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Making our Carbon Calculator better with Imperial College London

Our Carbon Calculator helps you work out your carbon footprint and offset it by funding carbon-reduction projects around the world. We’ve been working with independent researchers from Imperial College London to review the data behind the tool. In this post, we look at how they think we can improve it and our plans to do that.

Our Carbon Calculator asks you questions about your day-to-day life, like how you normally get around, or the things you buy. It crunches those numbers to come up with your carbon footprint. We've tried to keep it simple, so you can start reducing your footprint right away. That said, there’s some heavy-duty maths going on behind the scenes. And as any good maths teacher knows, it’s important to check your workings. So we asked some experts from Imperial College London to do just that.

We commissioned the team, through Imperial Consultants, to review our Carbon Calculator. We were pleased to hear they think the tool gives a good estimate of your carbon footprint. Their main recommendation for us was to make it really clear to users that the result we give is an estimate based on the questions we ask. They made lots of helpful recommendations to make the calculator better, which we’ve summarised below. You can read the full report here, too.

We're making the calculator better

At Bulb, we like to keep things simple. We’ve taken all of the Imperial team's recommendations on board to make the tool as accurate as it can be, whilst making sure it’s quick and easy to use.

There are lots of other features we want to add to make the calculator better - we’ll keep you updated on the blog. We want to hear your ideas for improving it in the Community, too.

Answer a few questions about your lifestyle to work out and offset your carbon footprint 

The report's key recommendations

Improve the question about flights

  • At the moment, the calculator asks how many flights you’ve taken in the last 12 months, and how long those flights were in hours. Imperial's researchers suggest we ask how long each leg of the journey is instead. 

  • We’re going to explore adding a feature asking the origin and destination for each flight. Though we may decide not to if it makes it much longer to use the tool.

Make home energy use more accurate

  • The energy you use at home differs hugely from person to person. At the moment, the tool uses Ofgem figures for average energy use in UK homes. 

  • But we’re an energy supplier, and Imperial knows we can do better than that. So we’re looking into ways we can better estimate energy use, like asking the number of bedrooms in your home. We’ll be updating this soon.

Be clearer on what a serving size is

  • Imperial's team recommend we’re clearer when asking how many ‘meals’ you eat each week that include different types of meat and dairy. And we think they’re right.

  • We’ve updated the egg illustration to show 2 eggs instead of 3, which reflects what the maths is doing in the background. 

  • We fixed a small error they spotted with our dairy calculation.

  • We’re also going to explore changing how we phrase the question, or updating the page explaining the calculations, to make it clearer.

We've updated the egg illustration to make it clearer what a serving size is

Improve data to work out the carbon impact of land travel 

  • The tool uses average speeds to calculate the distance travelled, which is multiplied by the emissions factor for that transport to work out the carbon impact. 

  • But in reality, people might drive faster on country lanes than in congested urban areas. And we know there are more electric buses in cities like London than in other parts of the UK. 

  • Whilst Imperial's team recommends asking for details about where you travel most, they also think using the average UK emissions factor is a good estimate. So we’re going to hold on this change for now. 

  • At the moment, we calculate the carbon impact of electric vehicles (EVs) using the average UK fuel mix, which incorrectly adds emissions if you have 100% renewable electricity and charge your EV at home. In future, we’re changing it so EV emissions are zero if you’re supplied by 100% renewable electricity at home.

Improve data to work out the carbon impact of shopping

  • The data we use to work out the carbon impact of shopping is from 2011. It was updated in 2019 for inflation, but Imperial explained it doesn’t include changes in supply chains or infrastructure since then. So they think it’s important we’re clear it’s an estimate here.

  • They suggest using more recent data, like the Eora Global Supply Chain Database. We’ve had a look, but we'd need to ask a lot more questions. Imperial agrees our current approach is a fairly good estimate, so we’ve decided not to update this as it could take much longer to use the calculator.