Climate and Energy Action Plan (CEAP)

CLIMATE TRENDS & PRO JECTIONS | CITY OF ASHLAND, OREGON | FINAL REPORT | 29 Climate Science Overview Climate is changing across the globe. T his is evident from many different observations. Human activities that release heat -trapping greenhouse gases into the atmosphere are primarily responsible for the past half - century of global warming . Global climate will continue warming throughout the 21st century and beyond. How much the Earth’s climate will warm in the future depends on the am ount of global greenhouse gas emissions, and the sensitivity of the climate to those emissions (NCA, 2014) . This section provides a dditional background on some of these key climate science concepts. How do we know the Ear th is warming? Multiple independent observations from weather stations, weather balloons, and satellites concur that the Earth has warme d for the last 150 years. This warming has set into motion many other well-documented changes to the Earth’s climate suc h as melting glaciers and sea ice and increased atmospheric water vapor (see Figure 21). The coherency of changes in all these indicators supports the conclusion that warmi ng of our planet is unequivocal (Walsh et al., 2014b) . Figure 21. Some of the many long -term global indicators that demonstrate that the Earth’s climate is warming (Walsh et al., 2014b) . What causes the Earth’s climate to change? Natural external forcings such as cyclical variations in solar output, episodic volcanic eruptions, and slow changes in the Earth’s orbit all affect the Earth’s climate to some degree. While natural forcings still affect climate today, the primary cause of the current warming is the accumulation of carbon dioxide and other heat -trapping greenhouse gases in the atmosphere due to human activities. According to Walsh et al. 2014a, “as the sun shines on the Earth, the Earth heats up. The Earth then re -radiates this heat back to space. Some gases, including water vapor (H 2O), carbon dioxide (CO 2), ozone (O 3), methane (CH 4), and nitrous oxide (N 2O), absorb some of the heat given off by the Earth’s surface and lower atmosp here. These heat -trapping gases then radiate energy back toward the surface, effectively trapping some of the heat inside the climate system.” Human activities are artificially intensifying this natural greenhouse effect , thereby increasing the amount of h eat trapped in the Earth ’s climate system (see Figure 22).