The climate is one aspect of a biosphere of unimaginable complexity.
Along with oceans, icebergs, lakes, rivers, glaciers, snow, sleet, hail, fog, mist, rain, water vapour, terrain varied in relief and texture, volcanoes and air comprising oxygen, nitrogen, carbon dioxide, methane, nitrous oxide, various trace gases and meteoric dust from space there is a multitude of living organisms integrated into and affecting the global climate system. Jungles, forests, grasslands, crops, flora, tundra, pollen, algae, bacteria, viruses, insects, reptiles, fish and mammals all have been shown to affect the weather.
Add to these 7 billion humans which have evolved powerful but polluting technology, including the ability to modify living systems through genetic engineering and which introduce into the biosphere all manner of pollutants previously unknown to nature.
It is hardly surprising that no one can predict climate with any degree of certainty.
Nevertheless it is possible to construct computer models which approximate the long term meteorology and have built into them laws of physics which have been thoroughly proved, tested and peer reviewed by networks of scientists over decades. Greenhouse warming, e.g., is as certain as the law of gravity. The problems and uncertainties arise from the chaotic nature of natural processes on a global scale and the inherent unpredictability of interactions between living systems of all kinds and the land, sea and air which they inhabit.
Numerous climate models have been loaded onto computers, all getting different results; yet as far as I am aware all agree that that things ain’t what they used to be before the Industrial Revolution and the long term temperature trend is upward.
Here are some of the difficulties faced by climate scientists:
- The Arctic is warming and melting much faster than other parts of the planet. These are cooling in some places but the overall average temperature at the Earth’s surface is rising. But by how much?
- Parts of the Antarctic are melting, parts are cooling, but the balance between these two trends is uncertain.
- Land-bound ice melting (e.g. glaciers in Greenland) is the only melting that causes the sea level to rise. Icebergs melting make no difference to sea level although this may well affect ocean currents which in turn can affect the weather. But how fast are the icebergs melting and how much fresh water do they hold? (A recently launched satellite, Cryosat, should help a lot.)
- Glacier melting is considerably accelerated by thin , invisible layers of soot from forest fires, older diesel engines and slash-and-burn agriculture. Again, just how much is the acceleration?
- ice and snow cover as well as changes in the nature of the earth's surface and atmospheric composition affect the amount of heat absorbed from the sun
- Algae in the sea affect precipitation by mechanisms which are imperfectly understood.
- There are 4 large scale chaotic systems, imperfectly understood and synchronised to varying degrees, which sometimes counteract, sometimes enhance, global warming: the El Nino Southern Oscillation, the North American Oscillation, the Pacific Decalal Oscillation and the North Pacific Index
- Sunspot activity is currently unusually low, as it is has been previously at various times over the last several centuries, and this has a small cooling effect to offset man-made greenhouse emissions. But what will the sun do next? No one is sure.
- Methane from ocean bed deposits and tundra is 20x more powerful as a greenhouse gas than carbon dioxide. The hotter the ocean and atmosphere the more methane escapes into the atmosphere but we don’t have enough data to know how quickly this is happening and whether it is likely to lead to runaway heating.
- Volcanoes emit greenhouse gases in very small amounts compared to artificial emissions yet it is possible that an unusually large one could erupt at any time. More significant is the sulphur dioxide from volcanoes which forms aerosols of sulphuric acid in the atmosphere and this causes cooling by blocking incoming radiant heat from the sun.
- Cosmic debris is burning up in the atmosphere all the time but there is always the chance of something big hitting the biosphere and disrupting it. The weather can be regarded as part of the biosphere. It certainly affects and is affected by it.
- Data on past climate change has to be indirect, based on such things as pollen and flora entrapped in lake or ocean sediments or ice layers as well as tree growth rates. The data has to be collated over large geopgraphical areas in order to reconstruct past climate scenarios.
- Clouds and aerosols of various types and thickness can have either a warming or a cooling effect and we don't have enough data on this - a major cause of discrepancy among climate models to date.
- The pollution by human beings is intrinsically unpredictable because we have ever more powerful technology coupled with free will (except for those who think they are machines).
- moss growing on rock causes CO2 to be absorbed into the dissolved rock
- plate tectonics affects the amount of CO2 in the atmosphere
The biggest danger is that some time in the next decade or so the 4 oscillating systems mentioned above will work in sync to cause a sudden jump in temperature and that this will set off a chain reaction (more heat causes more heating mechanisms causes more heat etc. etc.) leading to a catastrophic breakdown of the whole system. (Think of Venus, almost identical in size to the Earth, where the temperature is high enough to melt lead, partly because it is 27% closer to the sun but largely because of the prevalence of carbon dioxide.)
On the longer timescale of hundreds of thousands of years global temperatures are widely thought to be governed by the Milankovitch cycles associated with the orbit, rotation and tilt of the Earth. According to these we should now be entering a new ice age. Hopefully, this cooling trend will save us from the relentless upward trend due to man’s input since about 1800.
No one knows what the global temperatures and sea level will be in 100 years; but we do know that nature cannot continue to be arrogantly exploited without some kind of ecological breakdown.
Author, 2077 AD