Contrary To Contrarian Claims, IPCC Temperature Projections Have Been Exceptionally Accurate

Rajendra Pachauri, chairman of the IPCC

by Dana Nuccitelli, via Skeptical Science

There is a new myth circulating in the climate contrarian blogosphere and mainstream media that a figure presented in the "leaked" draft Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report shows that the planet has warmed less than previous IPCC report climate model simulations predicted.

Tamino at the Open Mind blog and Skeptical Science's own Alex C have done a nice job refuting this myth. We prefer not to post material from the draft unpublished IPCC report, so refer to those links if you would like to see the figure in question.

In this post we will evaluate this contrarian claim by comparing the global surface temperature projections from each of the first four IPCC reports to the subsequent observed temperature changes. We will see what the peer-reviewed scientific literature has to say on the subject, and show that not only have the IPCC surface temperature projections been remarkably accurate, but they have also performed much better than predictions made by climate contrarians (Figure 1).

Figure 1: IPCC temperature projections (red, pink, orange, green) and contrarian projections (blue and purple) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; black and red) for 1990 through 2012.

1990 IPCC FAR

The IPCC First Assessment Report (FAR) was published in 1990. The FAR used simple global climate models to estimate changes in the global mean surface air temperature under various CO2 emissions scenarios. Details about the climate models used by the IPCC are provided in Chapter 6.6 of the report.

The IPCC FAR ran simulations using various emissions scenarios and climate models. The emissions scenarios included business as usual (BAU) and three other scenarios (B, C, D) in which global human greenhouse gas emissions began slowing in the year 2000. The FAR's projected BAU greenhouse gas (GHG) radiative forcing (global heat imbalance) in 2010 was approximately 3.5 Watts per square meter (W/m2). In the B, C, D scenarios, the projected 2011 forcing was nearly 3 W/m2. The actual GHG radiative forcing in 2011 was approximately 2.8 W/m2, so to this point, we're actually closer to the IPCC FAR's lower emissions scenarios.

As shown in Figure 2, the IPCC FAR ran simulations using models with climate sensitivities (the total amount of global surface warming in response to a doubling of atmospheric CO2, including amplifying and dampening feedbacks) corresponding to 1.5°C (low), 2.5°C (best), and 4.5°C (high). However, because climate scientists at the time believed a doubling of atmospheric CO2 would cause a larger global heat imbalance than today's estimates, the actual climate sensitivities were approximately 18% lower (for example, the 'Best' model sensitivity was actually closer to 2.1°C for doubled CO2).

Figure 2: IPCC FAR projected global warming in the BAU emissions scenario using climate models with equilibrium climate sensitivities of 1.3°C (low), 2.1°C (best), and 3.8°C (high) for doubled atmospheric CO2

Figure 3 accounts for the lower observed GHG emissions than in the IPCC BAU projection, and compares its 'Best' adjusted projection with the observed global surface warming since 1990.

Figure 3: IPCC FAR BAU global surface temperature projection adjusted to reflect observed GHG radiative forcings 1990-2011 (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 1990 through 2012.

FAR Scorecard

The IPCC FAR 'Best' BAU projected rate of warming from 1990 to 2012 was 0.25°C per decade. However, that was based on a scenario with higher emissions than actually occurred. When accounting for actual GHG emissions, the IPCC average 'Best' model projection of 0.2°C per decade is within the uncertainty range of the observed rate of warming (0.15 ± 0.08°C) per decade since 1990, though a bit higher than the central estimate.

1995 IPCC SAR

The IPCC Second Assessment Report (SAR) was published in 1995, and improved on the FAR by including an estimate of the cooling effects of aerosols - particulates which block sunlight and thus have a net cooling effect on global temperatures. The SAR included various human emissions scenarios; so far its scenarios IS92a and b have been closest to actual emissions.

The SAR also maintained the "best estimate" equilibrium climate sensitivity used in the FAR of 2.5°C for a doubling of atmospheric CO2. However, as in the FAR, because climate scientists at the time believed a doubling of atmospheric CO2 would cause a larger global heat imbalance than current estimates, the actual "best estimate" model sensitivity was closer to 2.1°C for doubled CO2.

