THEN they play straw-man, citing a survey that asked scientists "Do you think human activity is a significant contributing factor in changing mean global temperatures?" What is wrong with that? What is wrong is the fact that a great many scientists believe that land-use changes has has MORE effect on climate than CO2. So this survey is completely useless in determining how many agree about CO2-based warming. [Jane Q. Public]

Could you please provide a citation documenting the claims made by these (unnamed) great many scientists you're talking about?

I have already pointed out that Doran is a straw-man argument, IF you are talking about CO2-based warming (what most people mean when they refer to AGW). The questions they asked do not specifically relate to CO2-based warming. Rather (example: "Do you think human activity is a significant contributing factor in changing mean global temperatures?"), it encompasses such things as land-use change, which many scientists consider to be a greater factor than CO2. [Jane Q. Public]

Here's a radiative forcings chart that actually does summarize research from many scientists:

1. Notice that humans release four significant greenhouse gases, and that methane, nitrous oxide and halocarbons have forced the climate by about +1.0 W/m^2 since 1750. This is a large fraction of the roughly +1.6 W/m^2 due to CO2 alone, which is one reason why climatologists don't focus solely on CO2.
2. Notice that land-use changes have produced an albedo effect that forces the climate by about -0.2 W/m^2. Clearing rainforests to plant endless fields of identical crops actually increases the albedo, reflecting more sunlight and producing a slight cooling effect.
3. Notice that the error bars on land-use change albedo forcings actually extend to zero. Modern science can't reliably distinguish land-use change albedo forcings from "zero", which is one reason why the Level of Scientific Understanding (LOSU) is listed as medium-low. Compare these error bars to those the on greenhouse gas forcings which has a high LOSU.

again, Doran was not about just "CO2-based" warming either, which is what most people mean when they say or write "AGW". It includes other anthropogenic causes like land-use changes. ... If you include climatologists their average drops below 90%. For ANY anthropogenic warming, not just CO2! [Jane Q. Public]

Yeah, ~88% is less than 90%. The higher percentages in the Doran survey already included all the climatologists who are active publishers on climate change. So agreement is only as "low" as ~88% when climatologists who don't publish regularly about climate change are included.

thanks to your reference, I have solid evidence that a good bit less than of 95% of "the experts" (less than 90% actually) support AGW theory -- and that is any AGW, not just CO2. [Jane Q. Public]

You seem to be implying that land-use changes can warm the global climate in ways that aren't related to CO2. As shown above, land-use changes actually cause a cooling albedo effect. But land-use changes actually do have a warming effect on the climate:

The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land-use change providing another significant but smaller contribution. Annual fossil carbon dioxide emissions[4] increased from an average of 6.4 [6.0 to 6.8][5] GtC (23.5 [22.0 to 25.0] GtCO2) per year in the 1990s to 7.2 [6.9 to 7.5] GtC (26.4 [25.3 to 27.5] GtCO2) per year in 2000–2005 (2004 and 2005 data are interim estimates). Carbon dioxide emissions associated with land-use change are estimated to be 1.6 [0.5 to 2.7] GtC (5.9 [1.8 to 9.9] GtCO2) per year over the 1990s, although these estimates have a large uncertainty. {7.3} [IPCC SPM, 2007]

In other words, land-use changes have a warming effect because clearing jungles releases a lot of CO2 stored in the vegetation. Note that in the 1990s, the upper bound of CO2 emissions due to land-use changes was less than half of the lower bound of those due to fossil fuel emissions.

I already mentioned the biggest one which many scientists believe is more important than CO2: land-use changes. From forest to farmland, field to parking lot. Is it enough to affect those figures compared to "CO2-only"? Probably. But of course I can't say for sure. [Jane Q. Public]

Again, could you please provide a citation documenting the claims made by these (again, unnamed) many scientists you're talking about?

In case you missed my previous reply:

The "mainstream" AGW tale is that the Medieval Warm Period and the Maunder Minimum were both less extreme than scientists thought in the past ... I'm not arguing that it is the truth. I'm simply saying that is the story that has been coming out of places like CRU and NASA. Deny it all you like: it's all over the press and even the peer-reviewed publications. [Jane Q. Public, 2012-08-28]

Please link to a peer-reviewed publication that supports your interpretation of mainstream climate science.

