The Fifth National Climate Assessment

This is the US Government’s preeminent report on climate change impacts, risks, and responses. It is a congressionally mandated interagency effort that provides the scientific foundation to support informed decision-making across the United States.

From the report:

• "Climate Is Changing, and Scientists Understand Why:  It is unequivocal that human activities have increased atmospheric levels of carbon dioxide and other greenhouse gases. It is also unequivocal that global average temperature has risen in response."

• "Earth’s climate is changing because humans are increasing the concentrations of greenhouse gases in the atmosphere by burning fossil fuels and through other activities. The increase in greenhouse gases is warming the planet and driving other observed climate trends, including increases in the frequency and severity of many types of extreme weather events. Future changes and impacts depend largely on the choices humans make about future greenhouse gas emissions."

• "The effects of human-caused climate change are already far-reaching and worsening across every region of the United States. Rapidly reducing greenhouse gas emissions can limit future warming and associated increases in many risks."

• Climate changes are making it harder to maintain safe homes and healthy families; reliable public services; a sustainable economy; thriving ecosystems, cultures, and traditions; and strong communities. Many of the extreme events and harmful impacts that people are already experiencing will worsen as warming increases and new risks emerge.

• With each additional increment of warming, the consequences of climate change increase. The faster and further the world cuts greenhouse gas emissions, the more future warming will be avoided, increasing the chances of limiting or avoiding harmful impacts to current and future generations.

• Large near-term cuts in greenhouse gas emissions are achievable through many currently available and cost-effective mitigation options. However, reaching net-zero emissions by midcentury cannot be achieved without exploring additional mitigation options. Even if the world decarbonizes rapidly, the Nation will continue to face climate impacts and risks. Adequately and equitably addressing these risks involves longer-term inclusive planning, investments in transformative adaptation, and mitigation approaches that consider equity and justice.

The IPCC Sixth Assessment Report: IPCC AR6

From Synthesis Report headline statements:

• "Human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850–1900 in 2011–2020. Global greenhouse gas emissions have continued to increase, with unequal historical and ongoing contributions arising from unsustainable energy use, land use and land-use change."

• Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred. Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. This has led to widespread adverse impacts and related losses and damages to nature and people."

• "Human-induced climate change, including more frequent and intense extreme events, has caused widespread adverse impacts and related losses and damages to nature and people, beyond natural climate variability."

• "Approximately 3.3 to 3.6 billion people... are highly vulnerable to climate change. A high proportion of species is vulnerable to climate change. Human and ecosystem vulnerability are interdependent."

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 3˚F 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.."