We’re edging closer to exceeding 1.5°C of warming globally, and scientists will soon gather to understand the implications of missing our climate change targets.
The first-ever Overshoot Conference in Austria will discuss how we might recover our climate targets through mitigation or carbon removal, and also what destructive climate effects might come from exceeding them. The conference begins on Tuesday 30 Sept.
The SMC asked local experts about climate overshoot.
Dr Andy Reisinger, independent climate scientist, comments:
What are the chances we’re headed towards an overshoot of 1.5 degrees warming?
“It’s inevitable by now that we will exceed global warming of 1.5 degrees within the next 5 years or so. There is no credible scenario left in which we could still avoid this.
“However, “overshoot” as defined by the Intergovernmental Panel on Climate Change means “exceed and decline” the 1.5 degree target. We will exceed 1.5 degrees, it’s an entirely different question whether we will take the actions necessary to bring temperature back down to 1.5 degrees again during the 21st century. We know what we would need to do, but that depends on collective social and political will. So “overshoot” in the scientific use of the word is both a threat and a promise of corrective action.”
What will be the worst climate effects of an overshoot?
“There is no single worst effect of climate change, but a rather comprehensive set of compounding pressures. Some ecosystems are under extreme stress already, directly linked to global warming – the great Barrier Reef is a key example, and many coral reefs are likely to degrade rapidly as global warming continues to climb. The frequency and intensity of many extreme weather events – floods, heat waves, and droughts in some regions – will continue to increase. Sea level will continue to rise and accelerate: the rate of rise during the 20th century was about 2cm per decade, and it’s now at more than 4cm per decade.
“Higher temperatures will further accelerate this rise through the loss of glaciers and ice in polar regions and could destabilise the polar ice caps and ocean currents. Bringing the temperature back down again could reverse some of those effects and slow down others.”
Is it still worth mitigating climate change if we’re going to overshoot?
“We know that risks and damages from climate change increase with every fraction of a degree – the more the planet heats up, the bigger the mess. It’s not a binary situation where everything is fine below 1.5 degrees and all is lost above that.
“If we manage to limit peak warming to 1.7 degrees that would still be a lot better than if we limit warming to only 2 degrees, let alone somewhere closer to 3 degrees under current policies. Every further bit of warming that we can avoid, even if it’s above 1.5 degrees, will help avoid or a least limit escalating damages from climate change. Every year, every tonne of emissions we can avoid matters.
“And the less we allow global warming to climb further, the greater the options we have to bring global warming back down to 1.5 degrees again.”
Can we remove CO2 and undo warming once we’ve gone past 1.5 degrees?
“There are many ways in which we can remove CO2 from the atmosphere. Some of it we’re doing already, by planting trees on land that didn’t contain trees before. The challenge is to ensure these trees keep standing for many generations to come, and what land to plant them on. We also know in principle how to capture CO2 from the atmosphere directly and to inject CO2 back into the ground so that it stays there.
“The main barrier is the scale at which we would have to do these things to make a meaningful difference. To achieve a decline in global temperature, we have to remove (much) more CO2 from the atmosphere than we still emit. That means we not only would need to remove hundreds of billions of tons of CO2 globally, but also minimise how much CO2 and other greenhouse gases we still put into the atmosphere every year in the first place.”
Do we need to change how we adapt to climate change if we’re going to exceed 1.5 degrees?
“Adapting to climate change always has to prepare for a range of outcomes. Our existing infrastructure in many cases is not even good enough for the current level of warming, and will be more and more compromised as temperature continues to climb.
“Adaptation is not about planning for the best estimate of global warming, let alone wishful thinking, but to ensure flexibility and preparedness for a wide range of potential outcomes. That will definitely need a lot more effort and coordinated actions. But infrastructure alone will not save us, it’s also a question of governance and institutions that can deal with increasing disasters and support affected communities, and help them deal with increasing risks.”
Conflict of interest: Dr Reisinger is an NZ Climate Change Commissioner but these comments are made in a personal capacity. He was the vice chair of the IPCC WGIII 6th assessment report, and is the lead author of the upcoming 7th assessment report. He is attending the Overshoot Conference in Austria.
Dr Rebecca Peer, Senior Lecturer Above the Bar, Civil and Natural Resources Engineering Department, University of Canterbury, comments:
What are the chances we’re headed towards an overshoot of 1.5 degrees warming?
“The chances of overshooting the 1.5-degree warming target are high, especially if we continue to accelerate our total greenhouse gas emissions year after year. In fact, last year (2024), we experienced an average surface temperature increase across the world above 1.5 degrees for the first time. If we, both as a global community and as individual nations, do not come together to curb our emissions, we will likely overshoot the 2-degree target as well.”
Why is it still worth mitigating climate change if we’re going to overshoot?
“This means it is still very much worth mitigating emissions as much as possible. We urgently need to transition away from fossil fuels. Every additional molecule of greenhouse gases that we emit to the atmosphere will contribute to climate change for decades to come. To help with this, we need an energy transition that focuses on renewable electricity, energy efficiency, and non-fossil-based fuels where appropriate. We also need to think about how we design our cities, how we get around, and how we can support decision-making for climate action from the local to the international level.”
Conflict of interest statement: Dr Peer receives funding from MBIE to research energy transitions and carbon removal.
Associate Professor David Dempsey, Department of Civil and Environmental Engineering, University of Canterbury, comments:
Can we remove CO2 and undo warming once we’ve gone past 1.5 degrees?
“It is possible to pull CO2 back out from the atmosphere – after all, trees do this all the time. But it’s usually cheaper to avoid CO2 emissions in the first place by switching to an alternative technology, like replacing a coal boiler with biomass. But for some industries, like cement production or air travel, the zero-carbon alternative is prohibitively expensive or doesn’t exist.
“So, you might choose to keep these industries but offset their emissions by burning biomass and storing the CO2 underground (called BECCS), crushing a reactive rock that strips CO2 from rainwater (called enhanced weathering), or some other carbon-negative process.
“Pulling CO2 levels back down makes sense in theory, but removal technologies would need to be massively scaled up across the world. Global emissions are like a huge ship changing course, an about-turn takes time – and carbon removal would help during that shift.”
Conflict of interest statement: I receive funding from MBIE for research into Carbon Dioxide Removal technologies.