Occasional Thoughts on Climate Change

[donsutherland1]

1 hour ago, blizzard1024 said:

 

First of all, a doubling of CO2 (which we haven't reached yet) leads to about 1C of warming with no feedbacks. BUT, the claim is that water vapor will increase and amplify the greenhouse effect (this is uncertain).  So, if the sun or some other factor like less cloud cover, leads to more surface heating then you get a positive water vapor feedback which enhances the greenhouse effect leading to cooling in the stratosphere.  I don't agree with the positive feedback. Clouds are what drives the climate. Cloud cover has decreased as sulfate aerosols are diminishing due to clean air laws and changes in shipping.  Plus, an active sun leads to more solar wind and less cosmic rays and hence less cloud cover. The albedo of the Earth has decreased by about 1% recently to 28.5% down from 29.5%. Also the effects of water vapor in the stratosphere from Tonga are still lingering. So you simplify the climate system to one small component which I don't agree with. 

CO2 never drove the climate system in the past in the ice core data. In fact, there is strong evidence from recent studies that ice sheets had a negative greenhouse effect with CO2 leading to cooling on the NH ice sheets due to the sharp temperature inversion.  This was documented recently over the Antarctic ice sheet. So, the faulty reasoning of something else leads to small warming, THEN CO2 is outgassed and "communicates" the warming to the planet and then leads to warming is wrong. Any increase in CO2 leads to slight cooling on the ice sheets. Its water vapor that can turn the sign to positive greenhouse effect on the ice sheets as seen in Antarctica.  So water and clouds rule our greenhouse effect and convection dominates our energy balance. CO2 is a factor but not a big one IMO. I am an independent thinker who has researched this for 30+ years. The fact the sun was very active in the late 20th century and the lag effect with the oceans is more than enough to explain the warming we have seen recently.  Doubling CO2 only changes the energy balance by 1%. How can that throw a climate system out of balance?  If the climate system is that sensitive, then any shocks of the past would have spiraled the climate out of control. Anyway, I do agree that we should still be pursuing clean sources of energy and am against big oil drilling etc. I just don't think the climate system is going to spiral out of control. 

 

 

 

That post was from six years ago. Science has continued to advance since then. Confidence in the anthropogenic driver for the current warming has increased since then.

The general ideas from that post remain largely accurate and have stood up quite well. That's a testament to the scientific work on which they were based. In general, credible science holds up over time, especially when basic physics is involved. The properties of CO2 have been understood since the 19th Century.

There is some nuance as it applies to central Antarctica where the surface is typically colder than the stratosphere. One paper suggests that there is a "negative greenhouse effect" that is unique to that region. The paper also makes clear that this is an exception that does not raise serious questions about the role of greenhouse gases in the warming of the Earth's climate. The paper states:

It is important to note that these results do not contradict the key statements of the Intergovernmental Panel on Climate Change (IPCC) ..., namely, the well-known warming effect that CO₂ has on the Earth’s climate. Yet we showed that for the cold Antarctic continent some care needs to be taken when discussing the direct warming effect of CO₂.

CO2 has not doubled from the pre-industrial level (it reached 430 ppm earlier this year vs. the pre-industrial figure of around 270 ppm -280 ppm). There are numerous feedbacks. Aerosols have gained some increased attention recently from some work by Hansen et al. The reduction in aerosols has limited the masking of warming and likely contributed, in part, to the recent acceleration in the rate of warming. A reduction in aerosols likely also contributed to the cloud-related changes that have been observed, but paleoclimate work suggests that more than aerosol changes are involved.

A growing body of evidence strengthens the argument that clouds have a positive feedback, namely that at higher CO2 levels, cloud-related changes amplify the warming. Back in 2019, there were some who still argued that clouds would be a negative feedback and help reduce the rate of warming. That idea has now largely lost merit.

Paleoclimate work by Jessica Tierney among others revealed that cloud-related changes at higher levels of CO2 enhanced warming. Recent data from NASA confirms changes to clouds consistent with promoting increased warming. Indeed, even more recent research on climate sensitivity has suggested that perhaps the CMIP6 models weren't "running hot" as initially thought, but that they might be doing a better job capturing cloud-related changes. A new paper, aside from Hansen's recent work, has suggested that climate sensitivity for a doubling of CO2 may be around 4.8°C based on the Pliocene Epoch. I'm not yet sold on that, but am open to this idea.

I didn't state or suggest that the climate system will spiral out-of-control so to speak from ongoing anthropogenic warming. No runaway greenhouse effect is likely on Earth. That won't happen until the sun starts moving into its red giant phase as it begins to exhaust its hydrogen and begins to boil away the oceans.

