We know that the Earth's climate is warming as the concentration of greenhouse gases, such as carbon dioxide, rises in the atmosphere. And since the 1950s, NASA temperature data shows a warming of 0.8 ° C until the last decade.

It is also almost certain that humanity is causing this latest warming, but what about future warming? How do climate scientists predict the future?

A new study has been published that gives a lot of certainty about how much future warming we might expect, and this study was led by climate scientist Stephen Sherwood of the University of New South Wales in Australia, along with many other international climate scientists.

It was covered in a report by the Science Alert website on August 23.

The great unknowns

The magnitude of future warming remains uncertain for several reasons; The largest of them is unknown, and it is the amount of carbon pollution that humanity will emit in the coming decades. This is based on political and economic systems - which we can hardly predict in the coming months - not to mention the coming decades.

So scientists have developed complex models of the Earth's system to predict the future, using a variety of future carbon pollution scenarios, ranging from the option to "burn all coal reserves" to the option to "close all coal-fired power plants tomorrow."

But there is another important element of the uncertainty, which is how sensitive the Earth's climate is to carbon dioxide. Scientists call this a "climate sensitivity balance"; It represents the warming of a sustained doubling of carbon dioxide concentrations.

The equilibrium sensitivity of the climate has always been estimated in a potential range of 1.5 to 4.5 ° C. This means that when carbon dioxide in our atmosphere reaches 560 parts per million, the Earth will warm somewhere between 1.5 and 4.5 degrees Celsius, which has long been uncertain.

The magnitude of future warming depends on how much carbon pollution will emit humanity in the coming decades (Grockley)

We're in the middle of the road

The new research is the most complete investigation yet of all available evidence, and found the most likely range to be 2.6 and 3.9 degrees Celsius. Sherwood says that the "equilibrium temperature" will take hundreds of years:

"It takes a long time to fully adapt to the change in the rate of incoming energy, perhaps hundreds of years. Nevertheless, most of the warming will occur within a decade of the change. The actual warming over the next century is closely related to the extent of global warming."

How far are we heading today to doubling atmospheric concentrations of carbon dioxide? We're almost halfway there. The concentration was ~ 280 ppm before industrialization (1880 ° C) and today it is ~ 413 ppm.

And based on a slowly increasing concentration without much political action by the world, this means the concentration will double to 560 ppm by 2070; So the new study suggests that we are likely already locked in somewhere between 1.3 and 2.0 ° C in long-term warming.

We are likely already locked in somewhere between 1.3 and 2.0 ° C in long-term warming (EF Brasil)

The most optimistic scenario

The most optimistic pollution scenario in the future involves the world drastically cutting off the use of coal, oil and gas until 2050. But even doing that means it's nearly impossible to stop the global temperature from rising below 1.5 degrees Celsius, says Sherwood:

"The most optimistic scenario in the future gives us an 83% chance of staying below 2 degrees Celsius, but only a 33% chance of staying below 1.5 degrees Celsius, so staying below 1.5 degrees Celsius will be very difficult, because this scenario will require somewhat extreme measures."

The most optimistic scenario does not actually happen, so the window is closing fast also to limit the warming to two degrees Celsius given current emissions trends, says Sherwood:

"A scenario close to what we expected under current global policies gives us a less than 10% chance of staying below 2 degrees Celsius, so we basically need to greatly intensify our efforts and commitments to get a decent chance to achieve the 2 degree Celsius target."

The most likely scenario - based on the new study - and the most likely future pollution scenario is between 2 and 3 ° C by the year 2100.