labs_title
Caldeira Lab

Key factors for assessing climate benefits of natural gas versus coal electricity generation

Xiaochun Zhang, Nathan P. Myhrvold & Ken Caldeira


Zhang, X., N. P. Myhrvold, and K. Caldeira, 2014: Key factors for assessing climate benefits of natural gas versus coal electricity generation. Environ. Res. Lett., 9, 114022, doi:10.1088/1748-9326/9/11/114022.

 

Xiaochun Zhang - click to read the video transcript

 

 

Abstract

Assessing potential climate effects of natural gas versus coal electricity generation is complicated
by the large number of factors reported in life cycle assessment studies, compounded by the large
number of proposed climate metrics. Thus, there is a need to identify the key factors affecting the
climate effects of natural gas versus coal electricity production, and to present these climate
effects in as clear and transparent a way as possible. Here, we identify power plant efficiencies
and methane leakage rates as the factors that explain most of the variance in greenhouse gas
emissions by natural gas and coal power plants. Thus, we focus on the role of these factors in
determining the relative merits of natural gas versus coal power plants. We develop a simple
model estimating CO2 and CH4 emissions from natural gas and coal power plants, and resulting
temperature change. Simple underlying physical changes can be obscured by abstract evaluation
metrics, thus we focus our analysis on the time evolution of global mean temperature. We find
that, during the period of plant operation, if there is substantial methane leakage, natural gas
plants can produce greater near-term warming than a coal plant with the same power output.
However, if methane leakage rates are low and power plant efficiency is high, natural gas plants
can produce some reduction in near-term warming. In the long term, natural gas power plants
produce less warming than would occur with coal plants. However, without carbon capture and
storage natural gas plants cannot achieve the deep reductions that would be required to avoid
substantial contribution to additional global warming.

 

(A)
(B)

Figure 2. Global temperature change from the (A) most efficient and (B) typical efficiency natural gas and coal power plants. The operational period is 40 years. Efficiencies of natural gas and coal power plants are 60% and 51% for the most efficient natural gas and coal power plants, respectively, (Whitaker et al 2012, O'Donoughue et al 2014); 40.3% and 34.3%, respectively, for global fleet average efficiencies (world typical plants, WEC 2013). The range of natural gas leakage rate considered is 0%–9% (Howarth 2014). Amount of warming from natural gas versus coal power plants for the first several decades depends sensitively on natural gas leakage rates and power plant efficiencies. Several decades after the plant ceases to operate, most of the methane no longer resides in the atmosphere; at that time, the relative warming from natural gas versus coal power plants depends primarily on power plant efficiency.

 

 
Above 2 Panels. Same as Figure 2, except showing ranges for only "best" (0%-1%) and "typical" (2%-3%) methane leakage rates.