North American hydroclimate during past warms states: A proxy
network-model comparison for the Last Interglacial and the mid-Holocene
Abstract
During the mid-Holocene (MH: ~6,000 years BP) and Last
Interglacial LIG (LIG: ~129,000-116,000 years BP)
differences in the seasonal and latitudinal distribution of insolation
drove northern hemisphere high-latitude warming comparable to that
projected in end-21st century low emissions scenarios, making these
intervals potential analogs for future climate change in North America.
However, terrestrial precipitation during past warm intervals is not
well understood and PMIP4 models produce variable regional moisture
patterns in North America during both intervals. To investigate the
extent to which the latest generation of models reproduces moisture
patterns indicated by proxy records, we compare hydroclimate output from
17 PMIP4 models with networks of moisture-sensitive proxies compiled for
North America during the LIG (39 sites) and MH (257 sites). Agreement is
lower for the MH, with models producing wet anomalies across the western
United States (US) where a high concentration of proxies indicate
aridity. The models that agree most closely with the LIG proxies differ
from the PMIP4 ensemble by showing relative wetness in the eastern US
and dryness in the northwest and central US. An assessment of
atmospheric dynamics using an ensemble subset of the three models with
the highest agreement suggests that LIG precipitation patterns are
driven by weaker winter North Pacific pressure gradients and steeper
summer North Pacific and Atlantic gradients. Comparison of this LIG
subset ensemble with simulations of future low emissions scenarios
indicates that the LIG may not be a sufficient analog for projected,
end-21st century hydroclimatic change in North America.