The measure and notion of forcings as applies to computer simulations like the Hansen paper can be confusing when applied/translated to immediate conditions at a point in time. As you note in your quote, the 2.75 number is the impact from the total change in GHG's(not just CO2, nor just human emitted GHG's) from 1880 through 2003. Hansen later notes the overall forcing(not just GHG) from 1880 through 2003:
The net change of effective forcing between 1880 and 2003 is +1.8 W/m2

I'm going to reference the +1.8W/M^2 for my prior example, because Hansen does the same later so it's easier to verify against his own words. With a net increase in forcing from 1880 to 2003 of +1.8, and with a imbalance today between 0.5 and 1 we can work out what has already been responded to and what has not. For ease of use, let's pick(as Hansen does) a current imbalance of 0.8W/M^2. In that case, the planet has already responded to 1W/m^2 of the forcing and has 0.8W/m^2 to go. Alternatively to state it as I did earlier, if we returned our atmospheric conditions to 1880 but at our current global temperatures, we'd see the energy imbalance drop by 1.8W/M^2, or a net -1W/m^2, and we'd be forcing ourselves back to an 1880 equilibrium. Hansen says the same thing in different words in your article :
This imbalance is consistent with the total forcing of +1.8 W/m2 relative to that in 1880 and climate sensitivity of +2/3-C per W/m2. The observed 1880 to 2003 global warming is 0.6- to 0.7-C (11, 22), which is the full response to nearly 1 W/m2 of forcing. Of the 1.8 W/m2 forcing, 0.85 W/m2 remains.

That is all to say that forcings are just measures of changes to the green house effect from one time to another, mostly used in climate simulations as a means to test and understand the workings of the underlying system. If removing XX W/m^2 of forcing from a simulation instantly and with no other changes DOESN'T shift the energy balance the exact same amount, then the underlying basic physics model of simulation is broken. That's why the effort and notes by Hansen to rectify the two and note they remain consistent with one another as one or the other rises.

Also observe that Hansen's work is entirely with simulations, with only about 9 variable forcings taken into account in effort to simulate a portion of what happened since 1880. He also doesn't distinguish which parts of the forcings are anthropogenic versus natural. His underlying effort was to look at the speed with which temperature and energy imbalance may have responded to the changes since 1880. His only references to observed energy imbalance reference Levitus Ocen heat work, and the note that from 1955 through 1998 the ocean's heated at a roughly steady rate of 10W/M^2, or approximately 1W/m^2 globally. Hansen later notes his simulations from 1993 through 2003 that show 0.6 W/m^2 recently are in good agreement with Levitus newer observations of that same time of 0.55 W/m^2.

I will observe that the energy imbalance is decreasing over time by observations, as stated by Hansen. That has been happening while our CO2 emissions and concentrations are still increasing. I count that cause for optimism versus panicking that CO2 impacts might be even worse than IPCC projections.

The energy imbalance is NOT a function of change in forcing over time. The energy imbalance is the energy leaving the earth at the top of the atmosphere subtracted from the energy entering. Forcings are anything that works to change the energy imbalance over time. The energy imbalance doesn't care about how we model or measure the changes to the atmosphere and climate system. The physics it operates under is energy from the sun trapped in versus what is reflected or otherwise bled off. GHG's like CO2 all work to absorb that radiation and help decrease the radiation out number.

Forcings, like our emissions of GHGs, work on the simple principle of increasing concentrations of gases that then absorb more energy. There are many calculations for what overall impact our emissions have had, one estimate as you say is a net contribution of trapping an additional 2.9 W/m^2. Subtract that concentration of gases we've contributed to absorb 2.9 W/m^2 and that much extra energy escapes, by definition. That moves the energy imbalance down by 2.9 W/m^2, by definition.

