Prof Andrew Macintosh spent years working on the integrity of the Australian government’s carbon credit system which gives credits for projects such as regrowing native forests after clearing. Now, he’s turned whistleblower, claiming this system is ‘a fraud’ on the environment, taxpayers and consumers – a claim that energy and emissions reduction minister Angus Taylor has described as ‘completely unfounded’. Climate and environment editor Adam Morton explains how Australia’s carbon credits system works and speaks to Macintosh about why he thinks this system is broken