Discussion:
What is a Carbon Budget?
A carbon budget is an upper limit of permitted GHG emissions to maintain a statistical probability of maintaining global temperatures to a certain threshold. Human activities since the industrial era have resulted in GHG emissions which, through planetary and atmospheric interactions, have increased global temperatures. These global temperature increases have resulted in climate change impacts which negatively affect habitability, productivity and quality of life. Reducing and limiting GHG emissions works to mitigate climate change by reducing the affect of atmospheric interactions and thus reducing temperature increases.
Carbon budgeting in a modern context works to prevent dangerous levels of climate change by restricting global emissions. The latest science indicates that in order to restrict warming to less than 1.5 degrees Celsius, total C0 2 emissions from all anthropogenic sources around the globe, since 1870 should not exceed 2500 Gigatonnes (Gtonnes). Presently, approximately 2100 Gtonnes had been emitted leaving 400 Gtonnes as a global carbon budget.
Per the Intergovernmental Panel of Climate Change (IPCC), warming needs to be maintained to 1.5 degrees Celsius in order to prevent “Climate Breakdown”. The IPCC compared impacts from of a changing climate at a 2 degrees Celsius increase over the goal of limiting temperature increases to a 1.5 Celsius increase, and found the following:
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As many as 457 million more people exposed to climate risks and related poverty;
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Twice as many people suffering from water scarcity;
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Twice as many plants and three times as many insects losing their habitat;
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An ice-free arctic every 10 years instead of 100 years;
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The exposure of 2.6 times as many people to extreme heat at least every five years;
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Double the decline in global fisheries.
In order to translate the global emissions budget to a localized, City-level, budget calculations are made using the IPCC C40 Cities Convergence and Contraction methodology.
Convergence and Contraction
Allocation of a carbon budget to specific cities is based on the approach known as Convergence and Contraction which allocates emissions budgets based on GDP and emissions levels. Cities with high GDP and high emissions are required to reduce emissions the fastest, while cities (primarily in developing countries) with low GDP and low emissions are permitted to increase their emissions to a certain level conducive to a standard in quality of life before eventually reducing them. This method ensures that the global transition to low-carbon societies is done so in an equitable manner, with the