I'm willing to rely on the scientific method and data collection to make best guesses at what impact it will have on the future. Then from that data making decisions that are sensible based on that data. Right now, catastrophe is strongly counter to observations and so your desire to panic is uncalled for. The cost/benefit of reducing our contribution is still very, very poorly known, but we do know that preparation measures are called for so we should start that before pouring dollars at 'solution' we know neither the cost nor value of.

That's not how physics works. With a human contribution of 2.9 @/m2 and net imbalance when including natural forcings of 0.6W/m2, the natural system already has balanced all but 0.6W/M2 of our 2.9W/m2 contribution at current temps.

Correct, that's the 101 portion. The next question is at what rate should we expect the rise to be. From a constant energy balance as we've seen since 1980 in Sat observations we should expect a linear increasing temperature. If you go look at the IPCC's fifth assessment report, you can look at the models long term projections all the way to 2300 in Chapter 12. If you go to the section on energy budget, you can see where each of the IPCC's 4 main scenarios project the energy imbalance to be in the future. If we take the shocking approach of expecting the trend from the last 30 years of Satellite data to continue, then our future should track somewhere under the IPCC RPC4.5 scenario and somewhere above their RPC2.6 scenario. If you look at the IPCC chapter 11, they model temperature projections out to 2100 for RCP4.5. The prediction from my above approach would be to expect that observations will track on the low end of or just under the RCP4.5 predictions. You don't have to wait to see if I'm correct, the IPCC also graphs Observed temperatures against their predictions, and so far observation track at the very bottom range of the RCP4.5 predictions.

What that means if you follow the RCP 4.5 and 2.6 actual climate scientists work, the expectations we should see by 2100 are linear temperature increase and an increase between 1 or 2C, with a better guess than at 1.5C. That's not a number that calls for panic, nor one that supports any fears of it could be so much worse so we better spend billions now to drop our CO2 emissions. We are facing warming, but we should be building stuff to deal with that because as demonstrated for all we know billions spent on CO2 reductions could leave us at 1.4C in 2100 instead of 1.5C which is a big wast of dollars that could've built up levies in New Orleans instead.

If you want to argue for 'playing things safe' that's exactly my point. With what we currently don't know, we could spend billions on reducing CO2 emissions, and make little noticeable difference to future conditions. We could spend those same billions on dykes, irrigation and water management to deal with the warming that we DO know is coming. You seem to think we should gamble on being able to make a difference with reducing our CO2 emissions, I'm saying let's have some better info before risking wasting dollars we could really use to deal with changes.

You need to read more closely, the numbers for total radiation coming into the atmosphere and leaving are in the hundreds, and the net difference is near zero. The impact of greenhouse gases, like human forced ones are the 2.9 W/m^2 you reference, are but of a bigger whole. That is meaning without the 2.9W/m^2 from our human emissions we'd be facing a much bigger imbalance, but in the opposite direction around -2.5W/m^2. If gaining energy at 0.6 is scary, losing it at -2.5 should be even scarier, no? Might really be disappointed in a hundred years if we spend billions to drop temps 3-4 degrees for fear of them warming by 1 or 2.

Reality would appear to dictate that our actual influence on the energy budget isn't nearly that extreme, as I've pointed out twice already. The entire time our contribution(forcing from human GHGs) has been rising steadily, the energy imbalance has remained oblivious to that, or at least hasn't changed to an extent that we have the precision to measure yet. More good news, if you look at the energy balance reconstructions and studies that have been done, the biggest historic forcings on the energy balance have been volcanoes. What's the good news? Well, the energy imbalance corrects itself back to were it left of in a very short time, and very close to were it left off, over and over again. That's pretty good evidence that natural forcings, like the poorly modeled and understood GHG known as water vapor, act heavily to drive the energy imbalance back to equilibrium when faced with an external forcing like volcanoes. That's good news because we can look for signals that those same natural forcings might affect CO2. We'd then expect to see an energy imbalance that doesn't run away in the face of continually increasing human GHG forcings... You know, exactly like what we are seeing.