The "mainstream" AGW tale is that ... we are experiencing "extreme" weather that is not in the historical (by that I mean ice cores, etc.) record at all. I'm not arguing that it is the truth. I'm simply saying that is the story that has been coming out of places like CRU and NASA. Deny it all you like: it's all over the press and even the peer-reviewed publications. [Jane Q. Public, 2012-08-28]

Please be more specific about what types of "extreme" weather you're referring to, and please link to a peer-reviewed publication where mainstream climate scientists claimed that ice cores provide a historical record of these types of "extreme" weather.

(Ed. note: I've been trying to post comments like this one since 2012-09-01, but they never appeared on my article at the San Gabriel Valley Tribune. So I finally posted this reply at my website, Slashdot, and Mike Haseler's website Scottish Skeptic.)

Let's get the facts straight. Even doubling CO2, means its greenhouse effect would only rise global temperatures by 1C. That is half the threshold for action set by the IPCC.

But, this scam has nothing to do with their real science. These charlatans would be predicting the same nonsense if CO2's effect were twice as high or half as much, because the real contribution of CO2 is much smaller than the natural variation.

And let's not forget:

1. This scam is based on a rise in temperature from 1970 to 2000 which happens to be coincident with rising CO2. The overwhelming bulk of this rise has nothing to do with CO2 greenhouse effect.

2. Largely the same academics who cry wolf over this short term trend were crying wolf over the short term cooling before the 1970s.

3. It all stopped in 2000 (1998 to be precise). That's 14 years without warming, compared to the 30 year trend they say proves warming will continue till the earth fries (much like we were heading for an iceage)

4. And just to cap it all, it warmed the same amount, for the same period, before CO2 was measured rising between 1910 and 1940 and guess what ... we didn't end up global warming doomsday then either. [Mike Haseler, 2012-09-01]

0. Many diverse lines of evidence (paleoclimate, modern observations, fundamental physics) show that doubling CO2 warms the planet by roughly 3C.

1. Human CO2 forcing has increased dramatically since 1970, while solar irradiance, volcanic activity, cosmic rays, solar flares, etc. have remained about the same.

2. Even during the 1970s, most scientific papers were predicting warming.

3. Skeptical Science's "going down the up escalator" shows at a glance that this often-repeated myth about global warming ending in 1998 is wrong.

4. The rate of warming from 1910 to 1940 was about 0.13C/decade compared to about 0.18C/decade from 1975 to 2005. But scientists don't simply compare the rates; they examine natural and human radiative forcings which change the global climate's total energy, which is indeed an average over at least several decades. In the early 20th century there was a lull in volcanic eruptions which usually cool the climate by blocking out the sun over a few years. Early human CO2 emissions and a slight increase in the Sun's brightness also played small roles. Internal variability modes, which shift energy from one part of the globe to another (i.e. climate cycles) are also important. Temperatures measured in the 1940s were warmer than the models; this discrepency is thought to be due in part to Arctic decadal variability.

The "mainstream" AGW tale is that the Medieval Warm Period and the Maunder Minimum were both less extreme than scientists thought in the past ... I'm not arguing that it is the truth. I'm simply saying that is the story that has been coming out of places like CRU and NASA. Deny it all you like: it's all over the press and even the peer-reviewed publications.

Please link to a peer-reviewed publication that supports your interpretation of mainstream climate science.

The "mainstream" AGW tale is that ... we are experiencing "extreme" weather that is not in the historical (by that I mean ice cores, etc.) record at all. I'm not arguing that it is the truth. I'm simply saying that is the story that has been coming out of places like CRU and NASA. Deny it all you like: it's all over the press and even the peer-reviewed publications.

Please be more specific about what types of "extreme" weather you're referring to, and please link to a peer-reviewed publication where mainstream climate scientists claimed that ice cores provide a historical record of these types of "extreme" weather.

I hoped to end this interview with a concise, uplifting challenge to build a better future through human ingenuity. Oh, well. The modern anthropogenic skyrocketing CO2 concentration is a trend I desperately want to reverse, but here's a more relevant answer:

Here is a related question: If the former case, volcanoes produced CO2 and that raised temps, that same rise should also cook CO2 out of the oceans, which would produce an even greater rise in temps. What could reverse this trend?