Using global climate models and the various IS92 emissions scenarios, the SAR projected the future average global surface temperature change to 2100 (Figure 4).

Figure 4: Projected global mean surface temperature changes from 1990 to 2100 for the full set of IS92 emission scenarios. A climate sensitivity of 2.12°C is assumed.

Figure 5 compares the IPCC SAR global surface warming projection for the most accurate emissions scenario (IS92a) to the observed surface warming from 1990 to 2012.

Figure 5: IPCC SAR Scenario IS92a global surface temperature projection (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 1990 through 2012.

SAR Scorecard

The IPCC SAR IS92a projected rate of warming from 1990 to 2012 was 0.14°C per decade. This is within the uncertainty range of the observed rate of warming (0.15 ± 0.08°C) per decade since 1990, and very close to the central estimate.

2001 IPCC TAR

The IPCC Third Assessment Report (TAR) was published in 2001, and included more complex global climate models and more overall model simulations than in the previous IPCC reports. The IS92 emissions scenarios used in the SAR were replaced by the IPCC Special Report on Emission Scenarios (SRES), which considered various possible future human development storylines.

The IPCC model projections of future warming based on the various SRES and human emissions only (both GHG warming and aerosol cooling, but no natural influences) are shown in Figure 6.

Figure 6: Historical human-caused global mean temperature change and future changes for the six illustrative SRES scenarios using a simple climate model. Also for comparison, following the same method, results are shown for IS92a. The dark blue shading represents the envelope of the full set of 35 SRES scenarios using the simple model ensemble mean results. The bars show the range of simple model results in 2100.

Thus far we are on track with the SRES A2 emissions path. Figure 7 compares the IPCC TAR projections under Scenario A2 with the observed global surface temperature change from 1990 through 2012.

Figure 7: IPCC TAR model projection for emissions Scenario A2 (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 1990 through 2012.

TAR Scorecard

The IPCC TAR Scenario A2 projected rate of warming from 1990 to 2012 was 0.16°C per decade. This is within the uncertainty range of the observed rate of warming (0.15 ± 0.08°C) per decade since 1990, and very close to the central estimate.

2007 IPCC AR4

In 2007, the IPCC published its Fourth Assessment Report (AR4). In the Working Group I (the physical basis) report, Chapter 8 was devoted to climate models and their evaluation. Section 8.2 discusses the advances in modeling between the TAR and AR4. Essentially, the models became more complex and incorporated more climate influences.

As in the TAR, AR4 used the SRES to project future warming under various possible GHG emissions scenarios. Figure 8 shows the projected change in global average surface temperature for the various SRES.

Figure 8: Solid lines are multi-model global averages of surface warming (relative to 1980-1999) for the SRES scenarios A2, A1B, and B1, shown as continuations of the 20th century simulations. Shading denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The grey bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios.

We can therefore again compare the Scenario A2 multi-model global surface warming projections to the observed warming, in this case since 2000, when the AR4 model simulations began (Figure 9).

Figure 9: IPCC AR4 multi-model projection for emissions Scenario A2 (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 2000 through 2012.

AR4 Scorecard

The IPCC AR4 Scenario A2 projected rate of warming from 2000 to 2012 was 0.18°C per decade. This is within the uncertainty range of the observed rate of warming (0.06 ± 0.16°C) per decade since 2000, though the observed warming has likely been lower than the AR4 projection.

As we will show below, this is due to the preponderance of natural temperature influences being in the cooling direction since 2000, while the AR4 projection is consistent with the underlying human-caused warming trend.

IPCC Projections vs. Observed Warming Rates

Tamino at the Open Mind blog has also compared the rates of warming projected by the FAR, SAR, and TAR (estimated by linear regression) to the observed rate of warming in each global surface temperature dataset. The results are shown in Figure 10.

Figure 10: IPCC FAR (yellow) SAR (blue), and TAR (red) projected rates of warming vs. observations (black) from 1990 through 2012.

As this figure shows, even without accounting for the actual GHG emissions since 1990, the warming projections are consistent with the observations, within the margin of uncertainty.