We know more energy will cause systems to be more chaotic. We don't know how much a given reduction in human CO2 emissions will reduce the energy imbalance. We don't know HOW costly the difference in adaptation is for that unknown change in energy imbalance. I'm not seeing a strong reason here to advocate for CO2 reductions over adaptation unless the CO2 reductions are really cheap, which no meaningful ones are.

In IPCC parlance adaptation is used to reference measures to adapt to changes to the climate. The word mitigation on the other hand is reserved for efforts to reduce the actual amount of change that will occur to the climate.

Seriously? You are arguing the urgency of taking action is HIGHER the more ignorant we are?

If you are correct, and the increase to energy imbalance from pushing CO2 concentrations up cancels that quickly from the increased temperature(nearly within the year), then you are advocating for an even lower impact from CO2 concentration increases than anybody I know of.

For reference, the actual data gives us the following pictures.
From ERBS, the papers from NASA and others assessing the energy imbalance from it come up with an average annual imbalance from about '89 through '99, I forget the number but it's about 0.6W/m^2 depending your method of error corrections. That is the best guess for the imbalance each year from 89 through 99, with no real noted difference or trend in the time frame, so a flat line of steadily gaining energy. Meanwhile CO2 concentrations(Mauna Loa) in 1989 were 353ppm and by 1999 were 368ppm, so a 4% increase in CO2 made no detectable increase to energy imbalance. Same story for the following CERES program from 2000 through to today. The IPCC observed in AR5 that there is very likely NO TREND to the energy imbalance since 2000, yet CO2 has gone from 369ppm in 2000 to 397ppm in 2013. A 7.6% increase from 2000 to 2013 left no noticeable trend in the energy imbalance. Or more telling still the increase in CO2 from 1989 to 2013 was more than 12% while the energy imbalance shows us no observable trend in either satellite observation over that same time frame.

So you could spend billions getting our CO2 concentrations back to 1989 levels and find that based on our satellite records, the energy imbalance wouldn't change a bit and we'd just have that much less money to spend on adapting to rising temperatures.

I have to applaud the focus on adaptation over mitigation. These changes are happening or likely, now what can we do to adapt. The other response of trying to drastically cut CO2 emissions to avoid or reduce climate change lacks two of the most important pieces of information required to evaluate it. How much does our reduction of CO2 emission mitigate future change, and what is the reduced cost of adaptation? Without knowing those two pieces, the decision to reduce CO2 emissions to 'save future dollars' is a blind guess, and there are a lot of much, much better reasons to reduce dependency on oil from places like the ME.

I know someone is going to jump in and claim we DO know the impact of increasing/reducing our CO2 emissions in the future. I say that the current research papers confirm the opposite, even the IPCC's latest paper. We've done lots of modelling of temperature change, but have badly neglected the energy balance. You know, the actual energy in versus out of the atmosphere that is the ACTUAL greenhouse affect that CO2 functions on. Luckily we started measuring observations by satellite in the late 80s.The ERBS and CERES programs from NASA have given us direct measurements of trends in the overall energy balance at the edge of space. The most direct measurement of global warming that we can have. The summary from each program, has let us find a decade level average energy imbalance, and we've found it is in good or at least general agreement with energy levels measured via Ocean Heat Content observations.

Here's the important bit though. As the IPCC's most recent AR has observed, the satellite measurements show that for the duration of the CERES project, there has been NO TREND in the energy imbalance. The earlier ERBS data showed the same as well. Our satellite measurements have shown significant and very steady trends in energy balance cycling monthly, but the average over the years and decades we've measured is just a steady and consistent average neither shifting noticeably up or down. Meanwhile, CO2 concentrations in the atmosphere over that same time have climbed like nobody's business. All our models and expectation for X degrees of warming for so much CO2 kinda hinges pretty heavy on CO2 pushing up the energy imbalance. If it's not, and observations suggest that. We may not need to be so worried as some of the panic ridden crowd wants. That said, we DO still have an annual energy imbalance adding energy to the planet, it just has been adding as much last year, as it did the year before, on back through to 2000. Even though in 2000 CO2 concentrations were lower, the imbalance just hasn't changed. We are thus facing increasing energy(general warming), but thus far our direct measurements can't detect the difference our increasing CO2 concentrations are making.

