London, Nov 21 : A new research has suggested that out of cars, planes, ships and trains, it is cars that have the worst effect on the climate.
According to a report in New Scientist, Jan Fuglestvedt of the Centre of international Climate and Environmental Research (CICERO) in Norway, and his colleagues, did the research, taking into account the different nature and life spans of transportation emissions.
The team inventoried all the different types of emissions that were generated by air, road, ship and rail transportation in 2000.
They then calculated how this one-year "pulse" of emissions from each sector would warm the globe over the coming century.
Their results show that the total emissions generated by the shipping industry in 2000 will, by 2020, have cooled the planet by about 0.0005 degree Celsius, thanks to the Sun-blocking effect of fine shipping soot.
By 2040, however, this cooling power will have been entirely overcome by the warming effect of shipping greenhouse gases.
These are long-lasting, to the extent that 100 years after a ship has crossed the Atlantic, they will still be having a warming effect.
The contrails puffed out by all the planes that flew in 2000 caused a 0.003 degree C rise in temperature by helping form warmth-trapping clouds. But like shipping soot, the effect is short-lived, and by 2020 it will have disappeared entirely.
The CO2 emitted by those same flights has six times less warming effect, but will persist for more than a century. Fuglestvedt's calculations show that, of all the forms of transportation used in 2000, trains were the least harmful.
Cars and trucks, though, win the dubious prize of having warmed the planet the most.
The initial, 20-year warming caused by their emissions is seven times greater than the temperature rise generated by all the planes that crisscrossed the globe in 2000.
Fuglestvedt and his colleagues calculated that if the transportation mix did not change, and emissions stayed at year 2000 levels for a century, the warming from cars and trucks would be four times greater in 2100 than the warming from planes.
But, according to him, the future is likely to be very different. His team now intends to look at the impact of each mode of transportation per amount of cargo carried.