So you know how you've heard that gas is cleaner than coal?

This needs a heckuva fact check. But first, gas is super complicated: this needs a heckuva definitions section.

Gas is a fossil fuel. Burning it produces carbon dioxide, but venting it without burning releases a very powerful greenhouse gas.

The primary ingredient of gas--fossil methane--is a live fast, die young warming agent, capable of warming the globe far more intensely than CO2.

If we burn gas perfectly, carbon dioxide enters the atmosphere.

But because methane is itself a powerful greenhouse gas, releasing it without burning, warms the globe >90 times more than the same amount of carbon dioxide in the short term.

Gas haemorrhages climate pollution at every stage of its extraction, processing and transport.

This results in vast quantities of methane going straight into the atmosphere.

This is a big deal, because you only need to lose a little methane before it's no better than coal.

Also, not all gas extraction is created equal in terms of its impact on the climate.

For our first set of new terms, we have "conventional" and "unconventional" gas.

Conventional gas just means that the gas is relatively easy to access. Unconventional means it is harder.

There was a time when only conventional gas could be extracted economically. There, you pierce the underground gas reservoir and the gas just flows straight up to you.

For unconventional gas, you need to do something more, but unconventional doesn't mean fracking necessarily.

There are three types of unconventional gas on the cards in Australia: coal seam gas, shale gas, and tight gas.

These names distinguish the different geologic formations that the gas is found in.

For those concerned by fracking (you should be off you aren't): ...

1) Coal seam gas often, but not always, requires fracking.
2) Shale gas requires fracking by definition.
3) Tight gas requires fracking by definition.

Fracking is always harmful. We just hope that the harm being done is far enough underground that it can't contaminate the productive uses of land at the surface.

We're extra specially that it won't harm groundwater either!

Fracking, or "hydraulic fracturing", involves injecting water, sand and a confection of chemicals deep underground under pressure to create a whole lot of tiny fractures in the rock.

This fluid is then extracted with the hope that gas can now flow freely up to the well.

The chemicals used in fracking are absurdly toxic. The symptoms of exposure to these chemicals is a laundry list of horrible ways to die.

Negligence and human error aside, we will hopefully never be exposed to them from fracking.

The problem is that we live in a world where negligence and human error actually happen.

The effects of these chemicals getting out, or getting into groundwater, because someone screwed up a survey would be locally catastrophic and impossible to rectify.

In terms of climate impact, generally we can say that conventional gas has less of an overall impact than unconventional gas due to other emissions in the supply chain.

But hold that thought for a second.

As well as differences in methods of extraction, there are a number of different end uses of gas.

I'm going to stick to the users of gas for electricity generation here, but even just within that in Australia we have:

a) Steam.
b) Open-cycle.
c) Combined-cycle.

Each of these has a very different purpose, and a very different efficiency.

Steam is generally big, old, inefficient and slow. It runs like an old coal-fired generator. We definitely don't need more of these and I don't think *anyone* is asking for them.

Open-cycle is super flexible but quite inefficient. While newer open-cycle gas turbines can be better, the worst open cycle gas power station in Australia (Dry Creek in SA) emits more greenhouse gas per unit of electricity than the very worst coal fired power station (Yallourn).

Open cycle turbines are what people are referring to when they say "peaking plants" and talk up gas for its ability to support renewables.

This is a furphy because we don't actually need new peaking plants to support renewables. There are other ways to skin that cat.

Then there's combined cycle generators, these are very efficient but they aren't good at fast response.

When people say gas is half the emissions of coal, they are referring to the emissions at point of combustion (ie, ignoring all other emissions) of a combined cycle generator.

But there's far more to the emissions of gas than what happens at the point of combustion in particular: fugitive emissions.

There are four main types of fugitive emissions:
- Venting,
- Flaring,
- Leaks, and
- Migratory emissions.

Venting is when gas is deliberately released straight into the atmosphere. This lets the methane and other gas wreak havoc on the global climate.

In flaring, the methane is set on fire. Combusting methane makes CO2 (ideally) so there's still a lot of greenhouse warming going on.

Leaks are what they say on the tin. In Australia, we assume that no gas is ever released to the atmosphere other than deliberate venting.

This is weird because our gas meter at home was leaking a couple of days ago. I should have called the Federal Department to let them know.

Migratory emissions occur when gas finds a path from deep underground to the surface.

This is a poorly understood phenomenon, because we just don't measure it. There are good reasons to suspect that as unconventional gas extraction has increased, so have these emissions.

The quality of our measurement here is:

1) Venting and Flaring: Rely almost exclusively on company provided numbers.
2) Other leaks: Assume these to be zero.
3) Migratory emissions: Don't discuss, don't measure and lalalanotlistening.

This is important because only a little gas has to make it to the atmosphere before gas is no better than coal overall. And there's room for these to add up to a lot.

I'm going to build on this another day.

If you appreciated this, might I suggest this? http://www.climatecouncil.org.au/donate/