Professor Trewavas (Letters, 5 August) questions the link between climate temperature and atmospheric carbon dioxide levels.
He refers to the situation 200 million years ago, when it’s estimated that carbon dioxide levels soared to many times their present-day levels, with a concomitant rise in temperature.
What he fails to mention, however, is that this coincided with one of the world’s greatest extinction episodes, the Triassic- Jurassic event, which saw at least half of the existing species wiped out. The fossil record does indeed show the diversity of species which existed around the time of this event, but their presence can be compared to photographs of deceased people.
The camera has captured them at a precise moment in time, confirming their previous existence, but giving no indication of their fate.
Scientists are unable to confirm the source, or sources, of the increase in CO2, but one potential candidate is thought to have been the rapidly warming oceans, which led to the release of vast amounts of methane into the atmosphere.
This is a current concern, which climate warming sceptics ignore when arguing about the “pause” in air warming.