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Double Inertia

The 1.5°C warming target is going to be impossible to meet

IS IT REALLY TOO LATE to keep the famed 1.5°C target alive? In my previous column, I indicated that this was the case – that it was no longer possible to halt global warming at 1.5°C above pre-industrial levels. In response, a reader wrote to tell me that such a perspective may be both exaggerated and pessimistic. I apologise, for I took something for granted: climate change inertia.

This mostly revolves around physics. The Earth’s climate system has a natural inertia – a resistance to change – due to its majestically complex nature. When greenhouse gases are emitted, they don’t immediately affect the climate. Instead, there’s a lag before temperatures adjust to the new concentration levels. In other words, even if we stopped emitting carbon dioxide, methane and nitrous oxide today, the planet’s temperature would keep rising for decades. This is why the Paris Agreement’s goal of keeping the temperature increase to 1.5°C is practically impossible to achieve.

The long lifetimes of greenhouse gases are the most glaring reason for this delayed cause and effect. Through the carbon cycle, CO2 is absorbed by plants and oceans, but it could linger in the atmosphere for a very long time (part of the CO2 emitted by Nazi tanks entering Paris in 1940, for instance, is still up there). Methane lasts for 12 years on average and some chlorofluorocarbons may live for more than a century. However, the climate’s inertia is inherent in many other phenomena as well.

As well as absorbing CO2, oceans retain more than 90 per cent of the excess heat produced as a result of greenhouse gas emissions. It’s a slow process, whereby the heat absorbed will continue to affect the climate system for centuries to come. Moreover, as ocean waters warm, they expand, contributing to sea-level rise. This rise is expected to continue even if the global temperature stabilises, due to the ongoing thermal expansion from past heat absorption.

Sea levels are currently rising because of the melting ice in Greenland and Antarctica, too. Again, even if the warming stops, the melting will continue for some time due to the heat already trapped in the Earth’s system. The reduction of ice and snow cover decreases the planet’s reflectivity, its so-called albedo. Darker surfaces, such as open water or bare ground, absorb more heat than lighter ones, leading to further warming and ice melt, a self-reinforcing – yet slow – cycle.

Forests, and vegetated areas in general, represent the other major carbon sink. However, global warming is now altering their ability to sequester carbon dioxide. Droughts, heatwaves and wildfires, which are already on a rising trajectory, can gradually taper off planetary photosynthesis, thus leading to more CO2 in the atmosphere. Warming temperatures can then lead to changes in soil moisture and composition, affecting their ability to store carbon. Not to mention the fact that drier soils tend to release additional carbon dioxide. 

James Hansen, probably the world’s most famous and outspoken climatologist, recently co-authored a paper that examines climate inertia and climate sensitivity (by how many degrees would the planet heat if the amount of CO2 doubled?) to conclude that ‘global warming will exceed 1.5°C in the 2020s and 2°C before 2050’. His estimates may outpace most other projections but they’re entirely possible. 

Hansen stresses the role of sulphate aerosols – particles injected into the atmosphere from the combustion of fossil fuels and the eruption of volcanoes, which have a cooling effect on the atmosphere by reflecting sunlight. The concentration of sulphate aerosols has recently decreased as a result of new international shipping regulations on the sulphur content of fuel. This contributed to the 2023 spike in atmospheric and oceanic temperatures. In other words, human-made pollution is masking – and delaying – the true impact of man-made warming. The paper recommends a global tax on emissions, East–West cooperation and a phase down of ‘today’s massive human-made geo-transformation.’ And here lies the second problem.

The physical phenomenon of climate inertia exists alongside societal inertia. There’s a troubling delay in implementing emission-mitigation strategies. Transforming energy systems, industrial processes and societal habits to drastically cut emissions takes time. This double inertia makes things doubly complex – and extremely worrying. Having squandered decades by postponing action, time is not on our side.

Published on Geographical Magazine, February 2024 issue


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