Carbon Offset Calculator

An offset is a claimed tonne of CO2 equivalent avoided or removed elsewhere, purchased to balance a tonne emitted here, so the arithmetic first has to build the footprint being balanced. Driving uses the EPA combustion figure of 8.887 kg CO2 per gallon of gasoline applied to miles divided by fuel economy, so 12,000 miles at 25 MPG yields about 4.27 tonnes. Flights use roughly 90 kg CO2 per passenger per flight-hour, an average of the scale ICAO applies to medium-haul narrow-body aircraft. Electricity uses a US average grid factor near 0.386 kg per kWh and natural gas 5.302 kg per therm. Offset pricing of 15 to 20 dollars per tonne reflects standard voluntary-market avoidance projects; engineered removals and credits with strong co-benefits trade far higher. Offset quality rests on four tests that price alone does not reveal. Additionality asks whether the reduction would have happened anyway. Permanence asks whether stored carbon stays stored, the weak point for forestry credits exposed to fire, pests, and harvest. Leakage asks whether the activity simply moved somewhere else. Baseline setting determines the counterfactual against which credits are issued. The tree figure used here, about 22 kg CO2 per tree per year, is a mid-range value hiding enormous variation, since a newly planted seedling may absorb under 10 kg annually for its first several years. For these reasons most guidance, including that of the Science Based Targets initiative, treats offsets as appropriate only for residual emissions after direct reductions.

Project-based offsetting began in 1989, when the US utility Applied Energy Services funded an agroforestry program in Guatemala, developed with the World Resources Institute, to counterbalance a new coal-fired plant in Connecticut. A compliance market followed the Kyoto Protocol of 1997, which created the Clean Development Mechanism and Joint Implementation; the operating rules were settled in the Marrakesh Accords of 2001 and the first Certified Emission Reductions were issued in 2005. The mechanism registered thousands of projects but drew sustained criticism over additionality, especially for industrial-gas destruction credits that appeared to create an incentive to produce the gases in the first place. The voluntary market built its own registries alongside it. Gold Standard launched in 2003 with backing from WWF, and the Voluntary Carbon Standard, now Verra's VCS, followed in 2006. Aviation gained a sector-specific scheme when ICAO adopted CORSIA in 2016. Scrutiny intensified sharply in the 2020s: a 2023 joint investigation by the Guardian, Die Zeit, and SourceMaterial challenged the emission-reduction claims behind a large share of REDD+ rainforest credits, and prices for older forestry credits fell steeply afterward. The Integrity Council for the Voluntary Carbon Market responded with its Core Carbon Principles in 2023, an attempt to establish a quality floor that applies across competing registries.