• Graham Harris

What is the global carbon budget?



We are all familiar with the concept of a budget when it comes to our household finances or government spending. A nice, simple definition of a budget is: “the amount of money you have available to spend”[1]. A carbon budget is based on the same idea. Thus, it could be defined as “the amount of carbon you can emit”.


Globally, the IPCC has calculated a scientific “global carbon budget” that is based on the impact our emissions will have on our environment. If we can stay within this global carbon budget, then we can limit climate change to a 1.5°C global average temperature increase. So, what is this global carbon budget? According to the World Resources Institute:


“To have a medium chance of limiting warming to 1.5°C, the world can emit 770 gigatonnes of carbon dioxide (GtCO2). To have a likely chance (67 percent), the remaining budget drops to 570 GtCO2.”


Those are big numbers and not intuitively understood. What’s perhaps more important is to understand what is required of us if we are to stay within this budget. To do this, we must reduce global emissions by around 50% by 2030, and to a “net zero” situation by 2050 [link]. For example, if your household emits 15 tonnes CO2e/yr now, it should aim to reduce that to 7.5 tonnes in the next 10 years; if your facility emits 10,000 tonnes CO2e/yr now, it should be targeting a 5,000 tonnes CO2e/yr reduction by 2030, and so on.


Bearing in mind that the IPCC’s global carbon budget is based on limiting change to 1.5°C (not preventing it), it’s clear that we have all been living beyond our means for some time, merrily burning our way through our carbon budget year-upon-year. We don’t have any “savings” to dip into – we are already in debt. If we don’t stay within this new budget, we can expect to live with the consequences of increased global heating beyond 1.5°C, with associated more severe impacts for our environment and our own health, economy and society: more severe wildfires; more severe storms; more loss of species and habitats; more deaths due to extreme weather, and so on.


For individuals, corporations, institutions and governments, therefore, the global carbon budget provides both context and a simple guide to the scale of action that is needed for us to avert the worst impacts.

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