I read Martin Williams's article (Fears as melting ice brings new interest in Greenland's oil and gas, January 17) with great interest, particularly his reference to the "campaigners' assertion that the melting of the ice is further evidence that climate change is not being tackled effectively". Presumably, this is a reference to current "inadequate" CO2 emission initiatives.

It so happened that I have been reading a book entitled Unstoppable Global Warming. In this book, reference is made to findings that temperatures were an average of 2-4C higher than at present in Greenland one thousand years ago when Norse Vikings occupied parts of west Greenland and lived there until driven out by encroaching ice around 1400 AD. This book makes an interesting assertion that climate change moves in 1500-year cycles (+/- 500 years) with our warming cycle having started around 1850 after an intervening cold period starting around 1400 AD.

If this theory is correct we can expect even higher temperatures before cooling starts to assert itself again in perhaps 200-300 years' time. It may even be possible to grow grapes in northern England - if not in the Scottish borders - in a hundred years' time as was apparently possible during the Viking occupation 1000 years ago.

The current attitude that further climate research into potential causes other than CO2 emissions can be shelved, as the CO2 case is beyond doubt, is detrimental to a continued objective assessment of the evidence.

While it makes a lot of sense globally to reduce emissions of harmful substances and lower our dependence on oil, I think that there should also be a more objective and continued assessment of the underlying causes of the current warming of mother Earth. It is by now well documented that the Earth has always been subject to major climate changes. It is unreasonable to suggest that suddenly we are seeing an unprecedented warming after a very long and stable climatic period.

I do not believe the evidence now available substantiates this view. It would appear that the assertion that CO2 emissions by humans is the only or main cause of the current warming trend is not finally proven beyond doubt.

I take the view that if there are other powerful forces causing the current global warming trend then the 1500-year cycle provides hope that there exists an "inbuilt" acceptable upper limit to temperature rises. The current play of politics does not imbue me with the confidence that the human race will reduce CO2 emissions sufficiently to comply with the current limits being bandied about as the minimum "to save the Earth". I may be wrong, but there can be no doubt that further research into this major issue should be encouraged rather than suppressed.

John Peter, 21 Monks Road, Airdrie.