Anthony Browne is MP for South Cambridgeshire.

In the forests of media coverage about the UK’s target to be net zero by 2050, very little attention has been paid to that one little word: “net”.

But those three letters leave open the door to huge new policy and technology possibilities – and will make the transition less of an economic challengeIt has also caused alarm in parts of the environment movement: some of which is justified, and some of which is unfounded. 

Net zero means our target is the difference between greenhouse gasses emitted into the atmosphere, and those taken out. Net zero doesn’t mean no emissions at all: it just means these are matched by negative emissionswith carbon dioxide (or other greenhouse gases) being taken out of the atmosphere.

It opens the prospect of the whole planet going to negative emissions at some point in the future, taking carbon dioxide in the atmosphere down to the level it was before the industrial revolution. 

Or rather, it opens the prospect of the planet going back to negative emissions. Because negative emissions is not some newfangled idea, but is actually what nature does if humans stop interfering.

Before life was created 3.5 billion years ago, atmospheric carbon dioxide was around 4,000 parts per million (and there was no atmospheric oxygen – all animals would die instantly, and fire was not possible). But life absorbed the carbon dioxide, turning it into living matter (initially micro-organisms, then plants and animals), and then burying it underground as oil, gas and coal, or as carboniferous rocks such as chalk and limestone.

In the process, it released oxygen into the atmosphere, enabling the evolution of animalsThe sea also played a role, absorbing carbon dioxide into its almost limitless mass. The level of atmospheric carbon dioxide slowly and steadily fell, reaching a low point of 280 parts per million about 20,000 years ago. It then started slowly rising, possibly because of man’s fascination with fire, but it wasn’t until the industrial revolution – and really the last few decades – that the levels really accelerated. Carbon dioxide levels are now over 415 parts per million, up 50 per cent as a result of man’s activities, and rising sharply 

You may wonder why it matters if CO2 levels are going up if they spent billions of years coming down. The issue is that, for the past 20,000 years, the Earth has enjoyed a remarkably benign and stable climate, allowing human civilisation to flourish. Life on earth and civilisation is optimised for this climate. Changing it will cause untold damage. 

If we can increase the amount of negative emissions – take more carbon dioxide out of the atmosphere – we can obviously reach our net zero target quicker than we otherwise would. As chair of the AllParty Parliamentary Group on the Environment, I hosted the global launch of the Coalition for Negative Emissions, a group interested in promoting negative emissions to get to net zero, but it was the environment groups that were most critical 

So why the controversy? There are two main ways to increase negative emissions. The first is nature based solutions, such as planting trees, increasing organic matter in soil, and ensuring that our peatlands are not depleted. These are “no regret policies” – things we would want to do anyway, even if we weren’t concerned about climate change. These are policies supported by all.  

Then there are the “negative emissions technologies”, which is where the controversy arises. This includes such processes as carbon capture and storage, whereby carbon dioxide is stripped from the chimneys of factories, and then buried underground.

Another such technology is direct air capture, which involves literally sucking carbon dioxide out of the atmosphere and sticking it underground. These negative emission technologies are at early stages, but developing rapidly. There are numerous pilot plants around the world, showing that it works (but is not yet economical).  

The negative emissions technologies are supported in principle by the UN’s International Panel on Climate Change, the UK’s Committee on Climate Change, and the UK Government, which is investing £800 million in CCS. Negative emissions are seen by governments as one tool in the toolbox needed to reach the net zero target. 

But many green groups are opposed.  Both Extinction Rebellion and the Green Party have called for negative emission technologies to be excluded from the Government’s net zero target. There is no doubt that many in the green movement are simply predisposed to oppose negative emission technologies. 

One concern is that negative emissions would be an excuse to give up on other measures to reduce emissions. Why develop wind power, ban petrol cars, and install double glazing, if we could keep burning fossil fuels and just suck their emissions out of the atmosphere?

However, I really do not detect in the UK or elsewhere any pressure to keep the gas power stations going because negative emissions will come to the rescue. Negative emissions are at too early stage to have such a scale impact in the next 20 years. Governments, in the UK and elsewhere, are setting binding targets to reach net zero come what may. 

There is a valid concern that negative emissions are not robust – that the carbon is not really taken out of the atmosphere and buried. Clearly it needs strong authentication and monitoring, to make sure the system isn’t gamed by cynical companies. There are fears that the carbon dioxide will not remain buried and will seep out.

But geologists are confident: nature stored gas underground for millions of years without it seeping out. The pilots so far show no sign of this happening. Sometimes green groups insist that negative emissions technologies are too new to work at scale, although the same applied to windpower 30 years ago, and that didn’t stop green groups championing that.  

There are strong arguments in favour of negative emission technologies. These are ultimately much more scalable than nature based solutions: there is (at some point) a limit to how many trees we can plant because land is limited, but there is no limit to the carbon that can be buried underground.

Negative emissions also puts a cap on the cost of reaching net zero since, if it is too expensive to reduce the emissions from a certain activity, such as making steel, then these could instead be offset by stepping up negative emissions elsewhere. If it costs £150 to remove a tonne of carbon from the atmosphere, but making steel from renewable energy costs £300 per tonne of carbon saved, then using negative emissions will help us reach net zero at lower economic cost. For the UK, CCS is seen as a huge opportunity, as our gas and oil industry has the skills and technology to put it into operation, and the North Sea geology is ideal for storing carbon.  

There is no valid reason not to push ahead with negative emissions technologies, bring them to maturity, make sure they are robust and do what they claim, and use them to reduce the cost of getting to net zero.

Carbon dioxide molecules are all equal. As far as the climate is concerned, it does not matter if a CO2 molecule is taken out of the atmosphere by a tree or a direct air capture plant. Negative emission technologies also give humanity the prospect at some point in the future of not just of stopping carbon dioxide levels rising, but bringing them back down. That will open up a whole new debate in the future: what is the ideal level of carbon dioxide in the atmosphere.