Forecasts for global warming have become more accurate

If “one” is the most lonely number, then “two” is the worst. Mankind should not allow global temperatures to rise by 2 degrees Celsius, according to the Paris climate agreement. The crossing of this line will mean a catastrophe. Uncertainty is a particular problem in the process of climate study. We can not predict what will happen and when, because there are thousands of variables in this massive and intricate system. But this can change. The other day in the journal Nature, an article appeared in which researchers stated that they managed to reduce the uncertainty of the key metric of climate change by 60%, narrowing the range of possible warming from 3 to 1.2 degrees Celsius. In addition, the new data does not draw such a terrible picture of the climate crisis. You can even call it moderately optimistic.

This metric is called the equilibrium sensitivity of the climate, but do not be intimidated by such a name. “In fact, this is the level of global warming that we could forecast if we doubled the carbon dioxide in the atmosphere and gave the atmosphere and climate an equilibrium with carbon dioxide,” says lead author Peter Cox, studying the dynamics of the climate system at the University of Exeter.

Over the past 25 years, the generally accepted range of potential warming has been between 1.5 and 4.5 degrees Celsius. This is a fairly large range, given that even one degree can change the world. This, for example, is 5-10% less than the precipitation during the dry season in the Mediterranean, in the south-west of North America and in southern Africa. Bring warming to 3 degrees – and the Earth will lose 100,000 square kilometers of wetlands and drylands.

We are talking about an incredibly complex system with an entire galaxy of variables. Scientists-climatologists are working to narrow the equilibrium sensitivity of the climate or, as they put it, limit. “The consequence of the fact that it is so big is that one camp claims that the warming will be minimal and should not be worried, and the other – that we should be worried that the warming will be serious, and that means catastrophes are coming, and we will not do anything” .

You can try to narrow this range by studying historical warming events. But Cox and his colleagues simply ignored the trend of warming. “It would seem that the most obvious thing to do is to study the climate change that has already happened. But it turns out that this is a bad limiter for the equilibrium sensitivity of the climate, primarily because we do not know how much additional heat we have included in the system. ”

Of course, scientists know quite a lot about the classic greenhouse factors of climate change, carbon dioxide and methane. But humanity pumped other particles into this system, and they cooled the system. Plants burning fuel, for example, emit sulfur dioxide, which leads to the formation of particles in the atmosphere, which repel the energy of the sun back into space. (Incidentally, this method may help us cope with climate change, not by burning fuel, of course, but by adding particles to the atmosphere).

The scientists’ approach to this research was to combine the 16 models in total – not with the warming trend, but with how the temperature fluctuated from 1880 to 2016. “In fact, these models tell us about the relationship of temperature variations and the sensitivity of the climate, and observations tell us about the temperature variations in the world,” says Cox. “Together they allow us to better assess the sensitivity of the climate of our planet.”

Now to the numbers. The researchers determined the climate sensitivity range of 2.2-3.4 degrees (compare this with the generally accepted 1.5- at the lower end would definitely not be a good future for our planet.) (For every degree of warming, one can expect 400 -The percentage increase in the area burned by forest fires is not exactly ideal.) Scientists say that the probability that warming will be less than 1.5 degrees is less than 3%, but the probability that warming will exceed 4.5 degrees, less than 1% and this is good news.

Climatologist Reto Knutti asks an interesting question: what is the probability that our models will have an error? Is it less than 1%? “I would say that there is more than one chance out of a hundred that in all models something is missed, because our understanding is not complete.”

It’s not that these scientists do not know much about science. Just a global climate is an extremely complex problem. No scientist can understand all the details of this complex system – changes in vegetation, small-scale hydrology, every single weather phenomenon, whether it’s a hurricane or a tornado. Therefore, scientists are looking for simplified descriptions of these small-scale events. “In the case of clouds, for example, you say: well, the higher the humidity, the more likely the rain, and if the saturation exceeds 95%, it rains,” Knutti says. “This is a special way to describe the rain without going into a detailed description of the formation of rain, because you are not capable of it.”

Questions are becoming increasingly uncertain when solid observational data ceases to be solid. Take, for example, the temperature of the ocean surface. Historically, different vessels used different methods, perhaps they threw a thermometer in a bucket of water or removed the temperature of the water from the engine in the engine room. Here you can calculate the discrepancy – the method with the bucket is inaccurate, because the water evaporates, and with the engine – because it heats the water – but there is always a chance to lose sight of something.

Therefore, scientists work with what they have, and with each new study of a rapidly changing climate, their understanding is growing. “We are getting better,” Knutti says, “but we will never be perfect. The chance that something is incorrectly calculated, systematic, we can not exclude it. ”

However, there are grounds for optimism: although the research conducted last summer showed that humanity has virtually no chance of raising the temperature by 2 degrees, new restrictions change this forecast. Now we can avoid such an increase, although, of course, we need to make some efforts.