Global warming vs Climate change

When reading discussions about climate change/global warming I often encounter people who say something along the lines of “scientists used to talk about global warming, but since that didn’t work they’ve started to talk about climate change”. The implication seems to be that global warming has been disproved and so scientists are now going to try again but instead will refer to it as climate change (i.e., they’re trying to have two bites of the cherry, rather than admitting defeat when their first hypothesis was disproved). I suspect that this will become a theme of my posts, but this – to me – illustrates a lack of understanding of the terms “global warming” and “climate change”. Something that confuses me is that it should be straightforward to explain the difference between these terms, and if people understood the difference, it would help – in my opinion – to make the discussion more constructive.

So, I’m going to try, here, to explain the basics behind the terms “global warming” and “climate change”. I’ll start with the term “global warming”. Basically, it means exactly what it says – a situation in which the planet (globe) is gaining energy (getting warmer). There is a nice post over at quakerattled called the higher you go, the hotter it gets, so I won’t go into too much detail. Essentially, however, the Earth gets energy from the Sun. Some of this energy is reflected back into space (albedo) and the rest is absorbed. The Earth then re-radiates energy back into space. If the amount of energy it loses is less than the amount it gains, it will heat up. If the amount it loses is greater than the amount it gains, it will cool down. The Earth will therefore tend towards an equilibrium temperature at which the amount of energy that is lost back into space matches the amount of energy that the Earth gets from the Sun.

Given that so many of the processes that provide and distribute energy are variable, we wouldn’t really expect the Earth’s temperature to remain at precisely the equilibrium value. Under “normal” circumstances, we would expect it to vary from being above the equilibrium value (global cooling) to being below the equilibrium value (global warming). We would expect, however, that – on average – the net amount of energy in the Earth’s climate system should remain constant. What is concerning people at the moment is evidence (satellite measurements, surface temperatures, ocean heat content, arctic ice volume) that suggests that we’ve been undergoing global warming for many decades. This is much longer than any of the known “natural” processes that contribute to providing and distributing energy through the Earth’s climate system and hence suggests that it may be related to the continued increased in CO₂ levels in the Earth’s atmosphere. In some sense, we should aim to distinguish between the evidence that global warming is happening (i.e., satellite measurements of the Earth’s energy budget, for example) and the interpretation of this evidence (i.e., what is causing this warming).

So, that’s my attempt to explain what is meant by the term “global warming”. The term “climate change” is also reasonably self-explanatory and simply refers to changes in the climate. In this case, the context is changes that are due to the increase in energy in the climate system as a result of global warming. I accept that precisely how the climate will change is not clear and debating the consequences is a perfectly fine thing to do. I would argue, however, that if global warming has been occurring for many decades (as some evidence suggests) then the extra energy should result in changes to the climate. We would expect sea levels to increase. We would expect more heat waves. We would expect changes to the jet stream and gulf stream. One can’t say with certainty what will happen, but adding energy should have an effect.

So, I hope this is clear and feel free to correct anything I’ve said that you think is wrong. What I was trying to get across is that there is a difference between the terms “global warming” and “climate change” and discussions about this topic would be much more constructive if people tried to understand this difference. Furthermore, we should distinguish between evidence that global warming is happening, and the interpretations of this evidence which try to explain why this global warming is happening.