How can scientists predict future temperatures when they cannot predict the weather accurately?

Firstly, climate scientists cannot predict the exact temperature of a particular place, in exactly 50 years, easily or at all, any more than they can predict the exact temperature at a certain time, in a specific place, in one month’s time. And while this is problem raised by ‘skeptics’, this predictive ability is not an ability claimed by any climate scientists that I have read, and is of no relevance to the ongoing issues of predicting general increase in average global temperatures.

Weather systems form complex systems, and prediction in complex systems is notoriously difficult over length of time. We can predict climate trends such as: the average global temperature may rise by a particular order of magnitude, or that sea ice will melt and ocean levels rise, that low lying land will be flooded, and that deserts will expand, that weather will become more tumultuous, that storms are likely to get bigger, and that people will move as a result. But you cannot predict exact weather patterns for particular places. If we could, it would actually make climate change less devastating, as we could plan for it.

You can also predict that given the continuance of the circumstances we are in, it is extremely improbable that average temperatures will trend towards decrease, or that weather will become simple and nicely warmer everywhere. Indeed the prediction that this will not happen has been born out for years, and there is no sign that such climate beneficence will happen. However, it is possible that as climate patterns change some particular places may get colder – for example, if the gulf stream stops or shifts southward, then this may happen with the UK.

The point to bear in mind, is that climate and weather are complicated, but continuance of, or return to, the normal weather patterns of 20 years ago seems improbable in the extreme, and it is far more likely that weather events will become even more extreme than they are now, until (possibly) a new ‘steady state’ arises when the forces producing climate change have ceased. However, I am told that when we look at the last time the earth had high levels of CO2 and high temperatures (50 million years ago), massive storms may well have marked that normality.

We might add that other factors of the Anthropocene (such as peak phosphorus), make the prediction of livability of earth systems even more complex and fraught, but that is another question.