Path independence of carbon budgets when meeting a stringent global mean temperature target after an overshoot
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Date
2019-12
Publication Type
Journal Article
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yes
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Abstract
Emission pathways that are consistent with meeting the Paris Agreement goal of holding global mean temperature rise well below 2 °C often assume a temperature overshoot. In such overshoot scenarios, a given temperature limit is first exceeded and later returned to, under the assumption of large‐scale deliberate Carbon Dioxide Removal from the atmosphere (CDR). Here we show that although such strategy might result in a reversal of global mean temperature, the carbon cycle exhibits path‐dependence. After an overshoot, more carbon is stored in the ocean and less on land compared to a scenario with the same cumulative CO2 emissions but no overshoot. The near‐path independence of surface air temperature arises despite the path dependence in the carbon cycle, as it is offset by path dependence in the thermal response of the ocean. Such behaviour has important implications for carbon budgets (i.e. the total amount of CO2 emissions consistent with holding warming to a given level), which do not differ much among scenarios that entail different levels of overshoot. Therefore, the concept of a carbon budget remains robust for scenarios with low levels of overshoot (up to 300 PgC overshoot considered here) but should be used with caution for higher levels of overshoot, particularly for limiting the environmental change in dimensions other than global mean temperature rise.
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published
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Journal / series
Volume
7 (12)
Pages / Article No.
1283 - 1295
Publisher
Wiley
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Software
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Date collected
Date created
Subject
Carbon budgets; Paris Agreement; overshoot scenarios; temperature overshoot; artificial carbon dioxide removal; net‐negative emissions
Organisational unit
03777 - Knutti, Reto / Knutti, Reto
ETH Zürich
Notes
Funding
820829 - LC-CLA-08-2018 | RIA | Constraining uncertainty of multi decadal climate projections (EC)