As our readers know, CO2 is the result of the combustion of any hydrocarbon. Ozone is what they call a "secondary pollutant", which is released to the atmosphere as a consequence of reactions where nitrogen oxydes (NOx) are involved. NOx are released with diesel fumes. The current Kyoto Protocol does not include any reference to NOx or CO (carbon monoxide).
The report points directly at road transport as the most important contributor since the end of the 19th Century, followed by air transport. Other means, such as railways, have reduced their impact in recent years. Remarkably, the report also finds that maritime transport might "cool" the planet in the medium term because of its emissions of SO4 and CO, which might reflect solar radiation.
[Source: ABC via Madrimasd]