• Ian Sutton

A Clunky Yet Memorable Sentence

Updated: Jul 16


IPCC conference came up with the slogan Net Zero by 2050.

The report Global Warming of 1.5°C, published in the year 2018 by the IPCC (Intergovernmental Panel on Climate Change), is important for two reasons. The first reason is that it provides a thorough summary of much of the research that had been carried out on climate change up until that time. Hence it has high credibility. The second reason for its importance is that it contains the following memorable sentence.

In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO₂ emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range). <my emphasis>

Of this statement, the journal Bloomberg Green says,

Like most statements the IPCC sets down, the most important sentence ever written is just terrible—clunky and jargon-filled. What it says, in English, is this: By 2030 the world needs to cut its carbon-dioxide pollution by 45%, and by midcentury reach “net-zero” emissions, meaning that any CO₂ still emitted would have to be drawn down in some way . . . . . . it may turn out to be the grammatical unit that saved the world. If not, it'll be remembered as the last, best warning we ignored before it was too late.

Because the phrase Net Zero by 2050 is so pithy and memorable it has been adopted by companies and governments around the world as a mission statement. Yet there is nothing inherently special about either the word ‘Zero’ or the year ‘2050’. Climate change is a process — it is not an event that takes place at a singular point in time. But the phrase ‘Net Zero by 2050’ provides an easy-to-grasp target that can be understood by people who do not spend much time studying climate change.


The danger with catchy slogans is that they can substitute for action. Therefore, it is important to look at how we are actually doing when it comes to actual CO₂ (carbon dioxide) levels. How much progress has been made in recent years, and what needs to be done to meet our “best warning”.


Human beings have walked this Earth for around 300,000 years. The chart shows that the concentration of CO₂ in the atmosphere has remained well below 300 ppm for most of that time. But then, around the year 1950, CO₂ concentrations took off. We are now at 419 ppm, and there is no end in sight.

CO2 concentration in the atmosphere for 300,000 years. Sudden rise in the year 1950.

Credit: NASA

The next chart is the ‘Keeling Curve’ — the measurement of CO₂ concentration at a site in Hawaii. It shows that the concentration of CO₂ in the atmosphere continues its inexorable, upward march. Indeed, it appears as if the rate of increase is itself increasing.


The chart overlays show the dates of key United Nations conferences and of IPCC reports. It can be seen that these events and reports have had little impact on the upward trajectory of CO₂.

Concentration of CO2 in the atmosphere for the last 70 years. IPCC and COP overlays show that these events have not had much impact.

The third chart shows emissions of CO₂ from human activities since the 19th century in gigatons (billion tons) per annum. Once more, we see an inexorable rise — starting around the year 1900, but really kicking in by the middle of the 20th century. (The value for 2021 is over 40 gigatons.)

Rate at which we are adding CO2 to the atmosphere. Need a dramatic reduction rate if we are to meet the Net Zero by 2050 goal.

The dotted line shows what we need to do in order to achieve ‘Net Zero by 2050’. To put it mildly, this will be a challenge. In words we can describe the situation as follows.

  • In 1850 CO₂ emissions from the burning of fossil fuels were negligible.

  • By the year 1950 emissions were 5 gigatons per annum. This is a significant value, but not enough to radically change the climate.

  • At that point the rate of emissions took off. Since 1950 is has increased at a rate of about 0.5 gigatons per year each year.

  • In that 70 year time span we have increased the emissions rate to its present value of around 40 gigatons per annum.

  • To meet the ‘Net Zero by 2020’ goal we need to cut emissions by 1.3 gigatons per annum. This is almost three times the rate at which we have been adding these self-same emissions over the course of the last seven decades.

Note: the above calculations omit two factors which counteract one another. The first factor is that carbon dioxide is not the only greenhouse gas. Methane is also being emitted from many sources in significant quantities. Its greenhouse impact is around 50 times greater than that of CO₂.


The second factor which is not included in the analysis is the impact of future carbon capture and sequestration projects. Although these are showing considerable promise, it does not look likely at this time that this technology will have a major impact on the overall climate picture. So, we have a great slogan, one that has been adopted by many organizations around the world. In response we see a flurry of activity, such as the rapid adoption of electric vehicles and the rise of web sites such as this one. But the reality is that we have not even started to “bend the curve”. In the words of the old English proverb, “Fine words butter no parsnips.”

17 views0 comments

Recent Posts

See All