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Key Findings

California’s Fourth Climate Change Assessment (Fourth Assessment) advances actionable science that serves the growing needs of state and local-level decision-makers from a variety of sectors.

Meeting California’s greenhouse gas emissions reductions remains a priority for the State, especially given updated climate impact results from the Fourth Assessment. Cal-Adapt.org provides access to the State’s projections, through data sets and visualization tools.

The Fourth Assessment is part of California’s comprehensive strategy to take action based on cutting-edge climate research. It was designed to address critical information gaps that decision-makers need at the state, regional, and local levels to protect and build resilience of California’s people and its infrastructure, natural systems, working lands, and waters.

The Climate-Safe Infrastructure Working Group is releasing recommendations that build on these findings to inform a robust and comprehensive approach to building for the future.

Graphic representation of State's approach to building resilienceThe State’s approach to building resilience in California, which recognizes the interconnections and interdependences across people, nature, and infrastructure.

The State’s approach to building resilience in California, which recognizes the interconnections and interdependences across people, nature, and infrastructure.

Temperature

Average annual maximum daily temperature is projected to rise by 5.6–8.8°F by 2100, depending on greenhouse gas emissions reductions.key-findings-temperature-text

Water

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By 2050, the average amount of water stored as snowpack is projected to decline by 2/3 of its historical average. key-findings-water-text

Water management practices in California face growing challenges from continued climate change and extreme weather. Promising technical adaptation options to reduce these negative water supply impacts include the use of probabilistic hydrological forecasts, groundwater storage, and better measurements of the snowpack.

Impacts to Agriculture

By 2050, under certain precipitation conditions, a study estimates California’s agricultural production could face climate-related water shortages of up to 16 percent in certain regions.

Hotter conditions due to climate change could lead to loss of soil moisture.

Models show that increasing soil organic matter increases the soil water holding capacity, demonstrating one adaptation option.

Wildfire

Average area burned 77% increase by 2100 if emissions continue to rise.key-findings-wildfire-area-burned
Insurance costs 18% increase by 2055 in highest risk areaskey-findings-wildfire-insurance

By 2100, if greenhouse gas emissions continue to rise, one study found that the frequency of extreme wildfires would increase, and the average area burned statewide would increase by 77 percent. In the areas that have the highest fire risk, wildfire insurance is estimated to see costs rise by 18 percent by 2055.

A Fourth Assessment review of forest health literature provides further scientific backing to the State’s Forest Carbon Plan to increase forest restoration and treatment, such as prescribed fire, to an average of 35,000 acres a year by 2020.

Sea Level Rise

31 to 67 percent of Southern California beaches may completely erode by 2100 without large-scale human interventions.

$17.9 billion worth of residential and commercial buildings could be inundated statewide by sea level rise by 2050, with a projected 50 cm (~20 in) of sea level rise. A 100-year coastal flood, on top of this level of sea level rise, would almost double these costs.

The Fourth Assessment funded a study providing technical guidance on design and implementation of natural infrastructure, such as the use of vegetated dunes, marsh sills, and native oyster reefs, for adaptation to sea-level rise.

There is also a model to estimate shoreline change along the California coast at a resolution useful for local planners.

Impacts to Transportation Infrastructure

Without implementation of protective measures, airports in major urban areas such as San Francisco, Oakland, and San Diego will be susceptible to major flooding from a combination of sea-level rise and storm surge by 2040-2080. San Francisco airport is already at risk of flooding from storm surge.

The miles of highways susceptible to coastal flooding in a 100-year storm event will triple from current levels to 370 miles by 2100, and with over 3,750 miles exposed to temporary flooding.

Caltrans is currently conducting climate vulnerability assessments to address these and other impacts, to ultimately develop climate adaptation strategies for each of its 12 districts across the state.

Communities

Impacts to Public Health

Heat waves in cities could cause 2-3X more heat-related deaths by 2050. Vulnerable populations will experience the worst of these effectskey-findings-temperature-heat-wave

Heat-Health Events (HHEs), which predict risk to populations vulnerable to heat, will worsen drastically throughout the state: by mid-century, the Central Valley is projected to experience average Heat-Health Events that are two weeks longer, and HHEs could occur 4 to 10 times more often in the Northern Sierra region.

A prototype heat warning system was developed for the Fourth Assessment: the California Heat Assessment Tool (CHAT), to support public health departments taking action to reduce heat-related morbidity and mortality outcomes.

Impacts to Energy

Hotter temperatures will increase annual electricity demand for homes, driven mainly by the increased use of air conditioning units. However, increases in peak hourly demand during the hot months of the year could be more pronounced than changes in annual demand. This is a critical finding, because electricity-generating capacity must match peak electricity demand.

California’s Public Utilities Commission (CPUC) recently issued an Order Instituting Rulemaking to consider strategies and guidance for climate adaptation for electric and natural gas utilities, which will be informed by the Fourth Assessment.

Governance

Climate change also presents a series of governance-related challenges for public agencies.One study surveyed local governments in California and found that while a lack of funding was identified as the most significant perceived barrier to climate adaptation, insufficient staff resources and capacity was identified as the second greatest perceived challenge among those surveyed. Interestingly, uncertainty related to climate projections was one of the lowest ranked barriers.

Because organizational barriers and governance challenges can delay and even prevent local governments from taking action, another study developed an “Adaptation Capability Advancement Toolkit.” The Toolkit allows local governments to assess their capabilities to overcome organizational barriers, and to identify key actions and resources for increasing their capability to undertake climate change adaptation.

In addition to these studies, the regional reports provide insight into regionally-specific governance challenges and, similarly, the topical reports highlight governance issues faced by tribes and environmental justice communities, as well as issues specific to California’s ocean and coast.

For more information, please download the overview brochure.

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