either, to avoid a patchwork of individual country regulations. That agreement was adopted by the International Civil Aviation Organization, however, capping airlines carbon emissions to the year 2020 level, while allowing airlines to buy carbon credits from other industries and projects. In 1992, aircraft radiative forcing was estimated by the IPCC at 3.5% of the total man-made radiative forcing. Per passenger As it accounts for a large share of their costs, 28% by 2007, airlines have a strong incentive to lower their fuel consumption, reducing their environmental footprint. Jet airliners have become 70% more fuel efficient between 1967 and 2007. Jetliner fuel efficiency improves continuously, 40% of the improvement come from engines and 30% from airframes. Efficiency gains were larger early in the jet age than later, with a 55–67% gain from 1960 to 1980 and a 20–26% gain from 1980 to 2000. The average fuel burn of new aircraft fell 45% from 1968 to 2014, a compounded annual reduction of 1.3% with variable reduction rate. By 2018, emissions per revenue ton-kilometer (RTK) were more than halved compared to 1990, at 47%. The aviation energy intensity went from 21.2 to 12.3 MJ/RTK between 2000 and 2019, a % reduction. In 2018, emissions totalled 747 million tonnes for passenger transport, for 8.5 trillion revenue passenger kilometres (RPK), giving an average of 88 gram per RPK. The UK's Department for calculate a long-haul flight release 102g of per passenger kilometre, and 254g of equivalent, including non-CO2 greenhouse gas emissions, water vapor etc; for a domestic flight in Britain. The ICAO targets a 2% efficiency improvement per year between 2013 and 2050, while the IATA targets 1.5% for 2009–2020 and to cut net emissions in half by 2050 relative to 2005. Evolution In 1999, the IPCC estimated aviation's radiative forcing may represent 190 mW/m2 or 5% of the total man-made radiative forcing in 2050, with the uncertainty ranging from 100 to 500 mW/m2. If other industries achieve significant reductions in greenhouse gas emissions over time, aviation's share, as a proportion of the remaining emissions, could rise. Alice Bows-Larkin estimated that the annual global emissions budget would be entirely consumed by aviation emissions to keep the climate change temperature increase below 2 °C by mid-century. Given that growth projections indicate that aviation will generate 15% of global emissions, even with the most advanced technology forecast, she estimated that to hold the risks of dangerous