Rahmstorf et al. (2012) Verify TAR and AR4 Accuracy

A paper published in Environmental Research Letters by Rahmstorf, Foster, and Cazenave (2012) applied the methodology of Foster and Rahmstorf (2011), using the statistical technique of multiple regression to filter out the influences of the El Niño Southern Oscillation (ENSO) and solar and volcanic activity from the global surface temperature data to evaluate the underlying long-term primarily human-caused trend. Figure 11 compares their results with and without the short-term noise from natural temperature influences (pink and red, respectively) to the IPCC TAR (blue) and AR4 (green) projections.

Figure 11: Observed annual global temperature, unadjusted (pink) and adjusted for short-term variations due to solar variability, volcanoes, and ENSO (red) as in Foster and Rahmstorf (2011). 12-month running averages are shown as well as linear trend lines, and compared to the scenarios of the IPCC (blue range and lines from the 2001 report, green from the 2007 report). Projections are aligned in the graph so that they start (in 1990 and 2000, respectively) on the linear trend line of the (adjusted) observational data.

TAR Scorecard

From 1990 through 2011, the Rahmstorf et al. unadjusted and adjusted trends in the observational data are 0.16 and 0.18°C per decade, respectively. Both are consistent with the IPCC TAR Scenario A2 projected rate of warming of approximately 0.16°C per decade.

AR4 Scorecard

From 2000 through 2011, the Rahmstorf et al. unadjusted and adjusted trends in the observational data are 0.06 and 0.16°C per decade, respectively. While the unadjusted trend is rather low as noted above, the adjusted, underlying human-caused global warming trend is consistent with the IPCC AR4 Scenario A2 projected rate of warming of approximately 0.18°C per decade.

Frame and Stone (2012) Verify FAR Accuracy

A paper published in Nature Climate Change, Frame and Stone (2012), sought to evaluate the FAR temperature projection accuracy by using a simple climate model to simulate the warming from 1990 through 2010 based on observed GHG and other global heat imbalance changes. Figure 12 shows their results. Since the FAR only projected temperature changes as a result of GHG changes, the light blue line (model-simulated warming in response to GHGs only) is the most applicable result.

Figure 12: Observed changes in global mean surface temperature over the 1990-2010 period from HadCRUT3 and GISTEMP (red) vs. FAR BAU best estimate (dark blue), vs. projections using a one-dimensional energy balance model (EBM) with the measured GHG radiative forcing since 1990 (light blue) and with the overall radiative forcing since 1990 (green). Natural variability from the ensemble of 587 21-year-long segments of control simulations (with constant external forcings) from 24 Coupled Model Intercomparison Project phase 3 (CMIP3) climate models is shown in black and gray. From Frame and Stone (2012).

FAR Scorecard

Not surprisingly, the Frame and Stone result is very similar to our evaluation of the FAR projections, finding that they accurately simulated the global surface temperature response to the increased greenhouse effect since 1990. The study also shows that the warming since 1990 cannot be explained by the Earth's natural temperature variability alone, because the warming (red) is outside of the range of natural variability (black and gray).

IPCC Trounces Contrarian Predictions

As shown above, the IPCC has thus far done remarkably well at predicting future global surface warming. The same cannot be said for the climate contrarians who criticize the IPCC and mainstream climate science predictions.

Richard Lindzen

One year before the FAR was published, Richard Lindzen gave a talk at MIT in 1989 which we can use to reconstruct what his global temperature prediction might have looked like. In that speech, Lindzen remarked

"I would say, and I don't think I'm going out on a very big limb, that the data as we have it does not support a warming...I personally feel that the likelihood over the next century of greenhouse warming reaching magnitudes comparable to natural variability seems small"

The first statement in this quote referred to past temperatures - Lindzen did not believe the surface temperature record was accurate, and did not believe that the planet had warmed from 1880 to 1989 (in reality, global surface temperatures warmed approximately 0.5°C over that timeframe). The latter statement suggests that the planet's surface would not warm more than 0.2°C over the following century, which is approximately the range of natural variability. In reality, as Frame and Stone showed, the surface warming already exceeded natural variability two decades after Lindzen's MIT comments.

Don Easterbrook

Climate contrarian geologist Don Easterbook has been predicting impending global cooling since 2000, based on expected changes in various oceanic cycles (including ENSO) and solar activity. Easterbrook made two specific temperature projections based on two possible scenarios. As shown in Figure 1, neither has fared well.

