Aug 13, 2025 04:37 PM
https://www.breakthroughjournal.org/p/wh...astrophist
EXCERPTS: Recently, in an exchange on X, my former colleague Tyler Norris observed that over the years, my views about climate risk have evolved substantially. [...] Norris is right. I no longer believe this hyperbole. Yes, the world will continue to warm as long as we keep burning fossil fuels. And sea levels will rise. About 9 inches over the last century, perhaps another 2 or 3 feet over the course of the rest of this century. But the rest of it? Not so much.
[...] At the time that we published Break Through, I, along with most climate scientists and advocates, believed that business as usual emissions would lead to around five degrees of warming by the end of this century. As Zeke Hausfather, Glen Peters, Roger Pielke Jr, and Justin Richie have demonstrated over the last decade or so, that assumption was never plausible.
There have been some revisionist claims that the reason for the downgrading of business as usual warming assumptions is due to the success of climate and clean energy policies over the last several decades. But five degrees of warming by the end of this century was no more plausible in 2007, when Break Through was published, than it is today. The class of scenarios upon which it was based assumed very high population growth, very high economic growth, and slow technological change. None of these trends individually track at all with actual long term global trends. Fertility rates have been falling, global economic growth slowing, and the global economy decarbonizing for decades.
Nor is there good reason to think that the combination of these three trends could possibly be sustained in concert. High economic growth is strongly associated with falling fertility rates. Technological change is the primary driver of long term economic growth. A future with low rates of technological change is not one that is consistent with high economic growth. And a future characterized by high rates of economic growth is not one that is consistent with high rates of population growth.
As a result of these dynamics, most estimates of worst case warming by the end of the century now suggest 3 degrees or less. But as consensus around these estimates has shifted, the reaction to this good news among much of the climate science and advocacy community has not been to become less catastrophic. Rather, it has been to simply shift the locus of catastrophe from five to three degrees of warming. Climate advocates have arguably become more catastrophic about climate change in recent years, not less.
This is all the more confounding given that the good news extends well beyond projections of long term warming... (MORE - details)
EXCERPTS: Recently, in an exchange on X, my former colleague Tyler Norris observed that over the years, my views about climate risk have evolved substantially. [...] Norris is right. I no longer believe this hyperbole. Yes, the world will continue to warm as long as we keep burning fossil fuels. And sea levels will rise. About 9 inches over the last century, perhaps another 2 or 3 feet over the course of the rest of this century. But the rest of it? Not so much.
[...] At the time that we published Break Through, I, along with most climate scientists and advocates, believed that business as usual emissions would lead to around five degrees of warming by the end of this century. As Zeke Hausfather, Glen Peters, Roger Pielke Jr, and Justin Richie have demonstrated over the last decade or so, that assumption was never plausible.
There have been some revisionist claims that the reason for the downgrading of business as usual warming assumptions is due to the success of climate and clean energy policies over the last several decades. But five degrees of warming by the end of this century was no more plausible in 2007, when Break Through was published, than it is today. The class of scenarios upon which it was based assumed very high population growth, very high economic growth, and slow technological change. None of these trends individually track at all with actual long term global trends. Fertility rates have been falling, global economic growth slowing, and the global economy decarbonizing for decades.
Nor is there good reason to think that the combination of these three trends could possibly be sustained in concert. High economic growth is strongly associated with falling fertility rates. Technological change is the primary driver of long term economic growth. A future with low rates of technological change is not one that is consistent with high economic growth. And a future characterized by high rates of economic growth is not one that is consistent with high rates of population growth.
As a result of these dynamics, most estimates of worst case warming by the end of the century now suggest 3 degrees or less. But as consensus around these estimates has shifted, the reaction to this good news among much of the climate science and advocacy community has not been to become less catastrophic. Rather, it has been to simply shift the locus of catastrophe from five to three degrees of warming. Climate advocates have arguably become more catastrophic about climate change in recent years, not less.
This is all the more confounding given that the good news extends well beyond projections of long term warming... (MORE - details)