Before I get citation needed shoved down my throat, here's a peer reviewed journal article published in Geophysical Research Letters. It is comparing observed atmosphere energy imbalance to the CMIP5 model runs. It finds good agreement, but also makes the very notable observation that the energy imbalance trend is dominated by volcanic activity(ie NOT the CO2 levels that are higher than they've been in millenia). Full abstract:
Observational analyses of running 5 year ocean heat content trends (Ht) and net downward top of atmosphere radiation (N) are significantly correlated (r~0.6) from 1960 to 1999, but a spike in Ht in the early 2000s is likely spurious since it is inconsistent with estimates of N from both satellite observations and climate model simulations. Variations in N between 1960 and 2000 were dominated by volcanic eruptions and are well simulated by the ensemble mean of coupled models from the Fifth Coupled Model Intercomparison Project (CMIP5). We find an observation-based reduction in N of 0.31±0.21Wm2 between 1999 and 2005 that potentially contributed to the recent warming slowdown, but the relative roles of external forcing and internal variability remain unclear. While present-day anomalies of N in the CMIP5 ensemble mean and observations agree, this may be due to a cancelation of errors in outgoing longwave and absorbed solar radiation.

So again in summary to the actual science, we should absolutely be looking at how to adapt to overall warming, because it's happening. Despite knowing that CO2 acts as a greenhouse gas and contributes to warming, we DO NOT have a strong and high confidence in just how much impact increasing CO2 levels will have on future energy imbalance and temperature change. That is to say, we can't confidently state the difference between spending millions, billions or trillions into CO2 reductions will have on future energy imbalance and temperature change. Without that, spending our dollars on coping with the changes that are coming is by far the most efficient spending we can make. Besides, with Oil coming out of the middle east and things like Tesla electric cars around the corner, we'll find plenty of reasons to cut way back on our oil burning soon enough for entirely different reasons.

You seem to be making the weakest of 'appeal to authority' arguments ever. Your just waving your hands saying there must be experts out there somewhere that have an explanation, but I'm not even gonna bother pointing out either the expert or the explanation.

If you want to go ahead and look at the latest IPCC report, they have temperature predictions out to the year 2100. Based on their scenarios, the temperature out at 2100 is expected to range from just a bit cooler than today, all the way up to 4.5C warmer than today. The scenarios are based on expected forcing, ie the energy imbalance, over those years. With the last 30 years(the entirety of the satellite record) showing a very much linear energy increase in energy to the system, that helps us make a guess which of the scenarios the IPCC used we might want to look at as an expected case or best guess. It turns out the IPCC's two lowest scenarios fall just below and just above a linear increase of forcing through to 2100. These are RCP secnario's 4.5 and 2.6, adn if you look in chapter 11 of the IPCC fifth AR you can find figure 11.9 is temeprature projected for Scenario 4.5, and it even graphs the observed temperature against the projected for us, and low and behold the observed tracks right along the lower limit of the projections. That's kind of exactly what we might expect from the observations of the energy imbalance from satellites matching that same point on the scenarios main variable. If you look in Chapter 12, you can see where they plot out to the year 2300, and even there scenario 4.5 hits around the 2C mark and scenario 2.6 is under 1C, so if we observe that current energy trends with our current increasing CO2 match the middle ground of those scenarios, it is rather in keeping with mainstream science to say, hey that's a good best guess. Incidentally, that also averages out at the 1.5C that the article is all excited for us to work hard to meet.

