Carbon Budget Calculations Assumptions
We have calculated that, for Canada to act in accordance with our Paris Agreement to keep global temperature increases below 2 degrees, our reduction in emissions must be at least 49% by 2020 and 100% by 2025. Our present targets will exceed the limit for a 3 oC increase in global temperatures and will not reach zero until 2060. The gap is enormous.
The limit on the total (cumulative) amount of CO2 that the atmosphere can safely contain is known as the carbon budget. IPCC carbon budgets represent the amount of CO2 that can be added to the atmosphere remaining in 2011. The budgets are from IPCC SYR_AR5_FINAL_full_wcover (Summary for Policy Makers)1 which was published in 2014. Table 2.2 from the report is below. There are different limits depending upon the maximum global temperature increase that is acceptable and the likelihood of this happening. In most cases we have subtracted cumulative emissions between 2011 and 2016 in the calculations and charts.
Many countries (Canada included) report their emissions in CO2e (which include gases such as methane which also cause global warming) as well CO2 units. We use Canada's statistics to find the equivalent amount of CO2e for our calculations.
All of our charts assume that annual emissions will be reduced by the same amount although in real life this is not going to happen. However, cumulative emissions are represented by the areas under the target lines so our calculations are a good approximation. We have different calculations based on different sharing strategies.
In order to calculate carbon budgets for Canada, Ontario and Toronto, we used various sharing strategies. Although there are many different sharing strategies, we primarily used population-based and emissions-based sharing. Ultimately all jurisdictions will have to agree on a common sharing strategy but that hasn't happened yet. Until it does, we think that population-based sharing is the fairest. It is likely that Canada and other developed countries will use a larger share but will have to contribute resources to developing countries so that they can increase their standard of living without using their full share of the budget.
We used the likely (greater than 66% chance) budgets for less than 1.5oC and 2oC from Cumulative CO2 from 2011 in GtCO2 (Complex models) budgets. Because the targets were set for 2011 we subtracted actual and projected emissions between 2011 and 2016 from the budgets for the charts.
The following table contains remaining global budgets in 2015 for a likely chance of keeping global temperatures from rising above 1.5, 2 and 3oC (cumulative emissions since 2011 were 310,905 MtCO2 in 2015 - according to the U.S. Department of Energy - http://cdiac.ornl.gov/GCP/).
1. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.