Dr Geoff Duffy: Methane stance way off track

Atmospheric physicists have long known the most plentiful greenhouse gas is water vapour. Photo / Nasa/AP

COMMENT: The recent statement from the Parliamentary Commissioner for the Environment, Simon Upton, about methane emissions from livestock conflicts with experimental data.

Computer climate models are accurate only if all significant variables are incorporated simultaneously. Leave one out or miscalculate its effects and model predictions will be inaccurate - no better than a guess and inadequate for policy.

The major elements of the global weather system are fairly well identified, but the magnitudes of many effects are poorly understood. For example, the International Panel on Climate Change doesn't know whether increased cloud cover, predicted to be caused by warming, would mean further warming or cooling.

Global cloud cover has been studied for many years, but the IPCC's latest report (AR5, 2013), admits it doesn't know whether it is expanding or shrinking, which means it can't say what warming - if any - our emissions might cause.

The factors involved in the weather are numerous and their interactions chaotic. Nearly three-quarters of the surface of our planet is covered in oceans and lakes, and two-thirds of land and sea at any moment is covered in clouds. Just over half the sun's energy actually reaches the Earth's surface, with its re-radiation back from land and water very important in heating the atmosphere, and there are many more mechanisms in play. The massive mixing effects of winds, storms and rain, ocean waves and currents and the creation and dissipation of clouds must be included in climate models. If they are not, predictions will be erroneous.

Evaporation at sea level and condensation of water vapour into clouds are important. Clouds can precipitate rain or snow, further cooling the atmosphere, land and ocean. Gaps in these areas of knowledge caused all 102 CMIP-5 climate models relied on by the IPCC to fail to predict recent global temperatures, which have been essentially constant for two decades, despite carbon dioxide rising 9 per cent in that time.

Conduction is another energy transfer mechanism between atmospheric molecules, water and land. Radiant energy absorbed by greenhouse gases (GHG) increases their speed (they get warmer), so when they collide with other molecules, even non-GHGs nitrogen, oxygen and argon, they transfer heat to them and the atmosphere warms.

Two factors stand out in the calculation of atmospheric energy transfer: a GHG's level in the air and how much electromagnetic energy it absorbs at different frequencies.

The electromagnetic energy spectrum has been studied for more than 200 years. Atmospheric physicists have long known that the most plentiful and effective greenhouse gas is water vapour which absorbs over 80 per cent of the entire energy spectrum, whereas carbon dioxide absorbs over less than 10 per cent of the spectrum. Methane is even weaker, absorbing under 1 per cent.

So the commissioner is wrong when he says, "The three main greenhouse gases are carbon dioxide, methane and nitrous oxide." Neither CO2, at 406 parts per million, nor methane at 1.8 ppm, can dominate, because their concentrations are insignificant. At 10,000 ppm, water vapour overwhelms them both. Comparing methane with water vapour is like putting a mouse up against an elephant. Water vapour is 25 times more abundant than carbon dioxide and 5000 times more abundant than methane.

Examining methane alone doesn't reveal what's happening in the atmosphere. The following statements from the commissioner's report are quoted and my comments follow.

"[Methane] is a more potent greenhouse gas than carbon dioxide". This is only true when the gases are at the same concentration, but they're not. Carbon dioxide is always and everywhere 220 times more plentiful and accesses a wider range of the energy spectrum. It is also much more potent than methane.

"[M]ethane traps ... heat". Absolutely no heat is "trapped". A GHG molecule absorbs electromagnetic energy, which energises it to move faster until it collides with another molecule (oxygen, nitrogen, argon, carbon dioxide and all), and gives up some energy in making the other molecule move faster. The authors of the report do not understand heat transfer, the "trapping" concept was debunked years ago. There is no "blanket", there is no greenhouse. If the modelling does not include all the effects other than radiation the predictions will be wrong.

"A constant flow of methane emissions results in a constant methane concentration after 50 years, but its impact on temperature continues to increase for several centuries." The claim methane continues to boost temperatures over centuries is wrong, because we don't observe it - there has been virtually no temperature change for 20 years or more, even as methane rose by 5 per cent and carbon dioxide by 9 per cent, and we do not have centuries of methane data.

"However, the warming effect of that methane would continue to increase, at a gradually declining rate, for more than a century. In the year 2050, holding New Zealand's livestock methane steady at 2016 levels would cause additional warming of 10-20 per cent above current levels". With the CO2 concentration 220 times greater than methane and rising for two decades without much increasing the temperature, it is wrong to reason that methane - the weaker, less numerous species - has more influence.

We should not use rudimentary models for simulation or prediction, without strong, consistent experimental data to support the claimed effects. Predictions will be inaccurate unless models include all the energy mechanisms (radiation, convection, conduction, molecular collision) and mass transfer effects (evaporation, storms, condensation, precipitation, etc) involved in the climate system. At crucial points this report mischaracterises the science and lacks proper scientific understanding. It should be withdrawn until verified. by independent scrutiny.

• Dr Geoff Duffy is a professor emeritus of chemical engineering at the University of Auckland.