Despite forecasts of floods, droughts, and rising sea levels, the climate record actually gives little guidance. Scientists don't know how climate variability depends on CO2, or if it does at all. In truth, climate is forever changing, and in many cases for reasons we do not yet understand.
Volcanic eruptions occur frequently and can have significant effects on climate over the short term.
On a longer time scale, the Earth has experienced some 17 Ices Ages in the last 2 million years. Ice cores, ocean sediment cores, and tree rings all show evidence of large and rapid climate changes, even in recorded history, i.e., the last 3,000 years. Also, studies have shown that urban growth around these ground-based temperature stations has created a false increasing temperature trend. It has only been since 1979, using weather satellites, that scientists have been able to record truly global temperature readings from the lower atmosphere. According to these satellite data, global temperatures over the last two decades have been heading slightly downward.