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Can you define weak quantitatively? What kind of radiative forcing in W/m^2 are you thinking. What kind of sensitivity in C per W/m^2 are you thinking?

Here is an attempt at modeling using established theory of the last 3 million years of the paleoclimate record including the transition from 40kyr cycles to 100kyr cycles as depicted in the graph. It's certainly not perfect, but it is reasonably successful nonetheless IMHO. https://advances.sciencemag.org/content/5/4/eaav7337

There is a lot of content here. For brevity's sake I'll just answer the question most relevant to my last post. I know that the established theory of climatic change is a better match to reality compared to non-GHG (or weak GHG) theories since 1960 because the observations say so. The observations over even longer stretches of time and through the paleoclimate record are more consistent with the established theory versus those that specifically ignore or downplay certain forcing agents like GHGs.

Harde has published questionable papers in the past. For example, he conflates the residence time of CO2 with the adjustment time (among other problems) to show that anthroprogenic emissions only account for 4% of the post industrial ppm increase. You can read more about that here. But his misunderstanding of the carbon cycle is no reason to dismiss his 0.7C sensitivity claim outright. For that we can just look at observations. Since 1960 the surface has warmed by 0.9C with very little if any of that being convincingly attributable to naturally modulated forcing agents. The hydrosphere has taken up heat equivalent to 0.6 W/m^2 of forcing for decades. If a natural (and non-GHG) forcing agent were a significant contributor of this uptake then given this magnitude it should have been quite easy to identify. Meanwhile the observed uptake of heat is a close match to the consensus theory which includes all known radiative forcing agents in their appropriate proportions including GHGs. As such the 0.7C sensitivity hypothesis has been convincingly falsified IMHO. Even the IPCC's lower bound of 1.5C is very likely to be too low. So if Harde truly believes only 4% of the CO2 increase is anthroprogenic and if the sensitivity is only 0.7C then I guess that means he only attributes 0.04 * (ln(410/280) / ln(2)) * 0.7 = 0.015C of the 1.1C since the pre-industrial era to anthroprogenic CO2. That's about 1% which is an extreme (and I truly mean EXTREME) outlier to the overwhelming majority of estimates. By the way, the journal in which he submitted this 0.7C claim is now defunct. I'm just saying...

An argument can be made for the IPCC to increase the lower bound on their estimate from 1.5C back to 2.0C.

I think you may be referring to the mid troposphere tropical hotspot again. And assuming "supposed to warm" is in reference to the various lat-hgt distributions of the warming (like those of the often cited and frequently misrepresented graphic from IPCC AR3) I'll point out that at the latitude of Fairbanks the warming at 300mb is marginal compared to the global mean. Please refer to following link for an example of such a lat-hgt diagram of the forcing response. https://data.giss.nasa.gov/modelE/efficacy/

Robert Rohde, who is a member of the Berkeley Earth project, tweeted that over the last 2000 years only 9 occurrences of melt at Greenland's highest point have occurred. 2 of 9 occurred with in the last 10 years so that is somewhat unusual.

Polyatomic molecules like CO2, H2O, CH4, CFCs, etc. both emit and absorb IR photons of certain frequencies. Outbound photons that would otherwise have escape trajectories are absorbed and then reemitted in all directions with roughly half having escape trajectories and the other half having surface trajectories. There is a process by which the quantized energy contained in the photon is "thermalized" as it is converted into kinetic energy as well.

CO2 concentration does lag (with caveats) the temperature trend for much of the glacial cycles. This is consistent, if not totally expected, with modern climate science theory. Remember, CO2 is both in a forcing relationship and a feedback relationship with the temperature. If CO2 dominates early as a catalyzing agent for temperature changes it will be observed to lead the temperature profile. If something else dominates early as the catalyzing agent for temperature changes it will be observed to lag. But, that does not preclude CO2 from also playing the role as a forcing agent as well. In fact, CO2 is essential in explaining the amplitude of the glacial cycles even though other agents like Milankovitch cycles, albedo feedback, randomly timed volcanic aerosols, etc. were likely the catalyzing agents that explain the timing. In other words, CO2 acted via its feedback first and its forcing second. But CO2 doesn't always lag the temperature in the paleoclimate record anyway. For example, the Paleo-Eocene Thermal Maximum (PETM) was characterized by a sudden release of CO2. Thus CO2 dominated early as a catalyzing agent itself. In other words, it acted via its forcing first and its feedback second. The point...we actually have examples of CO2 both leading and lagging the temperature profile in the paleoclimate record and each era is consistent with the idea that CO2 is both a feedback and forcing agent. Those eras by marked feedback dominance are typically long and drawn out similar to the glacial cycles while those marked by forcing dominance are quick and sudden similar to what is playing out today. The key to understanding when it leads vs lags is identifying what is modulating its release. H2O behaves differently. Yes, being a polyatomic gas species, it too is a GHG. But, it cannot, on its own, catalyze long term changes in temperature like how CO2 can which makes its relationship with temperature strikingly different.

