Climate change - Greenhouse gases from motor vehicle emissions are a growing concern. The Global Environment Facility estimates that the transport sector now contributes about 15% of all carbon emissions. According to forecasts in carbon emissions in the next ten years, transport might be responsible for as much as 50% of the predicted increase.

Ozone damage - While ozone in the stratosphere protects us from harmful UV raditation, tropospheric ozone is known to damage plants and crops. According to the US EPA, ozone accounts for about 1 to 2 billion dollars worth of agricultural losses each year.

Acid rain - Sulfur dioxide and nitrogen oxides are responsible for acid deposition, commonly known as "acid rain," which can destroy forests and aquatic life.

Eutrophication - NOx emissions can cause excess algae growth in aquatic ecosystems. This depletes the oxygen levels in the water, reducing populations of fish and other animal life.

Regional haze - Airborne particles obscure visibility.

Asian brown cloud - A layer of brown haze 3 kilometers above South Asia and the Indian Ocean. A UNEP study found that this haze is 75% man-made. It is known to disrupt the region's hydrological cycle.