<h3>Methane</h3>
<p>Methane is a powerful but relatively short lived greenhouse gas.&nbsp; Averaged over 100 years, the <strong>global warming potential</strong> of one tonne of methane is 25 times that of one tonne of carbon dioxide.</p>
<p>In New Zealand, most methane comes from belching by ruminant animals: sheep, beef cattle, dairy cows, and deer, and some from animal manure. Non-ruminants, such as poutry and pigs also produce methane from their manure but these constitute a very small source in New Zealand.</p>
<h3>Nitrous oxide</h3>
<p>Nitrous oxide is a much more powerful greenhouse gas than methane - 298 times more powerful than carbon dioxide over a 100 year timeframe on a per tonne basis.&nbsp; See <strong>Global warming potential</strong></p>
<p>Fortunately, the absolute amount of nitrous oxide emitted from agriculture is lower than methane. In New Zealand, most nitrous oxide is produced&nbsp;by the action of&nbsp;soil&nbsp;bacteria in urine patches in paddocks.&nbsp; Smaller amounts&nbsp;come from dung deposited during grazing, stored manures spread back onto pasture, and from nitrogen fertilizer.</p>
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