Greenhouse gases (GHGs) accumulating in the atmosphere are threatening major changes to the world’s climate. The main greenhouse gas, carbon dioxide (CO₂), has risen dramatically since the beginning of the industrial age.

(Source: Earth Policy Institute www.earthpolicy.org)

Much of this CO₂ comes from burning fossil fuels (coal, oil and natural gas), and most oil is consumed in the transportation sector. Climate experts predict that if we continue on our present path of increased burning of fossil fuels, the climate will most likely change dramatically with higher global average temperatures, reduced ice cover in the polar regions, rising sea levels, and potentially increased severity of storms and droughts.

Temperatures in northern hemisphere over 1,000 years: (Source: IPCC, 2001a)

450 ppm Goal: To avoid this potential outcome, climate experts have recommended that we set a goal of reducing GHGs to 80% below the 1990 emission levels, preferably by 2050. This is based on stabilizing GHGs at 450 parts per million (ppm), above current levels of 385 ppm. We have therefore set this as the benchmark for evaluating the light duty vehicle (LDV) transportation sector: we compare the projected GHG emissions from each alternative vehicle scenario with the benchmark that is 80% below 1990 level of GHGs from the LDV sector.

350 ppm Goal: However, some climate scientists are now worried that the effects of global warming are occurring faster than predicted by computer models.  Some are now saying that we may need to not only stabilize GHG levels but actually reduce them from 385 ppm today to 350 ppm by 2100 or 2200. This would require not only conversion to zero carbon energy sources like renewables and nuclear energy, but also significant net negative technologies, such as biomass gasification with carbon capture and storage; the biomass would remove CO₂ as the plant grows, and most of this CO₂ would then be sequestered underground (or in the sea?), thereby sucking CO₂ out of the atmosphere.  To achieve this net reduction, some are suggesting that we reduce GHGs by 97% below 1990 levels by 2050, instead of the 80% goal used in our model.

In the US, transportation accounts for 33% of all greenhouse gas emissions (almost all from petroleum) and electricity generation accounts for 40% (mostly from coal). Conclusion: we must “green” the grid as well as reducing the carbon footprint of our vehicles.

Global average temperatures over 140 years, and Northern hemisphere over 1,000 years: