Is it still possible to limit warming to 1.5 degrees celsius, even if we reduce carbon emissions to zero tomorrow?
Check out this answer from Consensus:
Limiting global warming to 1.5°C is still possible, but it requires immediate and stringent measures. The remaining carbon budget provides a narrow window of opportunity, and achieving this target will necessitate a rapid transition to low-carbon energy sources, significant reductions in energy use, and the deployment of CDR technologies. Policymakers must act swiftly and decisively to implement these measures and avoid the severe consequences of exceeding the 1.5°C limit.
The Paris Agreement aims to limit global temperature rise to 1.5°C above pre-industrial levels. This ambitious target requires significant reductions in carbon emissions and a shift towards sustainable energy sources. However, the question remains: is it still possible to achieve this goal even if we reduce carbon emissions to zero tomorrow? This article explores the feasibility of limiting global warming to 1.5°C based on recent research findings.
Carbon Budgets and Warming Projections
Recent studies have provided insights into the carbon budgets necessary to stay within the 1.5°C limit. According to one study, the median remaining carbon budget from January 2016 is 208 PgC, which corresponds to about 20 years of emissions at the 2015 rate1. This suggests that while challenging, it is not impossible to limit warming to 1.5°C if stringent measures are taken immediately.
Scenarios and Pathways
Various scenarios have been explored to understand the pathways that can limit global warming to 1.5°C. One study describes scenarios that limit end-of-century radiative forcing to 1.9 W/m², thereby restricting median warming in the year 2100 to below 1.5°C2. These scenarios involve a rapid shift away from fossil fuels towards large-scale low-carbon energy supplies, reduced energy use, and the deployment of carbon-dioxide removal (CDR) technologies. However, achieving these scenarios is challenging under socio-economic pathways characterized by strong inequalities, high baseline fossil-fuel use, or scattered short-term climate policies.
The Role of Carbon Dioxide Removal
The feasibility of limiting warming to 1.5°C without overshoot and without the deployment of CDR technologies has also been explored. One study finds that limiting warming to 1.5°C will require CDR or terrestrial net carbon uptake if 1.5°C-consistent budgets are smaller than 650 GtCO23. The earlier CDR is deployed, the more it can neutralize post-2020 emissions rather than producing net negative emissions. However, if the 1.5°C budget is smaller than 550 GtCO2, temporary overshoot of the 1.5°C limit becomes unavoidable if CDR cannot be ramped up quickly enough.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Gabriel Filippelli has answered Likely
An expert from Indiana University–Purdue University Indianapolis in Geochemistry, Paleoclimatology
Yes, we are nearing 1.5 degrees of warming. If we reduce carbon emissions to zero tomorrow, natural processes in the carbon cycle will slowly act to pull out the excess carbon, but these take decades to centuries. But the good thing is if we reduce emissions to zero tomorrow, temperatures will stop rising in just a few years and stabilize—so basically an immediate impact on temperature rise.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Max Callaghan has answered Extremely Unlikely
An expert from Mercator Research Institute on Global Commons and Climate Change in Climate science
No. According to the latest IPCC report (https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM_final.pdf, Table SPM.2), we are currently at 1.07 degrees of warming, and though additional warming is still locked in, even if we were to reduce emissions to zero tomorrow, scientists still estimate that there are 500 gigatons of cumulative CO2 emissions in carbon budgets that have a 50% likelihood of limiting global warming to 1.5 degrees. To have a chance of achieving the target we would need to start reducing emissions rapidly now and achieve net zero by the middle of the century.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Dennis Hartmann has answered Unlikely
An expert from University of Washington in Climatology
If we zeroed out emissions tomorrow we would likely not exceed 1.5C. This would mostly be due to zeroing out Methane emissions, whose lifetime in the atmosphere is only a decade or two. Without this unlikely zeroing in carbon release, however, as a practical matter, we are virtually certain to exceed 1.5C warming.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Adriana Gomez-Sanabria has answered Unlikely
An expert from International Institute for Applied Systems Analysis in Energy Systems, Environmental Science, Climate science
There is evidence that suggest that it is still possible to limit warming to 1.5 degree Celsius. However, actions to reach that limit have to be taken now. Pledges from countries have to go beyond the current goals and more ambitious targets are urgently required.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Adriana Gomez-Sanabria has answered Unlikely
An expert from International Institute for Applied Systems Analysis in Energy Systems, Environmental Science, Climate science
There is evidence that suggest that it is still possible to limit warming to 1.5 degree Celsius. However, actions to reach that limit have to be taken now. Pledges from countries have to go beyond the current goals and more ambitious targets are urgently required.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Aysha Fleming has answered Likely
An expert from Commonwealth Scientific and Industrial Research Organisation in Climatology, Agricultural Science, Sociology
Warming to 1.5 degrees Celsius is likely even if we reduce carbon emissions to zero immediately, that’s why we need to also sequester carbon as well as cease emissions.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Roger Jones has answered Unlikely
An expert from Victoria University in Climatology, Environmental Science, Economics
No. We can’t reduce carbon emissions to zero tomorrow but if we could, the reduction in forcing would reduce the amount of heat being trapped in the oceans. The tropical ocean would stabilise within decades. Climate has two states: forced and free – we are currently in a forced state driven by an excess of heat at the ocean surface that needs to be transported to higher latitudes. In a free state, the system relaxes, and can vary in both directions. Climate shifted from free to forced state between 1957 and 1972. Moving back to free state would be a huge win. However, due to the additional CO2 from fossil fuels climate would stabilise at higher than pre-industrial concentrations (don’t know the figure – no-one does), and there would still be some heat moving poleward in slower moving transport (ocean) and in feedbacks due to the removal of ice sheets. Removing all carbon emission would lead to concentrations decreasing and eventually slow cooling (in downward regime shifts – the last one was in 1901) but it would be slower on the way down than on the way up and would not reach pre-industrial temperatures.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Steven Sherwood has answered Unlikely
An expert from UNSW Sydney in Climatology, Atmospheric Science
We would probably avoid 1.5C if we could stop emissions now, and if we did pass 1.5 it would be only for a decade or so.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Gab Abramowitz has answered Uncertain
An expert from UNSW Sydney in Climatology, Hydrology
It’s difficult to be sure one way or another. We would certainly be in for more heating after emissions stop, but how much will depend on oceanic transport, carbon cycle feedbacks and many other parts of the system with some uncertainty. I’d argue a more relevant question is whether we have a realistic chance of avoiding 1.5ºC warming, given our abilities to manage this problem so far – I think not.
