- Carbon dioxide is rising as a component of Earth’s atmosphere (NOAA, 2017).
- The level of carbon dioxide in the atmosphere has not been this high for the past 5 million years (Stap et al. 2016).
- Beginning about 10,000 years ago and extending to the advent of the Industrial Revolution, carbon dioxide in the atmosphere was roughly constant, indicating that natural sources were well-balanced by removals from the atmosphere (Fluckiger et al. 2002).
- The current rise in carbon dioxide is due to human activities, especially combustion of fossil fuels (Hofmann et al. 2009).
- Carbon dioxide is a “greenhouse” gas, inasmuch as it absorbs heat radiation leaving the Earth’s surface (Tyndall, 1865).
- There is a natural greenhouse effect on Earth, which keeps its temperature above freezing (Houghton 1986).
- Water vapor, methane and nitrous oxide also act “greenhouse gases” in the atmosphere, but the human impacts are greatest for CO2 (Schmidt et al. 2010).
- Past period of high CO2 have been unusually warm (Luthi et al. 2008, Parrenin et al. 2013; Triparti et al. 2009).
- 2016 was the hottest year on record (Science 355: 331, 2017).
- Rising CO2 will affect the mean annual (not necessarily daily) temperature on Earth (Trenberth 1992).
- Mean annual temperature is an essential feature of climate (von Humboldt 1860).
- Different climate regions on Earth determine what crops we can grow, what diseases we experience, and how much water is available (von Humboldt 1860).
- Past changes in global climate have determined the position of sea level (Grant et al. 2012).
- Higher levels of CO2 in Earth’s atmosphere increase the acidity of seawater, making it difficult for shellfish to synthesize their shells (Ekstrom et al. 2014).
- CO2 is an essential component for plant photosynthesis, and it should increase the rate of growth of most plants—both crops and weeds—when other conditions are favorable (Taiz and Zeiger 1998).
- Measured increases in plant growth during the past few decades have been rather modest (Long et al. 2006; Groenendijk et al. 2015).
- Higher plant growth does not equate with greater carbon storage on land, as a way to mitigate rising CO2 in the atmosphere (Wieder et al. 2015).
- Higher temperatures are associated with greater occurrence of drought, which lowers plant growth (Rind et al. 1990).
- Drought is directly correlated to and a determinant of forest fires.
- Drought, famine, and losses of soil fertility are implicated in the downfall of several historical civilizations (deMenocal 2001).
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