The climate impact of transport is surprisingly complicated

Emissions in action. Image: Getty.

The 2020s will have to involve some very big decisions about transport – the UK’s most polluting sector. The UK government’s response so far has been erratic, choosing to intervene to prevent the collapse of Flybe (Europe’s biggest regional airline) and give the green light for the high-speed rail project, HS2.

Decarbonising transport would eliminate 26 per cent of UK CO₂ emissions that come from how people get around. But Prime Minister Boris Johnson recently said that doing this poses “difficult and complicated” questions. On this, Johnson is almost certainly right.

The gilets jaunes protests against fuel duty rises in France show the delicate balancing act between decisive climate action and continued economic growth and convenience. But shouldn’t the government allow a regional flight operator to fail and invest in high-speed rail instead? The answer is not so simple.

Carbon footprints can be misleading

Aviation is one of the fastest growing fossil fuel consumers, with airlines contributing about 3.5 per cent of all man-made greenhouse gas emissions. This might seem small, but a single transatlantic flight from London to New York can grow your personal carbon footprint by as much as the entire heating budget of the average European.

At high altitudes, contrails – the white lines we see in the sky – are formed in the wake of aircraft. These high altitude clouds are too thin to reflect much sunlight, but the ice crystals inside them can trap heat. Unlike low-level cloud, which has a net-cooling effect, contrails contribute significantly to global warming, effectively boosting the aviation industry’s share of greenhouse gas emissions to around 4.9 per cent.

For the most part, the environmental benefit of high-speed rail is taken for granted. Most, but not all, research suggests that high-speed rail can offset emissions from aviation if it can attract enough passengers from alternative air routes. But the relative climate impacts of aviation to other modes of transport depend on more than just engines and altitude.

We can compare the emissions of different forms of transport by calculating the emissions produced by each one when moving one passenger one kilometre. This effectively compares how much CO₂ leaves each vehicle’s exhaust, but it ignores greenhouse gas emissions from the building and maintenance of the vehicles, the infrastructure – such as tracks, runways and airports – and the production of fuel.

The warming effects of different greenhouse gases happen over different time periods, from a few days of short intensive warming to centuries of gentle influence. In order to provide a common unit to measure the impact of different gases, warming effects are standardised over a given time period. The time period normally used is 100 years.

But if it were five years, the effect of contrails would account for more global warming than all the cars in the world. They raise the temperature of the atmosphere in short, intense bursts. On longer timescales, like 20 years, the short term effects are less important and make aviation look considerably better – with flying looking potentially less damaging than some cars over the same distance.

This is still not the whole story though. The energy inputs for different modes of travel vary. The direct burning of fossil fuels in engines, for example jet kerosene in aircraft, emits greenhouse gases. In electrically powered high-speed rail, operating the train produces no emissions, except from the fossil fuels used to generate that electricity elsewhere.

Developing HS2 will mean deploying stations, tracks and centres of communication, and they’ll need ongoing maintenance. These all need energy and material investments, which will create further greenhouse gas emissions through manufacture, transport, and use. That could increase the carbon footprint of rail by between 1.8 and 2.5 times, over just accounting for the operation of the trains. For aviation, the same infrastructure requirements are relatively small, and are responsible for a 1.2–1.3 increase, with road transport showing a 1.4–1.6 increase.

Comparing life cycles

A life cycle approach gives a better understanding of where emissions are occurring and compares transport modes on a much more level playing field. This helps us understand that most greenhouse gas emissions in air and road travel come from flying and driving, whereas in rail travel, the climate effects are dominated by those emissions produced building the infrastructure itself. Emissions from operating trains are generally lower because of the heavy reliance on electricity. But there are still emissions from the manufacture and maintenance of renewable energy technologies to consider.

All modes of high-speed travel come with a cost to the environment. Being able to accurately compare the energy requirements and emissions of different transport options is the first step towards addressing their climate impact.

Governments often try to encourage people to change their behaviour and reduce the number of flights they take. But in the case of HS2, the continued availability of regional flights means that only 4 per cent of drivers and only 1 per cent of aeroplane passengers are likely to change their behaviour.

It’s easy to point the finger at aviation and view rail as a low carbon alternative. But governments need to consider and carefully balance the true climate impacts of a transport project, in every phase of its development.

The Conversation

Laurie Wright, Senior Lecturer, Warsash School of Maritime Science and Engineering, Solent University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.