My point is that clear scientific understanding of climate change now exists concerning what is happening (warming) and why it is happening (antropogenic greenhouse gas emissions). The scientific debate over those two issues is finished. No credible alternative hypothesis exists.

Nevertheless, that does not mean that there is anything close to perfect understanding. There remain some uncertainties, but those don't rise to the level of undermining the basic idea of anthropogenic warming. Feedbacks are real. Some amplify the warming as CO2 increases, while others damp the warming. 

Climate change has increased the frequency, magnitude, and duration of extreme heat events in the United States and worldwide. Evidence suggests that quasi-resonant amplification is contributing to the kind of "stuck patterns" that have led to long-duration severe heat outbreaks in parts of North America, Europe, Asia, and Africa, among other extreme events. Recent research also suggests that Pacific-related changes are creating a negative PDO-type scenario, which is contributing to the Southwest's growing hotter and drier. 

Finally, internal variability occurs within the context of increasing anthropogenic greenhouse gas forcing. Thus, there can be cold periods, including cold winters. Synoptic events also occur within the context of increasing anthropogenic forcing, so climate change impacts such events but does not necessarily cause them. Second order effects can see climate change driving changes in synoptic scale events e.g., aridification of regions can feed back into the development of more persistent and larger heat domes.

[blizzard1024]

1 hour ago, donsutherland1 said:

A new paper, aside from Hansen's recent work, has suggested that climate sensitivity for a doubling of CO2 may be around 4.8°C based on the Pliocene Epoch. I'm not yet sold on that, but am open to this idea.

My issue for many many years is that CO2 levels during the glacial to interglacial periods lagged the inferred temperatures from Oxygen Isotope Ratios by up to 1000 years.  This suggests strongly that it's the oceans outgassing and absorbing CO2 that is leading to these changes in CO2 and not CO2 driving the climate. Plus, one small absorption band around 15 microns is very small compared to water vapors much larger absorption in the IR spectrum. A doubling of CO2 leads to about a 1% change in energy balance. How does that equate to 4.8C?  Even 2-3C seems farfetched. All of this work is based on computer modeling and proxy records which are not definitive.  What about tropical convection? This has a huge impact on the global energy balance. Climate models don't explicitly predict this. Anyway, I have been trying hard to come around to the mainstream on this and my skeptical mind won't let me.  I guess my main sticking points are the ice core records, the small change in energy balance from a doubling of CO2, Earth is coming out of a little ice age and the small absorption band of CO2 relative to H20. 

Anyway, I do agree that we shouldn't pollute the atmosphere at all and should be weaning off of fossil fuels for cleaner sources of energy. So at the end of the day, I may not agree with the doomsday warming scenarios but I agree with you on what the world needs to do for the future. 

[donsutherland1]

10 hours ago, blizzard1024 said:

My issue for many many years is that CO2 levels during the glacial to interglacial periods lagged the inferred temperatures from Oxygen Isotope Ratios by up to 1000 years.  This suggests strongly that it's the oceans outgassing and absorbing CO2 that is leading to these changes in CO2 and not CO2 driving the climate. Plus, one small absorption band around 15 microns is very small compared to water vapors much larger absorption in the IR spectrum. A doubling of CO2 leads to about a 1% change in energy balance. How does that equate to 4.8C?  Even 2-3C seems farfetched. All of this work is based on computer modeling and proxy records which are not definitive.  What about tropical convection? This has a huge impact on the global energy balance. Climate models don't explicitly predict this. Anyway, I have been trying hard to come around to the mainstream on this and my skeptical mind won't let me.  I guess my main sticking points are the ice core records, the small change in energy balance from a doubling of CO2, Earth is coming out of a little ice age and the small absorption band of CO2 relative to H20. 

Anyway, I do agree that we shouldn't pollute the atmosphere at all and should be weaning off of fossil fuels for cleaner sources of energy. So at the end of the day, I may not agree with the doomsday warming scenarios but I agree with you on what the world needs to do for the future. 

Yes, Antarctic ice cores show that the temperature rose shortly before CO2 started rising by centuries to 1,000 years. The initial warming was triggered by changes in the Earth's orbit, which allowed for an increase in solar insolation. As oceans warmed, CO2 was released (the outgassing you mentioned). The released CO2 then drove a continuation of the warming.

Today, humanity has bypassed Milankovitch Cycles, which once served as the trigger for the initial warming. Humanity began reintroducing CO2 to the atmosphere via the burning of fossil fuels. As atmospheric CO2 has increased, that has driven temperatures higher. 

