Can large scale sea ice cover changes affect precipitation patterns over California?

There is a considerable uncertainty in projected precipitation changes in California under global warming. This is, in part, a consequence of being located in a region sensitive to both tropical and midlatitude atmospheric circulation changes. It has been suggested that high-latitude sea ice cover changes, another area of large uncertainty in climate model projections, impact atmospheric circulation across the midlatitides and tropics. Motivated by this, we investigate the possible links between large scale sea ice cover changes and precipitation over California.

Our approach is to sample uncertainty in sea ice physics parameters and variability in atmospheric initial conditions to obtain an ensemble of simulations with substantially different states of Arctic and Antarctic sea ice cover. This large ensemble isolates a robust, statistically significant climate change response arising from changes in sea ice cover only.

Our results show a significant link between Arctic and Antarctic sea ice cover changes and precipitation across the tropical Atlantic and Pacific basins, the Sahel, and the west coast of the United States. High latitude sea ice changes lead to a shift in the tropical convergence zone, and act to modify the subsidence over the southwest United States and the geopotential distribution in the North Pacific; all of these factors resulting in significant precipitation changes over California.

We conclude that high-latitude sea ice cover changes are an important driver of low-latitude precipitation. Consequently, reliable predictions of future precipitation changes over areas such as California (and the Sahel) will strongly depend on our ability to adequately simulate both Arctic and Antarctic sea ice changes.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and released as LLNL-ABS-676036.