Getting to zero is the goal and until then the planet has a remaining ‘carbon budget’

We can expect continued warming throughout the 21st century and beyond until the level of greenhouse gases are reduced to zero.

Increasing emissions results in temperature increase, keeping them the same results in increase. The only option for long term temperature stability is zero.

Note: This is very simplified. For a more comprehensive overview of the effect of emissions on temperature, see here.

As in, all power generation, all heavy industry, all transport pretty much has to go to zero emissions by 2050.

It’s pretty much rather than definitely must for two reasons. Firstly, the Earth doesn’t wear a wristwatch with a nice neat ‘2050’ on it. In reality, we give ourselves the best shot if we reduce emissions to zero ASAP, with the middle of the century a realistic objective.

Second, net zero is not absolute zero. The Earth is made of emissions sources — cars, factories and volcanoes and sinks, which absorb CO2 — trees, oceans. Net zero means that between these sources and sinks, the net result is zero.

Putting aside negative emissions technologies for one moment, the best way to enhance sinks is to reinforce and protect the natural environment.

This leaves us with a remaining budget.

It’s like any other type of budget. How quickly you spend it determines how long it will last.

If you had $1,000 in your pocket to last a month. You have the option to gradually draw on it, or spend it all at once.

Or alternatively, Greg wants to lose 10 kg in 10 weeks. To do so he needs to maintain a calorie average balance of 2000 kCal per day.

His source is food, his sink is exercise. His budget is the average daily calories times 70 days. He begins at Day 0 and gradually loses weight at a steady pace.

Alternatively, Greg can ignore the diet for the first five weeks and to lose the same amount of weight, he must crash diet in the last weight.

In the same vein, the longer humanity waits to begin the descent to zero, the harder and more costly the task is.

At the current rate of emissions, the budget to hold warming to 1.5°C would be used up in just under 10 years, which is where these headlines originate.

Credit: @ed_hawkins
UPDATE APRIL 2022: The Financial Times has created a game that allows users to select policies in order to reach net zero

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