Future Scenarios

Low warming targets

The availability of climate model experiments under three alternative scenarios stabilizing at low warming targets inspired by the COP21 agreements (a 1.5 C not exceed, a 1.5 C with overshoot and a 2.0 C) makes it possible to assess future expected changes in global yields for two staple crops, wheat and maize. An empirical model of the relation between crop yield anomalies and temperature and precipitation changes, with or without the inclusion of CO2 fertilization effects, is used to produce ensembles of time series of yield outcomes on a yearly basis over the course of the 21st century, for each scenario. The results suggest that for globally averaged yields of these two grains the lower targets put forward by the Paris agreement do not substantially change the expected impacts on yields that are caused by warming temperatures under the pre-existing 2.0 °C target, when CO2 fertilization effects are considered.

Tebaldi, C., D. Lobell, 2018: Differences, or lack thereof, in wheat and maize yields under three low-warming scenarios, Environmental Research Letters, 13, 6, 065001

Global climate policy is increasingly debating the value of very low warming targets, yet not many experiments conducted with global climate models in their fully coupled versions are currently available to help inform studies of the corresponding impacts. This raises the question whether a map of warming or precipitation change in a world 1.5 C warmer than preindustrial can be emulated from existing simulations that reach higher warming targets, or whether entirely new simulations are required. For this type of low warming in strong mitigation scenarios, climate change signals are quite linear as a function of global temperature. Therefore, emulation techniques amounting to linear rescaling on the basis of global temperature change ratios (like simple pattern scaling) provide a viable way forward. 

Tebaldi, C. and R. Knutti, 2018: Evaluating the accuracy of climate change pattern emulation for low warming targets, Environmental Research Letters, 13, 5, 055006

Future volcanic eruptions could cause more climate disruption

Major volcanic eruptions in the future have the potential to affect global temperatures and precipitation more dramatically than in the past because of climate change. The study focused on the cataclysmic eruption of Indonesia's Mount Tambora in April 1815, which is thought to have triggered the so-called "year without a summer" in 1816. They found that if a similar eruption occurred in the year 2085, temperatures would plunge more deeply, although not enough to offset the future warming associated with climate change. The increased cooling after a future eruption would also disrupt the water cycle more severely, decreasing the amount of precipitation that falls globally. The reason for the difference in climate response between 1815 and 2085 is tied to the oceans, which are expected to become more stratified as the planet warms, and therefore less able to moderate the climate impacts caused by volcanic eruptions.

The research, published in the journal Nature Communications, was funded by NSF, NASA and the U.S. DOE. The study was led by J. Fasullo and included co-authors R. Tomas, S Stevenson, B Otto-Bliesner, and E Brady, all of NCAR, as well as E Wahl, of the National Oceanic and Atmospheric Administration.

Fasullo, J.T., R. Tomas, S. Stevenson, B. Otto-Bliesner, E. Brady and E. Wahl, The amplifying influence of increased ocean stratification on a future year without a summer, Nature Communications, 8, 2017