In terms of incoming solar radiation, a 3.7 W/m² increase in forcing (just over 1%) may seem small. But it's the imbalance that matters. For example, during the last ice age, there was a -3.9 W/m² imbalance (1.1%). Nevertheless, the latest research now suggests that the Last Glacial Maximum was about -6.1°C cooler than current temperatures.

Regarding the recent 4.8°C estimate, I need to see more. I am open to it, because highly respected scientists in the field are now suggesting that climate sensitivity could be higher than consensus estimates when a better understanding of feedbacks is considered.  I will watch the evolution of the debate and incoming data on this matter. 

Finally, I think there's a world of difference between one's having honest questions (your case) and those pontificating on the matter when they provide no credible alternative explanations and/or have done no research whatsoever on climate/climate change.

 

[bdgwx]

It is important to understand that CO2 is both a forcing agent and a feedback agent. That means it can both cause a change in a temperature and it can respond to a change in temperature. That means it can both lead and lag the temperature temperature depending on circumstances.

For example, if it is released independent of a temperature and itself catalyzes a temperature change then it will lead. If, however, something else catalyzes the temperature change then it will respond and lag.

The PETM and modern warming eras are examples of scenarios in which it leads because flood basalt events and human injection occurred independent of temperature.

The glacial cycles in the Quaternary Period are examples where it lags because orbital perturbations in conjunction with the more randomly timed volcanic and dust events cause the temperature change first.

[bdgwx]

I should also mention that our understanding of CO2's radiative force, though not perfect, is actually pretty good. Remember that the Rapid Radiative Transfer Model (RRTM) and others like it are an essential component of most global and regional circulation models (like GFS, ECMWF, etc.) that we all rely on for weather forecasts and is used to design space based observational radiometers like those onboard the GOES-R satellites. Radiative transfer through the atmosphere plays a huge role not only in forecasting weather but also in the real time observation of it. Even the minor active bands of CO2 like that around 13.3 um (and which is several orders of magnitude less than its bending vibrational mode around 15 um) have to be modeled precisely otherwise the GOES-R channel 16 data would be useless.

Note that the RRTM says the radiative force of 2xCO2 is about 4 W.m-2 or about 0.3 W.m-2 higher than the often cited [Myhre et al. 1998] estimate of 3.7 W.m-2 using the older and less precise LBL, NBM, and BBM radiative transfer models.

2xCO2 is the equivalent of about 200 million years of solar brightening [Gough 1981] or ~10x (and likely higher) the magnitude of change from a grand solar minimum (like the Maunder Minimum) to maximum (like the Modern Maximum around 1950).

Basically what I'm saying is that we know with very high confidence that the change in CO2 is significantly more influential in the radiative balance of Earth than that of the Sun.

[Typhoon Tip]

https://phys.org/news/2025-08-europe-millions.html

[donsutherland1]

Phoenix's annual monsoon is changing in a warming climate. The most pronounced changes are fewer rainy days (days with measurable precipitation), reduced monsoon season precipitation, and a hotter monsoon season. 

The dramatic warming of the Monsoon Season shows up prominently in the Ed Hawkins-styled warming stripes:

These developments are consistent with some of the literature concerning climate change and its impact on North America's monsoon season. Two examples:

"It is found that the monsoon response to CO2 doubling is sensitive to sea-surface temperature biases. When minimizing these biases, the model projects a robust reduction in monsoonal precipitation over the southwestern United States, contrasting with previous multi-model assessments." 

Source: Pascale, S., Boos, W., Bordoni, S. et al. Weakening of the North American monsoon with global warming. Nature Clim Change 7, 806–812 (2017). https://doi.org/10.1038/nclimate3412

"Within climate science... focus has begun to include the growing role warming temperatures  are playing as a potent driver of greater aridity: hotter climate extremes;  drier soil conditions; more severe drought; and the impacts of hydrologic stress on rivers, forests, agriculture, and other systems. This shift in the hydrologic paradigm is most clear in the American Southwest..."

Source: Overpeck, Jonathan T. and Udall, Bradley. Climate change and the aridification of North America. PNAS, Vol. 117, No. 22 (2020). https://www.pnas.org/doi/pdf/10.1073/pnas.2006323117

 

[bluewave]

This new study really isn’t a surprise given the rapid warming of SSTs in North Pacific. But it’s good to see this new attribution technique correct the climate model errors. Similar shift in the North Atlantic so rapidly warming the climate leads to more persistent -PDO and +AMO patterns. 
 

https://www.colorado.edu/today/2025/08/14/human-emissions-drove-megadrought-western-us

Greenhouse gas and aerosol emissions from human activity have been driving the prolonged drought in the western United States through a complicated connection with the Pacific Ocean, according to a new CU Boulder-led study.