Syun-Ichi Akasofu

In 2009, Syun-Ichi Akasofu (geophysicist and director of the International Arctic Research Center at the University of Alaska-Fairbanks) released a paper which argued that the recent global warming is due to two factors: natural recovery from the Little Ice Age (LIA), and "the multi-decadal oscillation" (oceanic cycles). Based on this hypothesis, Akasofu predicted that global surface temperatures would cool between 2000 and 2035. Akasofu's prediction is the least wrong of the contrarian predictions examined here, but with a 0.02°C per decade cooling prediction between 2000 and 2012, has not matched the 0.06°C per decade warming trend, despite the fact that according to Foster and Rahmstorf, natural climate influences have had an approximately 0.1°C cooling effect since 2000.

John McLean

John McLean is a data analyst and member of the climate contrarian group Australian Climate Science Coalition. He was lead author on McLean et al. (2009), which grossly overstates the influence of the El Niño Southern Oscillation (ENSO) on global temperatures. Based on the results of that paper, McLean predicted:

"it is likely that 2011 will be the coolest year since 1956 or even earlier"

In 1956, the average global surface temperature anomaly in the three datasets (NASA GISS, NOAA NCDC, and HadCRUT4) was -0.21°C. In 2010, the anomaly was 0.61°C. Therefore, McLean was predicting a greater than 0.8°C global surface cooling between 2010 and 2011. The largest year-to-year average global temperature change on record is less than 0.3°C, so this was a rather remarkable prediction, and not surprisingly turned out to be very wrong.

IPCC vs. Contrarians Scorecard

Figure 1 at the top of this post compares the four IPCC projections and the four contrarian predictions to the observed global surface temperature changes. We have given Lindzen the benefit of the doubt and not penalized him for denying the accuracy of the global surface temperature record in 1989. Our reconstruction of his prediction takes the natural variability of ENSO, the sun, and volcanic eruptions from Foster and Rahmstorf (2011) (with a 12-month running average) and adds a 0.02°C per decade linear warming trend. Note that this was not a specific prediciton made by Lindzen, but rather is our reconstruction based on his 1989 comments. All other predictions are as discussed above.

Not only has the IPCC done remarkably well in projecting future global surface temperature changes thus far, but it has also performed far better than the few climate contrarians who have put their money where their mouth is with their own predictions.

Conservative IPCC Errs on the Side of Least Drama

Although the IPCC climate models have performed remarkably well in projecting average global surface temperature warming thus far, Rahmstorf et al. (2012) found that the IPCC underestimated global average sea level rise since 1993 by 60%. Brysse et al. (2012) also found that the IPCC has tended to underestimate or failed to account for CO2 emissions, increased rainfall in already rainy areas, continental ice sheet melting, Arctic sea ice decline, and permafrost melting. Brysse et al. concludes that the on the whole the IPCC has been too conservative in its projections, "erring on the side of least drama" - in effect preferring to be wrong on the conservative side in order to avoid criticism.

Dana Nuccitelli is an environmental scientist at a private environmental consulting firm in the Sacramento, California area. This piece was originally published at Skeptical Science and was reprinted with permission.

http://thinkprogress.org/climate/2013/01/03/1378431/contrary-to-contra

Leaked IPCC Draft Report: Recent Warming Is Manmade, Cloud Feedback Is Positive, Inaction Is Suicidal

Ultra-conservative report still concludes sea level rise could reach 6 inches a decade by century's end! Deniers duped by leaker's blunder.

Figure SPM.6.a. Warming in two IPCC scenarios reveals humanity's choice. With aggressive action to reduce greenhouse gas emissions (RCP 2.6 with 443 ppm of CO2 in 2100), warming is modest and adaptation is plausible. With continued inaction (RCP 8.5 with 936 ppm in 2100), warming is a catastrophic and unmanageable 10°F over much of Earth's habited and arable land - and more than 15°F over the Arctic. This projection ignores many key amplifying feedbacks, such as the release of permafrost carbon, which would likely lead to far greater warming.

