Carbon tax is more effective than cap-and-trade for decarbonisation

British Columbia's carbon tax is the most-studied implementation at scale. Peer-reviewed evidence shows a 5-15% reduction in emissions relative to the counterfactual, with minimal GDP impact and significant revenue recycling back to low-income households. The political durability is notable — introduced under a centre-right government, maintained under centre-left, now near-national in Canada. The simple mechanism (tax fuel at source) is harder for industry to game than permit allocation.

Carbon taxes provide price certainty, which is what businesses making long-lived capital investments in low-carbon technology actually need. A known, rising price schedule (say, $50/ton now, rising $10/year) lets a solar developer, grid operator, or EV manufacturer make a business case with confidence. Cap-and-trade produces price volatility: the EU ETS price fell from €30 to €3 during the 2008 recession and stayed depressed for years. This volatility deterred investment precisely when it was most needed.

The distributional argument seals it for taxes. Permit allocation in cap-and-trade creates windfall profits for incumbents (utilities pass through permit costs to consumers while receiving free permits). Taxes are more transparent, easier to rebate to low-income households, and harder to lobby into exemptions than permit design. Political economy: every carbon pricing scheme eventually faces rollback pressure. A tax with an explicit revenue-recycling mechanism (dividends or income tax cuts) builds a constituency for its survival. Permits build a constituency for exemptions.

I'll concede the distributional and simplicity arguments partly. But the core environmental case for caps remains: if we have a physical carbon budget consistent with 1.5°C, a tax set at the 'right' level is based on a model that might be wrong. A cap set at the right quantity is self-correcting — if the economy grows faster and demand for permits rises, the price rises automatically. Under a tax, faster growth means more emissions with no automatic adjustment. For climate, getting the quantity right matters more than getting the price right.

Cap-and-trade provides quantity certainty — you know the total emissions reduction because the cap guarantees it. Carbon taxes don't: if the price is too low, emissions stay high; if compliance is weak, the effective price is zero. The EU ETS's early failures were design failures (over-allocation, banking provisions) that were fixed in the reform period, producing the world's largest carbon market by 2021 with a functioning price. A well-designed cap gives you the environmental outcome; a well-designed tax gives you a price signal of uncertain effect.

California's cap-and-trade has been operating since 2013 and covers 85% of the state's emissions — the broadest coverage of any carbon pricing scheme in North America. It's linked with Quebec, has generated $20bn in climate investments, and its permit price has been stable within a price floor/ceiling design that addresses the volatility critique. Modern cap-and-trade with price collars has largely converged with carbon taxes on the price-stability problem. The remaining advantage of caps is the hard environmental guarantee.