The road (back) to Paris: Science-based pathways to return below 1.5°C

The authors  – PIK scientists Elmar Kriegler, Gunnar Luderer as well as PIK Directors Ottmar Edenhofer, and Johan Rockström – emphasize that global greenhouse gas emissions should have peaked before 2020 to keep warming below 1.5°C. As emissions continue to rise, long-term warming is now expected to exceed this threshold within the next decade. However, if deep and rapid emission reductions begin immediately and carbon dioxide removal (CDR) technologies and practices are scaled up, temperatures could still return below 1.5°C by 2100, following a so-called overshoot pathway. They warn, “Such a future remains in reach, but it will be extremely challenging”.

Such a pathway would require halving global greenhouse gas emissions by around 2035 reaching net-zero CO₂ by mid-century and reaching net-zero GHGs around 2060. Every tenth of a degree of additional warming increases the risk of crossing tipping points in the Earth system, including ice-sheet loss, permafrost thaw or weakening ocean circulation. The authors stress that immediate emission cuts are the most effective way to limit the overshoot and reduce the scale of CDR required later in the century.

Returning to below 1.5°C will depend not only on decarbonisation, but also on protecting and restoring natural carbon sinks and other life-supporting functions of the Earth system, the authors state. This includes transforming global food systems, stopping deforestation and keeping freshwater use, land-system change, biodiversity loss and other key indicators within planetary boundaries.

As warming will inevitably continue until at least mid-century, adaptation planning remains as crucial as ever to buffer the impacts of a warmer world, the authors conclude.