Hot, Hot, Hot….

Global Climate Change and What it means for the Overberg

By Professor Michael Orren

In this first part of a two part article, Professor Orren has a look at Global Climate Change in general. In the next issue he will analyse what the implications are for the Overberg.

“Global warming” implies that the planet is warming regularly everywhere – this is not so. Global Climate Change, abbreviated GCC, is a better name for this phenomenon. GCC is neither myth nor theory but founded solidly on observed facts and thousands of daily, quality-controlled, international scientific measurements from mountain top to seafloor and from space. So, what has happened?

Earth warmed by 0.8°C in the past century, polar regions more than the tropics. Physics tells us that warming increases energy; and chemistry tells us that warming speeds up reactions; and we observe both these phenomena on Earth’s surface.

Meteorologists and oceanographers now realise that atmosphere and ocean behave as one, very complex, system. The ocean is the major player; about 90% incoming energy is stored in the sea; in fact the upper 3.5m of the ocean holds as much heat as the entire atmosphere. Adding energy to the system resembles putting your foot on your car’s accelerator – it speeds up. Climate changes occur in “jumps”, both up and down; hence the long term average is the true indicator of change.

Weather in any area seems to vary randomly, but when many observations are combined statistically, a pattern emerges, that of climate.

Weather is powered almost entirely by solar radiation warming our earth; other energy sources are negligible. Earth should really have an average temperature of -18°C, some 33°C cooler than observed. “Something like a blanket” must warm the planet.  Invisible water vapour and carbon dioxide gas cause the earth to heat up by trapping outgoing infra-red (heat) radiation and radiating it back to the surface. This is the so-called “greenhouse effect”.

Greenhouse warming by water vapour is quite complex. Water is a ‘condensing gas’. As it cools, cloud forms, then rain or snow falls, reducing atmospheric moisture and hence the heating by water vapour. Conversely, warmed water evaporates adding atmospheric water vapour to the atmosphere. However, the heating is not simply additive, since clouds create complex “feedbacks” such as by reflecting heat and exerting a cooling effect. When water vapour condenses, it releasing its pent-up energy. This so-called latent heat of evaporation of water powers the atmospheric “heat engine” driving our weather.

Carbon dioxide, on the other hand, is neither condensing nor evaporating, and absorbs and emits far more heat per molecule than does water. While it occurs in smaller quantities, it acts as an efficient greenhouse gas.

Since the start of the industrial revolution the balance of nature has changed.  Burning fossil fuel adds 3.5 million tonnes carbon dioxide every single hour to our atmosphere-ocean system. Despite 1 million tonnes of carbon dioxide dissolving hourly in the ocean (and acidifying it in the process), this vast addition overwhelmed the system’s natural ability to absorb the excess CO₂.   Carbon dioxide is steadily accumulating, increasing the warming effect, adding energy to the Earth’s ocean, and then to the atmosphere.

Extreme weather events (exceptionally severe weather) have always occurred but the probability (chance) of these happening has dramatically increased through the extra energy added by GCC. Cold snaps and heat waves, severe floods and droughts and damaging storms are all increasing in frequency. The “one hundred year flood” now happens every 10 years. Carefully compiled insurance company statistics (e.g., from Munich Re and Santam) confirm this increasing damage. Winds have changed direction and speed; more powerful ocean waves crash in from new directions; sea level is creeping steadily upwards, while ocean temperatures are changing, many up, some down. Mighty ocean currents each transport gigantic amounts of energy, equivalent to the combined output of about one million nuclear power stations!

Today’s computer models are reliable and fed with high quality data, but models are not perfect and cannot reproduce the complicated atmosphere/ocean system exactly. Sciencemagazine reported (December 23, 2011) that the very latest “fancy, new” climate models are – reassuringly – not revealing any dramatic new changes. The results are the best we have, and while challenging, are far better than some sceptic’s opinion, guess, or belief, all unsupported by any scientifically acceptable evidence.

In the next edition Michael Orren will look at the expected implications of GCC for the Overberg.

Professor Michael Orren is a geochemist and oceanographer with a special interest in global climate change. He divides his time between teaching at the University of Belfast in Ireland and enjoying the charms of Bettys Bay. This article is based on a recent series of lectures he gave in Ireland on global climate change.