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Il bilancio di emissioni estima della riduzione necessaria a raggiungere l'obiettivo dei due gradi stabilito con l'Accordo di Parigi in assenza di emissioni negative, in base al picco di emissioni. [1]

Un budget di CO2, bilancio di emissioni, quota di emissioni o emissioni consentite, è una soglia massima delle emissioni totali di anidride carbonica (CO2) associata alla necessità di rimanere al di sotto di una specifica temperatura media globale. [2][3][4] Un budget di emissioni può anche essere associato a obiettivi relativi ad altre variabili climatiche correlate, come il forzante radiativo.[5]

I bilanci globali per le emissioni sono calcolati in base alle emissioni cumulative storiche derivanti dalla combustione di carburanti fossili, dai processi industriali e dal cambiamento dell'uso del suolo, ma variano in base all'obiettivo di temperatura globale scelto, alla probabilità di rimanere al di sotto di tale obiettivo, e l'emissione di altri gas serra non CO2 .[6][7] I bilanci globali per le emissioni possono essere ulteriormente suddivisi nei bilanci nazionali per le emissioni, in modo che i paesi possano fissare obiettivi specifici di mitigazione del clima. I bilanci per le emissioni sono rilevanti per la mitigazione dei cambiamenti climatici perché indicano una quantità finita di anidride carbonica che può essere emessa nel tempo, prima che ne derivano livelli di riscaldamento globale pericolosi. Dal luogo geografico dove vengono prodotte queste emissioni è anche delle stesse è in larga parte indipendente. [8][9]

In linea con il rapporto speciale del 2018 sul riscaldamento 1,5°C dell'IPCC il Mercator Research Institute on Global Commons and ClimateChange di Berlino stima il budget di CO2 associato ad un riscaldamento di 1,5°C si esaurirà nel 2028 se le emissioni si mantengono al livello registrato alla fine degli anni 2010.[10] Superata la soglia di 1,5°C, aumenta il rischio di conseguenze durature e irreversibili legate al cambiamento climatico.[11]

Un budget per le emissioni può essere distinto da un obiettivo per le emissioni, poiché quest'ultimo può essere fissato a livello internazionale o nazionale in funzione degli obiettivi diversi da una temperatura globale specifica.

Stime

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Global carbon budget for a two-degree world

La scoperta di una relazione quasi lineare tra l'aumento della temperatura globale e le emissioni cumulative di diossido di carbonio, ha favorito la stima dei bilanci di emissioni globali per rimanere al di sotto dei pericolosi livelli di riscaldamento.[9] Dal periodo preindustriale fino al 2011, approssimativamente 1890 Gigatonnellate di CO2 sono stati emessi globalmente; nei soli quattro anni successivi, dal 2011 al 2015, sono state emesse 2050 GtCO2.[12]

Scientific estimations of the remaining global emissions budgets/quotas differ widely due to varied methodological approaches, and considerations of thresholds.[12] Most estimations still underestimate the amplifying climate change feedbacks.[13][14][15][16]

Some common budget estimations are those associated with a 1.5 °C[17][18][19] and 2 °C global warming.[2][6][20] These estimates depend highly on the likelihood or probability of reaching a temperature target. The values for the budget exhausted in the following table have been derived from a scenario in which [[Carbon dioxide in Earth's atmosphere#Anthropogenic CO2 emissions|Template:CO2 emissions]] remain on the current level of 42 Gt per year.

Emissions budget estimations
Target for average

global temperature rise

budget exhausted in Likelihood

of staying below target

budget Gt of Template:CO2 Date range Source (Rogelj et al. 2016 has another list of estimates[12]) Page in source
1.5 °C = 2.7 °F 2034-2037 66% 810-920 2015-2100 Millar et al. 2017[17] 4
1.5 °C = 2.7 °F 2020-2025 50% 400-570 2011-2100 Rogelj et al. 2015[19] 3
1.5 °C = 2.7 °F 2047 50% 1400 2015-2100 Millar et al. 2017[17] 4
1.5 °C = 2.7 °F 2041 50% 1060 2016-2100 Matthews et al. 2015[18] subtraction in Table 2
2 °C = 3.6 °F 2025-2031 75% 610-830 2011-2100 Rogelj et al. 2015 3
2 °C = 3.6 °F 2034 66% 1200 2015-2100 Friedlingstein et al. 2014[6] 710
2 °C = 3.6 °F 2044 66% 1000 2020-2100 Friedlingstein et al. 2014 710
2 °C = 3.6 °F 2035 66% 990 2012-2100 2015 IPCC 2015[21] 1113
2 °C = 3.6 °F 2033 66% 940 2011-2100 Rogelj et al. 2015 3
2 °C = 3.6 °F 2035-2045 50% 990-1450 2011-2100 Rogelj et al. 2015 3
2 °C = 3.6 °F 2066 50% 2085 2016-2100 Matthews et al. 2015 subtraction in Table 2
2 °C = 3.6 °F 2051 50% 1500 2015-2100 Friedlingstein et al. 2014 710
3 °C = 5.4 °F 2084 66% 2900 2015-2100 Friedlingstein et al. 2014 710
3 °C = 5.4 °F 2094 50% 3300 2015-2100 Friedlingstein et al. 2014 710

