Global Warming? Same as usual, then!
Dr. Geoffrey Dobson, who lives in the Pas de Calais and writes on a number of science related topics, explains why climate change is nothing unusual.
Now that the ballyhoo of the Copenhagen Conference is over it might be useful to examine how Climate Change is not a uniquely modern phenomenon. In fact ever since the Earth was born, 3.6 billion years ago, the climate has undergone many cycles, influenced by a variety of effects.
1) Major ice ages
The most dramatic cycle is that of the major ice ages roughly every 150 million years lasting a few million years. One theory is that the galaxy completes one rotation about once every 300 million years, taking the solar system through denser and thinner regions of interstellar dust and through changing gravity and magnetic fields. The last major ice age was very long starting about 350 million years ago and finishing about 200 million years ago. The climate could flip into another one at any time. During a major ice age the Earth is completely covered in ice and snow (“Snowball Earth”). No living things on the surface of the Earth, including us, would be likely to survive.
2) Regular ice ages
During the intervals between major ice ages the climate cycles between periods of cold glacials and warm interglacials. During the glacials, glaciers and ice caps grow; in interglacials, they shrink. Glacials last approximately 100 000 years, interglacials last between 10 000 and 20 000 years. During glacials the Arctic ice sheet can spread to cover most of Europe. It is thought that glacials are caused by wobbles in the tilt of the Earth and changes in its orbit around the Sun (“Milankovitch cycles”). The last glacial age started 70 000 and ended 10 000 years ago, we are currently in an interglacial age that could end at any time during the next 10 000 years. The human race would survive a glacial period, but life in Europe and North America would become very uncomfortable.
Interglacial ages are relatively warm compared to glacial ages. However there is a 900-year cycle between warmer and colder periods. The Roman Warm Period (up to 500 AD), was followed by the Dark Age Cool Period (up to 1000AD), then the Medieval Warm Period (up to 1400 AD), then the Little Ice Age (up to 1900 AD), and the Modern Warm Period (up to now and ongoing). No one really knows why these cycles happen, but cooling periods may be caused by periodic major volcanic eruptions (e.g. Krakatoa in 535 AD) or variations in solar activity, or a combination of both. Both the Roman and Mediaeval warm periods were warmer than today. The Romans grew grapes for wine in Yorkshire; the Vikings colonised Greenland during the Mediaeval Period.. The present warm period with some fluctuations could last another 300 years
4) The Multi Decadal Oscillation
There is a 60-year oscillation of ocean temperatures with a corresponding oscillation in global temperatures. Global warming alarmists have emphasised the fact that the Earth warmed up steadily by approximately 0.6°C during the 20th century. However this warming trend has been far from constant. As we emerged from the Little Ice Age on the warming phase of the 900-year cycle, the 60-year ocean temperature cycle caused uneven warming. Thus we had cooling to 1910, warming to 1940, cooling to 1970, warming to 1998, then cooling since.
5) El Nino and La Nina
There is a Pacific Ocean warm current that changes direction every few years. It flows either towards the United States (El Nino) or away from the US (La Nina). These currents have a strong effect on the global climate causing their own heating and warming phases in the main continents. These show up as fluctuations in the temperature versus years trend line. 1998 was exceptionally warm due to a strong El Nino. The early years of this century were a La Nina period and the climate cooled. Another El Nino started at the end of 2009 so we might expect some warming in 2010.
6) Solar cycles
During the 20th century the sun was more active than at any time in the last 1000 years, while during the 17th century the sun was relatively inactive (the “Maunder Minimum”).
The activity of the sun varies over a 100-year cycle, combined with a shorter 11-year cycle. The sun has now entered a quiet phase, and there are currently no sunspots. Solar physicists think that, apart from direct heating effects, a lack of solar magnetic activity increases cosmic ray bombardment causing cloud formation, hence reducing solar irradiation of the Earth’s surface.
So what does it all mean for climate predictions over the next hundred years?
Are we all going to fry as the warming alarmists believe, will it all cool down again, or are we in a stable climatic period? The straight answer is that in the short term no one really knows. The combined effect of all these cycles means that the variation of the climate over a hundred years or so is chaotic and cannot be predicted by any computer model, no matter how big and fast we make our computers.
The pattern of global temperature fluctuations over the last 2000 years suggests that the current cooling phase will end around 2030. We might expect then that warming will resume until the end of the century, when temperatures will be similar to the peak of the Mediaeval Period. The climate might then start to cool down towards the next mini ice age, when rivers like the Thames will again freeze in winter. This is assuming of course that we do not plunge meanwhile into a glacial period when the whole of Europe will be permanently covered in ice.
Interestingly some climate scientists are beginning to predict such a future, although at the same time not abandoning the theory that the warming phase is due to human produced carbon dioxide. They predict that, while we might well have cooling and warming cycles, the overall trend will be for temperatures to continue to rise due to the increased Greenhouse Effect of carbon dioxide.
One thing that appears to be inevitable is that, compared to what nature has done to the Earth in the past and will do again in the future, our effects, long term, on the global climate are likely to be almost unnoticeable. Any efforts by us to control future climate are likely to be futile, we would be better occupied working out how to survive the next glacial. The Scandinavians might give us some worthwhile advice.