American policing never adjusted to the decades-long decline in urban violence

Joe Raedle/Getty Images

Princeton University’s Patrick Sharkey is an almost impossibly prolific academic, regularly publishing an array of well-regarded studies on everything from social distancing to neighbourhood change. But in recent years he’s become best known for his work on criminal justice and law enforcement – topics that have risen to the top of America’s policy agenda.  

Sharkey’s last book, Uneasy Peace, is about the dramatic decline in crime rates in American cities, what caused it, and what is needed to sustain it. Published in the wake of the Black Lives Matter movement’s emergence in 2014, it deftly analyzes issues that are again roiling America after the killing of George Floyd. 

Uneasy Peace, and the work Sharkey has published since Floyd’s murder, argues for a massive campaign to address violence in American cities. But that does not mean flooding the streets with more police officers. CityMetric spoke with Sharkey about the little-known factors behind America’s great crime decline, the need for massive public investment, and what community policing looks like without the police.

Why did violent crime in the US, and in American cities particularly, fall so sharply between the early 1990s and the early 2010s? 

Violence from the late 1960s through the early 1990s was at an extreme level. There was a crisis of violence throughout much of urban America, particularly in the big cities. Then something happened in the 1990s. It happened because both political parties took on crime and violence as central issues in their platforms. Bill Clinton ran on a platform that he was tougher on crime than the Republicans had been. The whole country saw violence as a national crisis.

What happened in the early 1990s is there was a large-scale mobilisation to retake public spaces and make cities safe. That consisted of several parts. There was a really large-scale effort to bolster police forces, to invest in more aggressive tactics of policing, to go after gang activity, to shut down drug markets.

At the same time there was a large-scale expansion of local organisations that really mobilised to make their communities safer: after-school programs, religious organizations, community centres, neighbourhood groups. These kinds of organisations expanded in a major way.

What I find is that the expansion of those kinds of community organisations stands alongside the expansion of police forces as components of why violence fell. They combined with expansion of video surveillance, camera systems, and private security. All these things happened at roughly the same time, and public spaces transformed. That's why violence fell so dramatically, beginning in the early 1990s.

The crime decline benefited everybody, making urban areas safer, and convincing more middle- and upper-income people to move back to cities. But you argue that those who live in the most violent neighbourhoods benefited the most, because violent crime declined most in those areas. What has changed in these communities as they've seen less crime?

The most obvious benefit is that tens of thousands of lives were saved, with the greatest impacts experienced by Black men. We found that for most groups, life expectancy wouldn't change that much if homicide never fell. But for Black men, there was an enormous change: the life expectancy of Black men rose by almost a year due purely to the drop in homicide mortality. That is a change as large as any public health advancement over the past several decades.

Then there are direct consequences for academic achievement. The places where violence dropped the most are places where statewide test scores rose the most. And children who were in places that became less violent over the course of their childhood were much more likely to rise up in the income distribution in adulthood and to make more income as adults.

Violence has a long reach. There's a direct effect of violence on every institution, every member, every child within that community. It damages kids’ cognitive development and academic functioning. So, when violence falls, kids are able to learn, kids are able to focus in school if they're not thinking about the threat of violence.

Then it has an indirect impact because life returns when a community becomes safer. Businesses start to set up shop, families invest in that neighbourhood, it becomes a vibrant place again, and that means more jobs are there, that means more opportunities are nearby. That changes the possibilities for a child as they near adulthood and enter the labour market. All this translates into improved economic outcomes later in adulthood.

You point to research that shows aggressive policing and imprisonment has been part of the story of America's great crime decline, but at immense human cost. You note that while every other kind of violence has fallen since the early 1990s, the rates of police violence remain consistent.

Why hasn't police violence responded to what's happened everywhere else?

We invested heavily in an aggressive style of policing. We asked police departments to go take over city streets and reduce violence by any means necessary. That was a conscious policy decision made in the 1980s and 1990s. It was supported by most Americans. Not everyone, but it had support across the political spectrum. It had support from Black and white Americans. Not universal support, but it did have strong support. 

What has changed over time is that as violence fell, as city streets became safer, the strategies that police departments use didn’t change.

I lay out two policy questions toward the end of the book. The first is how can we make sure that violence keeps falling? The second one is how can we do it with a new approach that doesn't rely on the prison system and the aggressive policing of the past few decades. That's the challenge right now: What's the next model?

