It is almost impossible to achieve carbon neutrality by 2050, through using land alone, and would require all the farmland on Earth to be forested, according to an Oxfam report.

Governments and major corporations are increasingly planting trees and reforesting farmland to offset the damage done by greenhouse gases that have been emitted into the atmosphere by their day-to-day activities.

It is believed that a fifth of the world’s 2,000 largest publicly listed corporations now have net-zero goals that depend upon land-based carbon sinks.

However, Oxfam’s Tightening the Net report said some companies are hiding behind “unreliable, unproven and unrealistic” carbon removal schemes. These are failing to cut emissions quickly enough to avert a catastrophic climate breakdown, the report’s authors said.

At least 1.6 billion hectares of new forests would be needed to achieve net neutrality, equivalent to five times the size of India or more than all the farmland on the planet, the report stated.

As a result, such schemes are also adding to food insecurity and could result in global food prices surging by 80 per cent by 2050.

Danny Sriskandarajah, Chief Executive of Oxfam GB, said: “Too many companies and governments are hiding behind the smokescreen of ‘net zero’ to continue dirty business-as-usual activities.

“Net-zero targets are vital to tackling climate change. Some governments and companies are taking bold action to cut carbon emissions but there are currently too few to give us a realistic chance of averting climate catastrophe and the widespread hunger and devastation that come with it.”

Oxfam is calling for a greater focus on “deeply cutting” carbon emissions in the near term, starting at home and with operations and supply chains.

Carbon removal is not a substitute for cutting emissions and should be counted separately, the report said, adding that net-zero targets must be measurable and transparent.

“Land is a finite and precious resource that millions of small-scale farmers and Indigenous people depend upon to feed their families,” Mr Sriskandarajah said. “Nature and land-based carbon removal schemes are an important part of the mix to lower emissions but more caution is needed to ensure good stewardship that doesn’t threaten food security.”

In November, Britain will host the Cop26 summit in Glasgow  where global leaders will meet to ensure steps to keep global warming below 1.5°C.

Scientists and climate experts say the world is far short of that target. Oxfam’s report warns the world should collectively be on track to reduce carbon emissions by 45 per cent by 2030 from 2010 levels, but only a one per cent reduction has been achieved.