Tag Archives: IPCC

ConCERN Trolling on Cosmic Rays, Clouds, and Climate Change

Image courtesy of Flickr user “Mr DeJerk”, used under Creative Commons

OR: Nope, cosmic rays still not driving climate change, cont’d, cont’d…

Clouded “Reporting”

Depending on where you get your science news, you might be hearing claims to the effect that CLOUD at CERN has “proven that cosmic rays drive climate change”, or something to that effect. That’s certainly the impression that climate “skeptics” would like you to get. Unfortunately for “skeptics” (and if we don’t rein in greenhouse emissions, everyone else), it’s not true. While cosmic rays may have some influence on cloud formation, they are not responsible for the present, human-driven climatic change or alleged changes in the geologic past.

What’s the deal?

Although seemingly out of fashion for a while until recently, the “cosmic rays are driving climate” myth has long been one of the mainstays of the self-contradictory climate “skeptic” argument stable, and it’s something covered fairly often at this blog (previous posts here, here, here, here, here, and here). And as with any good falsehood, it starts with a kernel of truth.

It is completely accepted in mainstream science that galactic cosmic rays (GCRs) might be able to influence the nucleation process of potential cloud condensation nuclei (CCN), and that it’s conceivable that this could influence cloud behavior at some level. As the IPCC AR4 noted (I’ll include the full text at the end, after the jump):

By altering the population of CCN and hence microphysical cloud properties (droplet number and concentration), cosmic rays may also induce processes analogous to the indirect effect of tropospheric aerosols. The presence of ions, such as produced by cosmic rays, is recognised as influencing several microphysical mechanisms (Harrison and Carslaw, 2003). Aerosols may nucleate preferentially on atmospheric cluster ions. In the case of low gas-phase sulphuric acid concentrations, ion-induced nucleation may dominate over binary sulphuric acid-water nucleation.

While a plausible mechanism exists, real world verifications are necessarily difficult to undertake. The CLOUD project at CERN is seeking to do exactly that. The “skeptic” and right wing blogospheres are abuzz because Jasper Kirkby, et al. have just published the first results in Nature (Kirkby 2011).

RealClimate has a good rundown of what Kirkby et al.’s results do and do not mean. The short version is that Kirkby et al. do find increased aerosol nucleation under increased ionization (i.e. “more cosmic rays”), particularly in the mid-troposphere, but the effect is smaller at warmer, lower levels where the cosmic ray-climate myth proponents claim it has its greatest climatic effect. Lead author Jasper Kirkby has tried to set the record straight, stating (all following emphases mine):

[The paper] actually says nothing about a possible cosmic-ray effect on clouds and climate, but it’s a very important first step.

While their results provide some confirmation of the potential mechanism by which GCRs might induce cloud nucleation, they in no way demonstrate that GCRs do significantly promote cloud formation in the real world, let alone support the myth that GCRs drive significant climatic change.

“But wait!” I’m sure some of you may be thinking, “the Kirkby et al. results certainly don’t disprove GCRs drive significant climatic changes.” And that’s true enough.

How Do We Know That Cosmic Rays Aren’t Driving Significant Climatic Change?

In reference to the present anthropogenic climatic changes that we’re driving through alteration of the planetary energy balance notably through greenhouse gas emissions, we can theorize what certain “fingerprints” of enhanced greenhouse warming should look like, and examine observational data to see whether those fingerprints show up. And they do.

Moreover, we can examine the claims made by Svensmark, Shaviv, and others who proclaim GCRs drive climate and see whether or not they hold up. They don’t:

We can look at the paleoclimatic record during periods of significant changes in GCR activity, and there is no corresponding change in climate, e.g. the Laschamp excursion ~40kya (Muscheler 2005).

We can examine the change in GCRs in response to solar variability over recent decades or the course of a solar cycle, and find there is no or little corresponding change in climate (Lockwood 2007, Lockwood 2008, Kulmala 2010).

We can look at alleged correlations between GCRs and climate in the geologic past due to our sun passing through galactic spiral arms, and find that these “correlations” were based on an unrealistic, overly-simplified model of spiral structure and are not valid (Overholt 2009). Standard climatic processes (like CO2) more parsimoniously explained the climatic changes even before taking the flawed spiral model into account (Rahmstorf 2004).

