With magical zero emissions tomorrow, equilibrium warming in the pipeline is now 10 degrees C (18 F) in several centuries and 6 to 7 C (11 to 13 F) in 100 years.
10 Degrees C Equilibrium Warming
James Hansen is the former 32 year director of the NASA Goddard Institute for Space Studies, the de facto US climate modeling agency. He is the originator of the warming target of 350 ppm CO2, where this is the highest CO2 concentration in our atmosphere where the Earth systems our advanced civilization evolved with are stable (Hansen 2008). NASA has released a prepublication copy of his next paper, “Global Warming in the Pipeline,” submitted to Oxford Open Climate Change. (Hansen’s email list summary communications are here and here.)
What Hansen’s team tells us in “Global Warming in the Pipeline” is that evaluation of evidence from prehistory shows current modeling of equilibrium warming is understated. Equilibrium warming, or warming in the pipeline, is the ultimate temperature of Earth when our ocean and terrestrial systems come into balance with the excess greenhouse gases in our atmosphere today — with no further emissions. Even more simply put, we have emitted so many greenhouse gases so much faster than they are emitted naturally, that our oceans, soils and forests are way behind in absorbing the excess and it will take them centuries to catch up. During this “catch up” period, we continue to warm as the cool oceans and ice sheets gradually warm to balance out with atmospheric warming. Hansen’s team’s new findings show that if we were to magically halt all emissions today, and hold everything else stable, equilibrium warming in the pipeline in several hundred years is 10 degrees C (18 F) above normal, and in 100 years it is 6 to 7 C (11 to 13 F).
This warming in the pipeline is a third higher than the worst-case scenario with additional emissions, where our current warming of 1.2 degrees C above the normal is only 0.2 degrees C above the maximum range of our old climate. It’s also important to note that this experiment is totally not an achievable thing, and this is not just because there is no way we can halt all warming today. Other processes continue, like greenhouse gas absorption by our oceans, and feedback emissions from natural sources.
This warming in the pipeline is what the direct evidence says, not the models. And remember, this is with only the climate pollutants that are in the sky already and does not include any future emissions.
Equilibrium warming is the temperature of Earth at some time in the future when all of Earth’s systems have come into balance without atmosphere and with one another. It takes time for our oceans to stabilize after such a large increase in atmospheric greenhouse gases; time for our ice sheets to stabilize at a new temperature where winter snows equal summer melt, time for forests to change their species composition that determines how much sunlight the reflect back into space…
The reason why this equilibrium warming is so much greater than previously understood is that previous knowledge has always been based on climate modeling. The challenge with the models is that they consistently and significantly understate because they cannot yet robustly reflect feedbacks. (See our review of Ripple 2023 on feedbacks, Risky Feedbacks – Not In Models; Understated Solutions.)
Hansen and his team have this to say about models and feedbacks, “We do not know how well feedbacks are modeled or even if the models include all significant real-world feedbacks. Cloud and aerosol interactions are complex, and even small cloud changes can have a substantial effect. That is why data on Earth’s paleoclimate history are so valuable; they allow us to compare different equilibrium climate states, knowing that all feedbacks were in operation.”
One has to only look at how poorly modeling has projected climate impacts to understand the great risk of using modeling to base our climate policy upon. Major hurricane intensity is 50 years ahead of model projections. Gulf Stream flow reduction is 90 years ahead (here and here). The Amazon has flipped from sequestration to emissions 70 years ahead of what models show. Antarctic ice discharge has begun 100 years ahead of widespread modelling predictions (here and here). Arctic sea ice is collapsing 70 years ahead. Permafrost collapse is happening 70 years ahead. Upper ocean stratification is happening six times faster than the models estimate. Ocean acidity is 62 years ahead. Ocean temperature is warming 40 years ahead of schedule. Winter storm extremes are 80 years ahead in the Southern Hemisphere. Air temperature in the Arctic is warming up to 80 years ahead of what the models say. The average 30-year Houston rainfall is 80 years ahead of consensus projections. Sea level rise is 80 percent greater than modelled. Ocean heat uptake is half again greater than modelled. Half of known tipping points are now active up to 100 years ahead of long-held projections of consensus climate science.
Hansen’s newest findings are important because they were developed from paleo evidence, not understated climate models. The real data they used came from prehistoric evidence when our climate was in different equilibrium states. In other words, all feedbacks were fully realized and there was no further warming in the pipeline from systems not in balance with greenhouse gases. Today with atmospheric greenhouse gases wildly out of balance with Earth’s temperature, feedbacks are just beginning to occur. The modelers attempt to divine what these feedbacks will do in the future and as the long paragraph above shows, they do not do this well. It will be decades or centuries before feedbacks play out fully and our atmosphere, oceans and biosphere balance out.
Hansen’s Global Warming in the Pipeline tells us, “The stunning conclusion is that the GHG increase since 1750 now produces a climate forcing equivalent to that of 2×CO2. The human-made 2×CO2 climate forcing imagined by Charney, Tyndall and other greenhouse giants is no longer imaginary. At this moment, humanity is taking its first steps into the period of consequences. Earth’s paleoclimate history helps us assess potential outcomes.”
The article goes on, “Earth’s climate history provides reliable assessment of equilibrium climate sensitivity [or warming in the pipeline], because it allows comparison of equilibrium climate states. All feedbacks are included in comparisons of real-world equilibrium climate states. In contrast, transient climate change such as that occurring today is affected by innumerable, partially complete, climate feedback processes that occur on a range of time scales.”
The gap between climate safety and our current climate state keeps widening. We are literally only 0.2 degrees C above the maximum range of our old climate today, and the repeatedly unprecedented extremes have created disaster after disaster after disaster.
It is time to change our climate policy to one of restoration, to cool our current climate back to within the boundaries of the evolution of our Earth systems where the mayhem reverts to its former rare levels.
The 350 ppm CO2 target paper Hansen led in 2008, “Target atmospheric CO2: Where should humanity aim?” set the bar for climate restoration. In a subsequent paper in 2017, “Young people’s burden: requirement of negative CO2 emissions” Hansen and colleagues first modeled 350 ppm CO2 and found the resulting temperature at 2100 was about 1 degree C warming above normal during the mid- to late 19th century. In this landmark paper, Hansen and nine others from Columbia, Yale, University of Sheffield, Boston and Wesleyan Universities and NASA , tell us, “If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that.” They go on, “If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.”
Hansen’s Newsletter Summary:
Full paper PDF:
Podcast with co-author Lean Simmons on Hansen’s new paper.