In 2022 it will be fifty years since the last astronauts returned from the Moon. Seeing the Earth from so far away, so beautiful and yet so fragile, changed their, and our, perception of our home world.
Since 1972, unmanned spacecraft have visited all the planets in the solar system, landing on Venus and Mars, while astronauts stay within 400 km of Earth’s surface. Above the atmosphere, they too are awed by its beauty, and see that all life, on land and in the seas, lives in a relatively thin surface shell, like a sheet of paper on a bowling ball. They see the white ice sheets at the north and south poles, noticeably smaller than when admired by the Apollo astronauts. They see vast dark clouds from wildfires in California and other regions suffering from unusual heat and lack of rain, while other places on Earth experience record rainfalls and floods.
Nearly 200 years ago, Joseph Fourier argued that sunlight warms the Earth’s surface, which then radiates heat; the atmosphere must act like a blanket, keeping in warmth. Much later, in 1896, Svante Arrhenius, attempting to understand ice ages, suggested that they were caused by changes in carbon dioxide levels in the atmosphere. He made calculations of the effects of changes in humidity. Warmer oceans increase water vapor, which makes things worse.
It is important to understand that weather and climate are very different things. Weather can change by the hour, even by several degrees in a single day, and is local; it can be freezing in Chicago while warm in Florida. Climate is an average over large regions or the whole Earth, averaging over years. Half of this year’s Nobel prize in physics was awarded to Syukoro Manabe and Klaus Hasselmann for mathematical models of how fluctuations in a physical system can result in predictable average behavior, “… reliably predicting global warming.” The atmosphere is extremely complicated and affected by many things, including human behavior. Unlike physics, behavior can be changed.
Venus is nearly as large as Earth and its orbit is closer to the Sun by only 28%, so why is its surface hot enough to melt lead, and the pressure of its acidic atmosphere nearly a hundred times that on Earth? Several USSR probes and one mission from the USA managed soft landings, but none survived for more than two hours in those hellish conditions. What happened there hasn’t happened here? Yet.
