What if global warming were simply the result of a natural cycle ? The Earth would therefore naturally revert to its previous state one day. Unfortunately, this is not the case. Our planet is certainly experiencing alternating phases of glaciation and warming. This is caused by slight changes in the terrestrial orbit called Milankovitch cycles. These cycles occur about every 100 000 years – moreover, the past millennia were part of a warming phase. However, the climate change that we are currently observing is taking place much faster than all those that came before it during the past 50 million years ! The two mechanisms therefore cumulate.
Other factors such as a change in sunlight intensity can interfere. The cycles of our star last for about 11 years. But this rhythm is too short to explain the length and the extent of what we can see today. Indeed, scientists even predict that we are entering a new phase of intense solar activity that will accelerate current global warming…
The Earth has already experienced hotter periods than it is experiencing today. By studying the microscopic air bubbles trapped in the polar ice for hundreds of millions of years, the size of tree rings, fossil coral deposits and the presence of certain isotopes etc, researchers have found a correlation with greenhouse gas concentration every time. But they have also shown that the latter has never experienced the type of change it is experiencing today. What is taking place before our eyes is therefore different from older cycles.
The greenhouse effect does indeed explain most of the phenomenon. To deny this would mean allowing mankind to shirk its responsibilities as well as stop action being taken against the cause – human GEG emissions.