A few weeks ago, a letter was carried in the Irish Farmers Journal maintaining the irrelevance of methane as a greenhouse gas.

Nobody disputes that global temperatures are increasing – what is disputed is why, by how much and what is the essential cause of the temperature increase.

The main focus has been on fossil fuels and the production of carbon dioxide.

ADVERTISEMENT

Again over the last 200 years there is no dispute that the amount of carbon dioxide in the earth’s atmosphere has increased.

What is disputed is how closely related is the increase in carbon dioxide levels to increases in temperature.

The general scientific consensus is that they are closely related but there is a group of really well-qualified physicists and climate specialists who dispute this.

From a narrow farming point of view, the more interesting question is the role of methane.

Again there is a consensus that methane in the short term is, by itself, a more potent greenhouse gas than carbon dioxide.

The fact that it lasts only 12 years in the atmosphere compared to carbon dioxide lasting many hundreds of years means that it is much less important in global warming regardless of the differences in opinion of the association between greenhouse gases and global warming.

However, two new recent developments should cause politicians to rethink their attitude to methane production in farming, especially from cattle.

Fallen

Leaving aside the fact that farming only accounts for one seventh of global methane production, the confirmation that Irish cattle numbers have fallen significantly means that cattle-based methane output is falling and theoretically leading to global cooling.

That’s assuming that we accept the relationship between global warming and greenhouse gas levels in the atmosphere.

But a more important point that needs debate (at least) is whether the methane that is produced is absorbed by the huge volume of water vapour in the atmosphere.

Water vapour itself is acknowledged by all sides in the discussion as a greenhouse gas. If water vapour absorbs methane, then it effectively means that it is irrelevant as a contributor to global warming.

At a minimum we need a rational appraisal of the differing views on the importance of methane in livestock farming and the influence of water vapour.

In last week’s interview Marie Donnelly, chair of the Climate Change Advisory Council rightly said that methane output can already be controlled by feed additives but we also need clarity on whether methane from livestock has been over-emphasised and farmers put to unnecessary expense in attempting to reduce it.

The reductions that have already taken place in the Irish herd sit uneasily with the statement we carried last week from the Brazilian secretary of trade and international relations where they are planning to bring another 100 million acres into production.