In this lesson, we studied the details of greenhouse gas emissions, including the sectors of the economy responsible for emissions of various greenhouse gases, the potential for mitigation in these various sectors, and the economic and ethical considerations of climate change and climate change mitigation. We observed that:
- CO2 from fossil fuel burning, deforestation, and other human practices, are the primary causes, responsible for roughly three fourths of net anthropogenic greenhouse gas emissions;
- there is a modest but non-negligible contribution (roughly 13%) from methane, produced largely from agriculture/livestock and dam projects; other minor contributors include nitrous oxide, which also produced as bi-product of agricultural practices;
- the primary sector of our economy responsible for greenhouse emissions is energy production, amounting for more than 25% of emissions; other major contributors are industrial practices (nearly 20%), deforestation (roughly 17%), and transport and agriculture (each at 13%). Residential buildings and waste management make up the balance;
- the largest absolute increase over the past two decades (roughly 3 gigatons CO2 equivalent per year) has been in the energy sector, while transport and forestry have shown similar (roughly 35%) increases;
- economists use cost-benefit analysis to assess market-based solutions to stabilization of greenhouse gas emissions;
- a quantity known as the social cost of carbon (SCC) is used to estimate the cost to society of emission of one metric ton of CO2 equivalent. Economists typically estimate the SCC as falling within the range of $20-$100/ton of CO2 equivalent, but this value depends critically on what is known as the discounting rate, a quantity which assumes that costs and returns calculated for the future are less than those calculated for today. Carbon emissions reductions will only pass the cost/benefit analysis when the SCC exceeds the cost of mitigation, i.e., it costs more to emit carbon than not to;
- a simple way to encourage emissions reductions is to raise the cost of emitting carbon through some financial intervention in the form of either a carbon tax or tradable emissions permits (e.g., cap and trade);
- there is a range of mitigation potential among the various sectors, with some of the most significant opportunities in the energy supply and industrial sectors owing to the availability of carbon sequestration for large point source emitters in addition to other mitigation opportunities. There are also substantial mitigation opportunities in the transportation sectors (e.g., use of alternative fuels) and agricultural sectors (e.g., the restoration of degraded agricultural lands);
- individuals have an important role in mitigation through reducing their personal carbon footprints; In many cases, no regrets strategies (i.e., things we ought to be doing anyway for health, financial, or ethical reasons) can greatly reduce greenhouse gas emissions. In the U.S., current emissions are roughly 20 metric tons of CO2 equivalent per year per person; A reduction to under 4 metric tons per year by mid-century would be consistent with a scenario of 450 ppm CO2 stabilization;
- only governmental policies and negotiated global treaties can ensure that proper economic and societal incentives are in place to limit carbon emissions below levels considered to constitute a dangerous anthropogenic interference (DAI) with our climate;
- ethical considerations arising from the disaggregation of costs and benefits of burning fossil fuels, with tropical/developing nations and future generations at great risk of suffering negative climate change impacts, complicate simple cost/benefit analysis approaches to climate change mitigation;
- ethical considerations related to the precautionary principle, i.e., that it is unwise and arguably unethical to be playing dice with the future of our planet, provide additional arguments for stabilizing greenhouse gas emissions beyond simple, and potentially flawed, economic cost/benefit analysis approaches.
Reminder - Complete all of the lesson tasks!
You have finished Lesson 12, the final lecture of the course. Double-check the list of requirements on the first page of this lesson to make sure you have completed all of the activities listed there. Good luck with the final exam!