For more than two decades, an extreme dry spell has drained the Colorado River, devastated local farms, and intensified wildfires across the American Southwest. The new prediction, published August 13 in Nature, could help water managers region develop better water use plans or invest in infrastructure accordingly, with relief potentially still decades away.

“Our results show that the drought and ocean patterns we’re seeing today are not just natural fluctuations—they’re largely driven by human activity,” said Jeremy Klavans, postdoctoral researcher in CU Boulder’s Department of Atmospheric and Oceanic Sciences and lead author of the study.

 

Worst drought in 12 centuries

 

The drought hitting the Colorado River Basin states and California is directly linked to a climate pattern of the north Pacific Ocean, known as the Pacific decadal oscillation (PDO).

The PDO is a natural fluctuation of the Pacific that waxes and wanes every two decades or so. In its positive phase, waters in the eastern Pacific Ocean along the U.S. West Coast tend to be warmer, whereas waters near Japan are colder. In its negative phase, the pattern flips, bringing cold water to the eastern Pacific.

Since the 1990s, the PDO has been stuck in a negative phase, an unusually long stretch for a typical cycle, Klavans said.

That has had profound impacts on the United States. The cold air and water along the U.S. West Coast hold less moisture than warm air, causing a reduction in precipitation. This extended cool phase also pushed storms that would have brought water to the region farther north.

As a result, scientists estimated that about 93% of the western United States is experiencing drought, with 70% facing severe dry conditions. Prior studies have shown that the past two decades have been the driest in the American Southwest in at least 1,200 years.

Scientists had long thought that the PDO was entirely determined by natural forces, such as the heat exchanges between the ocean and the air. Even the latest report from the Intergovernmental Panel on Climate Change (IPCC), a body of experts convened by the United Nations, said the PDO is controlled by natural forces with high confidence.

If that theory was correct, the PDO should have flipped from negative to positive in 2015 after a strong El Niño event warmed the Pacific.

Instead, the PDO shifted positive for a short time following the El Niño before reverting to the negative phase again.

New reality

To understand why the PDO has been stuck, Klavans and his team used a large collection of climate simulation programs to predict what would happen in the future.  

Using a new suite of over 570 simulations, the team found that between 1870 and 1950, changes in the PDO were almost entirely driven by internal forces. But since the mid-20^th century, greenhouse gas and aerosol emissions have accounted for more than half of the variations in the PDO.

The team discovered that existing climate models tend to overestimate the role of internal factors on the PDO while underestimating the influence of external factors, such as emissions. After correcting the imbalance, the team found that emissions, and their impacts on the PDO, have been responsible for nearly all of the precipitation decline in the western United States over the past three decades.

“People have been trying for a long time to find out why this part of the country is so dry, and we have an answer for that finally,” Klavans said.

Because the same imbalance has been shown in other regions, Klavans said the study’s implications could go far beyond the Pacific. For example, the North Atlantic Oscillation, a similar fluctuation over the Atlantic Ocean, is driving drought in places like Spain. He added that improving climate models to capture the role of external forces could help scientists predict future changes in precipitation across the globe.

As for the American Southwest, the outlook is grim. If greenhouse gas emissions continue to rise, the PDO will likely remain in its negative phase, and the drought will persist for at least the next three decades, Klavans said.

“With this information, water planners could set new expectations and make proper investments in water infrastructure now, knowing this drought is here to stay,” Klavans said.  

For example, some Californian cities are already building desalination plants to turn seawater into drinking water.  

“This study can allow us to better quantify the costs of continued greenhouse gas emissions for Americans,” Klavans said. “That can only help our region plan for a better future.” 

https://www.nature.com/articles/s41586-025-09368-2

This anthropogenic influence was previously undetected because the current generation of climate models systematically underestimate the amplitude of forced climate variability. A new attribution technique that statistically corrects for this error suggests that observed PDO impacts—including the ongoing multidecadal drought in the western United States—can be largely attributed to human activity through externally forced changes in the PDO. These results indicate that we need to rethink the attribution and projection of multidecadal changes in regional climate.

