Placing the Common Era in a Holocene context: millennial to centennial patterns and trends in the hydroclimate of North America over the past 2000 years

Abstract

A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years).The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800-1300 CE) was drier than the Little Ice Age (1400-1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permit-ted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3-7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.

The human impact on North American erosion, sediment transfer, and storage in a geologic context

“…3). Although climate has varied in North America through the studied time interval 32,33 (including an increase in precipitation since the early Holocene 33 ) there were no clear changes in hydroclimate that can account for the observed continent-wide increase in accumulation rates between pre-and post-settlement ages.…”

People, Fire, and Pine: Linking Human Agency and Landscape in the Boundary Waters Canoe Area Wilderness and Beyond

“…Detailed quantitative fire-climate analyses of our data show that widespread fire activity is associated with regional drought conditions but that the smaller, local fires that represent the majority of fire events in our record are unrelated to the available interannual climate variables for the region (Kipfmueller et al forthcoming). The spatial and temporal expressions of Little Ice Age conditions are variable across North America (Neukom et al 2019), with regionspecific paleoecological reconstructions indicating generally wetter conditions during the 1700s and 1800s (Shuman et al 2018) and a warming trend that began around 1700 and continues to this day (St. George et al 2009;Jaume-Santero et al 2016). Interannual tree ring-based reconstructions of summer drought indicate average to above-average moisture availability throughout much of the 1700s and early 1800s, drier conditions from about 1860 to 1900, and generally wetter conditions throughout the 1900s with the exception of a multiyear drought in the 1930s (Grid Point 197 from Cook et al 2010).…”

The potential role of intrinsic processes in generating abrupt and quasi‐synchronous tree declines during the Holocene

“…, Shuman et al. ). An additional challenge is the simultaneous statistical fitting of multiple taxa from multiple sites, accounting for potential differences among taxa and, for the same taxon, differences in dynamics among sites.…”

“…A key challenge to such approaches is the scarcity of colocated paleohydrological proxy data for the Holocene (Marlon et al 2017), although this is improving, particularly for the last two millennia (Rodysill et al 2018, Shuman et al 2018). An additional challenge is the simultaneous statistical fitting of multiple taxa from multiple sites, accounting for potential differences among taxa and, for the same taxon, differences in dynamics among sites.…”