This question spans much more than the minor climate change the Earth is experiencing at current. What will happen in a billion years? What will the Earth look like? What will its characteristics be? And most of all, what will be able to survive the brutal changes that will be experienced as such deep time passes? A computer simulation run by scientists at the University of St Andrews in Scotland has predicted that only microbes living in the deep Earth will survive and here’s why.
The climate and physical and chemical characteristics of Earth depend heavily on the Sun, our source of energy. As the sun ages it will grow larger and much more luminous and the heat given off will be so intense that it will vaporize all the oceans of the world; this will cause a dramatic increase in atmospheric water vapour levels and as water is a greenhouse gas, a runaway greenhouse effect will ensue much like that of Venus. As the temperature rises, and boy will it rise, reaching up to 100C or higher, mass extinctions will be seen across the planet with total loss of plants and larger animals as temperature and pressure rise while oxygen content decreases. At this point the only living organisms would be the extremophile microbes living deep in the Earth clustered around drops of water; however these too will disappear with time and it is thought that approximately 2.8 billion years in the future Earth will be completely devoid of life.
So, that’s.. Depressing. “What is the significance of this?” I hear you ask. The majority of the time that there has been life on Earth was purely microbial and it is thought that this would be the same for planets throughout the universe. Thus when we search for exoplanets it is much more likely that we will be seeing ‘microbial worlds’ as opposed to worlds with complex life. In light of this it is important that we have systems in place to help us detect the faint signals of microbial life such as methane in the atmosphere.