Appropriate and useful climate policy-making requires accurate and reliable data about the future. Nowhere is this more important than when setting carbon emission standards and projecting percentages of each energy source to match energy needs (coal, natural gas, nuclear, renewables, etc.). But projecting how emissions will change in the decades to come, say to meet the 2030 standards, is a tricky business. In particular, natural gas has been touted as a ‘bridge’ to a low-carbon future with predictions that it would take over a share of energy production from coal and thereby reduce net emissions (natural gas has about a fourth of the greenhouse potential of coal, if you take away methane leaks in transportation pipes).
But is this really true? Does the data back this up? These are the key questions policymakers must know the answer to when deciding whether to promote natural gas expansion with subsidies, etc. And it falls to researchers to answer this precisely.
Unfortunately, a new paper in Environmental Research Letters has modeled future emissions using a somewhat new method and answer these questions with a decisive no. Previous modeling methods would spread the total emissions of a source, say a coal-fired plant, across all the years it operated. This gave the impression of flexibility to easily reduce emissions by eliminating certain highly polluting plants with renewables or other low-carbon sources. But we all know how politically tricky it is to close a plant and remove those jobs. To account for this sociopolitical inertia, the new method, known as ‘commitment accounting’, includes all potential emissions within the year the plant began operating. The figure below shows the difference between these two ways of organizing the data:The top graph represents the old, traditional way of modeling future emissions – the blue squares show how units of CO2 emissions (boxes) are spread across time (say, if one box is 1 CO2 unit/ year, then this plant would be operating for five years with 1 CO2 unit per year). On the other hand, committed emissions include all 5 CO2 units in the year the plant started (vertical bar in the bottom graph) – this gives a truer sense of what we as a nation have already committed to in terms of fossil fuel emissions, and therefore the social inertia, if you will, that will prevent major reductions from emissions if the infrastructure is already in place. Now, if some of these plants are shut down, the model can always be updated to reflect this and reduce the amount of committed emissions from the remaining time in operation. But, in general, this is a much more accurate method for giving policymakers a true sense of where the nation is headed based on current production and infrastructure developed.
The data includes the date each CO2-emitting plant came online, its lifetime, annual emissions, and when they, if any, ceased operating. The data came from the Platts World Electric Power Plant and the Carbon Monitoring for Action (CARMA) databases. The authors then aggregated this data for years from 1950-2012 to understand the trends of emissions from multiple sources and to see if we are close to seeing the downward trend in emissions expected to result from increased natural gas production in place of coal.
So what news does this new method bring? Not very good, in general.
1) Natural gas is not reducing net emissions due to increased total energy production.This graph tells the main message – it plots total commitments (y-axis) across the past 62 years or so. You can see the dramatic rise in total committed emissions since around 1970. In particular, coal (purple) may be tailing of slightly over the past several years, as predicted by the gas boom, but this reduction is more than made up for by great rise in natural gas production since about 2005 (light purple). Emissions from this increased production has led to overall increased emissions. This seems to indicate that previous predictions indicating that natural gas would help reduce emissions did not take into account greater overall demand, demand at a rate great enough to offset any reduced emissions from natural gas.
2) Commitments show no sign of decreasing in recent years.This graph is helpful to identify trends for future years. The authors basically plotted the difference between the amount of new commitment and the amount of realized commitments for each year. Realized commitments are those are are completed that year (so no longer contribute to commitment after that year). So a positive number indicates increasing trends in the amount of infrastructure for that given energy source. Unfortunately, other than oil, we see coal and natural gas with positive commitment values, indicating that both sectors are continuing to grow in a way that is increasing greenhouse gas emissions. To reduce CO2 emissions, we must eventually get to a place where we are retiring fossil fuel-based infrastructure faster than we are building it. This data indicates we are not yet there!
So we see no tailing off of emissions that some policy reports have led us to believe would occur with a natural gas future. This is crucial information to get out to policymakers who might be pushing natural gas as a bridge to a low-carbon future. There seems to be no replacement for policies such as a carbon tax that would truly push for solar, wind, etc. development. Instead, natural gas, while great in the short-term for the economy, may be nothing but a detour on our journey to a sustainable, renewable future.
Steven J Davis and Robert H Socolow (2014). Commitment accounting of CO2 emissions Environmental Research Letters, 9 (084018)