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Crop Agriculture

Climate Change (see graphs below)

Human-caused climate change affects crops, wildfires, snow, and many topics not included on this website. Human-caused climate change, including global warming, is mostly caused by burning fossil fuels and, to a lesser degree, deforestation. See this NASA page for global warming information - 16 of the 17 hottest years on record have occurred since 2001 (1998 being the only exception). The information and links on this page provides a good basic understanding of climate change and global warming.

Global warming largely boils down to middle school Earth Science - more greenhouse gases than those occurring naturally in Earth's atmosphere (such as carbon dioxide, CO2, and methane, CH4) equals a warmer planet. Solar radiation is mostly shortwave radiation and, as a result, transmits/passes through greenhouse gases, heating the surface of Earth; the heat produces longwave radiation which the greenhouse gases can trap in the atmosphere, warming it. This is a simplified explanation, but explains the basics of the greenhouse effect and global warming. An analogy for the greenhouse effect, is why the air inside of a car with the windows up gets hotter than the air outside. Solar radiation transmit through windows, heating up the inside surfaces of the car; the hot surfaces produce long wavelengths which cannot transmit through the glass, heating the air in the car. Global dimming (the decrease in solar radiation reaching Earth's surface due to the absorbing and reflecting of radiation by air pollution, such as sulfur dioxide) has a mitigating effect on global warming, but does not nearly account for all the effects. Humans must adapt to manage natural resources in a sustainable way. A weather cold snap can still occur (which may even include a record cold temperature), but is meaningless in the big picture of global warming - recent research suggests that global warming may be contributing to areas of cold air that normally reside to the north moving farther south (and that cold air being replaced by warming air to the south) (Francis et al., 2017), such as the cold snap in the eastern USA that occurred from December 2017 to January 2018.

The most profound and important evidence that supports human-caused global warming is the Keeling Curve. In 1958, Charles David Keeling started recording the amount of CO2 in Earth's atmosphere from the Mauna Loa Observatory on the big island of Hawaii (measurement taken at about 11,400 feet above sea level). From this high and remote location, clean and representative samples of the amount of carbon dioxide in Earth's atmosphere can be taken. Though Mauna Loa is an ideal location, there are other stations in the world where CO2 is measured - the readings from those locations highly correlate with each other and the Keeling Curve at Mauna Loa. All graphs below are cited from the Scripps Institute of Oceanography website, Keeling Curve page at: https://scripps.ucsd.edu/programs/keelingcurve/).

The first graph shows the full Keeling Curve record, from the first measurement in 1958 to 12/29/2017. CO2 amounts change within a year due to the change in amount and vigor of vegetation (including crops and forests; more robust vegetation corresponds to lower CO2 levels). In 2016, CO2 amounts surpassed 400 ppm for the first time in millions of years (amount were higher a few millions years ago due to, essentially, a much different phase of Earth that is not very relevant to today's situation). The second and third graphs show longer term CO2 amounts.

 

 

 

At the long term time scale shown next, fluctuations in Earth's CO2 levels are mainly due to Earth's fluctuating orbit patterns, which affects the amount of solar energy Earth receives and, therefore, ice coverage. CO2 amounts increase as ice coverage decreases (negatively correlated), mainly due to outgassing of CO2 by oceans (when there is less ice, there is more ocean surface and, correspondingly, more CO2 outgassing); the amounts are fairly consistent through time, except for the more recent years when humans have caused increases in CO2.

 

 Reference

Francis, J.A., Vavrus, S.J., and J. Cohen. 2017. WIREs Clim Change. 2017, 8:e474. doi: 10.1002/wcc.474.