Climate is a chaotic system

     Climate is a chaotic system. It consists of a web of interconnected feedback loops. This makes it difficult to model precisely, since 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 two or more other feedback loops. Chaotic system are characterised by non-linear relations between causes and effects. Small (sometimes very small) changes in some factor can become magnified into huge effects.

Some chaotic systems cycle through a series of states ("the seasons") that vary within some range but average out over time (number of cycles). 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.

However, 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.

There is no question that burning fossil fuels has increased CO2 concentration in the atmosphere, now approaching double the concentration of pre-Industrial Revolution levels. This is having an effect on climate (ie, on 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: Predictions of the extent of summer seas ice (the extent of summer sea ice melting) have underestimated the melting. The general trend is faster melting than predicted by the models available at the time.

Answer to c) Nobody knows for sure how far climate change will go. Models are continually updated and tested with new data (both historical and current). Reserach uncovers new feedback loops. As these models get better they imply several (from my POV) important conclusions:

1) Climate can change very rapidly from one normal limit to the other (look up Little Ice Age).

2) Seasonal weather patterns can change in opposite directions;

3) Seasonal weather patterns can go from one extreme to the other within a year or two.

3) 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 popular yearning for "near certainty" in their predictions. But the certainty is higher than required in a civil law case ("balance of probabilities"), and IMO close to that required in a criminal case ("beyond reasonable doubt, emphasis on "reasonable").