The UK's plans to cut emissions by 80% by 2050 are fundamentally flawed and almost certain to fail, according to a US academic.
Roger Pielke Jr, a science policy expert, said the UK government had underestimated the magnitude of the task to curb greenhouse gas emissions.
He added that it would be more effective to "decarbonise" economic growth rather than focus on targets.
Professor Pielke made his comments during a speech at Aston University.
Professor Pielke said that a country's greenhouse gas trajectory was determined by three factors: economic growth; population growth; and changes in technology.
This meant, the academic from the University of Colorado suggested, that if people migrate to the UK and the economy boomed, it would be harder for politicians to achieve emissions cuts based on historic levels.
He calculated that the combined effects of possible population growth and economic growth could oblige the UK to increase energy efficiency and reduce carbon intensity of energy at an unprecedented annual rate of 5.4%.
Conversely, if migrants left the UK and the economy slumped, there would be a downturn in emissions, for which politicians would claim unearned credit.