What do you make of calls to defund or even abolish the police? In your book, you say that every video of police brutality makes it harder to reimagine a new role for the police. Did the George Floyd video make it impossible?

It might be impossible. There are lots of neighbourhoods where the institution has lost all credibility, and that happened a long time ago. More people are coming to that conclusion now.

We need a new model to deal with the challenge of violence. If we pursue a policy agenda that is designed to simply exact revenge against the police and try to destroy this institution, we're going to leave cities vulnerable. If we pursue an agenda that just attempts to dismantle the police before an alternative institution is ready to take responsibility, then we run the risk of destabilising neighbourhoods. That's my biggest concern.

Over a longer term, I think the role of the police should be dramatically reduced. We have great evidence that local community organisations, in combination with residents, are at least as if not more effective at controlling violence. They've just never been given the same resources, the same commitment.  

(Justin Sullivan/Getty Images)

At the end of your book, you call for a “war against violence.” To fight that war, investment is needed if these groups are going to take the place of the police. But we seem to be embarking upon a new age of austerity. What could the ramifications for urban violence be if the US Congress fails to support city and state governments?

Austerity is not inevitable, but it doesn't look like this Congress is preparing to invest in state and local governments. It's not inevitable that we're going to see a period of fiscal crisis in cities. That's a policy choice but if that happens, if city budgets are reduced and funding for local community organizations drops, we'll probably see a rise in violence.

When cities and communities are abandoned, that's what happens. That's why violence rose the first time. In the early 1970s, the federal government abandoned its support of central cities, the power structure of state governments shifted toward suburbs. If funding for cities and local organisations falls, we should expect a rise in violence. 

You write about a newer institution in Australia’s Aboriginal communities that patrols the streets, unarmed, to defuse situations and address issues – everything from domestic disputes to public drunkenness – in place of the police.  But the role of this community patrol, and neighbourhood groups in the US, is about prevention. Is there a role for law enforcement in ensuring that those who commit murder and violence are punished?

Yes. I think the model that we need to work toward is one where a different set of actors are responsible for overseeing public spaces and making sure everybody is safe, everyone is supported within those communities. Then the police play a secondary role.

That means when there's a mental health crisis, you have trained mobile response teams who are the first to respond to those incidents. Patrol of a neighbourhood should not be carried out by police officers, it should be carried out by advocates, by neighbours who are well trained and genuinely concerned for the well-being of their neighbours. At the same time, I argue that there is a role for police. In places where gun violence is extreme, it's potentially harmful to relieve the police of all responsibilities. There are weapons crimes where I think the police should still be the first to respond. There is a role for police because gun violence is so extreme in the US.

The biggest change, which is not often mentioned in these discussions, is in patrol. The people who are out in public space, making sure that no problems emerge, making sure that kids are safe, that they're getting where they need to go. Making sure that if someone comes home from the late shift, they have someone they can see in public space and know that they're okay, know that they'll be safe walking home.

That should not be police officers. There are too many communities where the level of mistrust is too severe. It should be other members of the community who are trained professionals, whose job is to be a pro-social presence in public space. That's one major change that I don't think is mentioned enough in these debates about who should do what. Who should be a pro-social presence in public space?

You cite research that suggests that despite the crime spike between the late 1960s and the early 1990s, the second half of the 20th century was less violent than the first half. So despite recent crime spikes in some cities, and what appears to be a surge in domestic violence related murders during the pandemic, does that mean we are living in one of the most peaceful periods in American history?

Yeah, without a doubt. The data before 1950 are not great. But the best evidence we have suggests that violence has been falling over the history of our country. There have been periods with more and less violence, but without a doubt, we are living in one of the safest periods in US history.

We need to focus a great deal of attention on violence. It is the fundamental challenge of cities. But along with urgency, we have to be aware of progress that's happened over time. New York is going to have a higher level of violence this year, in all likelihood, than it had a couple of years ago. That's something we need to maintain focus on. New Yorkers are dying.

But we also have to remember that there were 2,200 murders [annually] in New York in the early 1990s. There will be somewhere between 300 and 400 this year. That’s urgent, but let's also celebrate progress and make sure we have an accurate perception of the level of violence and that we don't exaggerate short-term fluctuations.

Jake Blumgart is a staff writer at CityMetric.