The end-Permian event and the PETM (linked above) were eventually reversed because accessible carbon sources are finite. Plate tectonics continually exposes new rocks which absorb CO2 as it weathers, and other biochemical sinks absorb CO2 from the air. Positive feedbacks such as those you describe don't necessarily involve runaway warming, any more than geometric series necessarily blow up to infinity. But life during one of these temporary excursions is usually... interesting.

GRACE can resolve nearly uncorrelated mascons that are blocks 400km on each side with a noise floor of ~1cm equivalent water height. (This is latitude dependent because GRACE's denser ground tracks near the poles allow for better resolution.) Each mascon has a mass of ~1.6 gigatons, and a fully-loaded coal train is ~10 kilotons, so GRACE falls short by about five orders of magnitude.

The improved laser ranging on the GRACE follow-on will increase sensitivity, and David Wiese analyzes improvements due to lowering the satellites' altitude and/or adding more satellites to the GRACE system.

You're right to suspect that detecting a tiny change in local gravity is limited by uncertainties in models such as atmosphere dynamics. I've discussed how GPS occultation data (among many other data sources) can be used to reduce these uncertainties.

Other anthropogenic effects such as groundwater depletion can already be detected with GRACE. Rodell et al. 2009 (PDF) and Tiwari et al. 2009 (PDF) observed this in northern India, and Famiglietti et al. 2011 (PDF) recently observed similar groundwater depletion in California.

CO2 levels parallel average global temperatures, in looking at the geological record, correct? That gives much credence to CO2 as a mechanism for current climate change.

Correct. Here’s a figure from Royer et al. 2007 which concludes that “a climate sensitivity greater than 1.5C has probably been a robust feature of the Earth’s climate system over the past 420 million years”.

What increased C02 in ancient times? It is also my understanding that volcanic action produced CO2 which raised temps, Correct? Also, at other epochs, certain orbital factors cooked CO2 out of oceans. In this latter case, I would expect CO2 levels to lag temps (and then force greater changes) and in the former (volcanic) case CO2 levels would precede temp rise. Correct?

Correct. I've discussed the difference between these situations.

Here is a related question: If the former case, volcanoes produced CO2 and that raised temps, that same rise should also cook CO2 out of the oceans, which would produce an even greater rise in temps. What could reverse this trend?

Human ingenuity.

That's a good question; I described the difference between climate and weather at the beginning of my article. I later updated it with a better analogy from NOAA: One way to distinguish between weather and climate is that the climate of your hometown will determine how many sweaters you have in your closet. The weather will determine if you should be wearing a sweater right now.

Many times the climate being discussed is global, so an average is taken over the entire Earth. For global temperatures, Santer et al. 2011 shows that one needs to average over ~17 years of data to obtain statistically significant climate trends. Here's another explanation by Tamino. Also, the Skeptical Science trend calculator helps visualize statistical significance.

What in the world was up with this letter from ex-employees [plantsneedco2.org] (also discussed on Slashdot [slashdot.org])? Was that just totally out of left field? Was there an internal reaction to it? Did you respond?

Yes, it was totally out of left field. I responded in an internal JPL email, and copied the email to my (other) website.

-Bryan Killett, aka khayman80, aka Dumb Scientist

(This was copied from very far down so readers don't have to wade through all these charming comments just to read my answer to eldavojohn's question.)

For those who may not be aware, GPS signals can be used to measure atmospheric properties. As GRACE (or any satellite with a modern GPS receiver) listens to a GPS satellite that's about to pass below the horizon, the GPS signal passes through the atmosphere. Thus the GPS signal is refracted and delayed in ways that can reveal the temperature, pressure, and refractivity of the atmosphere at different altitudes. These are known as GPS occultation measurements.

I've never used GPS occultation measurements, so I asked Gerhard Kruizinga about them at the weekly GRACE meeting. He pointed me to GFZ which has near-real time data (that page shows GPS occultation measurements taken today, but getting the data from GFZ probably requires filling out a quick form). Gerhard also mentioned that GPS occultation measurements from GRACE are regularly fed into the ECMWF atmosphere model, which is briefly described here.