[donsutherland1]

33 minutes ago, bluewave said:

This new study really isn’t a surprise given the rapid warming of SSTs in North Pacific. But it’s good to see this new attribution technique correct the climate model errors. Similar shift in the North Atlantic so rapidly warming the climate leads to more persistent -PDO and +AMO patterns. 
 

https://www.colorado.edu/today/2025/08/14/human-emissions-drove-megadrought-western-us

Greenhouse gas and aerosol emissions from human activity have been driving the prolonged drought in the western United States through a complicated connection with the Pacific Ocean, according to a new CU Boulder-led study.

For more than two decades, an extreme dry spell has drained the Colorado River, devastated local farms, and intensified wildfires across the American Southwest. The new prediction, published August 13 in Nature, could help water managers region develop better water use plans or invest in infrastructure accordingly, with relief potentially still decades away.

“Our results show that the drought and ocean patterns we’re seeing today are not just natural fluctuations—they’re largely driven by human activity,” said Jeremy Klavans, postdoctoral researcher in CU Boulder’s Department of Atmospheric and Oceanic Sciences and lead author of the study.

 

Worst drought in 12 centuries

 

The drought hitting the Colorado River Basin states and California is directly linked to a climate pattern of the north Pacific Ocean, known as the Pacific decadal oscillation (PDO).

The PDO is a natural fluctuation of the Pacific that waxes and wanes every two decades or so. In its positive phase, waters in the eastern Pacific Ocean along the U.S. West Coast tend to be warmer, whereas waters near Japan are colder. In its negative phase, the pattern flips, bringing cold water to the eastern Pacific.

Since the 1990s, the PDO has been stuck in a negative phase, an unusually long stretch for a typical cycle, Klavans said.

That has had profound impacts on the United States. The cold air and water along the U.S. West Coast hold less moisture than warm air, causing a reduction in precipitation. This extended cool phase also pushed storms that would have brought water to the region farther north.

As a result, scientists estimated that about 93% of the western United States is experiencing drought, with 70% facing severe dry conditions. Prior studies have shown that the past two decades have been the driest in the American Southwest in at least 1,200 years.

Scientists had long thought that the PDO was entirely determined by natural forces, such as the heat exchanges between the ocean and the air. Even the latest report from the Intergovernmental Panel on Climate Change (IPCC), a body of experts convened by the United Nations, said the PDO is controlled by natural forces with high confidence.

If that theory was correct, the PDO should have flipped from negative to positive in 2015 after a strong El Niño event warmed the Pacific.

Instead, the PDO shifted positive for a short time following the El Niño before reverting to the negative phase again.

New reality

To understand why the PDO has been stuck, Klavans and his team used a large collection of climate simulation programs to predict what would happen in the future.  

Using a new suite of over 570 simulations, the team found that between 1870 and 1950, changes in the PDO were almost entirely driven by internal forces. But since the mid-20^th century, greenhouse gas and aerosol emissions have accounted for more than half of the variations in the PDO.

The team discovered that existing climate models tend to overestimate the role of internal factors on the PDO while underestimating the influence of external factors, such as emissions. After correcting the imbalance, the team found that emissions, and their impacts on the PDO, have been responsible for nearly all of the precipitation decline in the western United States over the past three decades.

“People have been trying for a long time to find out why this part of the country is so dry, and we have an answer for that finally,” Klavans said.

Because the same imbalance has been shown in other regions, Klavans said the study’s implications could go far beyond the Pacific. For example, the North Atlantic Oscillation, a similar fluctuation over the Atlantic Ocean, is driving drought in places like Spain. He added that improving climate models to capture the role of external forces could help scientists predict future changes in precipitation across the globe.

As for the American Southwest, the outlook is grim. If greenhouse gas emissions continue to rise, the PDO will likely remain in its negative phase, and the drought will persist for at least the next three decades, Klavans said.

“With this information, water planners could set new expectations and make proper investments in water infrastructure now, knowing this drought is here to stay,” Klavans said.  

For example, some Californian cities are already building desalination plants to turn seawater into drinking water.  

“This study can allow us to better quantify the costs of continued greenhouse gas emissions for Americans,” Klavans said. “That can only help our region plan for a better future.” 

https://www.nature.com/articles/s41586-025-09368-2

This anthropogenic influence was previously undetected because the current generation of climate models systematically underestimate the amplitude of forced climate variability. A new attribution technique that statistically corrects for this error suggests that observed PDO impacts—including the ongoing multidecadal drought in the western United States—can be largely attributed to human activity through externally forced changes in the PDO. These results indicate that we need to rethink the attribution and projection of multidecadal changes in regional climate.

This was a very important paper--perhaps one of the most important weather/climate papers that will be published this year. It describes the mechanism by which climate change is driving Southwest aridification via marine heatwave-induced changes to the PDO.