How much time is left before we reach global warming targets of 1.5°C or 2°C?
What is it about?
The Paris climate agreement aspires to restrict the rise in global mean surface temperature since the pre-industrial period to 2°C or less for this century by reducing global carbon emissions. However, there are large uncertainties in how much carbon may be emitted before reaching a warming target. We demonstrate a new approach to reduce the uncertainty of climate projections; using theory and geological constraints we generate a very large ensemble of several thousand projections that closely match historical records for nine key climate metrics, including surface warming and ocean heat content. Our breakthrough is by ensuring our projections are consistent with the historical record, our analysis significantly narrows the uncertainty in surface warming projections. We find that there is less than two decades before we reach 1.5°C warming and less than four decades before we reach 2°C warming. In more detail, we find that a warming target of 1.5°C above the preindustrial requires that the total emitted carbon from the start of year 2017 to be less than 195 to 205 PgC in over 66% of simulations (equivalently 715 to 750 Gt CO2). At current emission rates, this 1.5°C warming target is reached in 17 to 18 years. We find that a warming target of 2°C is only likely if the emitted carbon remains less than 395 to 455 PgC in over 66% of simulations (equivalently 1450 to 1670 Gt CO2). At current emission rates, this 2 °C warming is reached in 35 to 41 years. In comparison to our work, 13 Earth system models forced by a realistic forcing suggest that 2°C warming might occur with cumulative carbon emissions ranging from 84 to 581 PgC from year 2017 (or equivalently 308 to 2130 Gt CO2). This range in how much future carbon may be emitted to meet specific warming targets is much larger than our projections. Note about units: 1 Peta gram of carbon is denoted by 1 PgC=10 power 15 gC, which may equivalently be written as 1 Giga tonne C denoted by 1 GtC. 1 GtC of carbon is equivalent to 3.7 Gt of carbon dioxide.
Why is it important?
We need to know how much carbon we may emit and over what timescale before we meet warming targets. In these windows of 17 to 18 years before 1.5°C warming or 35 to 41 years before 2°C warming, we need either to develop a more carbon-efficient future or prepare to mitigate for the adverse effects of a warming climate. To develop a more carbon-efficient future, we need to develop and adopt new technologies, and plan and organise our societies, to use energy more efficiently and reduce carbon emissions. Ultimately, we need to explore ways of moving towards a carbon-neutral future and ways of capturing carbon to reduce how much carbon dioxide is in the atmosphere. We all face challenges in making this transition, but the earlier that we start moving towards a more carbon-efficient future the easier it will be to meet these warming targets.
The following have contributed to this page: Professor Richard G Williams and Kudos Admin