Carbon

Mainstream: It accounts for the temperature record, sea-level rise, ocean acidification and shifting extremes, all from one mechanism.

Alternative: It accounts for satellite-observed greening and for yield gains from added CO2.

Mainstream: Showing that the damages (crop losses from heat and drought, sea-level rise, extremes) fail to grow as warming continues, while fertilization gains keep growing, would count against it. So far the warming trend and the physical effects have continued, and the damage evidence has not reversed.

Alternative: Fertilization gains fading under heat, drought and nutrient limits would count against it. That has been observed: the gains are uneven, nutrient-limited, and cut the protein and mineral content of some crops. The 2026 budget also shows emissions from peat fires and forest degradation linked to drier conditions.

Mainstream: Economic damage estimates for high-warming futures rely on assumptions about adaptation and tipping points that differ widely between models.

Alternative: The claim rests on greening and yield effects alone and does not account for the heat, drought and fire losses that the same CO2 produces, such as this year's Southeast Asian peat fires.

Mainstream: It accounts for observed warming, paleoclimate evidence and model physics together.

Alternative: It accounts for the claim that some models run hot, and for falling disaster death tolls.

Mainstream: Sustained warming well below the projected rate would show it wrong. Recent warming has matched or exceeded the central projections, not fallen below them.

Alternative: Observed warming tracking the low end would support it, and recent warming has not. Falling disaster deaths are consistent with it but do not test it, because richer societies and better warnings would lower deaths at any sensitivity.

Mainstream: The upper tail of the range and the high-emission scenarios are poorly constrained, and the scenarios are sometimes treated as likely when they are not.

Alternative: The fall in disaster deaths is used as evidence about sensitivity, but it reflects wealth and warning systems and would occur under any sensitivity.

Mainstream: It accounts for why pricing is cost-effective in theory and why hard-to-abate sectors need removal.

Alternative: It accounts for the over-credited offsets and for removal being tiny next to the 38 billion tonnes of annual emissions.

Mainstream: The policy fails if credits do not represent real, durable removals or if pricing does not cut emissions. Investigations of over-credited forest offsets show part of this has already happened, though quality standards could be tightened.

Alternative: It fails if well-verified removal and pricing demonstrably cut emissions without delaying phase-out. Some pricing systems have cut emissions, which counts against the blanket claim.

Mainstream: Verra-type forest credits were over-issued, which shows that the verification the mainstream relies on has not worked well in practice.

Alternative: Pricing systems and durable removals with strong verification are a different thing from bad forest offsets, and the position does not separate them.

Mainstream: It accounts for the cost-effectiveness of pricing and for the clean-energy gains that policy-driven deployment has produced.

Alternative: It accounts for the political fragility of carbon taxes and for the fall in solar and battery costs that came with deployment.

Mainstream: It fails if priced economies do not cut emissions faster than unpriced ones. This year's dip came from an oil shock, not policy, so the policy's effect is not shown by it.

Alternative: It fails if cheap clean energy is built out and fossil use still does not fall. Nuclear has often been slow and costly to build, which counts against it, and no wealthy economy has cut emissions at the pace degrowth requires through shrinking.

Mainstream: Global emissions remain near their peak despite decades of pricing, so the pricing mainstream has little global result to point to.

Alternative: The nuclear and abundance claim cannot explain why nuclear costs have risen in many countries, and the degrowth claim has no case of deliberate shrinking, so its plan is untested.