Why my (or your) carbon footprint matters

At the Ashden Awards in June, I was lucky enough to meet Emma Murphy, one of the founders of the green PR outfit, Life Size Media.  She combines great technical understanding of climate change mitigation with a creative flair for communicating the subject.  I mention this because they are now running a poll on the question, "Do you think it's important to know your carbon footprint?"  Quite apart from the audience selection bias of their followers, I suspect that very few people have a clear idea of their own carbon footprint and almost nobody can be sure of their own direct and indirect contribution to humanity's greenhouse gas emissions, the scale of which is illustrated beautifully by a post on Karina Rubiera's blog:

Here are some of the confusing carbon emissions measurements that I have come across today:
1) My local leisure centre used 6 million kWh of gas last year and its carbon emissions were almost 1500 Tonnes CO2e.  I go there once every few months: how much of that carbon footprint has my name on it?
2) The local boys' secondary school, that my son and I both attended and where my wife is a governor, had publicly reported emissions of 984 Tonnes CO2e in 2008.
3) Intensively reared lamb in the USA causes CO2-equivalent emissions of almost 40kg for every kilo of meat.  Some of this is due to methane emissions from the ruminant gut but much is due to the agricultural feedstock: lamb raised on hill-farms in Britain would, quite literally, embody much less carbon emissions than their grain-reared cousins imprisoned in American feedlots.
4) Duncan Clark, of 10:10 and the Guardian, has reflected deeply on the question of short-haul flights in his blog post today.  He concludes that our personal carbon emissions matter much less than the effect that our awareness-raising can have on those of others.

Of course, I agree that communication and awareness-raising are at the heart of the matter.  Duncan and Emma are both leading exponents of sustainability communications and yet even they, I think they would agree, have limited ability to reach out to the wider public, at home and abroad, and engage them in the battle against dangerous climate change due to fossil carbon emissions from unsustainable behaviours and practices in so many aspects of our contemporary lifestyles.  The clamour of commercial concerns, urging us to consume and spend so that they can grow and profit, is usually too loud and incessant for quiet voices of restraint and reflection to be heard.

This is one reason why I think it matters that each of us considers our own carbon footprint and makes sure to reduce it over time.  If you will excuse the clumsy analogy, it's the ethical equivalent of a medical thermometer for my environmental conscience.  The 10:10 campaign grabbed the attention of 100,000 people last year, along with 1000s of businesses and institutions, and focused them on the challenge of cutting their carbon emissions by 10% in 2010.  Positive, purposeful progress - what an amazing achievement!  It's still full steam ahead for the good ship 10:10 and their challenge to each of us now is to cut 10% every year.

However, it's not enough to know the amount of indirect emissions that feature in my personal carbon account simply for being a citizen - including healthcare, education, defence, government, transport and other infrastructure.  I cannot influence these through my own efforts.  The direct carbon impacts of my activities and decisions are much more important to me in measuring my personal responsibility for human-induced climate change.  I want to know, and reduce, the carbon footprint of my personal consumption - such as transport, diet, shopping, entertainment and home energy use.

Useful books and online tools abound to help me know my numbers but, where possible, I favour direct measurement.  It's simple, accurate and reflects my improvements every year.  At home, just put regular meter readings into a basic spreadsheet and, with a couple of standard conversion factors, you can see directly what progress you are making towards cutting your carbon year on year.  This graph shows our home's total energy use for the calendar years 2009 -11.

The next one is smoothed using Moving Annual Totals (MAT) for electricity and gas use, and carbon emissions, over the same period. You can see that the green line has been bumping along just above 4 Tonnes/year CO2 emissions since May 2011: by contrast, our home energy use in 2006 emitted more than 8 Tonnes CO2.

These direct measurements and graphs are not to everyone's taste but they motivate me to remain focused on our home's energy use.  If you don't want to make your own spreadsheet, Oxford University's Environmental Change Institute (ECI) have already done it for you!  Just sign up to iMeasure and they'll prompt you to type in your meter readings every Monday.  Over time, iMeasure shows you your home's energy consumption, and its carbon footprint, in a variety of ways.  The two features that I find most impressive are the weekly energy performance rating (A-G) that it gives your home and the rolling competition with neighbours in our local Carbon Club - we're nothing if not competitive!

Similarly, I keep a little logbook in the driver's door pocket of my car, to record my fuel consumption.  I multiply the litres of diesel purchased by 2.68 (kg CO2 per litre) to calculate my direct driving emissions. I have to make some estimates for maintenance and embodied emissions in the car's manufacture: these last go down for every additional year that I keep the car on the road but do they offset the direct emissions from a newer, more efficient vehicle?  Mike Berners-Lee wrote this excellent piece in the Guardian, from his book, "How Bad Are Bananas?".  There was also a great decision tree for keeping or replacing an older car - I'll post a link if I can find one.

