Bad News — The World is Getting Even Hotter Than We Thought
Researchers forecast higher chance of more warming in new climate models
Global warming has always been incredibly difficult to model. Since the 1970s, scientists have predicted that a doubling of atmospheric CO2 would lead to a temperature increase of 1.5–4.5 degrees Celsius over pre-industrial levels. Since then, many researchers have attempted to revise this estimate, but it has been extremely difficult to shrink this range.
This week, our models got a little bit better…but not in a good way. Researchers now predict that a doubling of atmospheric carbon dioxide is very likely to lead to 2.3–4.7 °C warming. That may seem like a minor adjustment, but it has massive implications.
Why does this matter?
Imagine a doctor said that if you maintained your current diet you were going to gain between 15–45 lbs in the next year. That is a really wide range! 45 lbs sounds really bad, but 15 lbs isn’t terrible. A couple months later, you go back to the doctor and they revise their estimate to 23–47 lbs. That range is still large, but our best-case scenario is much worse. Now we need to make even larger diet adjustments to avoid substantial weight gain. In the case of climate change, a revised range of 2.3–4.7 °C means that emissions targets might have to be even lower to avoid catastrophic global warming.
It should be remembered that the 2.3–4.7 °C figure is an average, and is not uniformly distributed across the globe or through the year. Some areas are hit much harder than others. Going back to our weight gain analogy, it would be like all the extra fat ending up on your stomach, rather than spread throughout the body. Scientists predict that the areas of the globe that will be hardest hit by global warming are likely the coldest regions during the periods. This is shown very clearly in the following figure from the Intergovernmental Panel on Climate Change (IPCC), illustrating what 1.5 °C and 2 °C warming are predicted to look like in practice.
Red areas represent regions that are predicted to experience the most warming. According to the IPCC, they expect the warming will be most intense close to the North and South Poles. This is bad news for the ice caps.
Why was the temperature range revised?
The report highlighted two main factors to explain why the researchers narrowed the temperature range. The first phenomenon is straightforward: the current temperature is about 1°C warmer than pre-industrial levels. It is very hard to create a model that shows 1 degree of warming now, but only gives us 1.5 °C when CO2 levels reach double pre-industrial levels. Using our weight gain analogy, if you have gained 10 pounds in the first two months of the year, it is pretty hard to believe that you will only gain 15 pounds by the end of the year following the same diet.
Feedback loops are the second factor in the revised estimate, though this is a bit more complicated. A feedback loop takes place when a phenomenon has the potential to reinforce itself. Take the example of ice loss in the arctic. Ice is white, which is reflective, meaning that light that hits the ice is largely deflected out into space. As ice melts it will often expose open ocean, which is darker in color, which absorbs more light, meaning more heat is trapped on earth. As more heat is trapped more ice melts, which leads to more heat capture. It is difficult to test exactly how much these loops will self-reinforce in the real world, particularly because different feedback loops will feed into one another.
Modern science has been able to better model feedback cycles like ice thaw. The report also cites increased ocean cover, and changes in atmospheric levels of ozone as some of the other feedback cycles that were considered. There is still uncertainty about these processes, but scientists have made enough progress to refine the global warming forecasts.
Why is the range still so large? Clouds are still incredibly hard to model. Cloud cover is great at shading the earth from sunlight, but they can also trap heat. Not only that, the balance of warming and cooling effects will depend on the type of cloud and the time of day. Scientists are continuing to work on this topic, but for now clouds remain the biggest challenge in our climate models.
Is it too late?
No! Dr. Marvel — one of the study’s authors — clarified this point on Twitter.
According to currently available models, we are on track to hit 560 ppm in the next 50–100 years. We still have a chance to decrease our CO2 emissions, or implement carbon capture technologies. Dramatic action will need to be taken — the coronavirus pandemic did briefly slow down CO2 emissions, but current reports indicate that some countries have already returned to pre-pandemic levels.
Hopefully, the pandemic acts as a lesson on the importance of following scientific advice, but it remains to be seen if the lesson will stick.