Climate & Climate Change

Two new papers examining the link between Hurricanes and climate have been published in the Journal of Climate.

In the July edition, Gabriel A. Vecchi and Thomas R. Knutson have a paper entitled: ‘On Estimates of Historical North Atlantic Tropical Cyclone Activity’

The Abstract states:

In this study, an estimate of the expected number of Atlantic tropical cyclones (TCs) that were missed by the observing system in the presatellite era (between 1878 and 1965) is developed. The significance of trends in both number and duration since 1878 is assessed and these results are related to estimated changes in sea surface temperature (SST) over the “main development region” (“MDR”). The sensitivity of the estimate of missed TCs to underlying assumptions is examined. According to the base case adjustment used in this study, the annual number of TCs has exhibited multidecadal variability that has strongly covaried with multidecadal variations in MDR SST, as has been noted previously. However, the linear trend in TC counts (1878–2006) is notably smaller than the linear trend in MDR SST, when both time series are normalized to have the same variance in their 5-yr running mean series. Using the base case adjustment for missed TCs leads to an 1878–2006 trend in the number of TCs that is weakly positive, though not statistically significant, with p 0.2. The estimated trend for 1900–2006 is highly significant (+4.2 storms century−1) according to the results of this study. The 1900–2006 trend is strongly influenced by a minimum in 1910–30, perhaps artificially enhancing significance, whereas the 1878–2006 trend depends critically on high values in the late 1800s, where uncertainties are larger than during the 1900s. The trend in average TC duration (1878–2006) is negative and highly significant. Thus, the evidence for a significant increase in Atlantic storm activity over the most recent 125 yr is mixed, even though MDR SST has warmed significantly. The decreasing duration result is unexpected and merits additional exploration; duration statistics are more uncertain than those of storm counts. As TC formation, development, and track depend on a number of environmental factors, of which regional SST is only one, much work remains to be done to clarify the relationship between anthropogenic climate warming, the large-scale tropical environment, and Atlantic TC activity.

The paper concludes:

Overall, our findings suggest that it is possible that Atlantic TC counts may have significantly increased since the late nineteenth century, although the evidence is decidedly mixed, with some other activity measures showing either no change or a decrease with time. Total storms per year and U.S. landfalling activity show no increasing trend, and average TC duration shows a significant decrease over time. Further, attribution of an increase in tropical storm counts to any particular mechanism (including increasing greenhouse gasses or natural decadal variations) would require further dynamical analysis to complement any observational results. It is noteworthy that in our adjusted record of TCs the sensitivity of basin-wide storm counts to local SST is smaller for the longest time scales (e.g., trend since 1878) than for the pronounced multidecadal variability, although the current observational “best estimate” would be that this sensitivity is positive. Additional study is needed to reconcile these findings with climate simulations of past and future Atlantic storm activity. Future work should also focus on including more ship-track information where possible and examining assumptions about landfall detection in earlier years, and historical tropical cyclone database reconstructions should be extended to include other basins.

See also Discovery Channel News: Warming Won’t Drive More Hurricanes, Study Says

In the August edition of the Journal of Climate, Philip J. Klotzbach and William M. Gray have a paper entitled: ‘Multidecadal Variability in North Atlantic Tropical Cyclone Activity’

The Abstract states:

Recent increases in Atlantic basin tropical cyclone activity since 1995 and the associated destructive U.S. landfall events in 2004 and 2005 have generated considerable interest into why there has been such a sharp upturn. Natural variability, human-induced global warming, or a combination of both factors, have been suggested. Several previous studies have discussed observed multidecadal variability in the North Atlantic over 25–40-yr time scales. This study, using data from 1878 to the present, creates a metric based on far North Atlantic sea surface temperature anomalies and basinwide North Atlantic sea level pressure anomalies that shows remarkable agreement with observed multidecadal variability in both Atlantic basin tropical cyclone activity and in U.S. landfall frequency.

The paper concludes:

This paper expounds upon previous research by highlighting Atlantic basin multidecadal variability in both large-scale atmospheric–oceanic fields as well as Atlantic basin TC (tropical cyclone) activity. Using an index of basinwide SLP (sea level pressure) and far North Atlantic SSTs (sea surface temperatures), positive and negative periods for the AMO (Atlantic multi-decadal oscillation) can be clearly delineated. When the AMO is in its positive phase, TC activity in the Atlantic basin is heightened, especially for MH (major hurricane) activity. Landfalling hurricanes along the U.S. coastline also become more frequent, with the most dramatic increases in a positive AMO phase being seen for the U.S. East Coast and the Florida Peninsula. Additional research involving potential physical drivers of the AMO should be conducted.

The Australian government is planning to introduce an emission’s trading scheme, also described as a carbon pollution reduction scheme, on the basis that that carbon dioxide from the burning of fossil fuels is contributing to dangerous global warming.

Many people assume that such a drastic action is premised on good evidence establishing a proven causal link between anthropogenic carbon dioxide and global warming.

For example, when establishing causality between an environmental pollutant and an effect on an animal species, scientists would be expect to establish not only a correlation between the presence of the pollutant and an effect (for example an illness in the population), but be also able to demonstrate a dose-response relationship and describe a credible toxicological basis for the proposed mechanism linking the proposed cause and effect.

Interestingly while anthropogenic carbon dioxide is now considered to be one of the worst pollutants,
there does not appear to be a body of work establishing the basic criteria for a claimed causal relationship between the purported pollutant, anthropogenic carbon dioxide, and the claimed effect, global warming; atleast not outside of the United Nations Intergovernmental Panel on Climate Change reports. In particular there does not appear to be a body of work published in reputable scientific journals.

