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Net Zero Cost Benefit

How much does net zero cool the planet?

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Take the United States. Today it emits about 6 billion tons of greenhouse gases a year.

Most of it is CO₂ from burning coal, oil and gas.

The rest is methane, nitrous oxide and other gases, much of it from farming.

Net zero means that by 2050, all these greenhouse gases must add up to zero.

But it is very hard to get farm emissions to zero: cows still burp methane, and fertilizer still gives off nitrous oxide.

So the typical net zero keeps some of them and makes up for them by taking CO₂ out of the air. CO₂ emissions end up a little below zero.

With current policies, US emissions fall much more slowly.

Current policies here follow the new medium scenario that feeds the UN Climate Panel's next report.

How much cooler could net zero make the world?

Put both paths into MAGICC, a standard climate model used in the UN Climate Panel's reports since 1995.

With current policies, the world warms by 2.86°C by 2100.

If the US goes net zero by 2050, and the rest of the world keeps its current policies, the world warms by 2.78°C.

The difference is 0.08°C in 2100.

This site does the same for every country, for groups of countries and for the whole world.

Notes
  1. Climate model. MAGICC 7.5.3 (Climate Resource n.d.) with its default parameters, one run per path (no uncertainty range) (Meinshausen et al. 2009; Meinshausen et al. 2011; Meinshausen et al. 2020). MAGICC, first built by Tom Wigley and Sarah Raper, has made temperature projections for the UN Climate Panel's assessment reports since 1995 (Cubasch et al. 2001, 577). In the Sixth Assessment Report it is one of the climate emulators of Working Group I (IPCC 2021, Cross-Chapter Box 7.1), and Working Group III used it to sort the scenarios with enough emissions data by their warming (Kikstra et al. 2022). Warming is measured against 1850–1900.
  2. Current policies. The CMIP7 "Medium" emission scenario, which "shows the consequences of the current policy situation (as of 2025)". CMIP7 is the World Climate Research Programme's Coupled Model Intercomparison Project, whose climate-model results are central to the UN Climate Panel's assessments of climate science; the CMIP7 results will inform its Seventh Assessment Report (Van Vuuren et al. 2026).
  3. Making CMIP7 compatible with the cost model. The cost model used here, AIM (Riahi et al. 2021), one of the few models with a scenario that actually reaches net zero by 2050 (see Costs), has no scenario similar to CMIP7 Medium. But it has one with generally more emissions, with the policies in place in 2020 (here called "2020 policies"), and one with fewer, called "pledges continued" (national pledges kept after 2030). So for each of AIM's ten world regions, the site interpolates between the two with one fixed proportion for the whole century, chosen so that the interpolated scenario emits as much over 2025–2100 as CMIP7 Medium, or as close as the two allow (for example, 95% "pledges continued" and 5% "2020 policies" for Europe; half and half for the world; in South Asia and Latin America CMIP7 emits more than both AIM scenarios, and in the Middle East less, so there the closer one is used in full). Every year, both emissions and GDP are taken in that same proportion, so the cost of going from the interpolated scenario to net zero (the GDP lost) is measured from the same starting point as its effect on temperature. AIM's scenarios were made in 2020 and expected somewhat lower emissions in 2025 than CMIP7, which is fitted to historical data. So the interpolated scenario starts from CMIP7's 2025 emissions and joins AIM's own path by 2050. That gives net zero a little more to cut, and so it delivers a slightly larger temperature effect. The cost of those extra cuts is not added (see Costs), which, if anything, makes net zero look a little better. On this site, "current policies" means this interpolated scenario: all temperatures, benefits and costs come from it. It gives 2.86°C in 2100 in MAGICC (CMIP7 Medium itself gives 2.87°C).
  4. Measuring the impact of US net zero. Under current policies, US emissions fall from 6.1 billion metric tons of CO₂-equivalent in 2025 to 3.8 billion tons in 2050 and 2.1 billion tons in 2100: down, but nowhere near net zero. With net zero, US emissions instead fall in a straight line from 2025 to zero in 2050 and stay there, while all other countries keep their current policies. Some methane, for example from farming, is very hard to eliminate: it falls to 11.3 million tons in 2050, 55% of today's level, and stays there. That is the US's present share of the 200 million tons the world still emits in 2050 in the net-zero pathways of Sun et al. (2021). Nitrous oxide and fluorinated gases follow the same pathways. The remaining greenhouse gases, about 0.6 billion tons of CO₂-equivalent in 2050, are balanced by negative CO₂ emissions, so that all greenhouse gases add up to zero each year from 2050 (100-year global warming potentials from the Fifth Assessment Report: methane 28, nitrous oxide 265). The difference between the two paths is the impact of US net zero: on temperature, and on costs and benefits.
  5. Air pollution. Cutting fossil fuels also cuts air pollution (sulfur dioxide and other particles) that otherwise cools the climate. The site uses the intermediate case: each pollutant falls in proportion to the world's net-zero cut (Sun et al. 2021), applied to the US's own current-policy path. With cleaner or dirtier assumptions the US result changes a little, and perhaps counterintuitively: the more net zero cleans the air, the smaller the temperature reduction, and the less it cleans the air, the larger the reduction, because the pollution it removes was cooling the climate.
  6. The same for everyone. The site runs the same experiment for every country and group of countries, each acting alone, and for the whole world, where net zero by 2050 gives 1.48°C in 2100 instead of 2.86°C.
References