LAUSR

The goal of limiting global mean warming to well below 2 °C, and possibly to 1.5 °C, emerged in the Paris Agreement, motivated by the belief that achieving these targets 'would significantly reduce the risks and impacts of climate change'. Understanding the climate impacts of relatively low levels of warming, in particular whether there are substantial benefits to reducing emissions to limit warming to 1.5 °C rather than 2 °C, is important for informing climate policy, but such studies are scarce. Here we evaluate the difference in global biophysical and economic impacts related to agriculture between 1.5 °C–2 °C warming. Given the small difference in global average temperature, accounting for uncertainties is important, and we include key uncertainties in three main components of the analysis: climate system (regional climate variability), biophysical system (crop response to CO2 fertilization), and economic system (trade responsiveness). We are unable to meaningfully distinguish the regional agricultural impacts occurring with 1.5 °C warming from those occurring with 2 °C warming when accounting for these uncertainties. Under some assumptions 1.5°C implies benefits relative to 2 °C, while under others it implies costs. Results are most sensitive to the uncertainty in the effect of CO2 fertilization on crop yield.