September 25, 2019

How bad will climate change be? Well: I’m writing this in the middle of an absolutely biblical rainstorm. It is hammering it down. Weather is not the same as climate and all that, but it is very easy to believe in climate change when north London appears to be experiencing a monsoon.

The argument over whether man-made climate change “caused” it is a grimly philosophical one that very quickly gets lost in the weeds of what it means to “cause” something. If I put weights in a die, so that it’s more likely to roll a six, and then I roll a six, did the weights cause the six? It might have rolled a six anyway. But what most of us will agree is that climate change is not only making the world warmer – each of the last three decades has been the hottest on record – it’s also making unusual weather more likely: droughts in some places, floods in others; higher average temperatures and more frequent extreme heatwaves. This is uncontroversial among climate scientists; it’s all from the 2018 IPCC special report.

What’s also relatively uncontroversial is that it’s going to carry on. Again referring to the IPCC report: if we literally stop producing any carbon emissions next year, then it is likely that the global mean surface temperature will continue to rise about another 0.5°C, to a total of around 1.5°C above pre-industrial levels. That’s not going to happen, so we’ll probably see a rise of about 2°C, perhaps more. The warming will likely be greatest in the high northern latitudes, so the Arctic ice sheet will suffer, more than it already has. Sea levels will rise. Weather patterns will change, causing unseasonal droughts and floods, affecting ecosystems and crop growth. Again, this is all pretty uncontroversial – have a read of the IPCC special report’s summary for policymakers.

The 2014 IPCC report warns that coastal areas will face greater risks of flooding and submergence. Many species and ecosystems will come under pressure as species move with the new climate. While some crop growth may be positively affected – warmer temperatures and greater carbon dioxide concentrations will help some plants – more will be negatively affected. It is likely that heat waves and fires, drought and starvation, and new disease vectors will kill many people. Migration, and wars over newly scarce resources, could kill people as well.

I’m stressing that this is all from the IPCC predictions. When people refer to “the science”, they’re usually referring to the IPCC; I don’t know if predictions of war are “science” exactly, but they’re reasonable forecasts made by respected domain experts. And it is bad; the very likely outcome is that climate change will have devastating impacts on humans.

But the question I think is worth asking is: how devastating? How many people will die? There was a ridiculous claim by Roger Hallam of Extinction Rebellion the other day that “the science” says six billion people will be killed by climate change this century. That is not something supported by mainstream forecasts.

The World Health Organisation, working off IPCC resources, suggests that between 2030 and 2050, there will be around 250,000 excess deaths per year due to climate change, caused by heat exposure among the elderly, diarrhoea, malaria, and childhood malnutrition. I think, and the WHO acknowledges, that could well be an underestimate.

The IPCC suggests, quoting a forecast of future crop growth, that by 2050, a world of unmitigated climate change could have up to 20% more malnourished children than in a world without climate change: around 138 million instead of 113 million. Both of those figures are smaller than the number of undernourished children around in 2000 when the forecast was made, about 148 million, but it’s a serious problem. Something like 3.1 million children die a year from causes related to malnutrition, about 2% of the total of underweight children. On a very naive analysis, having 138 million instead of 113 million underweight children means about 500,000 children dying a year from that alone.

The Climate Impact Lab, a collaboration between climate experts from various institutes including the universities of Chicago and California, forecast that climate change could cause a net 1.5 million deaths per year by 2100, if emission trends continue.

These deaths will be disproportionately focused in the developing world, where extreme heat and food shortages are already a major problem.

I think it’s worth putting into context, though. Let’s imagine that the WHO forecast is an underestimate and the Climate Lab forecast is closer to the truth, that about 1.5 million people will die per year who would not have died otherwise.

For comparison, diabetes directly causes about 1.6 million deaths a year, according to the WHO. Obesity kills about 2.8 million. Road traffic accidents kill about 1.25 million. Smoking, eight million. That’s roughly the sort of magnitude of problem that we’re dealing with.

Road traffic accidents, obesity, smoking and diabetes are huge societal problems. They deserve the many billions of pounds spent every year worldwide combating them. But they’re not existential risks. We don’t tend to think that we need to drop everything, derail our economies, and stop the world getting richer to prevent them.

There are counterarguments to be made, which have genuine merit. First, deaths are just one part of the problem: climate change will also cause economic damage, food insecurity, mass migration and various other bad things. That’s absolutely true, but it’s also true (in different ways) of the other problems I mentioned: the deaths they cause are just the tip of an iceberg of suffering that they cause.

More relevantly, there is no realistic possibility that smoking will suddenly spiral out of control and become far worse than we expected, or that diabetes will enter some positive feedback loop and start affecting dozens of times more people than we thought. But the inherent uncertainty in climate prediction means that we could, in fact, be entirely wrong about what happens.

The IPCC forecast suggests that if there is very little reduction in carbon emissions that temperatures will rise by a total of around 2°C above pre-industrial levels, but the climate is the archetypal chaotic system. It could be that they’ve overestimated, or it could be that they’ve underestimated. There is a (very small) possibility that climate change leads to the sort of utterly devastating outcome that Roger Hallam of Extinction Rebellion imagines.

This is absolutely true (when I was researching the existential risks bit of my book, someone pointed out that if you think climate models are wrong, you should logically believe that they’re just as likely to be underestimating as overestimating. You should be more worried about the chance of really bad outcomes than people who believe the IPCC). And it’s a good reason to treat the risks of climate change more seriously than the risks of, say, smoking. And that means reducing emissions.

But it’s also worth noting that the IPCC itself – “the science” that we all like to appeal to – thinks that even under “climate change” scenarios, global malnutrition will be less of a problem in 2050 than it is now, because of economic growth and technological improvements. It’s also clear that low-income countries are more vulnerable to the impacts of climate change than are rich countries: extreme weather events in rich countries kill fewer people than equivalent ones in poor countries; poorer countries are more reliant on agriculture; rich countries are more able to adapt because they have the cash reserves and infrastructure to do so.

So reducing emissions is good, but so is helping poorer nations grow in ways that improve their ability to adapt to climate change. And climate change will slow economic growth, but, according to the IPCC, the impacts of “drivers such as changes in population, age structure, income, technology, relative prices, lifestyle, regulation, and governance are projected to be large relative to the impacts of climate change”.

It’s also worth remembering that climate change is only one kind of environmental degradation – we could be pushing the oceans towards some sort of awful tipping point through overfishing, for instance, and plant fertilisation might be under threat from the apparent collapse in insect numbers. We seem to be going through a global mass extinction event, caused by humans. Humans are having a serious and negative impact on the environment and it’s important to acknowledge it, and to do something about it.

But we need to keep it in the correct context. “The science” seems, roughly, to say that climate change is going to be awful; that it will kill many people; that it will cause economic hardship and lost productivity and great suffering in much of the world. Roughly speaking, as much suffering and death and hardship as diabetes, or smoking. We are facing a challenge of that sort of order of magnitude. Claiming that it will kill billions, or destroy our lives utterly, is not quoting “the science” any more than it would be to say it’s a Chinese hoax.