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Climate Resilience May 18, 2021 Page 2 1 7 3 6 Climate Change The term climate refers to the general weather conditions of a place over many years. For example, Santa Ana’s climate is characterized by hot, dry summers and mild winters with moderate rainfall. The summer months of June to September average a daytime high of 83 °F and a nighttime low of 63 °F. The winter months of December to March average a daytime high of 70 °F and a nighttime low of 48 °F. Rainfall averages about 13.6 inches per year, most of which falls from November through April. While Santa Ana’s weather may vary slightly over time, its climate generally remains consistent. This slight variation is more commonly associated with changes in the weather. Unlike slight changes in the weather, climate change is a significant variation of average weather conditions. Examples of climate change include conditions becoming warmer, wetter, or drier—over several decades or more. What differentiates climate change from natural weather variability is that climate change is longer-term. And while “climate change” and “global warming” are often used interchangeably, global warming—the recent rise in the global average temperature near the earth’s surface—is just one aspect of climate change. Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect" — warming that results when the atmosphere traps heat radiating from Earth toward space. The greenhouse effect occurs when certain gases (commonly referred to as “greenhouse gas emissions”) in the atmosphere block heat from escaping Earth, thereby raising Earth’s overall temperature. Some of the most commonly occurring greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons. While the consequences of increasing greenhouse gas emissions are difficult to predict, below are likely consequences: On average, Earth will become warmer. Earth will experience more frequent extreme weather conditions, such as droughts, floods, wildfires, extreme temperatures, and more. Warmer conditions will likely lead to more evaporation and precipitation overall, but individual regions will vary, some becoming wetter and others dryer. Elevated carbon dioxide levels may increase plant growth. However, other factors, such as changing temperatures, ozone, and water and nutrient constraints, may more than counteract any potential increase in yield. Among the evidence for rapid climate change is a global rise in temperature, the warming of the ocean, shrinking ice sheets, glacial retreat, decreased snow cover, a rise in sea level, declining Arctic sea ice, extreme events and ocean acidification. Observable evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time. Climate change will certainly have a devastating impact on all of Earth’s ecosystems.