We can examine the specific mechanisms by which Svensmark and others have claimed GCRs influence climate via cloud behavior and show that alleged correlations between GCRs and clouds were incorrectly calculated or insufficiently large, proposed mechanisms (e.g. Forbush decreases) are too short lived, too small in magnitude, or otherwise incapable of altering cloud behavior on a large enough scale to drive significant climatic change (Sloan 2008, Erlykin 2009, Erlykin 2009a, Pierce 2009, Calogovic 2010, Snow-Kropla 2011, Erlykin 2011).

Basically, what’s actually been demonstrated by Kirkby, et al. isn’t at odds with the IPCC. What is at odds with the IPCC hasn’t been demonstrated by Kirkby, et al. And the claims by Svensmark, Shaviv, and other ‘GCRs drive climate’ proponents have been debunked at pretty much every step of the way. GCRs may have some influence on cloud behavior, but they’re not responsible for significant climatic changes now or in the geologic past.

To Be Continued?

The CLOUD project at CERN is essentially just getting started. Its preliminary findings will help aerosol modelers, and hopefully it will continue to provide useful results. After the initial furor of “skeptic” blog-spinning dies down, cosmic rays will probably find themselves falling out of favor once again. But there’s no such thing as too debunked when it comes to myths about climate change, and there’s little chance this will be the last time cosmic rays will be trotted out to claim that we don’t need to reduce greenhouse gas emissions.


  • Calogovic, J., et al. (2010): Sudden cosmic ray decreases: No change of global cloud cover. Geophysical Research Letters, 37, L03802, doi:10.1029/2009GL041327.
  • Erlykin, A.D., et al (2009): Solar activity and the mean global temperature. Environmental Research Letters, 4, 014006, doi:10.1088/1748-9326/4/1/014006.
  • Erlykin, A.D., et al (2009a): On the correlation between cosmic ray intensity and cloud cover. Journal of Atmospheric and Solar-Terrestrial Physics, 71, 17-18, 1794-1806, doi:10.1016/j.jastp.2009.06.012.
  • Erlykin, A.D., and A.W. Wolfendale (2011): Cosmic ray effects on cloud cover and their relevance to climate change. Journal of Atmospheric and Solar-Terrestrial Physics, 73, 13, 1681-1686, doi:10.1016/j.jastp.2011.03.001.
  • Kirkby, J., et al. (2011): Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature, 476, 429–433, doi:10.1038/nature10343.
  • Kulmala, M., et al. (2010): Atmospheric data over a solar cycle: no connection between galactic cosmic rays and new particle formation. Atmospheric Chemistry and Physics, 10, 1885-1898, doi:10.5194/acp-10-1885-2010.
  • Lockwood, M., and C. Fröhlich (2007): Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. Proceedings of the Royal Society: A. 463, 2447- 2460, doi:10.1098/rspa.2007.1880.
  • Lockwood, M., and C. Fröhlich (2008): Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. II. Different reconstructions of the total solar irradiance variation and dependence on response time scale. Proceedings of the Royal Society: A, 464, 1367-1385, doi:10.1098/rspa.2007.0347.
  • Muscheler, R., et al. (2005): Geomagnetic field intensity during the last 60,000 years based on 10Be and 36Cl from the Summit ice cores and 14C. Quaternary Science Reviews, 24, 16-17, 1849-1860, doi:10.1016/j.quascirev.2005.01.012.
  • Overholt, A.C., et al. (2009): Testing the link between terrestrial climate change and galactic spiral arm transit. The Astrophysical Journal Letters, 705, 2, L101, doi:10.1088/0004-637X/705/2/L101.
  • Pierce, J.R., and P.J. Adams (2009): Can cosmic rays affect cloud condensation nuclei by altering new particle formation rates? Geophysical Research Letters, 36, L09820, doi:10.1029/2009GL037946.
  • Rahmstorf, S., et al. (2004): Cosmic Rays, Carbon Dioxide, and Climate. Eos Transactions AGU, 85(4), doi:10.1029/2004EO040002.
  • Sloan, T., and A.W. Wolfendale (2008): Testing the proposed causal link between cosmic rays and cloud cover. Environmental Research Letters, 3, 024001, doi:10.1088/1748-9326/3/2/024001.
  • Snow-Kropla, E.J., et al. (2011): Cosmic rays, aerosol formation and cloud-condensation nuclei: sensitivities to model uncertainties. Atmospheric Chemistry and Physics, 11, 4001-4013, doi:10.5194/acp-11-4001-2011.

