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.