I was trying to think of a way to test the hypothesis that the UHI was a contributing factor to the magnitude of this summer's heat waves in Europe. I think most of us would agree that the UHI is probably not significant enough to influence weather patterns like the persistent ridging which spread over Europe on a synoptic scale. But maybe our perception of the magnitude of the events was skewed by the UHI. It seems like a falsification of this hypothesis could be attempted by trending the difference of urban vs rural readings over long periods of time as a means for quantifying the change in UHI. Is the UHI effect still increasing? Is the signal strong enough to explain part of the magnitude of the observations? I still don't think this experiment would tell us much about the frequency of such events since that seems to be more related to synoptic scale patterns. Thoughts?

Two reasons...First, CO2 isn't the only agent modulating the climate. It's the net effect of all climate forcing agents that drives the energy balance on the planet. CO2 happens to be an important player in the energy budget, but it's not the only player. Second, the surface temperature is influenced by the transport of energy between the various heat reservoirs in the geosphere including the hydrosphere, lithosphere, cryosphere, atmosphere, etc. It's possible for the temperature of one reservoir to decrease even though the energy uptake is positive across all reservoirs. Everything matters. What the abundance of evidence shows is that hypothesis that selectively ignore an agent (like CO2) provide poorer matches to reality than those that include everything.

I believe you are referring to the mid troposphere tropical hotspot problem. I agree. This is one deficiency in climate models though it is my understand that this discrepancy is improving. There are other discrepancies in modeling as well. Clearly there is more to learn. But that does not mean that our understanding of the climate is incapable of assigning radiative forcing estimates with reasonable margins of error to the various agents that modulate the climate. We do, in fact, have enough understanding of the major players in the climate system to draw conclusions with confidence. CO2 (and other polyatomic gas species) are an essential piece of the puzzle in explaining and predicting the climate system. Alternative theories that ignore it do a poor job at matching up with all available observations. The Vostok ice cores (and other proxies) are consistent with the theory that CO2 puts a positive/negative radiative forcing on the climate when it increases/decreases. What are you thinking is the problem? In the absence of CO2 how do you explain the magnitude of the glacial/interglacial cycles? How do you solve the faint young paradox?

Keep in mind that the chart from Christy above is for TMT (mid troposphere) between 20N and 20S latitude. It is also important to note that UAH's TLT (lower troposphere) isn't measuring the temperature of the surface and their TLT product is higher up than RSS's TLT product. Anyway, I believe on a global basis RSS actually has the better match to balloon, surface, and reanalysis datasets. UAH is the clear outlier from what I've seen. But that's okay with me. It provides a reasonable floor to the warming trend.

I'm not sure what JC's concern is on the sea level acceleration. According to the paper cited the acceleration early in the period of analysis lasted 10 years (1920-1930) 20 years (1920-1940) while we are currently in a 50+ year period of positive acceleration. And whereas the rate peaked at 2.0 mm/yr early in the period it is currently 3.5 mm/yr. And with the energy uptake in the hydrosphere being 0.8-0.9 W/m^2 with increasing GHG concentrations and significant ice sheet melting occurring I don't see this turning negative anytime soon. The data (at least in this publication) clearly shows that sea level rise late in the period is far more significant than early in the period.

I like the new NSIDC sea ice extent chart. You can add the ±2σ band to the display now.

According to a 5yr moving average from a consensus of many surface based datasets the warming trend is about +0.15C/decade from 1958 to 2018. Note that solar activity peaked in the late 1950's. And from 1998 to 2018 that trend is likely over +0.20C/decade. Oceanic Heat Content (OHC) is increasing at a rate of 10e21 joules/yr with OHC breaking records pretty much on a yearly basis now. The energy imbalance on the planet is at least +0.6 W/m^2 as of 2019.

No one is saying that the Sun can't ever be a significant agent for a warming event. What is being is said is that the Sun is not a significant agent for THIS particular warming event. And there's not just one line of evidence used to base that claim from. There's actually multiple lines of evidence; many of them quite convincing. Haven't I gone over all this with you before?

I agree. 3% is too low. 10-20% sounds pretty reasonable to me as well.

THE MYTH OF THE 1970s GLOBAL COOLING SCIENTIFIC CONSENSUS

Why does it say "using unadjusted temperature dataset"? Is the temperature displayed on it? What am I missing? And what agenda do you think the original charts had?

Yeah, it takes a lot of energy to make the phase change from solid to liquid. Global mean surface temperatures are running a bit behind of most model predictions while Arctic sea ice is declining faster than originally predicted. I wonder if more of the planetary energy balance is going into the cryosphere and less in the atmosphere could explain the discrepancy? Anyway, it does appear like 2019 is shaping up to have yet another well below normal minimum extent...possibly top 3 lowest.

Sea ice area continues to decline though. This means the ice is spreading out. As noted above this typically means extent is poised for a significant drop.

Arctic sea ice extents have taken a plunge recently and are now in record territory for this date dropping below 2006, 2016, 2017, and 2018 levels. So the melt season is already off to an aggressive start.

Yeah so it looks like the ensemble range on this study is 2040 to 2055 with a mean of about 2047 for the first ice-free (< 1e6 sq km) September.

You guys are so due for something big.