what does this graph show?

It shows when the world or a country needs to stop emitting CO2. In the Paris Agreement, the countries of the world promised to limit global warming to "well below 2 °C" and to "pursue efforts" to limit it to 1.5 °C. The Intergovernmental Panel on Climate Change (IPCC) has calculated how much CO2 humanity can still emit to reach these goals. This is the world’s "CO2 budget".

These global CO2 budgets can be distributed among all countries based on a country’s share of the world population. With these national CO2 budgets and the current emissions it is possible to calculate when a country needs to reach net-zero CO2 emissions assuming a linear reduction path.

Four different CO2 budgets:

Best case:
Limit to 1.5 °C with 66% probability

Medium case:
Limit to 1.5 °C with 50% probability

Elevated risk:
Limit to 1.8 °C with 66% probability

High risk:
Limit to 1.8 °C with 50% probability

It shows when the world or a country needs to stop emitting CO2. In the Paris Agreement, the countries of the world promised to limit global warming to "well below 2 °C" and to "pursue efforts" to limit it to 1.5 °C. The Intergovernmental Panel on Climate Change (IPCC) has calculated how much CO2 humanity can still emit to reach these goals. This is the world’s "CO2 budget".

These global CO2 budgets can be distributed among all countries based on a country’s share of the world population. With these national CO2 budgets and the current emissions it is possible to calculate when a country needs to reach net-zero CO2 emissions assuming a linear reduction path.

Four different CO2 budgets:

Best case:
Limit to 1.5 °C with 66% probability
Medium case:
Limit to 1.5 °C with 50% probability
Elevated risk:
Limit to 1.8 °C with 66% probability
High risk:
Limit to 1.8 °C with 50% probability

 

why are the IPCC budgets too big?

The IPCC does not include "Earth system feedbacks" in its CO2 budgets. But through these feedbacks such as the thawing of permafrost greenhouse gases are released as well. If these emissions were included, then the global CO2 budgets for humanity's use would be smaller, as would the budgets of individual countries.

Apart from the emissions from these feedbacks we cover all CO2 emissions any given country is responsible for: These are the emissions from fossil fuel use and cement production, but also the emissions from land use change and the emissions from international aviation and shipping. However, we don't cover emissions that are embedded in imported goods.

The IPCC does not include "Earth system feedbacks" in its CO2 budgets. But through these feedbacks such as the thawing of permafrost greenhouse gases are released as well. If these emissions were included, then the global CO2 budgets for humanity's use would be smaller, as would the budgets of individual countries.

Apart from the emissions from these feedbacks we cover all CO2 emissions any given country is responsible for: These are the emissions from fossil fuel use and cement production, but also the emissions from land use change and the emissions from international aviation and shipping. However, we don't cover emissions that are embedded in imported goods.