Scientists pinpoint how much time we have left before global warming reaches critical levels

Global warming is the most pressing environmental threat that humanity faces today. The harmful effects that it has brought about are visible, with glaciers melting, sea levels rising and wildfires ramping across the Earth. If global warming continues at its current rate, the Earth will soon be too hot to live on. Up until now, the Intergovernmental Panel on Climate Change (IPCC) used the General Circulation Models (GCMs) and predicted this dangerous warming (1.5 °C increase since pre-industrial levels) could occur anytime between 2030 until 2052. A global warming of 1.5 °C will likely bring about very extreme temperatures in many regions, increasing the frequency and intensity of heavy precipitation, and droughts in other regions.

Melting ice at sea by Mellissa Bradley via Unsplash

These sorts of  predictions are made by climate models like the GCMs. Climate models simulate interactions of different factors with the Earth’s climate, such as the atmosphere, ocean, cryosphere (ice), land surface and the Sun. These are known as factors within the climate system. As with any computational model, there are always uncertainties involved because what happens in real life is often much more complicated than anticipated. For example, in GCM-based simulations, if the CO2 concentration is doubled, the model would predict a global average temperature increase between 1.9 and 4.5 °C, which is a relatively large range – the lower bound suggests a moderate climate change whereas the higher end is catastrophic. 

This vast difference suggests room to ameliorate the current climate models, and has, at the same time, caused climate sceptics to argue that IPCC projections are untrustworthy merely because they are GCM-based. While this conclusion is unwarranted, it would be beneficial to devise GCM-free models using different methodologies to compare findings and minimise uncertainties. After all, the GCM-free approach yields comparable results albeit with less uncertainty. 

‘Our approach allows climate sensitivity and its uncertainty to be estimated from direct observations with few assumptions’

Raphael Heber

Recently, scientists published findings from their newly-designed climate model, the Scaling Climate Response Function (SCRF). This state-of-the-art technique uses historical climate data to predict the future. ‘Our approach allows climate sensitivity and its uncertainty to be estimated from direct observations with few assumptions’ said co-author Raphael Hebert, a former graduate researcher at McGill University, now working at the Alfred-Wgener-Institut in Potsdam, Germany.

The study, published in Climate Dynamics, projected the Earth’s temperature right up until the year 2100 and further narrowed down the time estimate for the Earth to warm up by 1.5 °C, to be between 2027 and 2042. This is a much narrower window than estimated by the GCMs (between 2030 and 2052). The SCRF projections up to 2100 were calculated  completely independent of the GCMs, but were found to agree wholeheartedly with them. The only discrepancy was that the new model was capable of pinpointing the exact moment more precisely.  This effectively eliminates one of the key climate sceptic arguments that GCM-based projections are unreliable. The more accurate range also rings a bell for governments and policymakers to mitigate challenges brought about by global warming and to take adaptive measures. 

This effectively eliminates one of the key climate sceptic arguments that GCM-based projections are unreliable.

However, the SCRF model isn’t perfect. It assumes a linear stationary relationship between climate forcing (external factors affecting the climate e.g. human-caused fossil fuel combustion) and temperature. This relationship, however, could also be nonlinear (a curve) which could arise as the system evolves. This could happen at any point in the foreseeable future, which would negate findings from the linear model. In the future, it would be critical for scientists to improve these projections in such aspects to improve data quality. Future work should also build climate models at a regional scale, having overcome the mentioned uncertainties surrounding SCRF.

To prevent this dangerous 1.5 °C warming on our planet, future emissions will be required to undergo drastic cuts. The IPCC have laid out a set of ‘very stringent’ guidelines for doing this, known as the Representative Concentration Pathway (RCP) 2.6, for which the scientific study found a 46% probability to remain under said limit. It requires CO2 emissions to start declining by 2020 and go to zero by 2100. Other greenhouse gases such as methane will also have to decline significantly by 2100 under this pathway. Currently, the goal of the Paris Agreement is to follow a similar pathway, known as the RCP 1.9 which is even more stringent.  

In conclusion, not only did the SCRF yield similar findings, but also provided even more accurate results than the GCMs. Alternative climate models are helpful to scientists, so that they can comprehensively understand the imminent challenges that are yet to come. Only then, will more policymakers and global leaders be convinced to take more rigorous actions.

Written by Ian Yang and edited by Ishbel Dyke.

Ian Yang is a 3rd year Chemistry student. Find him on LinkedIn @Xi (Ian) Yang

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