Why? Impact can be defined as changes in the real economy that have a direct or indirect effect on climate change mitigation or adaptation. Measuring it provides transparency on and can assist in increasing the real-world contribution of climate-related finance and investment.
How? The impact of mitigation activities is often quantified using GHG emissions metrics, however complementary metrics are also often seen as necessary. Metrics for measuring impact for adaptation activities are often context-specific and fit-for-purpose to accommodate the wide range of activities that may contribute to the adaptation of economies and societies. Institutions may distinguish the impact of counterparties and underlying assets financed, and the direct impact stemming from its own choices and means of intervention.
 Source: 2dii – Climate impact, What it is and how to achieve it? https://2degrees-investing.org/wp-content/uploads/2018/12/Final-draft_Climate-actions-impact.pdf