Image copyright Getty Images

There are many interesting news nuggets in BP's annual Energy Outlook that's just been published.

The document says that even as renewable energy becomes the world's major power source by 2040, demand for oil will stay strong over the next two decades.

But perhaps the most intriguing suggestion in the report is the idea that cutting back on plastic use could backfire and make matters worse.

You might think, a little cynically perhaps, that this is the kind of thing you would expect BP to say.

After all, as one of the world's biggest oil companies, it makes a lot of money from selling the main ingredient in plastic.

But let's look at the thinking behind BP's argument.

If the current global revulsion about the incessant use of plastic continues, BP speculates that there could be a worldwide ban on single-use plastics by 2040.

These throwaway items, such as coffee stirrers, water bottles and bags, account for over a third of all plastic material produced in 2017.

Image copyright BP Image caption BP Thunder Horse platform in the Gulf of Mexico

If the world shifts to use paper, glass and other materials, BP says this will limit demand for oil in the coming decades.

But the document argues that swapping plastic for other materials will have a bigger cost in terms of energy and carbon emissions.

"If you swap a plastic bottle for a glass bottle, that takes about 80% more energy. That will be more energy, more carbon emissions," said BP's chief economist Spencer Dale, speaking on the BBC.

"That bottle is a lot heavier so it takes an awful lot more energy to transport it around," he added.

"Yes, we should be concerned about plastics, but before we start whacking that mole, we should worry about where it pops up somewhere else."

The diesel experience

That all sounds like the law of unintended consequences in action.

One of the best examples of this economic law has happened in the UK over the past 20 years with diesel cars.

In the 1990s, diesels accounted for just 10% of the car fleet. By 2012, this had expanded to 50% as the government encouraged motorists to switch to the fuel to cut CO2 emissions.

This succeeded in cutting carbon but at a huge price. Diesels produced 15% less CO2 than petrol cars but four times more nitrogen dioxide (NO2) and 22 times more particulates, leading to a rapid uptick in air pollution that the government is still trying to get to grips with.

Paper, plastic, cotton

So would the same law come into play if plastics were banned, as BP maintains?

Certainly, there is some solid evidence that simply swapping plastics for other materials would have negative knock-on impacts.

When plastic bags are measured against paper or cotton substitutes, a BBC analysis found there wasn't a great deal of difference in their overall environmental impact.

Paper bags require marginally fewer reuses than "bags for life" to make them more environmentally friendly than single-use plastic bags.

On the other hand, paper bags are less durable than other types of bags, which means customers have to replace them more frequently.

Image copyright Getty Images Image caption Glass bottles are often recycled more than plastic

Last November, researchers at Heriot-Watt University published a study showing that an outright ban on plastics could cause significant damage to the environment.

"Banning or reducing their use would have a massive impact on the way we live," explained Prof David Buckland, who led the study.

"For instance, replacing plastics with alternative materials such as glass and metals would cost more to manufacture due to the energy consumed and resources - including water - required to process them," he said.

"Furthermore, because plastics are lightweight, transportation of consumer goods in plastic packaging means fewer vehicles are required for transportation of those goods, therefore burning less fuel and greatly reducing greenhouse gas emissions."

Counter argument

Campaigners though are not entirely convinced, and think that BP is stressing the downside of banning plastic because it is in the company's self interest.

"Fossil fuel giants will make countless billions in the future if the production of single-use plastic continues at current rates," said Louise Edge, from Greenpeace UK.

"So it's no wonder they are keen for the world to keep using more and more of it.

"While it's true that it takes less energy to produce and transport plastic than glass, a glass bottle can be reused dozens of times and is infinitely recyclable, unlike plastic. Plus, materials like glass when they escape collection don't go on polluting our oceans and rivers for hundreds of years."

Plastic 'alternatives'

BP says that its future scenario doesn't include the widespread deployment of efficient collection and re-use systems that could reduce the amount of extra emissions required for substitute products.

Steps to encourage recycling are already underway. The UK, for example, will introduce a new tax on the manufacture and import of plastic packaging that contains less than 30% recycled material, to come into effect in 2022.

There are also loads of developments taking place with alternative materials.

Danish company Arla is already introducing wood-based bioplastic cartons for milk that can be recycled just like cardboard.

And there's the promise of carbon taxes as governments look at ways of reducing emissions.

These could make plastics more expensive and also ensure that the alternatives don't make the climate situation worse. This may be the ultimate defence against the unintended consequences of plastic bans.