The number of times heads comes up when you toss a coin, number of students present in class, number of times a person has attended therapy sessions-these are all discrete variables. To help see the difference between continuous and discrete variables, imagine a really tall mountain with a trail leading up to the top.
Climate changes resulting from greenhouse gas increases could also significantly affect water supply and demand. For example, a local increase in temperature of several degrees Celsius could decrease runoff in the Colorado River Basin by tens of percent (25, 48).
The Direct Effect of an Increase in CO2 Over the years there have been numerous laboratory experiments which conclude that increases levels of CO2 result in increased plant growth no matter how that plant growth is quantified. Sylvan Wittwer in Food, Climate and Carbon Dioxide tabulates the results.