The previous post explained the methods used in the estimates of Canada’s fair share of the remaining global carbon budget under different levels of global warming. Here I answer five frequently asked questions about the remaining budget that I received from representatives of the federal parties, students, colleagues, journalists, television hosts, camera operators, friends, family, angry eggs on twitter, etc. For more on this subject, I recommend my interview with BNN Bloomberg.

I start with a very important question that no one explicitly asked me.

Do you think the Canadian government should propose emissions targets consistent with avoiding 1.5°C of global warming?

No, I do not. I say this even though my scientific research provided part of the argument for the 1.5°C limit. I’ll explain.

The most common reaction I heard to the Policy Options article was that I was criticizing the federal parties for not setting targets and policies that help the world avoid 1.5°C or 2°C of warming. If you only read the headline, or only looked at the graph, that would be a fair reaction.

In the article itself, I was making a much more nuanced argument. The take-home is that, realistically speaking, it is too late for Canada to do its fair share to avoid 1.5°C of global warming. Doing so would take an incredibly sharp reduction in greenhouse gas emissions: a 96-99% drop below current levels by the year 2030.

No reasonable political party is going to suggest that. Nor do I think any party should. That dramatic of a drop in emissions would require upending the economy, not to mention our ability to power our homes, get around, and to grow food – agriculture is 10% of Canadian emissions. It could end up doing more harm than good. This is the same reason why many climate experts are uncomfortable with Extinction Rebellion’s call for net zero emissions by 2025.

If I had one core criticism of the Liberal, Green Party, and NDP platforms,* it was not that their policies and targets needed to be more aggressive. It was the repeated claim that they would make sure Canada does its fair share to avoid 1.5°C of global warming, despite scientists and others repeatedly showing that doing so is next to impossible for Canada (I wrote about this in Policy Options in 2016).

The claim betrayed either a weak understanding of the issue or a preference of symbols – 1.5°C as a symbolic goal – over reality. I would prefer that parties serious about addressing climate change be more transparent about the challenge that lies ahead.

* The Conservative Party platform was not serious enough about climate change to even quality for this criticism. I’m not being partisan: the plan did not have any numbers. Imagine preparing a financial budget, but without any numbers. Would an economist take it seriously?

Why is the emissions decrease in your 1.5°C scenario so much greater than what the IPCC reports?

The 2018 IPCC Special Report on Global Warming of 1.5°C (SR1.5) reported that the world would need to reduce net emissions by 45% from 2010 levels by the year 2030 (with an uncertainty range of 40-60%). My estimated reduction for Canada (96-99%) is greater for two reasons: I use an equitable distribution of the carbon budget, and I do not consider negative emissions.

First, in order to estimate Canada’s fair share, I assigned Canada a share of the remaining global carbon budget pie based on our fraction of the world’s population. Since Canada is among the world’s highest emitters per person, an equitable slice of the future pie is much smaller than the mega-slice we are currently eating. That means reducing emissions much faster than developing countries with lower than average emissions per person.

Second, my analysis is based on total cumulative emissions remaining (for a two-thirds chance of limiting warming to a certain level). The 45% reduction often quoted from SR1.5 is based on net emissions, which refers to the actual emissions minus negative emissions – carbon dioxide permanently removed from the atmosphere by human activity. If Canada is to successfully deploy negative emissions techniques and technologies, the remaining budget would be larger and the rate of actual emissions cuts could be less steep.

These two differences notwithstanding, my analysis is actually conservative in that it uses a generous interpretation of the carbon budget. The SR1.5 provides an uncertainty range for the remaining global carbon budget (see Chapter 3, Table 2.2). As mentioned in the methods post, the values I used represent the high end of that range. If I had used the middle of the range, the budgets would all have been smaller (e.g., the remaining budget for a two-thirds chance of avoiding 2°C of global warming would be 8% smaller).

Are there any ways to increase Canada’s carbon budget?

Technically, yes. As mentioned above, the estimated remaining carbon budget for Canada could be increased through negative emissions, including land carbon uptake or direct air capture technology.

We can also increase the budget through purchasing credits on an international carbon market. The cost would not be trivial. For example, the gap in the year 2030 between Canada’s emissions target and mean trajectories consistent with a likely chance (66%) of limiting warming to 1.5°C is 495 Mt CO 2 e. If Canada made up the difference by buying credits at a price of $50/t CO 2 e, the cost in the year 2030 alone would be $25 billion, excluding inflation. Using the 2030 emissions gap for 2°C of 260 Mt CO 2 e, the cost would be $13 billion in the year 2030 alone.

While that outlay of money may be unrealistic, some purchasing of emissions credits is likely to happen. There is not, as of yet, a carbon trading method under the Paris Climate Agreement, but there are other carbon markets. The federal government expects to achieve some of the planned emissions cuts for 2030 through credits purchased from the Western Climate Initiative (WCI), a carbon market created by western U.S. states of which Quebec is a member and pre-Doug Ford Ontario was a member. The 2018 modelling estimated 13 Mt CO 2 e of credits from the WCI.

What if Canada claimed a larger share of the remaining global carbon budget?

To answer this question, I took an intermediate approach to determining Canada’s portion of the remaining budget, halfway between the population-based approach I used in the past analysis (0.49%) and one based on today’s fraction of the world’s emissions (1.59%). With this intermediate approach, the estimated future emissions budgets and trajectories shift such that the 1.5°C case is similar to the previous 2°C case (from the population-approach), and the 2°C case is similar to the previous 3°C case. For example, the 1.5°C trajectories using the intermediate approach involve reducing emissions by 65-72% by the year 2030.

Keep in mind, as I argue in the article and is apparent in the latest UN Emission Gap Report, it is hard to envision how the world could realistically avoid 2°C or 3°C of global warming, let alone 1.5°C of global warming, if countries like Canada claim a portion of the budget very disproportionate to their population.

How confident are scientists in the global carbon budget numbers?

There is a substantial uncertainty in budget estimates and new research is published every month or two that revises previous estimates. Glen Peters wrote a helpful perspective in Nature Geoscience on the nuance of carbon budget analyses, and the implications for policy.

On a most basic level, the uncertainty comes from the basic irreducible uncertainties in climate science. Due to the complexities and the path dependence of the climate system, science can provide a range, not an exact value, for how responsive the global average temperature is to an increase in carbon dioxide concentrations. It makes sense that there is no one correct estimate of the remaining carbon budget.