plattner, G-K., Tignor, M., Allen, S. K., Boschung, J., Nauels, A., Xia, Y., Bex, V. and Midgley, P.M. (Eds.) Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK.

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