The draft 2013 Fifth Assessment report of the Intergovernmental Panel on Climate Change leaked this week makes clear inaction on climate change would be devastating to modern civilization. The report finds that the human fingerprint on climate has grown more obvious, concluding "it is virtually certain" the energy imbalance that causes global warming "is caused by human activities, primarily by the increase in CO2 concentrations. There is very high confidence that natural forcing contributes only a small fraction to this imbalance."

Yes, I know, the easily-duped deniers and their media stooges have reported the opposite is true, that solar forcing has been a significant driver of recent warming, but the deniers are as likely to be right as the flat earthers. The only question is why anyone still listens to them. I'll repost a debunking of their nonsense below.

The draft Summary for Policymakers (the only thing 99% of people will ever read) finds:

It is extremely likely [">95% probability"] that human activities have caused more than half of the observed increase in global average surface temperature since the 1950s. There is high confidence ["About 8 out of 10 chance"] that this has caused large-scale changes in the ocean, in the cryosphere, and in sea level in the second half of the 20th century. Some extreme events have changed as a result of anthropogenic influence.

That multiply-hedged morass is pretty much the mildest statement that could possibly be made. A December 2011 study found it's "Extremely Likely That at Least 74% of Observed Warming Since 1950″ was manmade; it's highly likely all of it was (see Figure 1 below).

For me, the leaked draft, which has not yet been peer reviewed - and thus still has time to be watered down yet more - underscores how pointless the IPCC has become. Like the 4th assessment before it, this ultra-conservative and instantly obsolete report ignores the latest science - see "Fifth Assessment Report Will Ignore Crucial Permafrost Carbon Feedback!" Note that including the permafrost feedback would probably make the RCP8.5 scenario in the top figure as much as 1.5°F warmer!

And like the AR4, the AR5 scenarios low-ball future impacts - "Arctic sea ice area is projected to decrease by 28% for September" for the 2016-2035 period vs. 1986-2005. Seriously IPCC, a 28% drop is the scenario your touting? In fact, as we have reported, many experts warn of "Near Ice-Free Arctic In Summer" in a decade if recent ice volume trends continue.

Even so, the uber-conservative AR5 draft makes clear to anyone who reads between the lines that inaction would be suicidal for humanity, with devastating warming and sea level rise that could hit a half a foot a decade by 2100. How precisely does one adapt to that?

Indeed, the report guts the one remaining myth of those who downplay future impacts, that clouds would act as a negative (or weakening) feedback. It finds:

The net radiative feedback due to all cloud types is likely positive.

But the report fails to clearly spell out what the recent science says about inaction - for that you might try "An Illustrated Guide to the Science of Global Warming Impacts" or the recentWorld Bank report, which warned "A 4°C [7°F] World Can, And Must, Be Avoided" To Avert "Devastating" Impacts.

So I can't see why AR5 would motivate anyone to act more than AR4 and thus I see little real-world value in the entire effort - see my November 2007 post, "Absolute MUST Read IPCC Report: Debate over, further delay fatal, action not costly"! Plus ça change, plus c'est la même chose.

Once again, the authors twist themselves in pretzels to over-hedge every statement with their precise (but inaccurate!) terminology. And so we learn in the draft Summary for Policymakers (SPM):

It is very likely that the Arctic sea ice cover will continue to shrink and thin in the course of the 21st century as global temperature rises.

No, really, it is "very likely" - "> 90% probability" - which I guess means, what, that the IPCC seriously thinks there is an up to 10% chance Arctic sea ice cover will stop shrinking and thinning???

Observations and analysis of drought make clear it is already intensifying in many key regions thanks to global warming - see "NOAA Bombshell: Human-Caused Climate Change Already a Major Factor in More Frequent Mediterranean Droughts" and "Study: Global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse." But all AR5 can muster up for the probability of future "increases in frequency and/or intensity of drought" is "Likely [> 66% probability] in some regions" - which I guess means the IPCC thinks there is 1 in 3 chance it won't happen anywhere! How could that be with the kind of warming we will see in the RCP8.5 scenario, which, it must be added is really just business as usual emissions and far from the worst-case?

This failure to warn the public and policymakers echoes the great failing of their 2011 extreme weather report (see "Blockbuster IPCC Chart Hints at Dust-Bowlification, But Report Is Mostly Silent on Warming's Gravest Threat to Humanity").

