What if... every city had a congestion charge?

Nowadays it seems you hardly have to wait five minutes for a bus in London. But if, like me, you grew up here you'll remember it wasn't always the case. In the 1990s, the average speed on the roads of London was slower than it had been at the beginning of the century, before the motorcar was invented.  All that changed in 2003 when the newly elected mayor, the 'right on' Ken Livingstone, brought in Europe's first urban congestion charge. The impact on traffic was immediate. But what did it do for carbon emissions? And should every other city in the world follow in London's footsteps?

There's been relatively little research into the emissions impact of urban congestion charging - primarily because surprisingly few such schemes exist. The world's first congestion charge was introduced in Singapore in 1975. Then came London. And even more recently, Stockholm introduced its own charging scheme. Other urban road toll schemes exist but these have been introduced primarily to raise income rather than cut traffic. And several cities, particularly in the developing world, run car free days where vehicles are banned in urban centres. In Jakarta drivers must leave their car at home once a week!

Residents walk on the roads during Jakarta's weekly car free days

Congestion charges can reduce emissions in two ways. The first is obvious. Less cars on the roads means less vehicles emitting CO₂. But in addition less cars means traffic moves faster with less stopping and starting. And steady driving is efficient driving.

Transport for London estimated that the congestion charge reduced the number of cars on London's streets by a colossal 27% between 2002 and 2003 after the charge was introduced. This corresponded to about 65,000 - 70,000 less journeys. Passenger surveys suggested about half of these journeys had been transferred to public transport, primarily buses (the charge was brought in to coincide with a multimillion pound investment in London's bus network). About 10% switched to other private transport like bikes and taxis. And a further 35% chose to travel around the congestion charge zone, or travel at different times of the day. What does this correspond to in emissions? ... Well, nobody seems to have estimated that. 

Unlike us, the Swedes - being the green nation they are - have estimated the carbon impact of their scheme. Their charge resulted in a 16% reduction in traffic over the city centre. And this corresponded to a 14% reduction in emissions.

£100 million was invested in London's buses before the congestion charge was brought in

So what would happen if every city in the world had a similar congestion charge? Let's do some back of the envelope calculations. Half the world's population live in cities so let's assume half the world's billion cars are in cities too (I'm sure this isn't right - but I searched high and low for an estimate to no avail. If you know better - put it in the comments below). The IPCC says 13% of the world's carbon emissions come from transport and (rather lackadaisically) says 'about three quarters' of that is from road vehicles. So, do the number crunching and you'll find that, if every city introduced a congestion charge with the same impact as Stockholm's, global carbon emissions would be cut by about 0.1%.

It might not sound like a huge amount but there's loads of other benefits to a congestion charge. It takes less time to get about (vehicle speeds in London have increased 17% from pre-charging levels). And positive impacts on health have been reported in both London and Stockholm due to the decrease in atmospheric concentrations of airborne pollutants and nitrogen oxides. A King's College study estimated the congestion charge gave an additional 183 years of life per 100,000 of the population within the charging zone. Even the economy, ever the victim of emissions reduction schemes, doesn't seem to have suffered. A report by John Lewis found that, although takings had reduced at their central London stores, there was no measurable effect on central London retail overall. With stats like these, rolling out congestion charging to every city in the world seems like a no brainer!

What if... the world had a one-child policy?

I recently received a request to look at the emissions impact of sterilizing everyone on the planet. Good idea, I thought... But I'm not too keen on suggesting we implement the demise of the human species. So I thought I'd go for something a little less dramatic. In 1978 China's government introduced a one-child policy to tackle issues of overpopulation. What would be the impact on greenhouse gas emissions if the rest of the world were to follow suit?

There's lots of reasons to be worried about overpopulation. More people consume more stuff. And on a finite planet with limited resources, if the population increases too far - there might not be enough 'stuff' to go round. The video below sums it up nicely. But since this is a blog about climate change I'm going to look purely at greenhouse gas emissions.

I was surprised to find that globally, per capita emissions haven't changed much in the past 60 years. But total greenhouse gas emissions have seen an exponential upward trend. It follows then that the increase in emissions must be down to more people. This was certainly the conclusions drawn by a group of Washington based researchers who identified population size and affluence as the key drivers of human environmental impact.

Concerns such as this spurred the formation of the Optimum Population Trust, a group committed to curbing world population increase, in 1991. Today they count David Attenborough, James Lovelock and Jonathon Porritt amongst their members. They run a campaign which allows people to offset their carbon emissions by paying for contraception in developing countries. Increase access to contraception, they claim, and reduce the population expansion that is driving emissions. But will it work?

It turns out that the relationship between population size and emissions isn't quite so straightforward. Take Uganda for instance, a country with one of the highest birth rates in the world. The average person in Uganda is responsible for roughly 70 times less carbon emissions than a person in the UK. So even if the population of Uganda increases ten fold, the overall effect on global carbon emissions will be tiny. This pattern can be seen all over the developing world where rapidly increasing populations will result in little impact on emissions.

Far more important to emissions than population size, is population demographics. This paper by Michigan State University estimated that China's one-child policy had reduced births by 300 million by 2005. But this had been largely offset by an additional 80 million households brought about by increased divorce rates and children leaving home earlier. More homes consume more energy resulting in more emissions.  You might also want to look at age. Although here the outcome is less obvious. Some studies point towards people of a working age having a higher carbon footprint, others suggest that older people do.