[Ed.'s Note: This post has been lightly edited since publication for grammar, style, and the addition of relevant references.]

The full text from the IPCC AR4 section on cosmic rays and climate:

When solar activity is high, the more complex magnetic configuration of the heliosphere reduces the flux of galactic cosmic rays in the Earth’s atmosphere. Various scenarios have been proposed whereby solar-induced galactic cosmic ray fluctuations might influence climate (as surveyed by Gray et al., 2005). Carslaw et al. (2002) suggested that since the plasma produced by cosmic ray ionization in the troposphere is part of an electric circuit that extends from the Earth’s surface to the ionosphere, cosmic rays may affect thunderstorm electrification. By altering the population of CCN and hence microphysical cloud properties (droplet number and concentration), cosmic rays may also induce processes analogous to the indirect effect of tropospheric aerosols. The presence of ions, such as produced by cosmic rays, is recognised as influencing several microphysical mechanisms (Harrison and Carslaw, 2003). Aerosols may nucleate preferentially on atmospheric cluster ions. In the case of low gas-phase sulphuric acid concentrations, ion-induced nucleation may dominate over binary sulphuric acid-water nucleation. In addition, increased ion nucleation and increased scavenging rates of aerosols in turbulent regions around clouds seem likely. Because of the difficulty in tracking the influence of one particular modification brought about by ions through the long chain of complex interacting processes, quantitative estimates of galactic cosmic-ray induced changes in aerosol and cloud formation have not been reached.

Many empirical associations have been reported between globally averaged low-level cloud cover and cosmic ray fluxes (e.g., Marsh and Svensmark, 2000a,b). Hypothesised to result from changing ionization of the atmosphere from solar-modulated cosmic ray fluxes, an empirical association of cloud cover variations during 1984 to 1990 and the solar cycle remains controversial because of uncertainties about the reality of the decadal signal itself, the phasing or anti-phasing with solar activity, and its separate dependence for low, middle and high clouds. In particular, the cosmic ray time series does not correspond to global total cloud cover after 1991 or to global low-level cloud cover after 1994 (Kristjánsson and Kristiansen, 2000; Sun and Bradley, 2002) without unproven de-trending (Usoskin et al., 2004). Furthermore, the correlation is significant with low-level cloud cover based only on infrared (not visible) detection. Nor do multi-decadal (1952 to 1997) time series of cloud cover from ship synoptic reports exhibit a relationship to cosmic ray flux. However, there appears to be a small but statistically significant positive correlation between cloud over the UK and galactic cosmic ray flux during 1951 to 2000 (Harrison and Stephenson, 2006). Contrarily, cloud cover anomalies from 1900 to 1987 over the USA do have a signal at 11 years that is anti-phased with the galactic cosmic ray flux (Udelhofen and Cess, 2001). Because the mechanisms are uncertain, the apparent relationship between solar variability and cloud cover has been interpreted to result not only from changing cosmic ray fluxes modulated by solar activity in the heliosphere (Usoskin et al., 2004) and solar-induced changes in ozone (Udelhofen and Cess, 2001), but also from sea surface temperatures altered directly by changing total solar irradiance (Kristjánsson et al., 2002) and by internal variability due to the El Niño-Southern Oscillation (Kernthaler et al., 1999). In reality, different direct and indirect physical processes (such as those described in Section 9.2) may operate simultaneously.

WUWT not even going through the motions of fact-checking any more

I have been quiet of late in part because of real world obligations, and in part because I’ve been trying to do a little “communications outreach” at social media sites like Reddit. Over at their anything but skeptical “climate skeptics” sub-message board, a handful of people spam links from the same handful of denialist websites day after day (though some discussions are more productive than others). Today, I noticed a link from WUWT that was terrible even for Watts’s incredibly low standards. So much wrong packed into so few sentences. What follows is a brief fisking I undertook in the Reddit comments, that might be useful to anyone looking for a rebuttal.

It follows that temperatures must have been higher than those of today’s during that first settlement of Greenland which lasted from approximately 900 until the mid-1400s AD, when these settlements died out.

