Abstract

The climate of the Northeast United States has been changing rapidly since the 1970s, and cloud cover poses one of the biggest unknowns in climate modeling. Cloud cover changes have the potential to influence tree growth, and the temperate forests of the Northeast are poorly understood, partly due to the region’s long history of disturbance. In this study, nested principal component regression analysis was utilized to build a reconstruction of June through September (JJAS) cloud cover in the Northeast United States from 1801 to 2002. Sixteen oak ring width chronologies of various species and fourteen eastern hemlock (Tsuga canadensis) latewood blue intensity chronologies were used in modeling to create a time series that explains at most 43.18% of the variance in average Northeast JJAS cloud cover. The reconstruction suggested that cloudiness highs in the early 1800s were forced by volcanoes, and the subtle cloud cover changes from the late 1800s to the 1920s were likely caused by widespread deforestation. JJAS cloudiness dropped in the 1920s, possibly due to a shift to the warm phase of the Atlantic Multidecadal Oscillation. Rising sulfate aerosol emissions contributed to an increase in cloudiness beginning in the 1950s, which was intensified by a coeval shift in the Pacific Decadal Oscillation to the positive phase in the 1970s. The decreasing cloud cover trend after the 1970s was likely driven by the drop in sulfate aerosol emissions paired with the continued rise in greenhouse gases. High summer cloudiness is associated with less dense hemlock latewood and wider oak annual rings. However, summer cloudiness and precipitation are strongly correlated with each other, and precipitation has a more direct effect on tree growth than cloud cover. Hemlock trees are most impacted by decreased light availability and cloud-induced temperature changes, whereas the oaks are primarily limited by moisture. This study lays the groundwork for future paleoclimatic reconstructions of cloud cover using tree rings and provides a better understanding of Northeast temperate forest climate interactions, which will be integral given the uncertainty clouds pose in the wake of modern climate change.

Advisor

Wiles, Gregory

Department

Earth Sciences; Statistical and Data Sciences

Disciplines

Atmospheric Sciences | Climate | Geology | Longitudinal Data Analysis and Time Series | Statistical Models

Keywords

Dendroclimatology, Cloud Cover, Latewood Blue Intensity, Annual Ring Width

Publication Date

2026

Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis

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© Copyright 2026 Mary E. Palmieri