The 2015–2020 period saw the highest number of extremely hot days, slightly exceeding the record set in the early 1930s, and included the years with the second- and third-highest values (20 Figure 2a). Temperatures in California have risen almost 3☏ since the beginning of the 20th century (Figure 1). Less warming is expected under a lower emissions future (the coldest end-of-century projections being about 1☏ warmer than the historical average green shading) and more warming under a higher emissions future (the hottest end-of-century projections being about 9☏ warmer than the hottest year in the historical record red shading). Historically unprecedented warming is projected during this century. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Shading indicates the range of annual temperatures from the set of models. Temperatures in California (orange line) have risen almost 3☏ since the beginning of the 20th century. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions). For example, strong El Niño events often cause excessive precipitation in Southern California, but the effects in Northern California are inconsistent.įigure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for California. Because of its large north–south extent and the existence of several mountain ranges, extreme climate events often affect only a portion of the state. Annual average (1991–2020 normals) temperatures vary from less than 40☏ at the highest mountain elevations to less than 50☏ in the northeast and greater than 70☏ in the southeast. Due to the moderating effect of the Pacific Ocean, coastal locations experience mild year-round temperatures, while inland locations experience a wider range of temperatures. In winter, this system moves southward, allowing storms to bring precipitation to the state. During summer, the North Pacific High and the jet stream move northward, keeping storms north of the state and resulting in dry summers. The North Pacific High, a semipermanent high-pressure system off the Pacific Coast, and the mid-latitude jet stream play dominant roles in California’s seasonal precipitation patterns. The deserts in the south are some of the Nation’s hottest and driest areas, while higher elevations can experience low temperatures and heavy snowfall. California, the most populous and third-largest U.S.
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