AS 2015 gets under way, humanity's carbon emissions remain on course to catastrophically reshape the global climate over the next century or two.

Yet in his Agenda contribution ("Why cleaner gas has a vital role in delivering a lower carbon future", The Herald, January 29) Andrew Nunn is still able to ask "what is not to like?" in relation to the search for, and burning of, unconventional gas, such as shale gas.

The answer is, that natural gas is a fossil fuel, no matter how its benefits are spun. It will inevitably add to the world's carbon dioxide pollution problem if it does not remain in the ground.

According to a recent assessment by the International Energy Agency (IEA), global carbon dioxide emissions continue to rise. It increased 1.4 percent in 2012, achieving a historic high of 31.6 billion metric tons released in a single year. The Intergovernmental Panel on Climate Change has calculated that the total amount the world can afford to emit is 1,000 billion metric tons of carbon.

Beyond that, life on Earth will be required to adapt to an average global temperature 2°C higher than it is now. At this temperature most scientists agree that the climate will become genuinely catastrophic.

The world economies have already consumed 531 billion metric tons of the above "carbon budget". Concern for future generations demands that we avoid incinerating too much of the remaining 469 billion metric tons. This will require leaving most of the world's already-proven fossil fuel reserves unused and in the ground.

So, the desire to exploit new sources of gas by extreme extractive methods runs entirely counter to common sense. The only viable way forward is to employ the fossil fuel energy, that it remains safe to burn, to power the development of the renewables age.

It is instructive to note that after several years of decline because of its "dash for gas", total annual carbon emissions in the United States reversed in 2013, thanks largely to market shifts. In the neo-liberal corporate driven global market apparently benign changes in energy practices in one part of the world can have unintended negative consequences elsewhere.

Alan J. Sangster,

37 Craigmount Terrace, Edinburgh.

PETROCHEMICAL giant Ineos had a £645 million plan to drill for shale but nationalist Luddites put the future of the Grangemouth refinery in doubt by blocking fracking in Scotland ("Government makes U-turn and agrees to a block on fracking", The Herald, January 27).

Industry leaders also say we need to produce more of our own oil and gas for economic and energy security as viable reserves in the expensive North Sea basin begin to run out.

It was not always thus and Scottish pioneers led the industrial revolution, with James Simpson producing huge supplies of oil and gas from Scotland's vast shale beds as early as the 1850s.

Sadly with one or two exceptions such entrepreneurs died out or emigrated to America where their descendants have used shale to give the US and Canada indefinite energy security.

Scotland is now the fuel-poverty capital of Europe with one million of our poor and elderly unable to afford the heating of their homes - but that is of little account to the fervent green brigade.

Dr John Cameron,

10 Howard Place,

St Andrews.