The definition of "climate" by the American Meteorological Society is [[x] AMS Glossary of Meteorology].
Its first sentence corresponds to my item "3" I mentioned in the page [What is climate? ...]. The rest corresponds to my item "2". Dessler's discussion in the sections 1.1 and 1.2 mostly refers to my item "2".
Climate as in my item "2" is what can be expressed by statistics of meteorological elements. The statistics is not only averages. Extreme values are mentioned. Also, in Figure 1.1, frequency distributions (histograms) of a certain meteorolgical element (daily average temperture in August at Fairbanks, Alaska, USA) in two different time frames are shown. I think that histograms are the most basic thing of all statistics.
I plan to make an assignment to make a histogram of temperature like this from another data set, perhaps next week.
Temperature is expressed in degrees Celsius (oC, deg.C). In Japan, deg.C is used in everyday life. In the USA, degrees Fahrenheit (deg.F) is used in everyday life, and deg.C is used in science. (Another unit "Kelvin" (K) will be introduced in Chapter 3).
By the way, the attribution of the quotation "Climate is what you expect; weather is what you get." may not be true. It is found in a novel "Time Enough for Love" by Robert Heinlein published in 1973, but it is not found in Mark Twain's works. (A sentence "Everybody talks about the weather but nobody does anything about it." does appear in the book "The Gilded Age" written by Mark Twain and Charles Dudley Warner, published in 1873.)
The author considers that two curves ("two histograms" in my terminology) in Figure 1.1 is evidently different, without checking by formal testing. I can agree. If someone disputes, however, we may need to go to some established method of testing. (I confess that I cannot specify what is the appropriate method in that situation.)
The histograms of the same element in different time periods differ evidently. So we can say that climate (in the sense of my item "2") has changed here.
We use "latitude and longitude" to denote a position on the earth.
My figures somewhat similar to Figure 1.2 and 1.3 are in my page of [Physical quantities and SI units].
How science should interact with politics is a difficult issue. I will come back to this subject in a later part of the course.
It seems that the author needed to include this section in the introduction because many students in Texas are surrounded by such people who are skeptic to the science that predicts global warming.
Since climate change has become an issue of politics (since around 1988), some of discourses about it are politically motivated.
In the USA (as well as in Australia and Canada), such statements as "carbon dioxide will not make global warming" are advertised strongly. Part of the promoters are those who have vested interest in fossil fuels (coal, petroleum, natural gas). Another part are those who want regulations by goverments as little as possible. They do not want regulation to reduce emission of carbon dioxide. A few scientists are (really) skeptic to global warming. Industries employ those scientists and advertise their views as if they are credible science.
The situation in Japan is very different. Skeptics to global warming do exist, but they are not organized. Their views are different one another, but relative majority of them seem to be anti-establishment or anti-capitalistic. It is recognizable, because Japan does not have strong fossil fuel industry. On the other hand, the government strongly promoted nuclear power (until Fukushima accident in 2011) and they said that nuclear is better because it does not cause global warming. So there is a reasonable cause that those who are critical to the establishments tend to doubt global warming.
In Japan, since 2011, climate change in public discourse has faded. From the viewpoint of a person who thinks that countermeasures to global warming is necessary, the largest obstacle in Japan seems to be indifference of the general public to the subject, rather than explicit denial or skepticism to it.