Hasn’t the climate always changed?

My recent KLICE comment piece elicited an e-mail response from a Revd Dr wondering if the climate had always been changing, and (implicitly) if what we’re seeing is anything new. I don’t feel I should publish his e-mail in full, but here’s my reply:

Revd Dr […],

Thank you for your interest in my KLICE comment piece and the reply. Unfortunately given the constraints of space I couldn’t say everything about the subject, but let me address the questions you have.

You say that you are sure the climate has changed in the past, well before humanity’s ability to change it. This is true, and in fact there is an entire field of science, paleoclimatology, devoted to finding out what we can find out from the geological record, ice cores and other sources.

While this data can only take you so far, it is generally agreed that the various ice ages of the last few hundred thousand years saw global temperatures up to about 8C lower than present, but going back millions of years, there were periods in which global temperatures were a few degrees higher, so what is now England would have been tropical, helped by (at times) also being closer to the equator due to the continents moving round the earth. That is when the coal seams would have been laid down.

As well as the question of what the temperature was, research has been done into why it changes. There are numerous factors known or believed to contribute to both these longer term and short term variations in climate and weather. (Climate is taken to be variations over a 30-year period or more, weather is anything more short term.) These include variations in the orbit and axis of the earth, the changing positions of the continents and ocean currents, volcanoes, pollution, variations in the power of the sun, and the level of carbon dioxide and other “greenhouse gases” in the atmosphere. Some of these affect the global climate, others have more local effects. For instance, while Britain and neighbouring areas were distinctly warmer in the Middle Ages, there is no evidence that this was a worldwide phenomenon. And when we get to the level of months and days there are plenty of other factors which can cause the kind of extremes in weather we’ve been used to over recorded history.

It is the wide variety of factors that led to some fears about global cooling in the 1970s. At that point, pollution had increased rapidly, and many thought its cooling effect would dominate. What wasn’t foreseen was the increase in greenhouse gas emissions and the decrease in pollution subsequently which has led to the trend going very much the other way.

Given all this, why is there so much concern about greenhouse gases? The first is that the effect we understand they will have is far bigger than any other factor that has affected our climate recently. The last ten thousand years, in which all human culture has developed seems to have been unusually stable, with global temperature varying only by about a degree or so, and CO2 levels in the atmosphere varying between about 270 and 290 ppm (parts per million). We are currently right at the top of that temperature range and expecting to gain anything from 1.5 to 6 degrees C this century, and CO2 will hit 400ppm within a couple of years and anything between about 600 and 1000ppm by 2100. There is uncertainty in both the science and how much humans will act to reduce emissions, hence the relatively large ranges, but the question is only whether between whether we get an outcome which is merely ‘bad’ or ‘a complete disaster’.

So we are moving into a climate which humans have never known, probably reaching the warmest for around 30 million years within a few decades. This leads to fears of possible unknown factors coming into play, which may slow warming down or stop it, but may also accelerate it. For instance, there is a considerable amount of methane (an even more potent greenhouse gas) frozen into the Arctic tundra. If this melts and is released, then it will cause even more warming. By the time these factors are definitively understood, it will almost certainly be far too late to do anything about them.

We are talking about a relatively short period of time, but that is because the speed of change is also alarming. Similar rapid climate shifts have occurred in the past, maybe over tens of thousands of year, maybe faster – we can’t tell. But their effect on the planet has been immense, usually causing mass species extinction as animals and plants cannot adjust fast enough to their environment changing. The worst killed 95%+ of marine life, 70% of land life, and life took millions of years to be as fruitful again afterwards as it had been before.

The effects on humanity are likely to be similarly severe. We cannot yet ascertain with any reliability what they will be, but a warmer atmosphere generally leads to wetter (globally) but more extreme weather, and it is now pretty much certain that some areas of the planet are going to become very difficult or impossible for humans to live. Typical predictions include that in 50 years or so parts of Africa will be too hot for any food crop to grow reliably, and that the entire Mediterranean basin will become desert. While some new areas near the poles may become more fertile, they almost certainly won’t counterbalance what has been lost, and in any case we have the social problem of moving millions of people to new areas.

Now, it remains theoretically possible that what we are seeing is some natural effect which is causing warming and we are just incredibly unlucky it is happening in our lifetimes. It would also be an incredible coincidence that the climate is changing exactly at the same time we are pumping lots of carbon into the atmosphere! However, even in that case we should be avoiding the emission of greenhouse gases which are known also to increase warming – the science on this has been settled for a century- and would exacerbate this effect.

So if we are to take our mandate to care for creation seriously, or even just to live as responsible citizens of Planet Earth, we need to seriously consider reducing our carbon emissions and preparing to deal with the consequences of our past actions as a species which seem inevitably to get worse in coming decades.

I hope that all makes sense to you and fills in the background on the article.

Yours in Christ,

Colin Bell


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