Carbon Budgets

[br...@chesdata.com]

An article was published last year which provides a revised IPCC carbon budget for cumulative CO2 emissions from 2025 through 2100 (“Indicators of Global Climate Change 2024: annual update of key indicators of the state of the climate system and human influence” https://essd.copernicus.org/articles/17/2641/2025/).  I revised this to create a post-2025 carbon budget (see attached PDF).  Since the next IPCC Assessment Report (AR7) won’t be released until 2028, I thought it would be helpful to have a peer-reviewed revised carbon budget to use in discussing the need for SRM (and it will be interesting to see if the AR7 carbon budget essentially matches ESSD’s revised budget). 

 

Conclusion from analyzing the revised carbon budget:

 

The carbon budget for limiting global warming to 1.5°C by 2100 has already been exhausted.  In other words, staying within the 1.5°C carbon budget would require removing from the atmosphere an amount of CO₂ equal to all future emissions through 2100.

Because CO₂ emissions are expected to remain largely unchanged during this decade, avoiding exceedance of the carbon budget for a 2.0°C temperature increase by 2100 would require either reducing net CO₂ emissions by about 4% of 2030 emissions each year for 25 years or by about 7% annually for 35 years—neither of which appears likely. Table 4 lists several factors that could influence the size of the carbon budget.

 

 

Ways to Increase the Carbon Budget	Factors That Could Reduce the Carbon Budget
Significant carbon dioxide is removed at the source (CCS)	Planetary albedo decreases faster than expected
Significant carbon is removed from the atmosphere (CDR)	Emissions from carbon-cycle feedbacks are greater than expected
Non-CO₂ greenhouse gas emissions are lower than model projections	Non-CO₂ greenhouse gas emissions are higher than model projections

Table 4.  Factors that could affect the Carbon Budget

 

I’d appreciate comments and suggestions.

 

Bruce Parker