A new analysis has revealed that limiting climate change to target levels will become much more difficult to achieve and more expensive, if action is not taken soon.
The study from IIASA, ETH Zurich, and NCAR explores technological, policy, and social changes that would need to take place in the near term in order to keep global average temperature from rising above 2 degree C, a target supported by more than 190 countries as a global limit to avoid dangerous climate change.
This study for the first time comprehensively quantifies the costs and risks of greenhouse gas emissions surpassing critical thresholds by 2020. The findings of the study are particularly important given the failure of the recent climate negotiations in Doha to decide to increase mitigation action before 2020.
The researchers revealed that the 2 degree C target could still be reached even if greenhouse gas emissions are not reduced before 2020, but only at very high cost, with higher climate risks, and under exceedingly optimistic assumptions about future technologies.
The more emissions are reduced in the near term, the more options will be available in the long run and, by extension, the cheaper it will be to reach international climate targets.
"We wanted to know what needs to be done by 2020 in order to be able to keep global warming below two degrees Celsius for the entire twenty-first century," said Joeri Rogelj, lead author of the paper and researcher at ETH Zurich.
The team of researchers analyzed a large array of potential scenarios for limiting global temperature rise to 2 degree C above preindustrial levels, a target set by international climate agreements.
Projections based on current national emissions pledges suggest that global carbon dioxide equivalent (CO2e) emissions will reach 55 gigatons (billion metric tons, Gt) or more per year in 2020, up from approximately 50 Gt today. At such levels, it would still be possible to reach the 2 degree C target in the long term, though it would be more difficult and expensive than if near-term emissions were lower.
For instance, nuclear power would need to remain on the table as a mitigation option, or people would need to quickly adopt advanced technology strategies, including electric vehicles and highly efficient energy end-use technologies such as appliances, buildings, and transportation.
Meanwhile, coal-fired power plants would need to be rapidly shut down and replaced with other energy sources. IIASA Energy Program Leader Keywan Riahi, who also worked on the study, said, "You would need to shut down a coal power plant each week for ten years if you still wanted to reach the two-degree Celsius target."
According to the study, the only way to meet the long-term temperature target without carbon capture and storage is to ensure that emissions fall within this near-term range.
"Our analysis shows that we are very dependent on key technologies like carbon capture and storage and on land-consuming measures like afforestation and the cultivation of crops for biofuel production," said Rogelj.
"If we want to become less dependent on massive implementation of these technologies to make it below two degrees Celsius, we need to reduce emissions by 2020 and use energy more efficiently," he noted.
The new paper has been published in Nature Climate Change.