Unsurprisingly, global emissions have flattened for a third year in a row. The fortunate outcome is composed of the following building blocks: the peak of emissions in the OECD in 2007; the termination of a twenty-five year phase of heavy industrialization in China and its ability to convert coal growth to zero; and, the accelerated deployment of wind and solar.
Peering closely at the year-over-year changes in new electricity generation helps us understand better how global economic expansion can be pressing forward, without pushing emissions higher. In 2015, for example, nearly all of the marginal growth in global power generation was provided by 187 TWh of new wind and solar. In the years prior, combined wind and solar took minority shares of new generation, at 158 TWh in 2013 and 121 TWh in 2014—but the majority of new electricity ex-wind+solar was provided by natural gas. This trend, where natural gas replaces retiring coal, is set to continue through the end of the decade. But combined wind and solar will eventually go to work also, on natural gas: in 2016 and this year, 2017, they are already expected to take half of new power generation.
Climate scientists will remind you, however, that emissions actually need to enter outright decline. When might that happen? Well, emissions have to flatten first before they can decline. One way to answer this question is with another: when will 100% of marginal growth in global power generation be taken up by wind and solar (or other low carbon additions, like nuclear)? If you look ahead to the rough schedule of global coal retirements, natural gas additions, and the shift in marginal growth in wind and solar—in China, the US, and especially India—a reasonable guess is sometime after the year 2020.
But that still leaves the problem of emissions growth from oil.
As natural gas kills coal, it creates an emissions-saving gain. But those emissions-saving gains will eventually tail off. An actual decline in emissions after 2020 will be reliant not only on wind and solar dominance of powergrid growth, but a concurrent marginal transition of transportation growth, typically oil-based, towards electricity.
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