Simulations Probe Sun's Effects on Climate
Research shows that the Sun contributes minimally to modern global warming. An ongoing task is uncovering the star's role in decadal and regional climate change. To investigate complex, remaining questions about how radiation from the Sun affects Earth's climate, Duke University and NASA Goddard Institute for Space Studies (GISS) scientists ran century-long simulations under a variety of solar conditions at the NASA Center for Climate Simulation (NCCS).
The simulations used the GISS ModelE2 coupled atmosphere-ocean model with the atmosphere represented at 222-by-278-kilometer (km) resolution and the ocean at 111-by-139-km resolution. Besides atmospheric dynamics ModelE2 includes fully interactive chemistry operating from the surface up to 80 km, enabling it to capture the interactions of solar radiation with ozone and other chemical species.
For further realism, the simulations incorporated solar data from the Naval Research Laboratory (NRL) over the years 1991–2001, which serve as a representative 11-year solar cycle with maximum and minimum periods of activity. The researchers calibrated the NRL data with additional data from NASA's Solar Radiation and Climate Experiment (SORCE satellite.
After a 100-year control run to bring the ocean to near equilibrium, the team ran two sets of simulations on the NCCS Discover supercomputer :
- Set #1 entailed three simulations covering 110 years (10 solar cycles). The simulations modeled varying solar conditions at all, short (ultraviolet), and long (visible and near-infrared) wavelengths. Each simulation ran on 56 computing cores for ~60 days.
- Set #2 entailed four simulations covering 160 years. The simulations modeled fixed solar maximum conditions at all, short, and long wavelengths plus fixed minimum conditions at all wavelengths. Each simulation ran on 88 computing cores for ~50 days.
The computations revealed that “long-term changes in the Sun's output cause clear effects on Earth's climate that can be seen from the surface to the upper stratosphere,” said Drew Shindell , Nicholas Professor of Earth Sciences at Duke University. “In contrast, the roughly 11-year solar cycle has clear impacts in the stratosphere but relatively weak effects on surface climate that are similar in magnitude to natural variability.”
The study also showed that the tropics and high latitudes respond to solar variability at different wavelengths, especially during winter.
“Access to NASA supercomputing resources allowed us to not only examine the effects of both short-term and long-term solar output variations but also to perform additional simulations to separate the impacts of output changes at different wavelengths, providing insight into the mechanisms whereby the Sun affects our climate,” Shindell said.
Shindell, D.T., G. Faluvegi, and G.A. Schmidt, 2020:
Influences of solar forcing at ultraviolet and longer wavelengths on climate.