No issue in meteorology is as contentious as climate change. Is our planet warming? Does climate change amplify extreme weather events? Are humans responsible for it? What are the consequences of these changes? Climate scientists are studying these problems.
The Earth’s climate continuously changes, as science has deduced from examining material artifacts and digging into the Earth itself. Changes occur due to natural cycles, such as orbital variations of the Earth like we discussed in the first chapter, or glacial advancement and retreat, and even due to the movement of continental plates over millions of years.
Africa’s Sahara Desert is a great example of natural climate change. Changes in the Earth’s tilt over a 41,000-year cycle cause the Saharan region to alternate between wet and dry periods. This change in tilt causes a difference in the typical location of the African monsoon: during dry periods it is much further south.
Sometime around the year 17,000 the monsoons will come north, and the Sahara will again disappear as the Central African savannas and rainforests shift northward for a few dozen millennia.
Other changes happen at much shorter time scales – perhaps years or decades. This provides shorter-term variation. In nearly every case, we’re able to find evidence of these shifts in some way in ice and soil samples or by other means, and in times before any artificial release of greenhouse gases into the atmosphere could have occurred. This is commonly referred to as natural variability.
Today’s warming climate is much more difficult to explain away by natural variation. Temperatures since the beginning of the Industrial Revolution have increased at a rate that is unprecedented in history or scientific study. One study pegged the rate of increase at ten times what our planet normally experiences after Ice Ages (the last one ending roughly 11,700 years ago).