Crypto-currencies such as Bitcoin rely on enormous amounts of computing power, and therefore electricity. As the crytpo-boom gathered steam last year, the unsustainability of this approach was noted, with the energy used to run these computations making a significant contribution to climate change. Now scientists have calculated how long it would take before Bitcoin tips the world into a dangerous climate single-handedly, should it become the dominant form of currency transaction.

The Paris agreement commits the world to maintaining temperatures at no more than 2ºC (3.6ºF) above pre-industrial levels. Even that level may be unsafe, with 1.5 ºC (2.7 ºF) a better choice, but there are very few qualified climate scientists who argue we have room to go higher.

After considering the gas already emitted, estimations of how much carbon dioxide we can release without crossing that threshold range from 231-745 billion tonnes, depending on various assumptions. A paper in Nature Climate Change calculates that Bitcoin alone caused the release of the equivalent of 69 million tonnes of CO₂ in 2017, taking into account the spread of where the computations were done.

Whether paying for porn, illegal drugs, and currency speculation is the best way to use one three-thousandth of the world's remaining carbon stocks is a political matter, not a scientific one. However, Dr Camilo Mora of the University of Hawaii Manoa and co-authors demonstrate that the contribution could become much larger.

“Globally, ~314.2 billion cashless transactions are carried out every year, of which Bitcoin’s share was ~0.033% in 2017,” the paper notes. However, the people who caused the value of Bitcoin to rise in value thousands of times were doing so because they expected the currency to have a much bigger future.

Mora considered the rate of adoption of 40 widespread technologies, such as credit card payments and mobile phones. If Bitcoin were to rise as fast as the median of these examples, and the energy sources remain the same, it would consume the lower estimate of the world's carbon reserves in 16 years. Even at the rate of the slower technologies, it would take 22 years before we would be in dangerous climate territory, even if not a single lump of coal was burned for any other purpose.

The calculations assume that we continue powering crypto-currencies using the current mix of fuels in the countries where calculations have been run. Some bitcoin miners have tried to address the issue by powering their computers using renewable electricity. Often, however, these projects have simply diverted existing hydro energy that would otherwise have been used for a different purpose, rather than stimulating the growth of low carbon sources.

In this context, the damage Bitcoin is doing to the Search for Extra Terrestrial Intelligence looks minor, but if we can't find aliens, maybe they blockchained themselves to extinction.