مُقدر البُطء الكربوني

A tonne of CO2-equivalent is the unit climate scientists use to compare different greenhouse gases on the same scale. Methane, nitrous oxide, and refrigerant gases trap heat at different rates than CO2, so each is multiplied by its Global Warming Potential (GWP) over a 100-year horizon — methane is ~28x CO2, nitrous oxide ~273x — and the result is reported in tCO2e. One tonne of CO2 equals the emissions from burning about 113 gallons of gasoline or driving an average US passenger car for ~2,500 miles.

Grid intensity (kg CO2e per kWh) reflects the fuel mix that generates the electricity. France's grid sits near 0.056 kgCO2e/kWh because ~70% of generation is nuclear (zero-direct-emission) and most of the rest is hydro. India's grid sits near 0.713 kgCO2e/kWh because coal still provides more than half of generation. A heat pump or EV that looks 'clean' on paper is only as clean as the grid feeding it — which is why decarbonising the grid is a prerequisite for electrified end-uses to deliver their full climate benefit.

Aircraft jet engines emit CO2, but they also emit water vapour, nitrogen oxides, soot, and sulphate aerosols at altitude, where they form contrails and persistent cirrus clouds that trap additional heat. The total climate warming from a flight is roughly 1.7-3x the CO2-only number — the IPCC AR6 best estimate is 1.9x. This calculator uses that multiplier so a long-haul flight is reported closer to its real climate impact rather than just the fuel-burn CO2.

To stay within the 1.5°C carbon budget that the IPCC AR6 says gives a 50% chance of avoiding the worst climate impacts, global emissions need to roughly halve by 2030 from a 2019 baseline of ~50 GtCO2e/year. Divided by the projected 2030 world population (~8.5 billion), that works out to a per-capita 'fair share' of roughly 2-2.3 tCO2e/year. Most developed-country residents currently sit 4-8x above that line, which is why personal footprints matter as a benchmark even though structural change matters more.

Voluntary offsets are useful but imperfect. Reforestation and avoided-deforestation (REDD+) credits priced at ~/tonne have a long history of additionality and permanence issues — investigations have found many such credits represent little or no real avoided emissions. Renewable energy and biogas credits around 5/tonne tend to be more reliable. Engineered removals like direct air capture cost ~00/tonne but lock carbon away on geological timescales. The honest position is that offsets are a complement to — not a substitute for — directly reducing your own emissions.