The Fourth National Climate Assessment (v1): Causes

This report summarizes what NASA, NOAA, the EPA, DOD, DOE, and other major US scientific organizations understand about climate change and how confident they are in that understanding based on all the available evidence.

From the two-page Executive Summary Highlights:

"This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence."

The term "extremely likely" indicates a 95-100% level of confidence.

The Fourth National Climate Assessment (v2): Impacts and Risks

The Overview provides a national summary and Chapter 18 is about impacts on the Northeast: https://nca2018.globalchange.gov/:

• "Climate change creates new risks and exacerbates existing vulnerabilities in communities across the United States, presenting growing challenges to human health and safety, quality of life, and the rate of economic growth."

• "Climate change affects the natural, built, and social systems we rely on individually and through their connections to one another. These interconnected systems are increasingly vulnerable to cascading impacts that are often difficult to predict, threatening essential services within and beyond the Nation’s borders."

• "While mitigation and adaptation efforts have expanded substantially in the last four years, they do not yet approach the scale considered necessary to avoid substantial damages to the economy, environment, and human health over the coming decades."

• "The seasonality of the Northeast is central to the region’s sense of place and is an important driver of rural economies. Less distinct seasons with milder winter and earlier spring conditions are already altering ecosystems and environments in ways that adversely impact tourism, farming, and forestry."

• "The Northeast’s coast and ocean support commerce, tourism, and recreation that are important to the region’s economy and way of life. Warmer ocean temperatures, sea level rise, and ocean acidification threaten these services."

• "Changing climate threatens the health and well-being of people in the Northeast through more extreme weather, warmer temperatures, degradation of air and water quality, and sea level rise. These environmental changes are expected to lead to health-related impacts and costs, including additional deaths, emergency room visits and hospitalizations, and a lower quality of life."

The 2021 New Hampshire Climate Assessment

This report was supported by funding from the New Hampshire Department of Environmental Services and produced by NH State Climatologist M.D. Lemcke-Stampone, C.P. Wake, and E.A. Burakowski, from The Sustainability Institute, University of New Hampshire: https://scholars.unh.edu/sustainability/71/.

• "Temperatures across New Hampshire increased by an average of 3oF since 1901. The rate of warming was greatest during the fall and winter seasons and at night. "

• "There was a 12% increase in annual precipitation over the past 120 years largely due to an increase in heavy precipitation since 1971. The number of multi-day precipitation events exceeding four inches increased near the coast and in the White Mountains while areas inland and in the far north saw an increase in the number of daily one-inch events.."

• "From 1971-2020, the amount of water stored in the snowpack decreased from 59-91% across central New Hampshire. Over the same period, spring ice-out dates on Lake Winnipesaukee and Lake Sunapee shifted eight and 11 days earlier, respectively.."