How much CO2 can the world emit while keeping warming below 1.5°C and 2°C?

The budget to keep temperatures below 1.5°C is less than a decade of emissions at current levels. For 2°C, it’s less than 3 decades.

In the Paris Agreement, the world set the goal of keeping the global average temperature rise “well below 2°C” and “pursuing efforts to limit warming to 1.5°C.”

Our global efforts are now measured against these targets of 1.5°C and 2°C. Pathways are assessed on whether they are ‘on track’ to meet these commitments.

Researchers estimate how much more CO2 we can emit to keep temperatures below 1.5°C and 2°C. This is called the world’s ‘carbon budget’.

How much of our ‘carbon budget’ do we have left to meet these goals?

In the chart below, we see the remaining carbon budget for 1.5°C and 2°C. These are the latest estimates from Piers Forster and colleagues, published in 2023.1 It’s based on how much can be emitted from the start of 2023 onwards.

There is some uncertainty in how the climate responds to our emissions and the impact of other greenhouse gas emissions, such as methane and nitrous oxide. That means there is not a single ‘budget’. Instead, it is a sliding scale of probabilities. The lower our emissions, the more likely we are to keep temperature rise below our targets.

The budgets, therefore, are given as likelihoods of keeping warming below that level.

For a 50% chance of limiting temperatures to 1.5°C, we could emit a further 250 billion tonnes of CO2. But there would still be a 50% chance that we go over this target. If we wanted to be risk-averse – and have an 83% chance of staying below – the world can only emit 100 billion tonnes.

Bar charts showing the amount of CO2 that can be emitted to keep temperature rise below 1.5C and 2C.

What’s clear is how small our remaining budget for 1.5°C is.

The world emitted 41 billion tonnes of CO2 in 2022.2 To have a 50% chance of staying below 1.5°C, we can only emit 250 billion tonnes. That’s just 6 years of our current emissions.3

The budget for 2°C is significantly larger. For a 50% chance, the world could emit 1150 billion tonnes. That’s around 28 years of current emissions.4 For a two-thirds chance, it’s 23 years.

That might seem more achievable, but the world is currently not on track to achieve this. Current policies have us on course for around 2.5°C of warming. The world needs to reduce emissions much faster to keep temperatures below 2°C.


  1. Forster, P. M., Smith, C. J., Walsh, T., Lamb, W. F., Lamboll, R., Hauser, M., ... & Zhai, P. (2023). Indicators of Global Climate Change 2022: annual update of large-scale indicators of the state of the climate system and human influence. Earth System Science Data, 15(6), 2295-2327.

  2. This figure includes fossil fuels, industry, and land use change.

  3. [250 / 41 = 6 years]

  4. [1150 / 41 = 28 years]

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Hannah Ritchie (2023) - “How much CO2 can the world emit while keeping warming below 1.5°C and 2°C?” Published online at Retrieved from: '' [Online Resource]

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    author = {Hannah Ritchie},
    title = {How much CO2 can the world emit while keeping warming below 1.5°C and 2°C?},
    journal = {Our World in Data},
    year = {2023},
    note = {}
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