Upper Cretaceous Period
Does this prove Global Warming is part of a natural climate cycle?
The Upper Cretaceous Period was much warmer than today. This fact has lead a number of people to question whether todays temperature increase is not simply part of the natural climate cycle.
To answer this we need to understand the world during this Period.
The world during the Upper Cretaceous Period looked very different than it does today. Whilst many of the continents had already started to arrange themselves in the way we see them today, the land mass was divided into Northern and Southern continents with a vast sea across the Equator.
North America, Europe and Asia were a single land mass to the North, whilst Africa, South America, Antarctica and Australia were a second land mass to the South.
Large deciduous forests covered the North and South Poles and there were no polar ice caps.
Global sea levels were over 200 metres higher than they are today. Much of the UK and Western Europe was a large, shallow tropical sea: only isolated areas in the Highlands of Scotland and Wales were land.
The high levels of carbon dioxide in the atmosphere were due to volcanic activity and the break up of the huge Pangean land mass into different continents during the Jurassic and Early Cretaceous Period. New oceans were being created and all these oceans had volcanically active ocean ridges.
Evidence of this massive volcanic activity can be seen in the oceans of our world today. In the middle of the Atlantic Ocean is the Mid Atlantic Ridge: a long chain of extinct volcanos that stretches the full length of the American continent. The Western Pacific also has thousands of volcanos.
This huge amount of volcanic activity went on throughout the Jurassic and Cretaceous Periods, from 125 million years ago until 75 million years ago. The huge amount of carbon dioxide created from this volcanic activity is believed to be the main reason for the Cretaceous Period being so warm.
Over a period of millions of years, as volcanic activity reduced, carbon dioxide levels and global temperatures gradually dropped, eventually leading to the formation of the polar ice caps around 20 million years ago.
Global Warming has happened before. Higher temperatures on earth are not unknown. The most extreme was the earth's climate in the Upper Cretaceous Period (86 million years ago), which was far warmer than today. The Mean Surface Temperature across the Earth during this time has been estimated as being 11°c warmer than now.
These higher temperatures were as a result of two things: a significantly different layout of the continents that allowed for improved heat circulation in the oceans; and a much higher level of carbon dioxide in the atmosphere at the time, four times higher than today.
The Upper Cretaceous Period has been referred to as a 'greenhouse world' and much of the predictions of what could happen to the environment in the future has been based on our understanding of what the world was like during this time.