Cutting emissions may not be enough to stop global warming

12 November 2020

New paper shows Arctic may continue to melt even if we cut climate emissions. Large scale carbon capture may be necessary to halt global warming.

In a study published in Nature Scientific Reports, Professor Emeritus Jørgen Randers simulates the global climate between year 1850 and 2500. He estimates that global warming will continue for hundreds of years, even if we reduce climate emissions to zero.

If manmade climate emissions peak in 2030 and we reduce them to zero in 2100, the study estimates the global temperature will increase by 3°C in year 2500, compared to 1850. Sea levels will increase by 3 meters.

If we had cut all manmade climate emission by 2020, Professor Randers’ model shows global temperature would still increase by 3°C in 2500, and sea levels would increase by 2.5 meters compared with year 1850.

To stop this long-term increase in temperature, we would have had to eliminate climate emissions already in the 1960s or 1970s.

May cost 1-2 percent of global GDP

- The reason temperatures continue to increase after year 2100 even when we stop climate emissions is that arctic sea ice and permafrost will continue to melt. When ice melts, it makes the surface of the earth darker. Where ice reflects light and heat from the sun, darker materials such as earth and water absorb heat and increase global warming, says Randers.

Ice and permafrost also contain climate gases such as water vapor, methane and CO2. When the ice and permafrost melt, these gases are released to the atmosphere. This may cause global warming to continue, even if we eliminate all climate emissions from human activity such industry and air travel.

- Luckily, this development can be stopped through strong climate action. We must halt all use of coal, oil and gas by 2050, and implement large scale removal of CO2 from the atmosphere in the following 100-150 years, says Randers.

To counteract long term temperature increase, we may have to capture and store as much as 33 gigatons of CO2 from the atmosphere each year. That means restoring vast amounts of forest and land, developing and building carbon capture and storage plants, and making the earth’s surface brighter.

- It is an enormous task, but it is important to emphasize that we can do it. We estimate we will need to spend between 1 and 2 percent of global GDP. This includes moving 1-2 percent of the global workforce, and 1-2 percent of global capital to carbon capture and storage projects, says Randers.

An appeal to climate scientists

The study has sparked debate among climate scientists about the model used, and about how to communicate climate science.

Randers is open about the fact that other climate models are more comprehensive than his own, and may uncover new knowledge about how to stop Arctic melting. He has a clear message to other climate scientists:

- Climate action is urgent. Please recreate this study in other climate models, so we can get a clearer picture of what we need to do to reach the Paris goals. Nothing would make me happier than learning my study overstates the effect of Arctic melting. First we need to take the problem seriously and collect all the information we can.

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