NATURE → Climate Change
Is our climate and therefore our weather chaging? Undoubtedly yes, but how significant is this change and should we be worried?
Geological Background
Our climate and average gobal temperature has varied significantly over geological time. In the past our planet had been mainly tropical/sub-tropical with average global temperaturesin excess of 20 degrees C but there has also been periods when the earth has been fully covered by ice sheets (Ice Ages) and with average global temperatures at or below 8 degrees C. At least 5 major long lasting Ice Ages have been recognised, starting with the Huronian, apprximately 2.4 to 2.1 billion years BP, and most recently the Cenozoic Ice Age which began 2.5 million years ago and continues to this present day. So you might ask why is the earth not entirely covered in ice? Because within each Ice Age there is also significant variation in average global temperature with periods of less cold weather called inter-glacials. We currently live within such an inter-glacisl period. This inter-glacial began approximately 11,700 years ago and defines the start of the most recent geological period called the Holocene.
Average global temperatures through geological time
Historc Climate Changes
Even over the past 1000 years of earth history we have seen significant variations in our global climate. Of note was the Little Ice Age (1300 to 1850) where average yearly temperature in the northern kemisphere were considerably reduced (the River Thames froze several times during this period) and the Medieval Warm Period (950 to 1250). Factors that seem to influence this variation include volcanic eruption, (the 1257 catastrphic eruption of Samalas volcanoe in Lombok, Indonesia, is often quoted as as causing the start of the Little Ice Age) variation in ocean or atmospheric currents, variation in levels of solar radition (sun spots), fluctuations in the earth's tilt and variaiton in atmosphic composition, particularly levels of "greenhouse" gases such as water vapour, methane and CO2.
Frost Fair River Thames 1814
Conclusions
Rising CO2 concentratios in the earths atmosphere (currently at around 400 ppm) are driving media concerns over climate warming. In the past, however, CO2 levels have been well above this level. Many atribute this recent rise to the burning of fossil fuels. From a UK survival perspective I would rather it get warmer than colder. Personally, I do not relish the prospect of another Ice Age however short lived it might be.
CO2 concentrations (in ppm) through geological time