Editing IPCC:AR6/WGIII/Chapter-13 (section)

==== 13.6.1.3 Stringency and Overall Effectiveness of Mitigation Policies ====

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The stringency of mitigation policies varies greatly by country, sector and policy (Box 13.9). Stringency can be increased through sequential changes to policies ( [[#Pahle--2018|Pahle et al. 2018]] ).

Estimates of the effective carbon price (as an estimate of overall stringency across policy instruments) differ greatly between countries and sectors ( [[#World%20Bank--2021a|World Bank 2021a]] ). Countries with higher overall effective carbon prices tend to have lower carbon intensity of energy supply and lower emissions intensity of the economy, as shown in an analysis of 42 G20 and OECD countries ( [[#OECD--2018|OECD 2018]] ). The carbon price that prevails under a carbon tax or ETS is not directly a measure of policy stringency across an economy, as the carbon prices typically only cover a share of total emissions, and rebates or free allowance allocations can limit effectiveness ( [[#OECD--2018|OECD 2018]] ). At low emissions prices, mitigation incentives are small; as of April 2021, seventeen jurisdictions with a carbon pricing policy had a tax rate or allowance price less than USD5 per tCO 2 ( [[#World%20Bank--2021a|World Bank 2021a]] ).

Other policies, such as fossil fuel subsidies, may provide incentives to increase emissions thus limiting the effectiveness of the mitigation policy ( [[#13.6.3.6|Section 13.6.3.6]] ). Those effects may be complex and difficult to identify. In most countries trade policy provides an implicit subsidy to CO 2 emissions ( [[#Shapiro--2020|Shapiro 2020]] ). The analysis of emissions from energy use in buildings in [[IPCC:Wg3:Chapter:Chapter-9|Chapter 9]] illustrates the factors that support and counteract mitigation policies.

Furthermore, emissions pricing policies encourage reduction of emissions whose marginal abatement cost is lower than the tax/allowance price, so they have limited impact on emissions with higher abatement costs such as industrial process emissions ( [[#Bataille--2018a|Bataille et al. 2018a]] ; [[#Davis--2018|Davis et al. 2018]] ). EU ETS emission reductions have been achieved mainly through implementation of low cost measures such as energy efficiency and fuel switching rather than more costly industrial process emissions.

Estimating the overall effectiveness of mitigation policies is difficult because of the need to identify which observed changes in emissions and their drivers are attributable to policy effort and which to other factors. Cross-Chapter Box 10 in [[IPCC:Wg3:Chapter:Chapter-14|Chapter 14]] brings together several lines of evidence to indicate that mitigation policies have had a discernible impact on mitigation for specific countries, sectors and technologies and led to avoided global emissions to date by several billion tonnes CO 2 -eq annually ( ''medium evidence'' , ''medi'' ''um agreement'' ).

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