No. It follows that temperatures were probably warmer for longer than the modern period until recently, but it does not follow that the recent warming, which is unearthing the items described, has not exceeded the medieval warming of Greenland. And in fact, we can look at the Greenland ice core record to see that it has:

This plot was from the last time WUWT tried to promulgate BS about warmer than present Greenland temps, showing the GISP2 ice core and GRIP updates scaled to GISP values for the modern warming.

Yet the whole reason for the existence of the Intergovernmental Panel of Climate Change (IPPC)

The IPPC is it?

is to thrust upon the world’s population the idea that industrialisation in the West over the last 100 years and our profligate use of fossil fuels is producing a run-away heating of the planet

This is a strawman on several counts. We’re not worried about a “run-away” warming like that on Venus. We’re worried about changes to climatic norms that will prove more detrimental than the cost of limiting emissions to avoid those changes.

through the emission of greenhouse gases, mainly CO2, which unless checked will lead to [the planet's] — and humanity’s — death.

I’d like to see the cite for that from any of the ARs. Again, strawman.

So the possibility that temperatures were higher in the past in any part of the world was a thorn in the sides of those Climatologists who are wedded to the whole idea of Anthopogenic Global Warming (AGW), also known as Climate Change.

Again, this is false. Warmer than present temperatures undeniably took place in Earth’s geologic past, this has no bearing on the reality of anthropogenic warming or its potential to disrupt climatic norms.

Unfortunately for them, an English Climatologist, Hubert H Lamb, first formulated the idea of a Medieval Warming Period (MWP) in 1965 and other surveys have found that this warming did not just occur in the northwestern hemisphere but was global (6).

Lamb’s maximum warming took place hundreds of years after (i.e. 1100-1300) the peak warming of the NH is now recognized to have taken place (prior to 1000).

The IPCC FAR curve, based on Lamb, along with the updated CET instrumental record in blue with the same 50 year smoothing (Jones 2009).

NH paleoclimatic reconstructions from Mann 2008, Moberg 2005, Ljungqvist 2010, and the NCDC instrumental record, courtesy of Zeke Hausfather at The Blackboard

Lamb did not believe that the Medieval Climate Anomaly (or “Medieval Warm Epoch” as he originally called it) was a period of continuous temporally and spatially coherent global warming, but rather that it was more pronounced in the Atlantic Northern Hemisphere. You can see Lamb’s own discussion of the subject here (note, I haven’t read the other contents of that page beyond verifying that the quotes from Lamb’s writings are correct and in context. I’m in a hurry and couldn’t find a publicly accessible version of Lamb’s texts. If the guy starts talking about Lizard people, disregard his comments and stick to what Lamb says).

Much like Lamb, modern paleoclimate scientists believe the MCA was characterized by a warm North Atlantic, giving rise to unusual warmth in Western Europe and Eastern North America. Like Lamb, they believe that the MCA was marked by cooling of much of the North Pacific and Asia.

Unlike Lamb, they have a wealth of paleoclimatic and physics-based modeling data that has only become available in past several decades. The MCA seems to have been dominated by persistent La Niña-like and positive NAO conditions, similar to but differing in origin and some specific consequences than Lamb’s proposed proximate causes.

But Dr David Darning (University of Oklahoma College of Earth and Energy) in his recent testimony to Congress (7) said ‘…I received an astonishing email from a major researcher in the area of climate change. It said “We have to get rid of the Medieval Warm Period”’

Where is this email? Why quote this “Darning” instead of the email itself?

Possibly because it’s an apocryphal quote, based on the innocuous comment by Phil Jones indicating a desire to reconstruct temps far back enough to capture the entirety of any MCA: “it would be nice to try to “contain” the putative “MWP”, even if we don’t yet have a hemispheric mean reconstruction available that far back”.

Note that “Darning” does not actually appear to exist, and this claim should be attributed to David Deming, apparently from back in 2006.

In 1998 a graph was produced by geophysicist Michael Mann, known as the Hock Stick Graph’, which managed to almost air-brush out of existence the Medieval Warming Period .

Mann et al. 1998 only went back ~600 years, and said nothing about the time of the MCA.

This was published in the eminent scientific magazine Nature and also in several places in the IPPC Report of 2001 and created a world-wide sensation. Here was proof positive the world was overheating and it was All Our Fault.