For all the people saying we need to panic in case CO2 levels force the very non linear worst cases from the IPCC on us, I think it fair to observe the current record. To notice that the CO2 levels since 1900 have risen very rapidly indeed, as rapidly as we project them to continue increasing in the IPCC worst case scenarios. During that timeframe though, the energy imbalance/forcing has NOT been none linear, but instead from the entirety of the satellite record has been increasing very linearly indeed, and with peaks and troughs of that linear average dominated by volcanic activity. In chapter 12 and figure 12.15 you can compare for yourself the actual mainstream basis for the scenarios the IPCC used, it graphs both historical and projected Top Of Atmosphere energy imbalance. Note also that the historical older than 1980 though is reconstructions with admitted large margin of error as it's mostly based on ocean heat reconstructions, and scientists regret those data sets are not very extensive and more importantly, are until recently only include temperature at the shallowest layers of the ocean so trends in deeper currents are lost. If you take the 'best', 1980 onward of observed satellite energy in and out measures, I not only don't think I'm a skeptic to suggest the lower estimates for the future are better. I think you'll find a lot of the mainstream climate scientists agreeing right with me. If you go read the latest journal articles on CMIP5 simulations and comparisons to observations, you find a whole lot of notes and observations that are right in line.

Or more shortly, if you want to dismiss my reference and summary from a peer reviewed journal article with a vague, I'm sure the experts have explained that away, you need to try harder and maybe read what those actual experts are really saying rather than the summary for policy makers written by the political characters afterwards.

There has absolutely been an energy increase. The energy imbalance I was talking about is the net energy gain at the edge of space, that is how much more energy in/out was there in a year. The satellite results show us that the earth has been gaining more energy than it bleeds off for the entire satellite record. The rate at which energy has been accumulating is where there has been no trend. From 1960 through to today, what little trend there has been in more/less energy being gained has been dominated by volcanic activity and NOT the major increases to CO2 concentrations. Since 2000, the IPCC notes the imbalance has had no trend at all from volcanoes, CO2 or anything, we've just had an overall balance of more energy still coming in than out, but a decade and a half of increasing CO2 emissions have had no observable increase to the rate energy is being trapped.

Go back to high school and retake reading comprehension and basic physics please. I know that is far too rude and confrontational, but it doesn't sound like you read my post at all, which is tiresome.

I stated myself that surface temperature has been consistently rising. I and anyone trusting the meteorology community agrees that even the current 'slowdown' is as you reference, a matter of warming but at a slower rate than previously and than expected.

I don't comprehend where you ever got the notion I believed or claimed otherwise? I pointed out that the rate of net energy/radiation coming into the planet is the more important and direct measure. The basic physics of the greenhouse effect is trapping incoming radiation so that more is coming in than going out. The resulting extra energy leads to warming. What I observed and you again reference yourself in your quote of the article is that the changes to that energy imbalance at t edge of space, is dominated by volcanic activity since the 60s. With the major increases we've contributed to CO2 contributions in that same time, that gives some hope things aren't as bleak as many fear mongers wish. With no notable trend in the energy imbalance in the whole Ceres results of the last decade and a half, we certainly seem less likely to be facing catastrophic sensitivity to CO2. The increases of a decade and a half being in essence undetectable in the core measure of changes to the energy imbalance.

The basic physics of climate change is that increasing levels of gases trap more energy from the sun, increasing the amount of energy in our atmosphere and climate system. We know by and large, most of the energy is stored in the oceans as water holds energy much better than gases in the air.

With such a simple observation, I'd like to make the observation that it seems too few of the IPCC guys pushing for policy stuff are paying any attention to the energy budget. Instead, we have the only basis scientifically being that the average surface temperature is warming, and CO2 levels are rising and we are the ones pushing them up. That's all well and good, and they are important observations. About 30 years ago though we started sending up satellites to measure incoming and outgoing radiation. The ERBS and CERES programs from NASA have given us direct measurements of trends in the overall energy balance at the edge of space. The most direct measurement of global warming that we can have. The summary from each program, has let us find a decade level average energy imbalance, and we've found it is in good or at least general agreement with energy levels measured via Ocean Heat Content observations.

