Our carbon budget is all but spent, but who is counting?

6 May 2019

A majority of voters has put the environment ahead of the economy as the top election issue.  Yet the budget we haven't heard about in this so-called 'climate election' is the carbon budget.   That's the budget set by the laws of physics and chemistry to hold global warming to the safer side of 2 degrees.

The climate doesn't respond to UN negotiations, policy discussions, or electoral promises.  What the climate does respond to is the amount of greenhouse gases in the atmosphere, the most important of which is carbon dioxide.

For decades we've known that the release of carbon dioxide from fossil fuel use is the main cause of the global warming that is changing our Earth's climate.  Yet carbon dioxide in the atmosphere continues to increase year after year.  In fact, the rate at which it is increasing is itself increasing.  

We are accelerating toward disaster.   This is an emergency.

In estimating the remaining global carbon budget, and Australia's notional share, we assume the goal is to share equally the responsibility to keep warming strictly below 2 degrees with at least a 2/3 chance.   Barring some speculative technology deployed on massive, unprecedented scales in the next decade to pull more carbon down out of the atmosphere than we are putting up, the budget - from the beginning of the industrial revolution - that humans must not exceed is 1000 billion tonnes of carbon - give or take.

But the amount we have left to "spend" is much less, for three reasons.

First, humans have already emitted 585 billion tonnes of carbon over the course of history up until the end of last year.   That must be subtracted off to see what's left.

Second, other greenhouse gases, like methane and nitrous oxide also cause warming, so we have to account for their effects. That's another 210 billion tonnes of carbon we can't spend. 

Finally, the budget must be reduced by 110 billion tonnes more, because warming increases the release of land carbon to the atmosphere, specifically through wildfires and melting of permafrost, effects the IPCC reports have not taken into account.

After doing the sums, humanity has only 95 billion of the original 1000 billion tonnes left to spend on carbon dioxide emissions. To put that in perspective, globally humans emit 10 billion tonnes of carbon every year.

That means that in less than 10 years, without dramatic action, humanity will have spent all of its remaining 2-degree budget.  At that point, the chances of holding warming to 2 degrees will drop below 2/3, and we might as well flip a coin to estimate whether the climate will exceed boundaries maintained for over a million years.

Now let's put that in an Australian context.  Different opinions have been expressed about how much Australia can or should be allowed to emit, based on history, on our industrial base, international trade, or on ethics.  Nature is blind to these distinctions.

As a simple approach to gaining some perspective, let's divide up that remaining 95 billion tonne budget evenly across the world's population. With 0.33% of the world's population, that would give Australia a remaining so-called "fair share" budget of 310 million (million, not billion) tonnes of carbon going forward to "spend" on the release of carbon dioxide from burning fossil fuels.

Sound like a goodly amount?  Well, using recent numbers from the National Greenhouse Gas Inventory, Australia would use up that "fair share" carbon budget in just three years. 

Three years.  Now there's something that fits into an electoral cycle.  And that's not even counting the carbon dioxide that results from exported Australian coal burnt overseas.  

After that, we'd be dipping into someone else's pockets by spending their "fair share" of the global carbon budget, a budget that they are counting on to manage their own transition to net zero emissions.

Renewable energy technologies, electric cars, improved land use, and managing waste are all important pieces of a transition to a healthy, prosperous Australia living within a carbon budget.   But from a scientific point of view, the single most critical climate issue in this election is the elephant in the room. The rogue elephant that is trying desperately to remain invisible and not leave footprints on policy papers: the continued expansion of fossil fuel extraction in Australia. 

Since all paths to a reasonable chance of holding warming to 2-degrees involve dramatically cutting emissions from fossil fuels in the next ten years, it is senseless, dangerous and irresponsible to expand fossil fuel facilities in Australia (or anywhere else). Current fossil fuel reserves already being exploited contain more than enough carbon to consume the remaining carbon budget for the 2 degrees Paris target.

We are in the midst of a climate emergency that is disproportionately affecting the young, the poor, and the vulnerable.  In emergencies, good leaders take considered, immediate and extraordinary action to combat the biggest source of threat.    Australia needs leaders who acknowledge and commit to combating this climate elephant in the party room.  Will they step forward before 18 May?

Editor's note: The numbers presented by the authors in this commentary are tonnes of carbon in a carbon budget, not carbon dioxide (which weighs more than the carbon it contains, or carbon dioxide equivalent, which counts greenhouse gases we already subtract off).  Australia emits 380 million tonnes of carbon dioxide per year, which contains about 105 million tonnes of carbon.

This is an extended version of an article published in The Sydney Morning Herald on Monday 6 May 2019.

Penny Sackett, former Chief Scientist for Australia, is a physicist and honorary professor at the Climate Change Institute, Australian National University; Will Steffen is an emeritus professor at ANU and a councillor at the Climate Council.