The question often comes up whether the changes in climate over the last few decades are due to human caused “global warming” or whether it’s just part of nature taking its own course. To help answer this, we need to understand natural climate change.

There are different kinds of climate cycles with different causes. The biggest cycles are driven by tilts in in the Earth’s rotation axis and interaction with Earth’s orbit with Jupiter and Saturn. If you want to know more, look up Milankovitch cycles and dig in. These are the cause of the ice age cycles and can be considered constant during a human lifetime.

But while these astronomical cycles initiate the changes from ice age to temperate and back, they are not the full story. Carbon dioxide, like all gases, is less soluble in warm water than cold water. It is also strongly held by permafrost. The solar warmth increase comes before and begins the CO2 increase, but CO2 becomes the dominant source of temperature rise. There are other mechanisms also.

For the past several hundred thousand years, the Earth has been cycling the same available carbon through plants, animals, oceans, soil and back again, with the atmospheric carbon dioxide varying between about 180 and 280 parts per million (0.018% to 0.028%). This variation in CO2 levels has corresponded to a temperature range of 10 degrees C (16 degrees F). On this scale, the last 7,000 years, corresponding to recorded history or since Genesis 2, have been essentially constant.

We have now brought the CO2 level up to 380ppm (414ppm today). We have done this by burning oil made from ferns and dinosaurs, covered up long before the ice age cycles. This carbon is not part of the world that the human race has known. Perhaps God buried that stuff under miles of solid rock for this reason: Life will be hard in the world we will have when it is burned. There has always been enough energy available for our true needs.

How hard will life get? It will take some years to find out, but remember that the last 100ppm that was added—from 180ppm to 280ppm—increased the Antarctic temperature by 16 degrees Fahrenheit, though they expect less change elsewhere.

Shorter warming/cooling periods are caused by aerosols and sun spots. Aerosols, such as from volcanic activity, forest fires and pre-1970s coal plants, cause cooling. They wash out in a few years with little long-term effect. Solar activity is more important. Scientists think the Medieval Warm Period resulted mainly from increased solar radiation and that might be responsible for some of the temperature increase we have seen in the last decades.

Most of our weather systems come from energy released by condensing water vapor, guided by variation in ocean currents and prevailing winds. These make highs and lows, good years and bad years, beyond our current ability to predict.

Some multiyear patterns are predictable. People have been aware of El Nino for a long time. We now know that El Nino is a periodic ripple in the huge Pacific Ocean. While it gets warm at one end it gets cold at the other and the average global temperature doesn’t change.

It is important not to confuse any combination of weather in the U.S. or Europe with global climate changes. Even the melting of the Arctic would not be that catastrophic if Antarctica wasn’t also melting and it had not gotten to 99 degrees in Moscow.

Feedback loops put limits on patterns like El Nino. The carbon cycle will also even out. Melting permafrost and warming oceans will still drive CO2 up for a couple of decades, but in a few thousand years the CO2 will be incorporated into the soil. Ice will cover much of the Earth again for 100,000 years, and after that the trees will grow back just as if all this had never happened.

David Rieck is a Janesville resident.


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