Here's the important bit though. As the IPCC's most recent AR has observed, the satellite measurements show that for the duration of the CERES project, there has been NO TREND in the energy imbalance. The earlier ERBS data showed the same as well. Our satellite measurements have shown significant and very steady trends in energy balance cycling monthly, but the average over the years and decades we've measured is just a steady and consistent average neither shifting noticeably up or down. Meanwhile, CO2 concentrations in the atmosphere over that same time have climbed like nobody's business. All our models and expectation for X degrees of warming for so much CO2 kinda hinges pretty heavy on CO2 pushing up the energy imbalance. If it's not, and observations suggest that. We may not need to be so worried as some of the panic ridden crowd wants.

Before I get citation needed shoved down my throat, here's a peer reviewed journal article published in Geophysical Research Letters. It is comparing observed atmosphere energy imbalance to the CMIP5 model runs. It finds good agreement, but also makes the very notable observation that the energy imbalance trend is dominated by volcanic activity(ie NOT the CO2 levels that are higher than they've been in millenia). Full abstract:
Observational analyses of running 5 year ocean heat content trends (Ht) and net downward top of atmosphere radiation (N) are significantly correlated (r~0.6) from 1960 to 1999, but a spike in Ht in the early 2000s is likely spurious since it is inconsistent with estimates of N from both satellite observations and climate model simulations. Variations in N between 1960 and 2000 were dominated by volcanic eruptions and are well simulated by the ensemble mean of coupled models from the Fifth Coupled Model Intercomparison Project (CMIP5). We find an observation-based reduction in N of 0.31±0.21Wm2 between 1999 and 2005 that potentially contributed to the recent warming slowdown, but the relative roles of external forcing and internal variability remain unclear. While present-day anomalies of N in the CMIP5 ensemble mean and observations agree, this may be due to a cancelation of errors in outgoing longwave and absorbed solar radiation.

Thanks for agreeing and confirming the only facts I pointed out:
Ukraine willingly gave up it's nuclear arsenal.
Russia is now invading Ukraine.

I'd second the SA blame for 911, but even more directly responsible than them would have to be Pakistan.

The American support for the mujahideen during the Soviet-Afghan times wasn't solely to Al Qaida chaps, but to anyone willing to fight the Russians, including Al Qaida and the Taliban and the Afghan Northern Alliance folks that were their enemies. It's not lying per se to claim that America supported people that would later become key players in the Taliban and Al Qaida, but it's certainly less than half of the truth.

Pakistan however had continued to support the Taliban right on through. Part of Pakistan's war planning against India was 'strategic depth' into Afghanistan where the friendly and allied Taliban forces gave room for them to move into and operate alongside. The Taliban being as largely uneducated and prone to fanatacism as they were made Al Qaida a moderate voice for Pakistan to work with the Taliban through as well. Pakistan's ISI(equivalent of the CIA) was deeply, deeply in bed with the Taliban and Al Qaida. When the towers went down, the American response was who could have or might have done this? The immediate response in tribal Pakistan was different and two fold. First, shock that Bin Laden actually went through with it and actually did it. The second, was when the Americans go to war with the Taliban, whose side will Pakistan take, and bets where 50/50.

Make no mistake, the Afghan war was 100% about Pakistan's response and ensuring that it and it's nuclear arsenal took sides against jihadists and severed it's buddy, buddy relationship with them. It was never stated outright publicly though, because that would be impolite and push Pakistan to refusing on principal, which it very nearly did anyways.

Indeed. And all Gadhafi had done was use his military to crush and murder peaceful protests, and when that turned ugly, promising to 'exterminate the cockroaches house by house'. Stopping him was certainly an unjustifiable failure of international relations.