The Canadian carbon tax cases are important because they are fundamentally about the federal government’s power to regulate climate change on a national scale. The Greenhouse Gas Pollution Pricing Act, SC 2018, c 12 (GGPPA), the subject of dispute, sets up a federal carbon tax, and (this is the disputed part) imposes a carbon tax on provinces which are not taking sufficient measures of their own.
Let’s be realistic, a carbon tax is not going to save the world, or save us from climate destruction. It’s a step. It is also not going to bankrupt Alberta, ruin the oil and gas economy, or cause the sky to fall. The oil and gas economy is already effectively on life support and the question of its resuscitation, or not, is addressed elsewhere. So why is it such a focus of ideological dispute between some provinces and the feds?
This case will determine whether the federal government can take national action to mitigate climate change, most importantly whether the feds can impose measures on the provinces. Without being able to do so, and with the provinces having jurisdiction over many heads of power which are critical to dealing with climate change (such as the management of public lands, timber and wood, and most importantly property and civil rights, it is not clear that the federal government could even reach their Paris commitments if they wanted to (still an open question).
These cases will give us a preview of the extent and depth of the federal legal capacity to regulate climate change and meet present and future international legal commitments.
Saskatchewan: The Saskatchewan Reference was heard in February 2019, and the Saskatchewan Court of Appeal issued its decision on May 3, 2019 (Reference re Greenhouse Gas Pollution Pricing Act, 2019 SKCA 40 (CanLII)). The Attorney General of Saskatchewan filed a Notice of Appeal at the Supreme Court of Canada on May 31, 2019.
The SKCA opened its judgement with this, upholding the carbon tax:
4 The factual record presented to the Court confirms that climate change caused by anthropogenic greenhouse gas [GHG] emissions is one of the great existential issues of our time. The pressing importance of limiting such emissions is accepted by all of the participants in these proceedings.
Ontario: The Ontario Reference was heard in April 2019, and the Ontario Court of Appeal issued its decision on June 28, 2019 (Reference re Greenhouse Gas Pollution Pricing Act, 2019 ONCA 544 (CanLII)). The Attorney General of Ontario (“Ontario“) filed a Notice of Appeal at the Supreme Court of Canada on August 28, 2019. All of the case documents, and video of the proceedings, can be found here.
The ONCA said, also in upholding the carbon tax;
 The Act is within Parliament’s jurisdiction to legislate in relation to matters of “national concern” under the “Peace, Order, and good Government” (“POGG”) clause of s. 91 of the Constitution Act, 1867. Parliament has determined that atmospheric accumulation of greenhouse gases (“GHGs”) causes climate changes that pose an existential threat to human civilization and the global ecosystem. The impact on Canada, especially in coastal regions and in the north, is considered particularly acute.
 The need for a collective approach to a matter of national concern, and the risk of non-participation by one or more provinces, permits Canada to adopt minimum national standards to reduce GHG emissions. The Act does this and no more. It leaves ample scope for provincial legislation in relation to the environment, climate change and GHGs, while narrowly constraining federal jurisdiction to address the risk of provincial inaction.
And aptly quoted the Paris Accord to say;
 Climate change was described in the Paris Agreement of 2015 as “an urgent and potentially irreversible threat to human societies and the planet”. It added that this “requires the widest possible cooperation by all countries, and their participation in an effective and appropriate international response”.
Alberta: The Alberta Reference was heard on December 16, 17, and 18, 2019, and the Alberta Court of Appeal issued its decision on February 24, 2019 ( Reference re Greenhouse Gas Pollution Pricing Act, 2020 ABCA 74 (CanLII)). British Columbia filed a notice of appeal on March 25, 2020.
The ABCA opened very differently, signalling at the start that they were finding the carbon tax unconstitutional;
 Calls to action to save the planet we all share evoke strong emotions. And properly so. The dangers of climate change are undoubted as are the risks flowing from failure to meet the essential challenge. Equally, it is undisputed that greenhouse gas emissions caused by people (GHG emissions) are a cause of climate change. None of these forces have passed judges by. The question the Lieutenant Governor in Council referred to this Court though – is the Greenhouse Gas Pollution Pricing Act, SC 2018, c 12 (Act) unconstitutional in whole or in part – is not a referendum on the phenomenon of climate change. Nor is it about the undisputed need for governments throughout the world to move quickly to reduce GHG emissions, including through changes in societal behaviour. The federal government is not the only government in this country committed to immediate action to meet this compelling need. Without exception, every provincial government is too.
University of Ottawa professor Nathalie Chalifour gives an excellent and very in-depth preliminary discussion here and Chalifour wisely notes that “[t]his question has many dimensions, including the scope and applicability of multiple heads of powers, such as the national concern and emergency branches of the residual peace, order, and good government (POGG) power, taxation, criminal law, and the trade and commerce powers.”
Chalifour’s article was before the ABCA case was merged, however, and the ABLawg gives a great analysis of the later Alberta decision here. There are many other excellent analyses of the cases, including from an Indigenous feminist legal perspective, and an argument for climate change as a sui generis area of law.
When will they be heard?
The Saskatchewan and Ontario Appeals were originally tentatively scheduled to be heard in December 2019 and then January 2020. This was adjourned to March 24 and 25, 2020. These dates were in turn adjourned tentatively to unspecified dates in June 2020 because of the Covid-19 pandemic. The cases are now all tentatively scheduled to be heard by the SCC in September via live webcast. Since you’re not in live court, popcorn is welcome in this highly technical, but high-stakes hearing. It will be interesting to watch counsel for each of the 3 AGs – whether they open/close arguments with the big picture, or the technical.