Changes in global temperature are natural. They happen in cycles, and the current warming is no different. The Earth has passed though countless ice ages and thaws. More recently we have seen the Medieval Warm Period (900-1150 AD) and the Little Ice Age (1450-1850 AD), both of which occurred without any significant CO2 emissions by humans.
Fact:
Large temperature changes are natural over many millennia (ice ages and thaws), as are small changes over many centuries. We know what causes these changes, and those factors do not apply at present.
The current level of warming is unprecedented – 1.2°C in a century and 0.65°C in the past 30 years! During a thaw from an ice age, it takes between 1,000 and 2,000 years for the atmosphere to warm by 1.0°C. This means the Earth is currently warming at 33 times the natural rate. There is absolutely nothing natural about this!
As far as the Medieval Warm Period and the Little Ice Age are concerned, they involved significant temperature changes in northern Europe and the Atlantic, but not in other parts of the planet. Scientists estimate that the average global temperature changed by between 0.2°C and 0.6°C from the height of the Medieval Warm Period to the lowest point of the Little Ice Age. During the latter period, winters in Europe were colder than today, but summers were not significantly so. There is little evidence of a widespread breakdown of food production.
It should also be noted that the Little Ice Age was not actually an ice age, or anything like it. Many climate sceptics are obsessed with it simply because of its name. They seem to think that because it’s been dubbed an ‘ice age’, it actually was one.
The temperature variance between the Medieval Warm Period and the Little Ice Age [Source: Wikimedia Commons]