Overshoot likely needed to keep to 1.5C rise by end of century

Could the world stay on track to keep global temperature rise to 1.5°C above pre-industrial levels by the end of this century?

Yes, with ambition it could be. But increasingly, this almost certainly implies some form of ‘overshoot’ in which the temperature rise exceeds the 1.5°C threshold before falling again towards the end of the century. If this happens, several questions are relevant, including: the duration of any excess; how far above 1.5C any overshoot could be; and consideration of what the broader environmental impacts might be.

Any excess of 1.5°C above pre-industrial levels will put increasing pressure on parts of the environment, including the cryosphere, such as here in Antarctica. Image: Shutterstock.

On Monday, April 4, the IPCC will publish the third part of its AR6 assessment, the most comprehensive review of climate science in nearly a decade. Working Group III will present the scientific evidence around mitigation: considerations on how to avoid the worst impacts of climate change by slowing the rate of greenhouse gas emissions and even removing greenhouse gases from the atmosphere that are causing the global temperature to rise.

Dr. Andy Wiltshire is the Bureau of Meteorology’s Chief of Earth System Sciences and Mitigation. He said: “According to the latest IPCC assessment, the earth’s temperature is around 1.1°C above pre-industrial levels, generally recognized as the period between 1850 and 1900. This really doesn’t give us much room for avoid breaking one of the Paris Agreement ambitions of not exceeding 1.5C.

“At COP26 in Glasgow last November, countries updated their individual commitments to reduce greenhouse gas emissions. When we add up these pledges, known as Nationally Determined Contributions (NDCs), they go some way to avoiding the worst impacts of climate change, but the analysis shows that there is hardly any chance that any of the scenarios current climate change scenarios bring us to a point where we can avoid a spike above 1.5C for a period of time without more urgent and immediate action.”

Andy and his team have been working on an academic paper using scenarios prepared by the IPCC for their SR1.5 report in 2018. Andy added: “Our study reveals that it is extremely difficult to find a scenario consistent with the promises of CoP26 that can keep the world rises above 1.5C with confidence. In this set of scenarios, meeting COP26 commitments is likely to involve a 30- to 70-year overshoot, reaching an average value of around 1.7°C before falling back to around 1.5°C by the end of the year. of century”.

Although feasible, overshoot trajectories carry additional risks of climate impacts along with apparent optimism. These include:

  • Reliance on unproven technologies at scale:
    It relies on more aggressive action to deal with greenhouse gas concentrations in the atmosphere to help bend the curve down after the temperature spike. This is likely to increasingly require the use of technologies to ‘suck’ additional greenhouse gases from the atmosphere; If greenhouse gas removal cannot be scaled, the world will stay above 1.5°C for longer.
  • Commitment to increased long-term climate risks:
    By the end of the century, sea levels will have risen more than without an overshoot due to the period of greatest warming. In addition, the Cryosphere, the world of ice, will have lost even more volume due to higher temperatures. Furthermore, some impacts, such as species loss, will be irreversible.
  • Exposure to a higher probability of passing key climate tipping points:
    While we don’t know the precise trigger points for large-scale climate tipping points, even a temporary foray above 1.5C will bring us closer to thresholds that could initiate tipping points.

Prof. Jason Lowe OBE is the Head of Climate Services at the Met Office Hadley Centre. He said: “Addressing climate change is ultimately about trying to avoid every fraction of a degree of increase in the global temperature of the earth and adapting to the fraction of warming that is inevitable. Each delay in reducing emissions increases the risks of climate impacts and increases reliance on technologies to improve carbon dioxide removal that have not yet been tested on a large scale.

“There are reasons to be optimistic. The promises made during CoP26 have further bent the curve downwards and the ratchet mechanisms of the Paris Agreement are having an effect. “However, we are increasingly looking to a future where we will have to actively remove the greenhouse gases we currently emit into the atmosphere if we want a 1.5°C warming limit.”

The Working Group III report will provide more information on the range of options available to reduce emissions, including their costs and feasibility at scale. It will also help us better understand how to develop climate-resilient development pathways that consider mitigation, adaptation and other social development needs in a more holistic way.

Andy Wiltshire concluded: “Emissions reductions are unavoidable if we are to avoid the worst impacts of climate change. Each year of delay in reaching maximum emissions further commits future generations to a technological solution that is currently untested at the scale that will be required.”

Met Office science is increasingly focused on making a net-zero resilient future a reality. Our experience can improve the deployment and operation of renewable energy generation. Our ability to simulate the Earth system provides tools that can help us better work with the natural system to absorb carbon, methane, and other greenhouse gases. Our observational data sets can help us monitor progress towards a net-zero future, with our investment monitoring approach helping to identify emission sources.

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