A lot of the climate section of the VP debate focused on hydraulic fracturing (e.g. fracking). Its a complex subject – one that I've published a few papers about – and worthy of an exceedingly long twitter thread.

For more, read on! 1/
First, a bit of background about the debate. Fracking primarily occurs on privately owned land, and states rather than the federal gov't have primary jurisdiction over it. That said, the fed gov't can regulate it in some ways (e.g. rules around flaring or fugitive methane). 2/
Fracking is used to produce both oil and natural gas by fracturing shale rocks deep underground. When combined with horizontal drilling it allows for cost-effective extraction of both. 3/
Fracking has radically transformed the US energy sector, dramatically increasing our gas and oil production, to the point that (before COVID hit) the US was rivaling Saudi Arabia as an oil producer. 4/
Arguably fracking has had an even bigger impact on US oil production than gas production. And while the climate impacts of fracked gas are complex – as I will discuss later – the increase in oil production from fracking is pretty unambiguously bad for the climate. 5/
The rapid expansion of gas fracking has led to a dramatic drop in natural gas prices; gas prices today are less than half what they were a two decades ago. 6/
Cheap natural gas has been primary factor killing coal in the US; coal today is only 23% of our generation compared to >50% two decades ago, while gas has risen to 38%. But renewables are also growing, and will likely overtake gas as a bigger driver of coal's decline soon. 7/
New natural gas plants are produce less than half the CO2 emissions per kWh generated compared to existing coal plants, both because they are much more efficient at converting chemical energy into electricity (~50% vs ~33%) and have less carbon content (~50% less). 8/
To-date natural gas has been the single largest driver of declining US power sector CO2 emissions; the latest EIA data that just came out shows that even in 2019 it played a larger role than renewables in reducing CO2 emissions: https://www.eia.gov/environment/emissions/carbon/index.php 9/
However, it is worth noting that there are many drivers of overall US CO2 reduction across all sectors of the economy, and while gas plays a large role its by no means represents the majority of realized economy-wide emissions reductions: https://www.carbonbrief.org/analysis-why-us-carbon-emissions-have-fallen-14-since-2005 10/
However, looking just at CO2 provides an incomplete picture. Natural gas is primarily comprised of methane (CH4), which is a greenhouse gas much more powerful than CO2. 11/
A fair amount of the gas we produce – likely upwards of 2% – leaks into the atmosphere before it makes its way to gas powerplants. While its in the atmosphere, a ton of methane has around 120 times more warming effect than a ton of CO2! 12/
However, unlike CO2, methane has a very short atmospheric lifetime. If we emit a ton of CO2 about half is left in the atmosphere, about half remains after 100 years (and 20% after 10,000 years!). For CH4, nearly all is gone after 12 years. 13/
This means that the warming effect of methane, while much larger than CO2, is also much shorter lived. This makes comparing them difficult, as methane matters more in the short term and CO2 more in the long term. 14/
For more on the important differences between CO2 and CH4, see this (slightly less long!) thread: https://twitter.com/hausfath/status/1230573108949446657?lang=en 15/
So, lets see what happens if replace a coal plant with a natural gas plant, taking into account both the CO2 and CH4 emissions (from both, as coal production results in some CH4 emissions as well). Following bits draw on my 2015 paper on the subject https://www.sciencedirect.com/science/article/abs/pii/S0301421515300239 16/
First, lets compare climate impacts of same amount of coal and gas generation if each is run for 100 years, based on their warming influence (radiative forcing). Dotted black line is a typical existing coal plant, while solid black line is a new state-of-the-art coal plant. 17/
The green line is new gas with our best-estimate leakage rate of 2%, while the grey range represents leakage rate from 1% to 6% to account for the large uncertainty in methane leakage from gas production. 18/
Over first 20 years theres periods in which gas could be worse than existing coal with high leakage rates. In long run, however, gas is better than existing coal under any reasonable leakage rate. Heres leakage rates required to make gas worse than coal over diff time periods 19/
The difference between long-run climate impacts of gas and coal are even more pronounced if we examine a shorter generation period. If we compare gas and coal over 30 years (and assume both are replaced by, say, renewables after that), we get the figure below: 20/
Here new gas is well below half the climate impact of current coal by the end of the century even under high leakage rates, simply because relatively little methane leaked from gas is left a that point (leaked CH4 oxidizes into CO2, which is accounted for in my model). 21/
However, even half the long-term climate impact is still too much. We have a goal of decarbonizing the electric power sector by 2035, which would mean no gas generation left (at least without accompanying carbon capture and storage) by that point. 22/
So while gas has been a bridge fuel away from coal and won't disappear tomorrow, it is a bridge that has to quickly end if we are to meet ambitious climate targets. Building new gas plants will not make much sense today if they will only be around for 15 years max. 23/
That said, if we were to ban gas extraction tomorrow, the short-term effects would be a large resurgence in coal generation. Remember, gas is still the main factor driving coal retirements, and we have a lot of coal plants running at ~50% capacity that could easily ramp up. 24/
So what should we do? Prioritize closing coal plants ASAP. Look really hard at building any new gas plants going forward. Pass clean electricity standard to increase share of clean generation even faster. Modernize our grid and build out storage to support more renewables. 25/
Right now gas plays an important role in our grid as its firm and dispatchable. Gas plants are cheap to build; most of their costs come from the gas they burn. This means that they can sit idle until the sun sets or the wind stops blowing and ramp up to fill in the gaps. 26/
To effectively replace gas, we need to get more firm clean generation on the grid (geothermal, advanced nuclear, gas with CCS), get cheaper energy storage, invest in higher capacity factor renewables like offshore wind, and modernize our grid to better balance intermittency. 27/
Gas will play an important role in allowing high amounts of renewables on the grid in the near term, but we need to avoid making it too much of a crutch going forward (at least barring cheap and effective CCS), as we will have to ultimately leave it behind to decarbonize. 28/
So while the symbolic debates around banning fracking (on federal land where little gas is produced) suck up a lot of oxygen, the reality is that we need to work to kill coal today and prepare for a gas-free (sans CCS) future a bit down the road. 29/
(Today I learned twitter limits you to 25 tweets per pre-written thread; TBH I'm rather surprised I never hit the limit before!)
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