As has been pointed out exhaustively, the millennial NH reconstructions say very little on the issue of attribution, and indeed if you throw out all of our late Holocene reconstructions, that would have virtually no impact on the evidence for attribution of the present warming to human causes.

However, investigation of the graph by historians and climatologists who doubted the existence of global warming, brought criticism centred around the statistical method used and the associated computer programme. It was eventually called the most discredited study in the history of science

The author of this article was eventually called the dumbest person in the history of dummies. I was eventually called the tallest matador in all of Spain. Gee, this is fun!

and quietly dropped by the IPPC from the latest 2007 IPPC report for policy makers.

Mann et al. 1999  was plotted along with other paleoclimatic reconstructions published between the TAR and the AR4:

IPCC AR4 Figure 6.10: Records of NH temperature variation during the last 1.3 kyr.


Debunking Jim Manzi in 5 Easy Steps

Via Michael Tobis, it seems that Jim Manzi is generating a bit of buzz for a non-denialist challenge to the case for mitigating climate change recently published at TNR: Why the Decision to Tackle Climate Change Isn’t as Simple as Al Gore Says.

First off, let me echo others who’ve stated that it’s a pleasure to engage with someone who doesn’t typically deal in the fringe, anti-science nonsense that dominates so much of the right in American political discourse. To his credit, Jim Manzi doesn’t attempt to de-legitimize the scientific basis of anthropogenic climate change and chides his conservative colleagues for exactly that sort of tinfoil hattery.

With that said, it’s disappointing to see Manzi engaging in an only slightly less silly argument against mitigation, which utilizes a superficial gloss on some figures from the 2007 IPCC WGII Summary for Policy Makers to propose that costs incurred from unchecked warming don’t justify the cost of preventing it. This is an argument Manzi has made before in other venues, and one I’ve engaged him on previously.

Manzi’s argument can be fairly summarized as “according to the IPCC, the most warming we can realistically expect is 4°C, which will only cost ~3% global GDP using economic models like DICE, which is less than mitigating against that warming will cost according to an analysis of my choosing, ergo mitigation isn’t an optimal strategy”.

  1. There is only one SRES scenario that reasonably tracks real world emissions growth per observations and infrastructure legacy: A1FI.
  2. The “likely” temperature range for A1FI is 2.4-6.4°C.
  3. The high end cost of ~6°C warming in Manzi’s source is upwards of 11% global GDP, yielding a range/estimate of 1-11%/5.5% GDP, not 1-5%/3%.
  4. Manzi cites a third party estimate of mitigation costs as ~6% GDP for stabilization at 450 ppm, while other analyses by experts in the field put the cost far lower- e.g. 2.5% at 350-400 ppm.
  5. Being generous and more than splitting the difference- rather than using my own preferred analysis outright- gives a cost of 4.25% GDP for 450 ppm, compared to a non-stabilization cost of 5.5%GDP.

In short Manzi’s analysis depends on a suspiciously narrow reading and selection of source material that doesn’t hold up to even a cursory amount of scrutiny.

Further points: This simple debunking has ignored other problematic assumptions implicit in Manzi’s analysis- the absurdly conservative damages of the DICE model, for example. Notoriously, DICE shows a warming of 20°C resulting in a loss of only 50% of global GDP, a warming so extreme that it would exceed humans’ (and other mammals’) capacity to endure heat stress, resulting in mass extinction. It’s fairly safe to say that there wouldn’t even be a “Gross Domestic Product” much less one half as large as today’s 2100’s expected. Ocean acidification, non-linear ice sheet collapse and resulting sea level rise, and other costly consequences of unchecked emissions are likewise ignored by DICE. [And yes, I realize that Manzi will simply claim that the IPCC deserves a similar criticism, with which I agree- though in its defense the IPCC doesn't attempt to hang its conclusions on such a slavish acceptance of this modeling.]

Work by others (like Annan and Hargreaves) finds losses from DICE to be understated in the AR4 compared to their own papers. This isn’t a problem with Manzi’s formulation of the issue, but is relevant to the discussion.

