How To Offset Your Carbon Emissions

I don't believe carbon-offsetting can ever solve the climate crisis. For obvious thermodynamic reasons it's cheaper, in terms of energy and money, to avoid releasing CO₂ into the atmosphere than it is to retrieve it from the atmosphere where it is diluted to 450ppm (and rising).

However, if done correctly, it can help individuals and particular industries go carbon-neutral, typically only where the available budget is sufficient to pay for the thermodynamic inefficiency.

I believe most carbon-offsetting and carbon credit schemes are not truly reversing the CO₂ emissions they claim to, eg planting trees in the UK displaces food production, deforesting the Amazon; preserving a fixed area of rainforest can only offset a fixed total amount of emissions, and only if it was really going to be cleared.

Climeworks genuinely reverses CO₂ emissions by harnessing cheap (but limited) geothermal energy in Iceland. On https://climeworks.com/co2-removal under "Direct air capture, combined with storage, has multiple benefits:"

The removed CO₂ goes through rapid mineralization to become stone: a safe and natural process.

I promise I am not sponsored by or affiliated to Climeworks.

Offsetting Car Journeys

I was inspired to act when my friend Paul, who was kindly giving me a lift in his petrol-powered car, admitted that he felt terrible each time he turned the ignition. Suddenly it dawned on me that I could pay to remove those emissions from the atmosphere.

Our journey used about 4 gallons of petrol. Burning petrol releases about 10kg of CO₂ per gallon or 2.3kg of CO₂ per litre. I needed to remove 40kg CO₂, as follows:

  • Go to https://climeworks.com/subscriptions.
  • Scroll down and choose "Custom Plan".
  • Choose Frequency = "One-time".
  • Enter a "Custom amount" that removes the required amount of CO₂ - about £1 per kg CO₂.
  • Check out and pay.

Job done!

You can do this per journey or each time you refill your tank. Burning diesel releases about 10% more CO₂ per gallon/litre than burning petrol.

Current petrol grades in the UK contain up to 5% bioethanol, known as E5. E10 fuel increases the share of the renewable energy produced using crops to 10%. However, growing crops for bioethanol has its own carbon footprint by displacing food production, to eg the Amazon, driving deforestation.

NB: the extraction, refining and transportation of petrol and diesel leaks raw methane into the atmosphere, which causes additional climate warming.

Offsetting Flights

You can offset the CO₂ emissions from a plane journey as follows:

For example: a return flight from Manchester to Chennai with a change in Dubai emits about 2,700kg CO₂; a one-way flight from Gatwick to Nice emits 210kg CO₂.

NB: CO₂ emissions account for only a minority of the climate impact of flying - see Carbon-Neutral Flying. But it's still important to remove them.

Offsetting Domestic Gas

Just like Paul and his petrol car above, it's galling needing to run a gas boiler (in my rented flat). I decided to calculate how much it would cost to offset the CO₂ emitted from my gas boiler, as follows.

My utility bills tell me:

  • Opening [gas meter] read on 7th May 2021: 2201.
  • Closing read as of 6th August 2022: 2580.
  • I've used 2580 - 2201 = 379 units.
  • kWh gas used = "Metered volume x metric conversion factor x daily calorific value x 1.02264 (volume correction) / 3.6"
    where "we convert the gas use into kWh according to your meter type - 2.83 (imperial) or 1 (metric)"
    and "the calorific value of gas changes every day and can range from 37.5 to 43.0"

Reversing the calculation on my gas bill I need to multiple by 11.1 to convert from units to kWh of gas. That matches the formula above for a metric gas meter.

https://bulb.co.uk/carbon-tracker/ says CO₂ emissions are "0.183 kg per kWh of gas", and this matches the spreadsheet on their link to https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2022.

So over 15 months covering two summers I have burned 379 x 11.1 = 4,206kWh gas. And emitted 4,206 x 0.183 = 770kg CO₂.

Great! Paying https://climeworks.com/subscriptions to offset those emissions is affordable.

NB: the raw methane that leaks into the atmosphere during the extraction, processing and transportation of gas causes additional climate warming.

Offsetting Domestic Heating Oil

If you heat your home using oil, you can remove the CO₂ emissions this causes as follows:

  • Look up how many litres of oil you've used.
  • CO₂ emitted = volume of oil x 2.96 kgCO₂/litre
  • Follow the instructions in the first section.

Suppose you refill your tank with 1,000 litres of oil. Burning that oil will release 1,000 x 2.96 = about 3,000 kg CO₂.

NB: the extraction, refining and transportation of oil leaks raw methane into the atmosphere, which causes additional climate warming.

Offsetting Domestic Electricity

I don't need to investigate offsetting the emissions from domestic electricity use. It's simple to switch to a tariff that uses only renewable electricity. And that tariff will be cheaper than offsetting the emissions from non-renewable electricity.

Credits

Thank you to Paul Thearle for inspiring me.



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