Although the average global temperature was warmer than the pre-industrial average by at least 1.5°C last year, it is well known that this breach does not mean that we have failed to meet the Paris Agreement goal of keeping global warming under 1.5°C. This is because the Paris Agreement's goal is for long-term warming. So how long will it take for long-term warming to breach the 1.5°C threshold? Expectedly, the answer to this question depends on how we define long-term. However, a statistical analysis shows that waiting for long-term warming to get close to the threshold might make the breach inevitable.
The Paris Agreement goal is tied to long-term warming because individual years can breach the 1.5°C threshold because of short-term factors. (AP)
The Paris Agreement goal is tied to long-term warming because individual years can breach the 1.5°C threshold because of short-term factors. In other words, one year of high warming due to freak events does not mean that we are living in a climate that is warmer than pre-industrial period by 1.5°C. That said, we have data for over a hundred years to check how long it takes for long-term warming to reach a particular threshold after its first breach.
An analysis of NASA’s GISTEMP (Goddard Institute for Space Studies Surface Temperature Analysis) dataset (it is one of the six datasets tracked by the World Meteorological Organization (WMO) and one where warming is not the highest or lowest compared to other datasets) shows that the time taken for long-term warming to become consistent at a particular threshold after the first instance of the threshold’s breach depends on how we define long-term.
HT tested each level of warming starting from 0.1°C, with increments of 0.1°C. To begin, HT calculated the first year when annual warming breached a particular threshold. Then HT found the first year when the 10-year and 20-year averages consistently started breaching that threshold. This shows that the 10-year average became consistently higher than the threshold at a median of 10 years after the first breach. On the other hand, the 20-year average became consistently higher than the threshold at a median of 15 years after the first breach. Clearly, when the world reaches long-term warming of 1.5°C is somewhat dependent on how we define long-term, something which the Paris Agreement is not clear on.
To be sure, as chart above shows, the median number is not the number taken for each breach. When earth was relatively cooler in the early twentieth century, it took very long for long-term warming to breach a threshold consistently after the first breach. It is only for thresholds starting from 0.5°C that long-term warming follows the first breach almost mechanically: reaching a threshold in the 10-year average around 10 years after the first breach and the 20-year average somewhere between 10 and 20 years after the first breach. In fact, the 20-year average reached the 1.1°C threshold in just nine years after the breach in annual temperatures, the shortest time taken by the average after its breach of the 0.2°C threshold.
What do the trends described above mean? It means that air temperatures – this is what is meant by temperatures – are warming up now more consistently than in the early twentieth century. This can be seen in the chart below. Annual temperatures had far more variation in the early twentieth century and, therefore, the long-term averages were not rising as consistently as they are now. The relatively short time in which the long-term averages breached the 1.1°C and 1.2°C threshold also means that the pace of warming in the past decade has been quicker than in the past.
The consistent and fast warming in recent years makes it clear that the breach of the 1.5°C threshold in even long-term averages is near inevitable. However, the statistical trend is not the only reason why even scientists think the breach is inevitable. The other reason is detailed by James E. Hansen (a former NASA scientist whose research raised awareness about global warming) and others in a paper published on February 3. The central argument of the paper is that Earth’s energy imbalance – the energy from the sun that gets trapped on Earth because of increasing greenhouse gases (GHGs) – got a bump in 2020 because we suddenly reduced air pollution in the North Atlantic Ocean. Reducing this pollution caused by sulphur in marine fuels means that less energy from the sun is reflected back, which has given a sudden boost to warming. While some self-perpetuating warming cycles are already working (such as melting polar ice, which leads to less sunlight reflection, which leads to more warming, and hence even more melting of polar ice), the extra warming because of less pollution can take us to long-term 1.5°C warming even faster. This breach could put us beyond a set of points of no return, forever altering Earth’s climate as we know it.
Does the paper’s argument mean that we should pollute more to keep ethe arth cool? That would, as the paper argues, just replace one kind of death with another. “Aerosol offset of GHG warming is a Faustian bargain, that is, a bargain providing present benefit without regard to future consequences. The aerosols providing a cooling benefit are also inherently dangerous particulate air pollution responsible today for several million annual deaths by respiratory, cardiovascular, and even neurological diseases worldwide; thus, as global pollution control has improved and clean energies are introduced the cooling effect of aerosols is lost: with the change of ship regulations, our first Faustian payment came due,” the paper says. Clearly, blanketing our skies with soot is not a long-term solution to preventing a warmer earth.
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