On a final note, it’s also disappointing  to see that the pro-mitigation punditry (e.g. Klein, Plumer) don’t even appear to seriously investigate Manzi’s argument, but rather grant his flawed premises and hand-wave in favor of mitigation anyway. Or as Tobis puts it (emphasis in the original): “The answer from the punditry to Manzi is not to call the absurdly small cost into question, but to say that we should take drastic action anyway, even though the [economic] risk is trivial.” As much as I appreciate the interest of Klein and Plumer in climate issues, they do not appear to be sufficiently conversant with the relevant material to proficiently engage their opposition.


Did the IPCC Fourth Assessment Report oversell the climate-malaria connection?

In light of a recent paper by Gething et al. published in Nature that challenges the notion that malaria will be on the march in a warming world, it might be useful to see whether or not there is a basis for accusing the IPCC for yet another “error”.

You be the judge: Malaria

The spatial distribution, intensity of transmission, and seasonality of malaria is influenced by climate in sub-Saharan Africa; socio-economic development has had only limited impact on curtailing disease distribution (Hay et al., 2002a; Craig et al., 2004).

Rainfall can be a limiting factor for mosquito populations and there is some evidence of reductions in transmission associated with decadal decreases in rainfall. Interannual malaria variability is climate-related in specific ecoepidemiological zones (Julvez et al., 1992; Ndiaye et al., 2001; Singh and Sharma, 2002; Bouma, 2003; Thomson et al., 2005). A systematic review of studies of the El Niño-Southern Oscillation (ENSO) and malaria concluded that the impact of El Niño on the risk of malaria epidemics is well established in parts of southern Asia and SouthAmerica (Kovats et al., 2003). Evidence of the predictability of unusually high or low malaria anomalies from both sea-surface temperature (Thomson et al., 2005) and multi-model ensemble seasonal climate forecasts in Botswana (Thomson et al., 2006) supports the practical and routine use of seasonal forecasts for malaria control in southern Africa (DaSilva et al., 2004).

The effects of observed climate change on the geographical distribution of malaria and its transmission intensity in highland regions remains controversial. Analyses of time-series data in some sites in East Africa indicate that malaria incidence has increased in the apparent absence of climate trends (Hay et al., 2002a, b; Shanks et al., 2002). The proposed driving forces behind the malaria resurgence include drug resistance of the malaria parasite and a decrease in vector control activities. However, the validity of this conclusion has been questioned because it may have resulted from inappropriate use of the climatic data (Patz, 2002).Analysis of updated temperature data for these regions has found a significant warming trend since the end of the 1970s, with the magnitude of the change affecting transmission potential (Pascual et al., 2006). In southern Africa, long-term trends for malaria were not significantly associated with climate, although seasonal changes in case numbers were significantly associated with a number of climatic variables (Craig et al., 2004). Drug resistance and HIV infection were associated with long-term malaria trends in the same area (Craig et al., 2004).

A number of further studies have reported associations between interannual variability in temperature and malaria transmission in the African highlands. An analysis of de-trended time-series malaria data in Madagascar indicated that minimum temperature at the start of the transmission season, corresponding to the months when the human–vector contact is greatest, accounts for most of the variability between years (Bouma, 2003). In highland areas of Kenya, malaria admissions have been associated with rainfall and unusually high maximum temperatures 3-4 months previously (Githeko and Ndegwa, 2001). An analysis of malaria morbidity data for the period from the late 1980s until the early 1990s from 50 sites across Ethiopia found that epidemics were associated with high minimum temperatures in the preceding months (Abeku et al., 2003). An analysis of data from seven highland sites in East Africa reported that short-term climate variability played a more important role than long-term trends in initiating malaria epidemics (Zhou et al., 2004, 2005), although the method used to test this hypothesis has been challenged (Hay et al., 2005b).

There is no clear evidence that malaria has been affected by climate change in South America (Benitez et al., 2004) (see Chapter 1) or in continental regions of the Russian Federation (Semenov et al., 2002). The attribution of changes in human diseases to climate change must first take into account the considerable changes in reporting, surveillance, disease control measures, population changes, and other factors such as land use change (Kovats et al., 2001; Rogers and Randolph, 2006).