For travel by public transport, eating, reading, holidays, gadgets, etc., the Guardian's quick carbon calculator, posted by Duncan Clark in 2009 and created by Small World Consulting, is the best footprint calculator I know.

To sum up, I think it does matter that we each care about our individual carbon footprint, gain some idea of its size and become engaged in whittling it down over time.  It's not going to stop dangerous, manmade climate change in its tracks but it is an ethical, personal response to the moral challenge of treading lightly on the Earth and the living world that we continue to share it with.

10:10 performance - deeply technical stuff!

In my first post of 2010, I set the target for my home's 10:10 challenge - to cut our domestic emissions to 4.5 Tonnes CO2-e by Christmas eve.  This required our annual energy use to drop by 10%, to 4,770kWh electricity and 12,655kWh gas.

And the results are: SUCCESS with electricity but FAIL with gas.  I am disappointed with this because, despite the cold and snowy weather we had in February, our moving annual total gas consumption was 13,000kWh from February to May and it hadn't risen much over the summer.  It had crept up to 13,600 by mid-November and I was determined to keep the thermostat turned down but this made no difference when one week of snow was followed by our current, much harsher freeze.  In the last four weeks of Arctic weather, our annual total gas usage has jumped to 14,850kWh.

My friend and neighbour, Vincent Jansen, has just introduced me to the concept of degree-days.  The Environmental Change Institute at Oxford University run the i-measure website, where you can benchmark your home's energy use and emissions each week.  They also publish tables of heating demand for buildings, measured at a number of sites around the country - available here.  These record the effective temperature difference that has to be maintained in buildings, in units called degree-days.  You can plot these weekly or monthly data sets against your home's heating energy usage to see how much benefit your insulation improvements or boiler upgrades have given you.  As you can see, the correlation between degree-days and gas usage in my home is remarkably strong.

Each record has a columns of degree-days recorded against a range of reference temperatures and it is important to choose the appropriate reference temperature for your building.  15.5°C is traditionally used for homes and offices (and 18.5°C for hospitals) but my records fit closest to the 14°C curve.  I have split the difference and used a base temperature of 15°C.

If you plot a building's energy use against degree-days, the line is called the performance line and the slope of this line is the building's energy loss rate.  Here are three separate performance lines for my family's home in 2008 (red), 2009 (blue) and 2010 (green).  The slope of the green line is noticeably less than the blue and red, suggesting that the extra-thick loft lagging I added last autumn has been of some benefit.

So the bottom line is that I missed my 10:10 target for home heating energy but, given the extreme weather we are experiencing this month, I could quite well have used 10% more gas than I have done, if it weren't for the extra insulation that I put in to meet my 10:10 commitments.

What about the 'leccy?  You may recall that I fitted LED lights in the kitchen and in the bedrooms.    I also switched my tower PC off last Christmas and replaced it with the amazing Fit-PC 2 net-top computer, running on just 8 watts.  The result has been remarkable.  Our moving annual total usage has dropped smoothly throughout the year and is almost on target, at 4798kWh.

One last picture shows my home's cumulative gas and electricity use through 2009 and 2010.  The effect of our prolonged cold spell is strikingly clear when this year's gas usage jumps ahead of  last year's at the end of November.  Nationally, this must have led to a huge surge in energy demand, emissions and customers' bills.

So far, I have neglected the carbon-intensity of my electricity provider.  In calculating my home's carbon emissions, I use DECC's national average carbon-intensity of 430g CO2 per kWh electricity.  However, as a British Gas customer, my electricity has the lowest carbon-intensity of any of the big 6, at 371g CO2 per kWh supplied.  If I recalculate using the British Gas carbon intensity, my home emitted 4.6 Tonnes CO2 for the year to Christmas Eve 2010.  So I can console myself that, despite missing my target for gas usage, our overall carbon emissions are almost where I had hoped.

For the broader aspects of carbon footprint, such as diet, lifestyle, shopping and travel, I don't have any hard and fast measures.  If we all eat less meat and dairy, buy more local and seasonal food, make our clothes and electronic gadgets last longer and keep our feet firmly on land (or water) when we take our holidays then I suspect we'd make a big dent in Britain's climate-changing carbon emissions.  The transition to a sustainable economy is going to be a major theme of the coming decade and I hope many people here and around the world will jump at the chance to make life better for all the generations to come.