Benjamin Todd

Unplug your mobile phone charger when it's not in use.

This so annoyed David McKay, a physics professor at Cambridge, that he decided to find out exactly how bad leaving your mobile phone plugged in really is.

The bottom line is that even if no mobile phone charger were ever left plugged in again, Britain would save at most 0.01% of its personal power usage.

And that's leaving aside industrial usage and the like.

So even if entirely successful, a quick estimate shows that this BBC campaign could have no noticeable effect.

McKay said it was like trying to bail out the Titanic with a tea strainer.

Instead, that effort could have been used to change behaviour in a way that could easily have a thousand times as much impact on climate change, such as installing home insulation.

Decades of research has shown that we're bad at intuitively assessing differences in scale.

For instance, one study found that people were willing to pay about the same amount to save 2,000 birds from oil spills as they were to save 200,000 birds, even though the latter is objectively 100 times better.

This is an example of a common error called scope neglect.

To avoid scope neglect, we need to use numbers to make comparisons, even if they're very rough.

In Chapter 2, we said that social impact depends on the extent to which you help others live better lives.

So, based on this definition, a problem has greater scale, the larger the number of people affected, the larger the size of the effects per person, and the larger the long-run benefits of solving the problem.

Scale is important because the effect of activities on a problem is often proportional to the size of the problem.

Launch a campaign that ends 10% of the phone charger problem and you achieve very little.

Launch a campaign that persuades 10% of people to install home insulation and it's a much bigger deal.

There's a cartoon illustration here with a character looking in the fridge with an alarmed look while their apron is on fire as is the stove and the tea towel attached to the stove.

The room is rapidly filling with smoke and the person is saying, holy crap Susie, we're out of coriander.

It's captioned, if we cared so little about the relative importance of different problems in our personal lives.

2.