"Greenhouse Gas (GHG) Mitigation" is a term for reducing GHG emissions in order to reduce or "mitigate" the impacts of climate change. It contrasts with the other main climate change emphasis area, which is "climate adaptation," which entails adapting to climate change (such as through adjusting transportation design standards to withstand more intense storms and higher sea levels).
The goal of GHG mitigation is not to avoid climate change. Climate scientists have established that climate change is already happening and will intensify even if strong steps are taken to reduce GHG emissions. Overall, to avoid the worst impacts and highest risks of climate change, climate scientists are recommending 60 percent to 80 percent GHG reductions below 1990 levels to be achieved by 2050 - with the need for near- and mid-term GHG reductions as well.
Many U.S. states and countries around the world have adopted GHG reduction targets. These targets can take many forms, but all of them have three basic elements:
It is not enough to say "achieve a 50 percent GHG reduction," because it is important what the base year is and what the target year is. A common set of targets is to reduce GHG emissions by 20 percent below 1990 levels by 2020 and by 80 percent below 1990 levels by 2050. In 2009, the U.S. House of Representatives passed a climate change "cap and trade" bill with somewhat different GHG reduction targets - it calls for 17 percent reductions in U.S. GHG below 2005 levels by 2020 and also for 80 percent reductions in U.S. GHG below 2005 by 2050.
These GHG targets do not necessarily require the same percentage reductions from all sections - power plants, industry, agriculture, buildings, and transportation. In fact, economists generally call for GHG mitigation plans to emphasize cost-effectiveness - i.e., selecting GHG reduction strategies based on the lowest cost per ton of GHG reduced. This approach would minimize the costs to the U.S. economy, and to the world, of achieving GHG mitigation. "Carbon cap-and-trade" policies are designed to achieve the lowest cost per ton of GHG reduced by allowing different businesses and different sectors to buy and sell GHG emission rights.
Many experts have concluded that it will be more difficult and more costly to achieve deep reductions in transportation GHG than in other economic sectors, such as power plants, buildings, and agriculture. That is not to say that all transportation strategies are relatively costly. Across transportation, there are relatively low-cost strategies to achieve GHG reductions, such as the 2010 federal auto fuel economy and GHG standards promulgated by the National Highway Transportation Safety Administration (NHTSA) and the Environmental Protection Agency (EPA). In fact, NHTSA and EPA have estimated that while light-duty vehicles that meet these standards are likely to cost more, the costs will be more than offset by savings from reduced fuel consumption - with net lifetime savings to consumers of $3,000 per vehicle, on average. However, other transportation strategies to reduce GHG could be extremely expensive per ton of GHG mitigated.
For surface transportation, GHG mitigation strategies fall into five categories:
Additional information on mitigation strategies for transportation can be found in the AASHTO report, Real Transportation Solutions for Greenhouse Gas Emissions Reductions, AASHTO's Primer on Transportation and Global Climate Change, and in the report, Strategies for Reducing the Impacts of Surface Transportation on Global Climate Change: A Synthesis of Policy Research and State and Local Mitigation Strategies (National Cooperative Highway Research Program 20-24).
This section of the AASHTO Transportation and Climate Change Resource Center website provides more information on GHG mitigation (reduction) for surface transportation.