1 GtC (carbon) = 3.67 GtCO2 [22]

Alternative to budgets set explicitly using temperature objectives, emissions budgets have also been estimated using the Representative Concentration Pathways, which are based on radiative forcing values at the end of the century.[23] (Although temperatures may be inferred from radiative forcing). These were presented in the International Panel on Climate Change Fifth Assessment report.[5] According to the World Meteorological Organization there is a 20% chance that in the years 2020 - 2024 at least in one year the average temperature will be higher than 1.5°C above preindustrial level.[24]

Carbon capture

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Lo stesso argomento in dettaglio: Carbon dioxide removal, Carbon sequestration e Carbon capture and storage.

Researchers expect emissions will exceed any of these remaining budgets. In order to comply with the budget limits, they expect Template:CO2 will need to be captured from the atmosphere and stored in products, the environment or underground. A 2015 study in Nature says carbon budgets can only be met by capturing Template:CO2, "in all but the most optimistic cases, we also find negative emission requirements that have not yet been shown to be achievable"[25]

Scientists widely agree this research is needed. IPCC says, "All pathways that limit global warming to 1.5°C [2.7°F] with limited or no overshoot project the use of carbon dioxide removal (CDR) on the order of 100-1000 GtCO2 over the 21st century. CDR would be used to compensate for residual emissions and, in most cases, achieve net negative emissions to return global warming to 1.5°C following a peak (high confidence)."[26]

Even for the less strict goal of 2 °C [3.6 °F] warming, carbon capture is needed. IPCC has only one scenario (they call it a "Representative Concentration Pathway" RCP) which limits warming to 3.6 °F: "RCP2.6 is representative of a scenario that aims to keep global warming likely below 2°C above pre-industrial temperatures. The majority of models indicate that scenarios meeting forcing levels similar to RCP2.6 are characterized by substantial net negative emissions by 2100, on average around 2 GtCO2/yr."[21]57

National emissions budgets

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Template:CO2 Emissions by country

In light of the many differences between nations, including but not limited to population, level of industrialization, national emissions histories, and mitigation capabilities, scientists have made attempts to allocate global carbon budgets among countries using methods that follow various principles of equity.[27] Allocating national emissions budgets is comparable to sharing the effort to reduce global emissions, underlined by some assumptions of state-level responsibility of climate change. Many authors have conducted quantitative analyses which allocate emissions budgets,[28][29][30][4] often simultaneously addressing disparities in historical GHG emissions between nations. National 'Paris-compliant' emissions budgets have also been calculated that quantify the discrepancy between the emissions reductions resulting from current national mitigation pathways and those needed to live up to the temperature and equity commitments enshrined in the Paris Agreement.[28]

One common principle that has been used to allocate global emissions budgets to nations is the "responsibility" or "polluter-pays" principle.[27] This principle recognizes nations' cumulative historical contributions to global emissions. So those countries with greater emissions during a set time period (for example, since the pre-industrial era to the present) would be most responsible for addressing excess emissions. Thus, their national emissions budgets would be smaller than those that have polluted less in the past. The concept of national historical responsibility for climate change has prevailed in the literature since the early 1990s.[31][32] Consequently, some have quantified cumulative historical emissions of states, to identify who has most responsibility to take the strongest actions.[33] This principle is often favoured by developing countries, as it gives them larger emissions budgets.[34]

Another common equity principle for calculating national emissions budgets is the "egalitarian" principle. This principle stipulates individuals should have equal rights to pollute, and therefore emissions budgets should be distributed proportionally according to state populations.[27] Some scientists have thus reasoned the use of national per-capita emissions in national emissions budget calculations.[29][30][35] This principle may be favoured by nations with larger or rapidly growing populations.[34]

A third equity principle that has been employed in national budget calculations considers national sovereignty.[27] The "sovereignty" principle highlights the equal right of nations to pollute.[27] The grandfathering method for calculating national emissions budgets uses this principle. Grandfathering allocates these budgets proportionally according to emissions at a particular base year,[35] and has been used under international regimes such as the Kyoto Protocol[36] and the early phase of the European Union Emissions Trading Scheme (EU ETS)[37] This principle is often favoured by developed countries, as it allocates larger emissions budgets to them.[34]

See also

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References

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  1. ^ Three years to safeguard our climate, in Nature, vol. 546, n. 7660, 29 June 2017, pp. 593–595, DOI:10.1038/546593a.
  2. ^ a b Greenhouse-gas emission targets for limiting global warming to 2 °C, in Nature, vol. 458, n. 7242, April 2009, pp. 1158–1162, DOI:10.1038/nature08017.
  3. ^ Focus on cumulative emissions, global carbon budgets and the implications for climate mitigation targets, in Environmental Research Letters, vol. 13, n. 1, 1º January 2018, p. 010201, DOI:10.1088/1748-9326/aa98c9.
  4. ^ a b Sharing a quota on cumulative carbon emissions, in Nature Climate Change, vol. 4, n. 10, 21 September 2014, pp. 873–879, DOI:10.1038/nclimate2384.
  5. ^ a b Climate Change 2013: The Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, 2014, ISBN 978-1-107-05799-9.Template:Pn
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  7. ^ (EN) Tim Jackson, 2050 is too late – we must drastically cut emissions much sooner, su theconversation.com.
  8. ^ Is the climate response to CO emissions path dependent?, in Geophysical Research Letters, vol. 39, n. 5, March 2012, pp. n/a, DOI:10.1029/2011gl050205.
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  10. ^ [[:Template:CO2]] countdown, su mcc-berlin.net, Mercator Institute. Wikilink compreso nell'URL del titolo (aiuto)
  11. ^ Summary for Policymakers of IPCC Special Report on Global Warming of 1.5°C approved by governments (citation Hans-Otto Pörtner, Co-Chair of IPCC Working Group II), su ipcc.ch, IPCC.
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  13. ^ Estimating and tracking the remaining carbon budget for stringent climate targets, in Nature, vol. 571, n. 7765, 17 July 2019, pp. 335–342, DOI:10.1038/s41586-019-1368-z.
  14. ^ (EN) Naomi Oreskes,Michael Oppenheimer,Dale Jamieson, Scientists Have Been Underestimating the Pace of Climate Change, su blogs.scientificamerican.com.
  15. ^ Edward Comyn-Platt, Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks (PDF), in Nature Geoscience, vol. 11, n. 8, 2018, pp. 568–573, DOI:10.1038/s41561-018-0174-9.
  16. ^ (EN) Climate tipping points — too risky to bet against, in Nature, vol. 575, n. 7784, 27 novembre 2019, pp. 592–595, DOI:10.1038/d41586-019-03595-0.
  17. ^ a b c Emission budgets and pathways consistent with limiting warming to 1.5 °C (PDF), in Nature Geoscience, vol. 10, n. 10, 18 September 2017, pp. 741–747, DOI:10.1038/ngeo3031.
  18. ^ a b Estimating Carbon Budgets for Ambitious Climate Targets (PDF), in Current Climate Change Reports, vol. 3, n. 1, 27 February 2017, pp. 69–77, DOI:10.1007/s40641-017-0055-0.
  19. ^ a b Mitigation choices impact carbon budget size compatible with low temperature goals, in Environmental Research Letters, vol. 10, n. 7, 1º July 2015, p. 075003, DOI:10.1088/1748-9326/10/7/075003.
  20. ^ Setting cumulative emissions targets to reduce the risk of dangerous climate change, in Proceedings of the National Academy of Sciences of the United States of America, vol. 106, n. 38, 22 September 2009, pp. 16129–16134, DOI:10.1073/pnas.0805800106.
  21. ^ a b Climate Change 2014 Synthesis Report https://ar5-syr.ipcc.ch/topic_futurechanges.php
  22. ^ Comparing CO2 emissions to CO2 levels, su skepticalscience.com.
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