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Michael Wehner has answered Near Certain
An expert from Lawrence Berkeley National Laboratory in Climatology
Yes, for a variety of reasons. First and more importantly, let’s get real. It seems highly unlikely that the drastic emissions reductions required to stabilize the climate to 1.5 will be palatable to the governments of the high carbon emitting countries. Second, if we ever get to zero carbon emissions, we would also have zero sulfate aerosol emissions. These particles mask about 0.3C of warming that we would otherwise already have. This is partly offset by zero methane emissions that would allow existing methane to gradually oxidize into less potent carbon dioxide. And of course, the ocean time scales are long and will continue to warm by a few tenths of a degree C after zero emissions. But as the planet is already at 1.1C above preindustrial temperatures, I see no practical way to limit global warming to 1.5C
Is the 1.5 degree celsius warming locked-in, even if we reduce carbon emissions to zero tomorrow?
Richard B. Rood has answered Likely
An expert from University of Michigan in Environmental Science, Climate science
This question is full of potential controversy. I have seen it posed as reducing all carbon emissions, eliminating all carbon dioxide emissions, stopping all burning of fossil fuels, eliminating all human forcing to the climate, and several other variations. It is also true that it is not possible to do any of these things “tomorrow.” Therefore, all of these are thought experiments, and the answers to any of these can be turned to fit many purposes.
The value of the question is, perhaps, a framing of the Paris Agreement’s ambitions to limit warming to 1.5ºC. To be clear, this goal would be to limit the global average surface air temperature to 1.5ºC. There are many parts of Earth that have already exceeded this threshold.
It is possible to conceive scenarios for managing atmospheric greenhouse gas concentrations that would, arguably, lead to an equilibrium temperature that would meet the 1.5ºC goal. Some of these scenarios require overshooting 1.5ºC and then returning to it in the future. Any potentially realistic scenario requires managing other greenhouse gases and accelerated removal of carbon dioxide. In my class, I state that these scenarios are so unrealistic as to be deceptive in framing the future temperature rise.
I stated, above, that these unrealistic scenarios “arguably” meet the 1.5ºC goal. They rely on model simulations. The science-based conclusions from these models have a hierarchy of uncertainties associated with them. As the science-based knowledge from both observations and simulations is advanced, these uncertainties change. They do not always decrease. There is no doubt that these models provide solid guidance on the scale of the reductions that are needed to meet goals of 1.5ºC or 2.0ºC; however, the combination of scientific uncertainty and narrow tolerances of the scenarios to reach the 1.5ºC goal stress the credulity of the simulations.
Are we locked in? Many realize that when one bakes a cake or roasts meat, after the heat is turned off, the temperature in the center of the cake or the roast will continue to rise. Likewise, the temperature at the edge will start to decrease. The ocean has been absorbing most of the Earth’s heat, and there will be an equilibration process where the atmosphere, ocean, land, and ice come into balance. There is imprecision in the calculation of how long this will take and how much the atmospheric temperature might rise. At best, if we manage, tomorrow, to quit adding greenhouse gases, we are on the edge of whether or not we would meet the 1.5ºC goal.
Likewise, meeting the 1.5ºC goal would depend on how rapidly the oceanic and land processes which remove carbon dioxide might work. They would depend on how much the Arctic and Antarctic have been altered by warming and whether carbon dioxide and methane currently in cold storage is released.
Though we can conceive of scenarios to avoid 1.5ºC average warming, they are unrealistic and require the best-case outcome at virtually all points of uncertainty. There is no evidence-based reason to expect that we will not see 1.5ºC. I expect it to occur in the decade of the 2030s.
Though I expect to see 1.5ºC rise, that in no way suggests that we should let up on our efforts to decarbonize our energy production as soon as possible. 1.5ºC warming is dangerous to many. Where we are headed, greater than 2.0ºC, is dangerous to many more. We need to be realistic about the disruption and adaptation we are facing and to discourage the false choice of 1.5ºC versus the “most dangerous effects.”