In it most extreme scenario, RCP8.5 - about 936 ppm of CO2 in 2100 (not a worst-case in the real world because of permafrost and other feedbacks) - sea level rise in 2100 is only about 2 feet. That assumes you can figure out what this means: "The contributions from ice sheet dynamical change and anthropogenic land water storage are treated as independent of scenario, since scenario dependence cannot be evaluated on the basis of existing literature, and as having uniform probability distributions, uncorrelated with the magnitude of global climate change." Clarity ain't the IPCC's strong suit.

In any case, most climate scientists expect considerably higher sea level rise, especially if we don't act. That's what the recent literature says - see "Sea levels may rise 3 times faster than IPCC estimated, could hit 6 feet by 2100" and "JPL bombshell: Polar ice sheet mass loss is speeding up, on pace for 1 foot sea level rise by 2050."

Finally, if you read the denier blogs or columnists - and if so, you have no one to blame but yourself - you've probably heard something about how the IPCC finds cosmic rays are a major climate driver. In fact, the SPM finds:

Cosmic rays enhance aerosol nucleation and cloud condensation nuclei production in the free troposphere, but there is high confidence that the effect is too weak to have any significant climatic influence during a solar cycle or over the last century.

For debunkings of the latest denier spin, see here and here and especially here, which has an interview with the lead author of the key draft chapter.

Below I'm reposting a Skeptical Science piece on the subject.

IPCC Draft Report Leaked, Shows Global Warming is NOT Due to the Sun

Posted on 14 December 2012 by dana1981

Alec Rawls, an occasional guest poster on the climate contrarian blog WattsUpWithThat who signed up to review the upcoming Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (as anyone can), has "leaked" a draft version of the report and declared that it "contains game-changing admission of enhanced solar forcing." This assertion was then repeated by James Delingpole at The Telegraph (with some added colorful language), and probably on many other climate contrarian blogs.

If the IPCC was to report that the sun is a significant player in the current rapid global warming, that would indeed be major news, because the body of peer-reviewed scientific literature and data clearly show that the sun has made little if any contribution to the observed global warming over the past 50+ years (Figure 1).

Figure 1: Percent contributions of greenhouse gases (GHGs), sulfur dioxide (SO2), the sun, volcanoes, and El Niño Southern Oscillation (ENSO) to the observed global surface warming over the past 50-65 years according to Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, green), Lean and Rind 2008 (LR08, purple), Huber and Knutti 2011 (HK11, light blue), Gillett et al. 2012 (G12, orange), and Wigley and Santer 2012 (WS12, dark green).

So why would the latest IPCC report contradict these studies when its purpose is to summarize the latest and greatest scientific research? The answer is simple - it doesn't. Rawls has completely misrepresented the IPCC report.

Cosmic Source of Confusion

The supposedly "game-changing admission" from the IPCC report is this:

"Many empirical relationships have been reported between GCR [galactic cosmic rays] or cosmogenic isotope archives and some aspects of the climate system...The forcing from changes in total solar irradiance alone does not seem to account for these observations, implying the existence of an amplifying mechanism such as the hypothesized GCR-cloud link."

This statement refers to a hypothesis of Henrik Svensmark from the Danish National Space Institute, who has proposed that galactic cosmic rays (GCRs) could exert significant influence over global temperatures. The GCR hypothesis suggests that when they reach Earth, GCRs (high-energy charged particles originating from somewhere in our galaxy) are capable of "seeding" clouds; thus at times when a lot of GCRs are reaching the Earth's surface, more clouds will form. Clouds generally have a cooling effect on the Earth's temperature, because they reflect sunlight.

So the hypothesis goes like this: high solar activity means a strong solar magnetic field, which deflects more GCRs away from Earth, which means less cloud formation, which means less sunlight is reflected away from Earth, which means more warming. This GCR-caused warming would amplify the warming already being caused by increased solar activity. Conversely, cooling from decreased solar activity would hypothetically be amplified by more GCRs on Earth, more clouds, more reflected sunlight, and thus more cooling.

