Human threat

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I TOTALLY agree with Professor Trewavas’ statement about the complexity of climate change (Letters, 7 August), but the more specific term “climate warming” highlights the current 
upward trend in planetary heating, which has been linked to human activities, specifically those which lead to an increase in atmospheric carbon dioxide and other greenhouse gases.

My reference to the Triassic-Jurassic extinction was in relation to his statement about the fossil evidence of burgeoning life around that time, despite high levels of CO2.

I question the order of events. In fact the extinction may have been the cause, rather than the result, of the catastrophic rise in CO2 levels, due to the break-down in global carbon cycling following the obliteration of marine and terrestrial life.

The earlier catastrophic end-Permian extinction was the subject of a joint study in 2001 led by the University of Leeds and the China University of ­Geosciences.

It was the first to show that water temperatures close to the ocean’s surface can reach 40C – a near lethal value at which marine life dies and photosynthesis stops.

My suggestion that methane may also have been a potential contributor to those extinction events was based on the hypotheses of researchers.

The current destruction of rainforests and the rapid rise in urbanisation, which destroys green areas and leads to greater pollution, should be seen as threats to the planet’s health.

Humans have become a major contributor to the breakdown in global carbon ­cycling.

Carolyn Taylor

Wellbank

Broughty Ferry

Dundee

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