So the idea of simply reducing population may not have such an obvious impact on emissions right now. A one-child policy might work to reduce emission in the UK, where our per capita emissions are large. But it won't make an immediate impact in the developing countries where populations are growing at their fastest. However if these countries develop in a similar fashion to the UK in the future, expanding their per capita emissions, population policies introduced now could play a vital role.

And if you don't like the thought of a Chinese style forced family planning regime, take solace in this report by the UN Population fund. They found that by far the most effective way of reducing birth rates in developing countries is to empower women, giving them the choice of when, and if, to have children. It's cheap, increases women's education rates and encourages them to play a more active role in society. I think you'd be hard pressed to find someone who didn't agree with that!

What if... the world switched to wind power?

The ongoing debate over wind power intensified last week when Tory minister John Hayes claimed 'Enough is enough!'. Wind farms are causing an irreversible blight on our green and pleasant land and new developments must be stopped.

Whatever your thoughts on wind turbines (personally I think they're beautiful, certainly less of an eyesore than the pylons that stretch across the countryside) there's no denying that there's more of them about these days. The world produces 13 times more energy from wind now than it did at the turn of the century. But I was surprised to find that, despite the Sustainable Energy commission stating the UK has the 'best wind resources in Europe', it produces relatively little wind power compared to its European counterparts. Take Germany for instance. According to the IEA, Germany produces 6% of its electricity from wind and the UK, just under 3%. So we can't be that hard done by.

But just how bad could things get? What if the entire world switched to wind power?

If you're looking for energy stats, there aren't many better sources that David Mackay's brilliant Sustainability without the hot air. Mackay looks at the numbers to bring a much needed level headedness to the energy debate. In the video below he outlines the huge scale of the energy challenge more concisely than I could ever hope to.

Mackay calculates that covering 10% of the UK in wind turbines (An area bigger than Wales) would produce 20kwh a day per person of energy - half the energy used to drive a 50km daily commute. Of course, stronger winds mean there's greater potential for generating energy out at sea. Mackay calculates that, if the shallow waters around the entire UK coastline were covered in a strip of turbines 4km thick (total area 13,000km²) we'd get an additional 16 kwh a day per person. Currently we're limited to these shallow waters  - wind turbines in deeper waters are just not economically viable.

So if we covered Wales in wind turbines and fully exploited our coastal waters, wind power could produce 36kwh a day per person - a long way short of the 195kwh a day we currently use.

Norwegian company Statoil have developed floating wind turbines that could be used in deep waters

The average person on Earth uses much less energy than us - about 56kwh a day per person. So how big an area would we need to provide this energy with wind turbines alone? Well if we assume global wind speeds are similar to those Mackay has used for his UK calculations (a gross simplification I know) and there are 7 billion people on the planet - a quick calculation reveals you'd need to cover 6.85 million km² of land in wind turbines - about twice the size of India!

When it's put like this, the need for an energy mix is obvious. It's impossible to rely solely on one energy source such as wind - the engineering challenge would be unimaginably big. And that's before we've even considered that it's not windy all the time. So if we want to make sure we can produce electricity 24/7, we a range of energy sources. 

What if... everyone bought locally?

I'm continuing the food theme for this latest post. Maybe it's my love of eating; or maybe it's because the more I read into it, the more fascinating the carbon economics of food seem to be. This time round it's the local food movement. We should all buy locally, right? Well, what would happen if we did?

You're probably familiar with the concept of food miles - the distance our food travels before it reaches our supermarket shelves. Transporting goods causes greenhouse gas emissions. Reduce your food miles, the theory goes, and reduce emissions from your food. And when 14% of global emissions come from agriculture, there's big savings to be made!

If you've read any of my previous posts, you'll know that things in the world of emissions are never as simple as they first appear. Take the case of Young's, who got in trouble a few years back when it was revealed their locally sourced Scottish prawns where flown to Thailand for shelling before returning to the UK to be sold in our supermarkets. Customers thinking they were buying local produce were unsuspectingly buying a product with 12,000 embedded food miles!

Luckily studies have shown that it's not food miles that count - the methods used to grow your food are much more important. It's helpful here to have a look at a few case studies. Consider the tomato. A 2008 DEFRA study found that tomatoes grown in the UK were responsible for three to four times more emissions than those imported from Spain, even when the additional food miles were taken into account. This is because UK tomatoes tend to be grown in gas heated greenhouses. A similar study by New Zealand researchers found British lamb was four times more energy intensive than New Zealand lamb, even allowing for transport to the UK - due mainly to the use of larger quantities of fertilisers by UK farmers.

He may look tasty. But if he's from the UK, his carbon emissions may be bigger than you think

All the evidence seems to say that, if you're looking to reduce emissions from food, you need to look at the entire lifecycle of the foods you eat. If you do that, as these American researchers did, you'll find that food miles account for only about 11% of emissions from our food. Even more scarily, a study by the University of California looked at what would happen if everyone in their local area of Santa Barbara County bought locally. Amazingly they found it would reduce emissions from food by less than 1%!

So there you have it. If we all ate locally, the impact on food emissions might be as low as one percent!

Tesco now put carbon footprints on products to help consumers make informed choices

So what should you buy? Well in his excellent book How bad are bananas? author Mike Berners-Lee says you can't go wrong with a banana. Good advice if you ask me. Imagine the detrimental impacts to countries like Ecuador - where 61% of the agriculturalGDP comes from banana exports - if we all stopped eating bananas. When you start looking at situations like this, you can see the issue of buying locally extends far beyond just carbon emissions.

If you want more about food miles, the ever brilliant Freakonomics team have produced this excellent podcast. In it they speak to the authors of the Santa Barbara county study.