Despite the known causal links between climate and malaria transmission dynamics, there is still much uncertainty about the potential impact of climate change on malaria at local and global scales (see also Section 8.4.1) because of the paucity of concurrent detailed historical observations of climate and malaria, the complexity of malaria disease dynamics, and the importance of non-climatic factors, including socio-economic development, immunity and drug resistance, in determining infection and infection outcomes. Given the large populations living in highland areas of East Africa, the limitations of the analyses conducted, and the significant health risks of epidemic malaria, further research is warranted.

Was an imminent collapse of the AMOC a mainstream climate prediction?

The denialosphere is all atwitter over a recent Josh Willis paper, which found no evidence for a present weakening of the Atlantic Meridional Overturning Circulation (AMOC), presenting its findings as though they contradict mainstream climate science and conflating the latter with the Hollywood disaster flick The Day After Tomorrow.

Fact vs. Fiction

Below are simulated depictions of the global thermohaline circulation from NASA, NOAA, and a cheesy Hollywood movie. Can you guess which is which?

Abrupt climate change (though nothing like in the movie) due to a slowdown/collapse of the AMOC is a genuine climatic phenomenon. A collapse of the AMOC within years or decades due to global warming, which plunges the North Atlantic into an ice age is decidedly not, however.

What does mainstream climate science say?

A fairly standard benchmark for assessing claims of what is considered to be “mainstream” climate science is its treatment in the most recent Intergovernmental Panel on Climate Change’s Assessment Report.

On whether or not the AMOC is currently (as of 2007) weakening-

AR4 WG1 Box 5.1, Has the Meridional Overturning Circulation in the Atlantic Changed?:

In summary, it is very likely that up to the end of the 20th century the MOC was changing significantly at interannual to decadal time scales. Given the above evidence from components of the MOC as well as uncertainties in the observational records, over the modern instrumental record no coherent evidence for a trend in the mean strength of the MOC has been found.

On whether or not we can expect an abrupt collapse of the AMOC this century-

AR4 WG1 10.3.4, Changes in the Atlantic Meridional Overturning Circulation:

Taken together, it is very likely that the MOC, based on currently available simulations, will decrease, perhaps associated with a significant reduction in Labrador Sea Water formation, but very unlikely that the MOC will undergo an abrupt transition during the course of the 21st century. At this stage, it is too early to assess the likelihood of an abrupt change of the MOC beyond the end of the 21st century, but the possibility cannot be excluded (see Box 10.1). The few available simulations with models of different complexity instead suggest a centennial slowdown.

Likewise, the U.S. Climate Change Science Program’s Synthesis and Assessment Report on Abrupt Climate Change found:

  • No current comprehensive climate model projects that the AMOC will abruptly weaken or collapse in the 21st century. We therefore conclude that such an event is very unlikely. Further, an abrupt collapse of the AMOC would require either a sensitivity of the AMOC to forcing that is far greater than current models suggest or a forcing that greatly exceeds even the most aggressive of current projections (such as extremely rapid melting of the Greenland ice sheet). However, we cannot completely exclude either possibility.
  • We further conclude it is unlikely that the AMOC will collapse beyond the end of the 21st century because of global warming, although the possibility cannot be entirely excluded.

Current Observations and the Consequences of Future Slowdown

In a follow up post, I plan on looking at Willis’s latest paper in the context of the last few years of observational studies of potential AMOC slowdown, and what a slowdown or even a collapse could mean in terms of modern climate change.

Predictions made easy


The denialosphere is going to do the same thing it has always done- trumpet the very existence of this as a victory, and yet simultaneous proclaim that it is compromised from the get-go because of “groupthink”, back-scratching, or some other imagined insufficiency of independence. The concern trolling from the usual suspects will be something to behold. [UPDATE: They never let me down.]

In the eyes of denialists, the only legitimate reviews, investigations, etc. are the ones that reach the conclusions they want.

Guilty until proven innocent and all that.

I report, you decide

Who knows? *shrugs* Maybe this was run-of-the-mill media sensationalizing of the not particularly news-worthy IPCC party line: that limiting warming to 2°C is a relatively “safe” target.

Or maybe “China’s top climatologist” really loves biblical plagues.

[B]efore them there were no such locusts as they, neither after them shall be such. For they covered the face of the whole earth, so that the land was darkened; and they did eat every herb of the land, and all the fruit of the trees which the hail had left: and there remained not any green thing in the trees, or in the herbs of the field, through all the land…
~ Exodus 10:14-15, King James Bible