The main business of climatologists until the mid-20th century was the simple drudgery of compiling statistics. Knowledge of average and extreme temperatures and rainfall and the like was important to farmers, civil engineers, and others in their practical affairs — never mind guessing at explanations. But people could not resist trying to explain the numbers. A textbook would start off with the main factor, the way sunlight and thus warmth varies with latitude (perhaps with some calculations and charts). There would follow sections on the prevailing winds that brought rain, and how mountain ranges and ocean currents could affect the winds, and so forth. It was all soundly based on elementary physics.

It was a dry exercise, however, not so much a theory of climate as a static regional description

The approach expressed a generally sound intuition about the nature of climate as a process governed by a complex set of interactions, all feeding back on one another. But romantic views that stability was guaranteed by the supra human, benevolent power of Nature gave a false confidence that every feature of our environment would stay within limits suitable for human civilization.

     

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"As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the Earth's surface." Thus in 1862 John Tyndall described the key to climate change. He had discovered in his laboratory that certain gases, including water vapor and carbon dioxide ( CO2), are opaque to heat rays. He understood that such gases high in the air help keep our planet warm by interfering with escaping radiation.(9)      

This kind of intuitive physical reasoning had already appeared in the earliest speculations on how atmospheric composition could affect climate. It was in the 1820s that a French scientist, Joseph Fourier, first realized that the Earth's atmosphere retains heat radiation. He had asked himself a deceptively simple question: what determines the average temperature of a planet? Sunlight bathes the planet and warms it up while outgoing heat rays, now called infrared radiation, cool it down. In balance, what would be the temperature of a bare rock at the Earth's distance from the Sun? Fourier decided it must be very cold. That was a leap of intuition, for the physics known in his time lacked the tools to make a calculation. Yet he was right to believe that something keeps our planet warmer than a bare rock, and he realized that the something is our atmosphere.