Carbon credit speculators could lose billions as scientific evidence shows many offsets they have bought have no environmental worth and have become stranded assets. Amid growing evidence that huge numbers of carbon credits do nothing to mitigate global heating and can sometimes be linked to alleged human rights concerns, there is a growing pile of carbon credits ... that are unused in the unregulated voluntary market, according to market analysis. Many of the largest companies in the world have used carbon credits for their sustainability efforts from the unregulated voluntary market, which grew to $2bn (£1.6bn) in size in 2021 and saw prices for many carbon credits rise above $20 per offset. The credits are often generated on the basis they are contributing to climate change mitigation such as stopping tropical deforestation, tree planting and creating renewable energy projects. A new study in the journal Science has found that millions of forest carbon credits approved by Verra, the world's leading certifier, are largely worthless and could make global heating worse if used for offsetting. The analysis ... found that 18 big forest offsetting projects had produced millions of carbon credits based on calculations that greatly inflated their conservation impact. The schemes, which generate credits by avoiding hypothetical deforestation, were found not to reduce forest loss or to reduce it by only small amounts, far less than the huge areas they were claiming to protect, rendering the credits largely hot air.