Milutin Milanković was a Serbian climatologist who back in the 1920s put forward theories concerning how variations in the Earth’s orbit and axial tilt might affect the amount of solar radiation impinging on the Earth (now known as the Milanković cycles) so causing periodic variations in the Earth’s climate (eg, ice ages).
He wasn’t the first but by his time it was possible to measure these variations and geology was sufficiently advanced to verify his conclusions on the ground.
Eccentricity. The orbit of the Earth is not circular but an ellipse. The ellipse is not constant as it is affected by the gravity of Saturn and Jupiter. The long axis of the ellipse also moves around in a 112,000 year cycle.
Velocity. The speed of the Earth is not constant, due to the elliptical orbit. This affects the length of the seasons. For example, if the Earth is moving slower during Winter, Winter will be longer.
These two combined repeat every 100,000 years.
Tilt. The Earth’s axis is tilted with respect to the orbital plane. This too varies between 22 and 24.5 degrees, Another cycle repeating every 41,000 years.
Precession (Wobble). The Earth wobbles like a top slowing down. Each wobble lasts 25,771 years. (Now isn’t that an exact figure!) This is caused by the sun and moon.
Orbital tilt. Relative to the average for the rest of the solar system. This is about 1.5 degrees but varies over a 70,000 year or 100,000 year period depending on how measured.
All of these factors have a tiny effect on the amount of solar radiation falling on the Earth. However, at regular intervals, all of the maxima coincide and we get an exceptionally warm or cold period. Milankovic reckoned the complete combined cycle lasted 45.000 years.
However, there was a problem; geological/glacier evidence pointed to a 100,000 year cycle. In fact, it turned out to be even more complex. A few million years ago we did have a 45,000 year cycle only more recently have we got a 100,000 year cycle. The reasons are unclear but all agreed we were heading for an ice age in a few thousand years. For example, John Imbrie, a more recent sage (1980s), reckoned that a long term cooling cycle that began 6,000 years ago would continue for the next 23,000 years.
But Err…we are actually warming, fast, by climatological standards. Clearly something was overriding the reduction in solar radiation we are having as we were heading for the next ice age. There have been glitches in the past caused by massive volcanic eruptions. Interestingly, these have made things cooler by reason of volcanic ash thrown high in the atmosphere reflecting the sun’s rays. The latest glitch was the 1991 eruption of Mt Pinatubo, which lowered the global temperature by 0.5 to 0.6°C for a couple of years.
Simultaneous research had been going on into “greenhouse gases,” which slow down heat losses from our planet. The main ones are water vapour, carbon dioxide and methane. Four billion years ago, the Earth’s atmosphere was nitrogen and carbon dioxide. There was a massive greenhouse effect. Fortunately the Earth was further away and the sun not so bright at that time.
Only because the Earth has a benign climate was plant life able to evolve and turn the carbon dioxide into oxygen and carbon. Some of the carbon got locked away in the ground, fortunately for us. Some of the carbon dioxide got locked way as limestone (sea shells) as marine life evolved. The chances of the above happening were vanishingly small, but here we all are. Without the greenhouse gases in the atmosphere creating a warming effect, we would never exist.
The system is in a fine balance; little disruption is needed to upset things. This is because of runaway or “positive feedback” effects. All positive feedback systems are inherently unstable. So, a slight warming effect sets off other events that add to the effect. For example, we now have a situation where arctic permafrost bogs are melting and releasing methane (a strong greenhouse gas). As ice and snow disappear, the surface of the Earth becomes less reflective (albedo) of solar radiation. As the sea warms, frozen undersea methane is released from huge reserves of methane hydrate on the ocean floors. Soot from industrial pollution lands on glaciers, so making them less reflective of the sunlight and thus melt faster. Natural gas exploration also releases methane gas (especially fracking).
Once these emissions are initiated, they are impossible to stop and they will get worse. This is why it’s imperative to reduce emissions of CO2. As the atmosphere warms, it holds more water vapour, again boosting the greenhouse effect. But then, there might be more clouds which would reflect solar radiation. There are lots of unknowns and unquantifiables. However, doing nothing is not an option; the consequences would be massive disruption to the eco-system, the world economy and all our lives.
I hear the sceptical say, “How can even a degree of global warming make that much difference?” Well, our weather systems are driven by temperature differences not absolute temperature. A four-degree difference can drive a lethal storm, if it were five degrees it would be far worse. Anyone born around the middle of the last century has witnessed global warming. When I was a child, non-white Christmases were rare. Snow-free Winters were unknown. Every child had a sledge. Most of them these days don’t even know what one is. Once uncommon weather events are becoming the new norm. Australia has gone from desiccation to extreme rain overnight. Locally, we have had four separate flood events in as many weeks.
We now seem to have a culture of telling people what they want to hear as opposed to truth (started by politicians). We have got to the stage where they just don’t listen to bad news. Lots of them don’t want their comfortable existence disturbed but it will happen. There will be economic consequences arising from the effects of climate change for everyone. Well, ignoring it won’t make it go away. As an example there must be thousands now ruing the day they ignored advice about buying houses liable to flooding. The recent flooding severely affected food production and this will get worse, resulting in shortages and price hikes.
Furthermore, we ain’t seen nuthin’ yet, we all need to be preparing.