A shift from air to rail for passengers travelling between Scotland and London has led to a major reduction in carbon emissions, according to a report.
Transform Scotland said rail journeys between central Scotland and London rose from a 20% market share to 33% between 2005 and 2015.
It said the move to rail had saved more than 680,000 tonnes of emissions.
This would be equivalent to removing all traffic on the M8 between Glasgow and Edinburgh for two years, it said.
The figures were included in Transform Scotland's A Green Journey to Growth report, which said that additional emissions would be saved should rail use continue towards a 50% share of the travel market between Edinburgh and London by 2023.
The 50% target has been set by Virgin Trains, which operates services between London and Scotland's two largest cities.
The report also said further emissions reductions could be expected through the introduction of the new Virgin Azuma trains on the East Coast route, which aim to cut the journey time between Edinburgh and London to four hours.
Transform Scotland estimated that a flight from Edinburgh to London emits 177kg CO2 per passenger, while existing trains emit 34kg per passenger.
But it said an Azuma will emit 28kg - 84% less than a flight.
The sustainable transport alliance's director, Colin Howden, said: "The Scottish transport sector has failed to take significant action to tackle climate change, and has recently become the single largest source of carbon emissions.
"However, one area where there has been significant progress is in Anglo-Scottish travel, where rail's share of the travel market has grown strongly over the past decade.
"For Scotland to meet its challenging climate targets, it is imperative that further action be taken to ensure that rail can grow to at least a 50% market share of the Scotland-London travel market over the next decade."
He said this would include increased investment in the rail network, public bodies using the train rather than flying their staff to London, and a fairer taxation system for Anglo-Scottish travel.
The Transform Scotland report coincided with Virgin Trains revealing that the percentage of people travelling by train to London had reached its highest level for more than 20 years.
Virgin - which is a member of Transform Scotland - said it had recorded an 18% year-on-year growth in passengers travelling between Glasgow and Edinburgh and London in June.
David Horne of Virgin Trains said: "When we took over the east coast route, we set out ambitious plans to gain a 50% market share between Edinburgh and London by 2023.
"These figures show an encouraging start to that journey and confirm a historic shift in travel patterns towards train."
Scotland's transport minister, Humza Yousaf, said increased use of railways was a fundamental part of the Scottish government's greener transport aspirations.