Coherent Identifier About this item: 20.500.12592/frm9m5

BT Breifing Notes - CARBON BUDGETS FOR 1.5 & 2°C_V2.indd

7 April 2021

Summary

• The 2018 IPCC Special Report on Global Warming of 1.5°C increased the 1.5°C budget by underestimating the warming to date by around 0.2°C, and using an estimate of climate sensitivity — the TCRE or transient climate response — which underestimates warming at system equilibrium. [...] Bringing together the IPCC’s carbon budgets for a likely chance of 2°C with the equity steer of Paris, a carbon budget for developed nations is 95 to 136 billion tonnes of CO2 from 2020. [...] IPCC CARBON BUDGETS HAVE UNACCEPTABLE RISK OF FAILURE • Poor risk management: IPCC carbon budgets are often associated with a 50 or 66% chance of staying below the target, that is, a one-in-two, or one-in-three, chance of failure, for example in the IPCC Fifth Assessment Report and the 2018 Special Report on Global Warming of 1.5°C. [...] Likewise, scenarios with a 50% chance of not exceeding the 1.5°C target have a 33% chance of exceeding 2°C of warming, and a 10% chance of exceeding 3°C of warming. [...] The evidence shows that none of these policies accord with the physical realities for a country such as Australia, which has amongst the highest per capita emissions in the world, alongside the USA and some Gulf states.

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