The climate is changing.
There’s very little real debate about this; it’s been experimentally tested on many separate occasions. Multiple forms of evidence, including satellite readings, tree cores, ice cores, and geological data confirm this.
So, then, why is climate change such a contentious topic? It boils down to two main areas: the extent of the change, and the cause of the change.
The consensus among the vast majority of climate scientists is that climate change is caused by humans, and that it will warm the planet enough so that devastating, irreversible change will eventually be caused. However, some believe differently.
The largest point of dissention is that humans are the ones causing climate change. Proponents of a non-human based explanation point to previous periods of climate change.
Throughout the Earth’s geological history, there have been countless cycles of warm and cold climate. While this may make it tempting to conclude that the present period of climate change is just a continuation of this trend, the Earth’s climate does not randomly change. For there to be a long-term shift in the climate, something has to cause it.
In the past, these causes have been diverse – ranging from a supervolcano eruption to an asteroid impacting the Earth to massive deforestation. The point is, something big has to happen for the planetwide climate to change. Presently, there is something big happening – an intelligent civilization has been dumping chemicals into the atmosphere on an industrial scale.
However, some are of the opinion that any human-caused climate change pales in comparison to the changes caused by the sun. In the past thousand years, the sun has caused measurable changes in the Earth’s climate. For example, a period of low solar activity in the late 1600s is believed to have contributed at least in part to major cooling during that period.
However, there’s a reason why this hasn’t been widely considered as a possible cause of current global warming: there hasn’t been a large enough increase in solar activity. However, there has been some confusion about this in the public mind. The sun has an 11-year cycle of slightly increasing and decreasing activity. We’re currently going though the part of this cycle with the most activity, just like we did 11 years ago and we will 11 years in the future.
So, while the sun has been ramping up its activity, this is completely normal and natural, and not sufficiently erratic to drive a long-term trend in the Earth’s climate.
The other major area of debate is the extent to which the climate will change. The number 2 degrees Celsius (around 3.6 degrees Fahrenheit) above pre-industrial levels is a number commonly cited as a limit which we should not pass.
While a little over 3 degrees may seem like a small number, climate scientists say that it’s enough to disrupt ecosystems and throw them out of balance, creating a cascade of events that will drastically harm both everything living there, as well as us.
Most of the ideas floated around as alternatives to the scientific consensus on climate change were already considered, researched, and consequently ruled out. The current theory is the best we have, and all credible data reaffirms it. If any new evidence is found that contradicts it, either the theory or the data will have to be reconsidered.
For now, nothing of the sort has been credibly found.