A study from the Yale School of the Environment examined the two core modeling approaches used to calculate the cost of reducing global greenhouse gas emission.
The bottom-up model is used by the United Nations Intergovernmental Panel on Climate Change. The model argues that there are several cost effective ways to reduce emissions, like electric cars, which might be estimated at a lower price than gas-powered vehicles. The model states that if countries would invest $50 per ton to mitigate emissions, global emissions could be reduced by 43%.
The top-down model is used by economists and studies how investment in greenhouse gas mitigation comes at the cost of other potential investments. The model shows that all activities to cut emissions are going to be costly. Compared to the bottom-up model, this model only predicts a 26% reduction in emissions.
Matthew Kotchen is an economist at Yale, and one of the authors of the study published by Science. His study shows the truth lies somewhere in the middle.
“I think while there is no such thing as a free lunch, there actually may be some less costly lunches out there that we actually could obtain," Kotchen said. "And I think that the truth estimate is probably between these two.”
Kotchen said he believes that the bottom-up model is overly optimistic about how much it will cost to reduce emissions — while the top-down model is overly pessimistic.
In the study, he outlines four ways for scientists and economists to come together to resolve the issue.
He said scientists should investigate the cost-saving measures that the bottom-up model suggests to cut costs. These measures account for almost all of the difference between the two models.
Next, connections between economists and scientists should be strengthened in order to promote collaboration and figure out where the cost truly lies between the two models.
More research should be done to understand the barriers surrounding the adoption of mitigation programs and energy efficiency measures. Especially in a behavioral and social sense. Like, for example, people who don't want to buy an electric car because they are concerned about performance or change.
Finally, the standard model for determining climate mitigation costs should be updated regularly to reflect new information on emission reducing measures.
Kotchen said it is important for scientists to come to an agreement on these costs, so they can properly set targets and goals for reducing emissions.
“I think it's important that we have a good sense for what the cost should be," he said. "So that when we set our goals and our targets, we actually know what we're giving up or what the trade-offs are.”
