The Fifth National Climate Assessment (NCA5), released November 14, 2023, is a comprehensive analysis of the current and future effects of climate change on the United States, its ecosystems, agricultural production, natural resources, and residents. The report, a four-year collaboration between 14 federal agencies and nearly 500 authors, spans 17 topics and 10 regions. Additionally, chapters on physical science provide scientific context for the report and chapters on adaptation and mitigation analyze how to best improve our responses to climate change.
While the full report contains an impressive level of detail, this summary is meant to provide a tailored view of five chapters with immediate relevance to our stakeholders managing California’s natural and working lands.
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California will continue to see the profound effects of climate change on the water cycle, with long stretches of drought punctuated by extreme precipitation events and flooding. This increased variability in precipitation combined with increased evapotranspiration — the evaporation of water from plants, soil, surface water, and snow — will lead to lower soil moisture and groundwater availability.
One particularly relevant effect of climate change on California's water supply may be snow drought, the phenomenon where areas used to receiving winter snowfall, like the Cascade Range and Sierra Nevada, receive less snow, leading to lower summer flows in the rivers and streams that transport water across the state.
These climate change effects pose a major risk to human health and statewide agriculture. While water management strategies have improved alongside data and technology, outdated infrastructure and water rights allocation systems have been major barriers to meaningful change.
Read more in Chapter 4: Water.
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A major disturbance made worse by climate change in California’s forested ecosystems is wildfire, specifically high-severity wildfire driven by dry air, reduced rainfall, and high forest density. Climate change also drives other disturbances in forests, including insect and disease outbreaks. Bark beetle outbreaks, for example, are bolstered by warm conditions that speed up insect reproductive cycles and reduce overwintering deaths, leading to larger populations.
Forests provide essential ecosystem services, like carbon sequestration and air quality improvement, but climate change impacts reduce their ability to do so. Additionally, many economic and cultural resources — including food, medicinal, and timber products — will continue to become less available as plant, animal, and fungi populations decrease.
One major barrier to adaptation in forests is rapid expansion of the Wildland-Urban Interface (WUI). Chapter authors stress the importance of using proactive adaptation strategies in forested ecosystems, like forest thinning and prescribed burning.
Read more in Chapter 7: Forests.
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There is growing evidence that conservation management practices improve the resilience of agricultural operations to climate change, and that agroecological management practices, diversified agricultural landscapes, and a focus on soil health are meaningful strategies for reducing greenhouse gas emissions. Conservation programs supporting the adoption of agroecological management practices — like those offered by the Natural Resources Conservation Services, Farm Service Agency, and Risk Management Agency — not only increase adaptation and mitigation but bring economic opportunity to rural communities.
Livestock producers will continue to face difficult management decisions caused by climate change impacts, including fluctuations in precipitation, reduced forage availability and quality, and increased feed costs. They will also face increased pressure to reduce their greenhouse gas (GHG) emissions. Some mitigation technologies are available to help livestock producers meet this demand, but GHG accounting needs to be improved to assess the global warming potential of short-lived gasses like methane (CH4), the major emission of livestock.
Read more in Chapter 11: Agriculture, Food Systems, and Rural Communities.
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This chapter provides an overview of the most pressing current and future climate risks facing Arizona, California, Colorado, Nevada, New Mexico, and Utah:
- Climate change will continue to affect California with drought, inconsistent rain, and extreme heat, stressing the state’s livestock, reducing crop quality, and putting Californians at risk.
- Sea level rise, and associated flooding and saltwater intrusion, will affect natural resources along California’s coast.
- High severity wildfires, caused by a history of fire exclusion combined with the effects of climate change, will continue to place California’s ecosystems and residents at risk.
Read more in Chapter 28: Southwest.
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While fire is a critical process in many of California’s ecosystems, historical land management has led to forests overstocked with vegetation and rangelands dominated by flammable annual grasses. Combined with the effects of climate change, the ecosystems have been subject to more severe wildfires than they are adapted to.
When large swaths of land are burned at high severity, changes in plant populations can lead to larger habitat changes, turning forests into shrublands and shrublands into grasslands. These large fires also have detrimental impacts on water and air quality, as smoke particulates enter water flows and create human health risks, especially for outdoor workers and firefighters.
Read more in the special chapter Focus on Western Wildfires.
As part of the release of NCA5, the U.S. Global Change Research Program, the federal program responsible for developing and distributing the assessment, hosted a series of webinars where chapter authors presented their findings and answered audience questions. Linked below are the recordings of webinars for relevant chapters: