The postglacial warming trend culminated in the so called climatic optimum, about 5,000to 7,000 years ago, a time when global temperatures were somewhat warmer than at present. The most notable feature of this record is the relatively mild conditions of the middle ages and the sharp cooling that followed from about 1,400 to 1,850 – a period that has come to be known as little ice age. Thus first and foremost lesson of the climatic past is that climate is inherently variable and it varies over a wide range of time scales from years to millennia.
It’s a real mess. It’s probably necessary to point out, though, that it’s not the end of the world. It may be the end of your personal world, if you happening to be vacationing on Cape Cod when a forty-foot tsunami comes rolling in from the southern end of Greenland, or one of those rat lungworms decides that your brain is its next meal. It may be the end of your economic world, if your job depends on overseas trade at a time when rising sea levels are making the infrastructure of every seaport in the world an example of (literally) sunk costs, or you still have your net worth invested in Florida real estate when enough people realize that the ocean’s just going to keep rising. It may be the end of your social world, if your nation gets torn apart by the inevitable conflicts of a world in chaos, or the neighborhood where you’ve put down roots happens to be a little too low-lying and you have to flee to higher ground.
Human activity is not solely responsible for climate change. It can occur due to natural causes as well. Large volumes of sulphur dioxide, ash, water vapor and dust escape into the atmosphere when a volcano erupts. Volcanoes also produce aerosols which reflect solar energy back into space. This cools the atmosphere. However, although volcanoes produce CO2 and greenhouse gases it is minor when compared to what we humans emit into the atmosphere. Changes in the Earth’s orbit and changes to the ocean’s currents are also natural causes that cause climate change.