Dealing with probabilities

There are probabilities in climate science that are not acceptable. Here is why.

A probability describes the likelihood that a certain event will occur, with 100% indicating that the event will definitely occur, and 0% indicating that the event will very likely not happen ever. Probabilities thus give us some idea about the security of a decision we take.

For example: In Germany, people who play lottery have a chance of 1:140 million to crack the jackpot. Even though this probability is incredibly low, thousands and thousands of people keep hoping to win one day.

Let’s take another example: the likelihood that a given airplane will crash is extremely low, about one out of 2 – 3 million. This probability does not change with the number of times a person is boarding an aircraft; each time the probability of crashing stays the same. That’s why even huge airplane crashes do not deter most of us from flying – after all, the likelihood of dying in an airplane crash is extremely low. Still, many people prefer driving over flying – mostly not due to reasonable worries about higher CO2 emissions from airplanes, but due to the unreasonable thought of being safer in a car – even though the number of deaths from car accident far exceeds the number of deaths from airplane accidents. For example, in 2000 the number of deaths due to traffic accidents in the US was a sobering 41.821 (Forbes), with fewer than one thousand from airplane accidents

It is well known by social scientists that our risk perception often does not match the true risks we are willing to take. We, as single individuals, mostly feel as if probabilities do not include ourselves. Such a perception is quite worrisome, especially when our decisions do not only affect us personally, but also others. Let’s take a test:

How worried are you about getting breast cancer?

Worried? Actually, I wasn’t worried at all. But in fact, the probability of an US American women to be diagnosed with breast cancer at some time during her life-time is 12.7% (National Cancer Institute). That means, that on average more than 10 out of every 100 woman in the US will be diagnosed with breast cancer. That is kind of scary. So you better send all your female friends older than 40 to get a mammogram rather today than tomorrow. It would be really unfortunate if this disease would kill a friend, only because she was too lazy and uninformed to act in time, or because you were too shy or polite to speak up.

Now what if there were a 25% chance of dying from a disease that could be prevented if you went to the doctor in time? That means, what if there were a 1:4 probability of dying, less than the chance to get a certain number on a dice. Ok, sorry, silly question. I know what every reasonable person would do.

So…how come that a 75% chance of staying within the 2°C warming limit is considered a „likely chance“(see Question 24 here), and that it is therefore OK to emit 1000 GT of CO2 between 2000 and 2050 (see study at PIK)? Please note that

100 – 75 = 25

So  we would have a 25% chance (with a range of ca 10 – 40%) of NOT staying below a 2°C warming, and thus of very likely passing irreversible tipping points. Do media headlines really grab the almost terrifying chance of NOT making it, such as the one in Reuters: „World can burn almost 25% of world coal, oil, ’safely‚“?

It would be really unfortunate if we would pass tipping points, only because we were too lazy and too uninformed to act in time, or too shy or polite to speak up.

If you are reading this portal regularly, you might have noticed that this entry is somewhat similar to this one. I wrote this second entry, as I feel that it is of utter importance that we better understand the probabilities we are talking about, to better understand the immense urgency to act; and to be more motivated to demand effective action from our politicians.

We must not be satisfied with half measures.

Maiken Winter

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