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<br /> <br />2021 Multijurisdictional Local Hazard Mitigation Plan <br /> <br />Source: NASA, 2020 <br /> <br /> Figure 17-1. Global Carbon Dioxide Concentrations Over Time <br /> <br />For hazards that are affected by climate change, the assumption that future behavior will be equivalent to past <br />behavior is not valid if climate conditions are changing and therefore accelerating or amplifying natural hazard <br />frequency and intensity. As flooding is generally associated with precipitation frequency and quantity, for <br />example, the frequency of flooding will not remain constant if broad precipitation patterns change. The California <br />4th Climate Assessment predicts high year-to-year variability with prominent “booms” and “busts” resulting in <br />very wet and very dry years. Specifically, as hydrology changes, storms currently considered to be the 100-year <br />flood might strike more often than their name suggests, leaving many communities at greater risk and introducing <br />risk to communities that historically have been considered low risk. <br /> <br />The risks of landslide, severe storms, and wildfire are all impacted by climate change. For this reason, an <br />understanding of the relationship between climate change and the efforts to mitigate natural hazards is critical. <br />Information about how climate patterns are changing provides insight on the reliability of future hazard <br />projections used in mitigation analysis. <br /> <br />17.1.3 Current Indicators of Climate Change <br />Global Indicators <br />The major scientific agencies of the United States—including NASA and the National Oceanic and Atmospheric <br />Administration (NOAA)—have presented evidence that climate change is occurring. NASA summarizes key <br />evidence as follows (NASA, 2020a): <br /> Global Temperature Rise—The planet’s average surface temperature has risen about 1.62 ºF since the <br />late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions <br />into the atmosphere. Most of the warming occurred in the past 35 years, with the five warmest years on <br />record taking place since 2010. <br /> <br /> <br /> <br />17-2