Humans will have to 'wait decades' to see the effects of emissions cuts

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 global warming.

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

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

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

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.’

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.’

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