Humans may need to “wait for decades” to see the results of large emission cuts on global surface temperatures, scientists have said.


Researchers in Norway used computer simulations to analyse various scenarios that looked at the effects of rapid reductions in several types of greenhouse gas emissions, such as carbon dioxide (CO2), methane and black carbon.

They found that although large-scale emission cuts are needed to achieve the global climate goals, it may take decades before the effects of the reductions on temperatures can be measured.

The researchers estimated that even for the most optimistic scenarios, it will take at least 15 years to establish the impact of emission cuts on climate change.

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Bjorn H Samset, of the Centre for International Climate and Environmental Research (Cicero) in Oslo, who is one of the authors of the study published in the journal Nature Communications, said: “Human-induced climate change can be compared with a tank ship at high speed and in big waves.

“If you want the ship to slow down, you will put the engine in reverse, but it will take some time before you start noticing that the ship is moving more slowly.

“It will also rock back and forth because of the waves.”

The authors have done an extensive investigation of this effect and, thus, we have a better quantification of the effect than we previously had
Tim Palmer, University of Oxford

The Earth’s surface temperature has, on average, risen by 0.2°C every 10 years over the last five decades.

Climate experts have attributed this rise in temperatures to human-induced emissions of greenhouse gases.

Samset said: “If we are to reach the Paris Agreement ambition of limiting global warming to no more than 2°C – or less – the first step will be to slow down the warming process.”

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Looking at various hypothetical emission reduction scenarios, the researchers found CO2 and methane to have the biggest impact on global warming.

Study author Jan S Fuglestvedt, also of Cicero, said: “If these emissions are reduced very strongly, we will see the effect quickly.

“But if reductions follow more realistic pathways, it will, unfortunately, take longer.”

If we're going to combat climate change, we need to tackle air pollution too © Getty Images
Cutting sulphur dioxide emissions could actually speed up global warming © Getty Images

The team also analysed what would happen if air pollutant emissions such as sulphur dioxide (SO2) were reduced significantly and found that unlike soot, methane and CO2, cutting SO2 emissions would, in fact, speed up global warming.

Cicero’s Marianne T Lund, who is also one of the authors on the study, said: “SO2 turns into sulphate particles in the atmosphere, and they have a cooling effect because they reflect sunlight.”

Commenting on the research, Tim Palmer, Royal Society research professor at the University of Oxford, who was not involved in the study, said: “Fundamentally, these are not new results: just as we knew that it takes some time for the climate-change signal to emerge from the noise on the way up, we knew that it will take some time for a reduced climate change signal to emerge from the noise on the way down.


“However, the authors have done an extensive investigation of this effect and, thus, we have a better quantification of the effect than we previously had.”

In what ways are humans making the Earth less habitable?

In quite a lot of ways, I’m afraid. Humans have thrived on the Earth for more than 200,000 years, but we have caused significant environmental damage – threatening the basic resources needed for the survival of our species, including water, air, soil and food.

By burning fossil fuels, we’ve sparked a rapid increase in global temperatures, which is predicted to cause a raft of issues from rising sea levels to more intense droughts and heatwaves. Intensive agriculture, deforestation and overfishing have damaged ecosystems and threaten many plant and animal species that we – and other species – rely on. We’ve contaminated our air and water with harmful gases, heavy metals, plastics and other pollutants. A growing population could exacerbate the problem.

But all hope is not lost. Tangible solutions to slow or even halt these trends are within our reach. Clean energy sources promise to replace fossil fuels; more sustainable agricultural practices might ensure our planet continues to feed us; and less wasteful consumption could preserve precious resources such as water.

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Alexander McNamaraOnline Editor, BBC Science Focus

Alexander is the former Online Editor at BBC Science Focus.