Jim Hessell: Climate change and hot air

Jim Hessell writes, 'the 'experts' do not appreciate the complexity of the atmosphere and how it responds as part of the planetary system which also includes the oceans.' Photo / JMA

Many of the heated debates on global warming often arise from one or both of two reasons.

Attitudes become entrenched in a position from which it is difficult to retreat or the protagonists expect their area of expertise to explain everything. Also it is not uncommon for inconvenient truths to be ignored, for example a strenuous advocate of global warming will ignore outbreaks off extreme cold which occur at about the same frequency as heat waves. This seems to me to be because the "experts" do not appreciate the complexity of the atmosphere and how it responds as part of the planetary system which also includes the oceans.

A basic requirement of anyone discussing the atmosphere is to understand that thermodynamics (temperature effects) and dynamics (wind effects) are mutually dependent. We know that since the beginning of the industrial revolution the composition of the atmosphere, an important part of which is the increasing concentration of "greenhouse" gases, has been changed by the activities of mankind including its burgeoning population. The concentrations of methane and carbon dioxide, monitored over the last 50 years show an irrefutable upward trend. The impacts of these are affecting and threatening our existence on a planet of limited resources.

Nearly all of the computer models predict, and has as now been observed, that the temperatures at the poles increase more rapidly than at the equator. Let me simplify the results of this. It means that the mean thermal gradients between the poles and the equator are decreasing.

This gradient is best understood by considering the mid-level of the atmosphere, with regard to mass, i.e. at the 500 hPa height (Mean sea level pressure is approximately 1000 hPa or millibars). At 500 hPa the wind flow (dynamics) is largely governed by the mean thermal gradient (thickness) down to seal level, and a weather map at 500hPa is basically a horizontal wave structure in a stream flowing from west to east.

The amplitudes and speeds of movement of these waves, being largely influenced by the rotation of Earth, change with the mean temperature gradient. With a reduced gradient causing a larger amplitude the flow reaches further towards the relevant pole and the speed of the wave slows. Together these result in a greater, or lesser, transport of heat (depending on whether the trough of the wave lies to the east or west of the position of reference).

This explains why the frequency of cold outbreaks in both hemispheres matches that of heat waves. This apparent paradox can explain why, as various distinguished scientists have commented, the extremes of weather (caused by global warming!) which are observed, are becoming more frequent and severe.

How many of our "climate experts" have understood these simplified explanations? This article explains some of the apparent pros and cons of global warming. It must be recognised by all concerned that global warming is here to stay unless it is soon mitigated against in some way. In fact various scientists have evidence to show that even if we ceased increasing the greenhouse gas content of the atmosphere immediately, global warming would continue to perilous levels by the end of the century, or sooner.

They make such statements with a knowledge of the thermodynamics, together with the dynamics, of the atmosphere, including the effects on the stratosphere and higher levels.

So much for the thermodynamics, but the dynamic affects such as the increasing strength and frequencies of hurricanes, tornadoes and intense rainfalls, will also occur for reasons which are now well understood by teams of scientists who have the advantages of inter-communication and of advanced observation and computer resources. We can do no better than accept their advice and prepare for a future which, at the least, will greatly affect the average standard of living.

In this potted course on meteorology and climatology, I have not ventured into the impacts of the oceans on the atmosphere. These cannot be ignored, not only as contributing to the thermodynamic system but, as is commonly expressed, the rising sea level, particularly on our coastal cities.

These views are a result of amalgamating meteorological considerations over a period since I joined the Meteorological Service (now MetService) in 1957. They are an attempt to summarise the many considerations gleaned in a variety of professional positions I have occupied over that period.

* Jim Hessell is a former weather forecaster with the Meteorological Service and lecturer in theoretical and practical meteorology.