Question 1

What is Japan's electricity CO2 emission factor?

Accepted Answer

Japan's electricity CO2 emission factor varies with the energy mix, but the actual value for FY2023 is approximately 0.44 kg-CO2/kWh. France, with a high share of renewables, is about 0.06; China is about 0.60; and the world average is about 0.48 kg-CO2/kWh. Utility-specific individual factors are also published and updated annually by Japan's Ministry of the Environment.

Question 2

What is Life Cycle Assessment (LCA)?

Accepted Answer

Life Cycle Assessment (LCA) is a method for quantifying environmental impacts (CO2 emissions, energy consumption, etc.) across all stages from production to disposal of a product or service. It is standardized under ISO 14040/14044 and is evaluated under Scope 1 (direct emissions), Scope 2 (purchased electricity), and Scope 3 (entire supply chain) categories.

Question 3

How much CO2 does one tree absorb per year?

Accepted Answer

A typical 20–30 year old tree (e.g. cedar) absorbs approximately 14 kg-CO2 per year (Forestry Agency standard). However, this varies significantly by species, age, and environmental conditions; fast-growing tropical trees can absorb tens of kg per year. This tool uses 22 kg-CO2/tree/year.

Question 4

What is the difference between carbon offsets and RECs (Renewable Energy Certificates)?

Accepted Answer

A REC (Renewable Energy Certificate) is issued for every 1 MWh of electricity generated from renewable sources; purchasing one allows the electricity-related Scope 2 emissions to be treated as zero. A carbon offset monetizes emission reductions or removals from activities such as afforestation or energy efficiency investments, and is mainly used for Scope 3 reductions. Both are traded via the J-Credit Scheme (Japan) and I-REC.

CO2 Emissions & Life Cycle Assessment Tool

Emission Calculation (IPCC Tier 1)