Although meeting the 1.5 °C temperature target set by the Paris Agreement would not be impossible, it will probably require a strengthening of current pledges for emissions reductions, suggests a study published online in Nature Geoscience this week. The paper indicates that the remaining allowable carbon emission budget that is compatible with this target is larger than originally thought.

Human-induced warming led to global mean surface temperatures in 2015 that were about 0.93 °C higher than in the mid-nineteenth century.

Richard Millar and colleagues used a simple carbon-climate model together with key properties of the climate system and the present-day climate state to assess remaining carbon budgets that are compatible with limiting warming to 1.5 °C. With ambitious mitigation of greenhouse gases other than carbon dioxide as well as continuous downward adjustments of carbon dioxide emissions, future net carbon emissions as large as 250 to 540 GtC could be compatible with limiting warming to 1.5 °C above pre-industrial temperatures by 2100, the authors calculate. They suggest that regular updates of human-induced warming based on a transparent methodology will help countries to adjust their commitment to climate change mitigation.

Also published online in Nature Geoscience this week is a Correspondence by Gunnar Myhre and colleagues, who find that the greenhouse effect caused by human-induced increases in atmospheric carbon dioxide concentrations is now half-way to doubling, compared to pre-industrial conditions. Although the concentrations themselves have not yet reached the halfway mark, this marks an iconic point as global warming unfolds.