Carbon Budget Calculator

A carbon budget is a cumulative emissions ceiling rather than an annual rate. Its physical basis is the near-linear relationship between cumulative CO2 emitted and peak global warming, expressed as the transient climate response to cumulative emissions, roughly 0.45 degrees C per 1,000 gigatonnes of CO2. Because the relationship is cumulative, what matters for a temperature target is the total ever emitted rather than the path taken to get there. Dividing a remaining global budget by world population gives a per-person allocation, which is the comparison made here. Household activity is converted using published factors: 8.887 kg CO2 per gallon of gasoline, 5.31 kg per therm of natural gas, about 0.417 kg per kWh of US grid electricity, and roughly 0.9 tonnes per round-trip flight. Reference points matter for interpretation. US per-capita emissions run near 14 to 16 tonnes CO2 a year, the EU near 6 to 7, and the global mean around 4.7, against roughly 2 tonnes per person for a mid-century 1.5 degree C pathway. Diet spans about 1.5 tonnes for a vegan pattern to 3.3 tonnes for a beef-heavy one. The electricity factor is a national average and ranges from under 0.05 to over 0.8 kg per kWh across US states, so location dominates that line item. Flight figures count CO2 only and omit contrail and nitrogen-oxide effects that can roughly double aviation warming, and emissions embodied in imported goods are not counted at all, typically understating a developed-country footprint by several tonnes.

The idea that cumulative carbon, not the annual rate, sets peak warming was established in two papers published in Nature in 2009, one led by Myles Allen at Oxford and one by Damon Matthews at Concordia. Both showed that peak temperature scales with total emitted carbon and is largely insensitive to timing. The IPCC adopted the framing in its Fifth Assessment Report in 2013 and published the first official remaining-budget figures; the Paris Agreement in 2015 then set the temperature goals against which those budgets are drawn. The Sixth Assessment Report in 2021 gave roughly 500 gigatonnes of CO2 remaining from the start of 2020 for a 50 percent chance of holding 1.5 degrees C. The personal side has separate roots. Mathis Wackernagel and William Rees introduced the ecological footprint in their 1996 book Our Ecological Footprint, translating consumption into land area. The narrower carbon footprint entered common use after a 2004 BP advertising campaign built around a personal calculator, a framing later criticized for shifting attention from producers to consumers. The emission factors behind tools like this come from government inventories: the EPA has maintained its Greenhouse Gas Equivalencies Calculator and Emission Factors Hub since the 2000s, revising grid intensity downward as coal generation has fallen. Annual budget updates now come from the Global Carbon Project, which has published a Global Carbon Budget assessment every year since 2006.