Once more with feeling: Climate Change (longish read)

A comment based on my current understanding of the science

     Climate is a chaotic system. It consists of a web of interconnected feedback loops. For example, cloud cover cools the ground below, which reduces evaporation, which reduces the amount of water in the air, which reduces the odds that there will be rain. However, water doesn’t cool as rapidly as the ground, so evaporation from large lakes continues, which increases the amount of water vapour in the air, which increases the odds that there will be rain. Which is why cloud cover over the Great Lakes usually signals rain, while cloud cover over the Prairies does not.

     These links between feedback loops makes it difficult to precisely model the weather and hence the climate. Some feedback loops cancel the effects of other loops, and some feedback loops enhance the effects of other loops, and all of them are entangled with one or more other feedback loops. Such systems are characterised by non-linear relations between causes and effects. Small (sometimes very small) changes in some factor can become magnified into huge effects. Hence the sometimes rapid development of afternoon thunder storms after a bright, cloudless morning.

     A chaotic system cycles through a series of states ("the seasons") that vary within some range but average out over time (average annual seasonal temperatures, etc.) This average is called the attractor. "Regression to the mean" is a common effect: Think of a baseball pitcher's performance over time. Pitching is the influenced by many factors, most of which affect each other. The pitcher's performance is a chaotic system: sometimes he's hot, sometimes he's not, most of the time he performs near his average level.

     Chaotic systems can change radically. If some factor or factors exceed some limit (too much or too little), the whole system will shift into a new series of states, some or all of which are radically different from the previous ones. Hence climate change, or global warming.

     There is no question that burning fossil fuels has increased CO2 concentration in the atmosphere, now (about 400 parts per million) coming closer to double the concentration of pre-Industrial Revolution levels (about 280 parts per million). (See this graph) This is having an effect on climate, the  annual weather cycles. The important questions IMO are:
a) How fast is this happening?
b) Is it happening faster in some climate zones than others?
c) How far will it go?

     Answer to a) Unknown, but climate models so far have understated the expected changes. This is shown in:
     Answer to b) Yes. For example, the Arctic is warming about twice as fast as the temperate zone. Predictions of the extent of summer sea ice have repeatedly underestimated the numbers. The general trend is melt beginning earlier and proceeding more quickly than predicted by the models available at the time. Thus, there is less sea ice, and it’s thinner. The last ten years or so have seen record ice loss almost every year.
     Answer to c) Nobody knows for sure how far climate change will go. Models are continually updated and tested with new data, both current and historical (from Greenland ice cores, for example). As these models get better, they imply what I think are several important conclusions:

1) Climate can change very rapidly from one normal limit to the other. For example, the Little Ice Age, a fairly sudden cooling of the northern winter, which among other things destroyed the Viking settlements in Greenland.

2) Seasonal weather patterns can change in opposite directions, for example, rainfall shifting from winter and summer, hence wetter springs and falls, and dryer summers and winters. This means flash flooding and drought when neither was common in the past.

3) Weather patterns can change from historic averages within two or three years, for example the now five-year drought on the West Coast of the USA.

4) There's a lag between the warming effects of CO2 and climate change because of heat-sinks, chief of which is the ocean: Over half of the recent rise in ocean levels is caused by the expansion of water as the oceans warmed up.

It's true that climate models aren't good enough to satisfy the non-scientist's yearning for certainty. But I think the certainty is higher than required in a civil law case ("balance of probabilities"), and close to that required in a criminal case ("beyond reasonable doubt”, emphasis on "reasonable").

(Revised 2020 09 21)