The world’s governments have committed to keeping global warming below 2 Celsius. But what does this mean for carbon emissions? When will global emissions have to peak to give us a chance of staying below 2 Celsius – and what needs to happen after the peak year? This interactive graph allows you to choose the peak year – and to see the implications of your choice.

The graph shows scenarios that give a 50% chance of keeping global warming below the 2°C ceiling. This is based on analysis by the Intergovernmental Panel on Climate Change (IPCC). It calculates that total emissions of 1,300 gigatonnes (Gt) of CO2 would give that 50% chance; and each of our scenarios meets this ‘carbon budget’.

The later that global emissions peak and begin to decline, the sharper the fall in emissions needed to keep within the carbon budget of 1,300Gt CO2. The maximum feasible rate for reducing carbon emissions is thought to be around 3.5% per year. However, peaking emissions in 2020 or later means that emissions would subsequently need to fall faster than this.

If emissions peak even later, the carbon budget can only be achieved by deploying ‘negative emissions’ – taking CO2 from the air. This is most likely to happen through use of Bio-Energy with Carbon Capture and Storage (BECCS) – growing plants (that absorb carbon), burning them, capturing the CO2 and storing it underground. However, there is a limit, as BECCS requires a lot of land; negative emissions of 10 Gt CO2/year in 2100 may be the maximum possible.

In our scenarios, it is impossible to stay below 2°C without negative emissions if the emissions peak occurs in 2030 or 2035. We do not give a curve for peaking in 2040 or later because we could not find a way of keeping global warming below 2°C if this happens.

For detailed information on the methodology please see: eciu.net/blog/2015/how-we-made-the-emissions-peaking-tool.