It's important to note that so far virtually all scientific research on GCRs has shown that they are not effective at seeding clouds and thus have very little influence over the Earth's temperature. In fact, as Zeke Hausfather has noted, the leaked IPCC report specifically states this:

"...there is medium evidence and high agreement that the cosmic ray-ionization mechanism is too weak to influence global concentrations of [cloud condensation nuclei] or their change over the last century or during a solar cycle in any climatically significant way."

But more importantly in this context, even if GCRs did influence global temperature, they would currently be having a cooling effect.

Solar Activity is Down, Greenhouse Gases are Up

Rawls also provides the following quote from the IPCC report (emphasis added):

"There is very high confidence that natural forcing is a small fraction of the anthropogenic forcing. In particular, over the past three decades (since 1980), robust evidence from satellite observations of the TSI [total solar irradiance] and volcanic aerosols demonstrate a near-zero (-0.04 W m^-2) change in the natural forcing compared to the anthropogenic AF increase of ~1.0 ± 0.3 W m^-2."

The term "radiative forcing" refers to a global energy imbalance on Earth, which may be caused by various effects like changes in the greenhouse effect or solar activity. A positive forcing will result in warming temperatures, while a negative forcing will result in cooling.

Here the IPCC is saying that since 1980, the sun and volcanoes have combined to cause a slightly negative global energy imbalance, which means they have had a slight cooling influence on global temperatures over the past three decades. Indeed, solar activity has decreased a bit over that timeframe (Figure 2).

Figure 2: Global temperature (red, NASA GISS) and Total solar irradiance (blue, 1880 to 1978 from Solanki, 1979 to 2009 from PMOD), with 11-year running averages.

As we would expect, lower solar activity including a weaker solar magnetic field has translated into a slight increase in GCR flux on Earth (Figure 3). Note that on the left-hand axis of Figure 3, GCR counts decrease going up the axis in order to show the relationship with temperature, since fewer GCRs hypothetically means fewer clouds, less reflected sunlight, and higher temperatures.

Figure 3: Global average surface temperature (red, NASA GISS) vs. GCR flux on Earth (blue, Krivova & Solanki 2003), with 11-year running averages.

So, if GCRs really do amplify the solar influence on global temperatures, since 1980 they are amplifying a cooling effect. In fact, GCRs reaching Earth recently hit record high levels (Figure 4), yet temperatures are still way up.

Figure 4: Record cosmic ray flux observed in 2009 by the Advanced Composition Explorer (NASA)

Physical Reality Intrudes on Rawls

Rawls has argued to the contrary by claiming that the climate is still responding to the increase in solar activity from the early 20th century, and that GCRs are amplifying that solar warming from over 60 years ago. This argument is simply physically wrong. As Figure 2 illustrates, when solar activity rises, temperatures follow suit very soon thereafter. In fact, during the mid-20th century, solar activity and global surface temperatures both flattened out. Are we to believe that the planet suddenly began responding to the pre-1950 solar activity increase in 1975-2012, after not warming 1940-1975? The argument makes no physical sense.

On top of that, the hypothetical GCR process is a relatively rapid one. Cloud formation from GCR seeding should occur within days, and clouds have very short lifetimes. For GCRs to have a warming effect, solar activity must be increasing right now. It is not, in fact solar activity has been essentially flat and slightly declining in recent decades. Changes in solar activity from 60+ years ago have no bearing whatsoever on GCRs today.

IPCC Shows Global Warming is NOT Solar

To sum up,

• The leaked IPCC report states that there may be some connection between GCRs and some aspects of the climate system.

• However, the report is also consistent with the body of scientific literature in stating that research indicates GCRs are not effective at seeding clouds and have very little influence on global temperatures.

• Solar activity has been nearly flat and slightly decreasing in recent decades, meaning that if GCRs do amplify solar influences on climate, they are amplifying a cooling effect.

The body of peer-reviewed scientific literature is very clear: human greenhouse gas emissions, not solar activity or galactic cosmic rays, are causing global warming. The leaked IPCC report is entirely consistent with this conclusion. In fact, in attempting to argue to the contrary, Rawls has scored an own goal by showing that if anything, GCRs are currently amplifying a solar cooling effect.

http://thinkprogress.org/climate/2012/12/16/1334921/leaked-ipcc-draft-