Furthermore, much of the science underpinning the need for a proposed carbon pollution reduction scheme in Australia appears to be based on the claim of a scientific consensus and the observation that there have been increasing levels of atmospheric carbon dioxide over the last 150 years and over this period temperatures have also been generally increasing.

I posted a note on my blog and John Quiggin’s blog on Sunday evening suggesting this deficiency and requesting “research results that have been published in reputable scientific journals that: 1. examine the causal link between anthropogenic carbon dioxide and warming, and 2. quantify the extent of the warming from anthropogenic carbon dioxide.”

Several papers were suggested to me, I believe in good faith, as fulfilling this criteria including a paper entitled ‘Causes of Climate Change Over the Past 1,000 Years’ by Thomas Crowley (14 July 2000, Vol 289, Science).

I was disappointed with the paper when I read it this afternoon. The paper essentially compares output from a reconstruction of past climate with output from an energy balance climate model. In other words, the paper looks at the fit between output from two models. So the paper is about correlation not causation.

But most disappointing, the reconstruction of past climate in the Crowley paper is based on the work of Michael Mann and colleagues which has been the source of much controversy and many believe completely discredited by a report from a team of statisticians led by Edward Wegman, chair of the National Academy of Sciences’ (NAS) Committee on Applied and Theoretical Statistics, assembled at the request of U.S. Rep. Joe Barton and U.S. Rep. Ed Whitfield .

Indeed what has become known as the hockey stick controversy is illustrative of the nature of climate science in what Aynsley Kellow, Professor and Head, School of Government, University of Tasmania, has described as post-normal science with an extensive reliance upon models and the potential for significant manipulation of their source data.

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Part 1, Causal Linkage between Carbon Dioxide and Global Warming:
Part 2, Causal Linkage between Carbon Dioxide and Global Warming (Part 2): Still Searching for Evidence

On Sunday a colleague and I discussed the general issue of correlation versus causation in science. He suggested that 1. There must be a body of work establishing a causal link between anthropogenic carbon dioxide and warming, and also 2. Some work that quantifies the extent of the warming from the anthropogenic carbon dioxide. He assumed as much because our government, the Australian government, is planning major perturbation to our economic system on the basis that carbon dioxide from the burning of fossil fuels is contributing to dangerous global warming. He assumed that the Australian government would not undertake such an action lightly, indeed that such an action would be premised on good evidence establishing a proven causal link between anthropogenic carbon dioxide and global warming. I replied that I was not so sure.

He said he would do a search of the scientific literature on Monday. I said it would be interesting to compare what he turned up from this systematic search of library databases with a few random requests on the internet.

So, Sunday evening I posted a note at my blog, at John Quiggin’s blog and at a yahoo climate science group of mostly so-called climate change skeptics.

Perhaps not surprisingly one of the first to claim that a body of work existed was John Quiggin; a well known climate alarmist. Professor Quiggin went as far as to claim that there are “hundreds of papers on both the causal link and the question of sensitivity” but could only cite a few papers which dabble with the issue of sensitivity later in that blog thread.

By early Monday evening (when I started writing this blog post) the thread at Professor Quiggin’s blog had thrown up only three papers that I thought could potentially provide a causal link and a quantification of the extent of warming. Interestingly one of them was published as long ago as 1938. I had listed the papers earlier in the day at the threads at both Professor Quiggin’s and my blogs to see if other papers were put forward in preference to these, but they weren’t. The papers are:
1. Callendar, G.S., 1938. The artificial production of carbon dioxide and its influence on temperature. Q. J. R. Meteorol. Soc., Vol 64, 223–237.
2. Hofmann, D.J., J. H. Butler, E. J . Dlugokencky, J . W. Elkins, K. Masarie, S. A. Montzka and P. Tans, 2006. The role of carbon dioxide in climate forcing from 1979 to 2004: Introduction of the Annual Greenhouse Gas Index, Tellus B, Vol 58, 614-619.
3. Crowley, T. 2000. Causes of Climate Change Over the Past 1000 Years. Science Vol 289: 270-277.

The Hofmann et al. paper initially looked the most promising to me, is available on the internet (click here) and is the first that I shall consider. (I plan to post comment on the Crowley or Callendar paper tomorrow.)

While the title of the Hofmann et al paper does suggest a “role” is established for carbon dioxide as a forcing/warming agent, in fact it is just assumed in the body of the paper.

The authors simply taken a set of gases (including carbon dioxide) and ascribed an effect: climate forcing. They do not demonstrate a mechanism, or even shown a correlation, between levels of anthropogenic carbon dioxide and global warming.

So, I shall have to conclude that this paper fails the criteria (1. There must be a body of work establishing a causal link between anthropogenic carbon dioxide and warming, and also 2. Some work that quantifies the extent of the warming from the anthropogenic carbon dioxide).

Reading the paper I was struck by the extent to which the authors assume that the increase in atmospheric levels of carbon dioxide since 1750 is primarily a result of “anthropogenic emissions” without explaining why.

There is an extensive scientific literature discussing the notion of causation and how this might be established, for example between environmental stressors and observed effects in natural systems. This literature emphasises that where there are potential alternative explanations for an observed correlation these should be considered.

In the case of carbon dioxide and global warming, Lance Endersbee (former Dean of Engineering and Pro-Vice Chancellor of Monash University) has suggested a direct physical relation between increasingly levels of atmospheric carbon dioxide and increasingly average global sea surface temperatures over the last few decades (click here) suggesting the carbon dioxide is being released from the warming oceans.

Thanks to everyone who has posted and/or emailed papers and comment following my three random requests on the internet last night.

I intend this to be just the second in the series. I shall endeavour to consider the submissions beginning with those that appear the most promising and as a series of blog posts. Of course guest posts, and with alternative opinions, are welcome.

The following chart is largely self-explanatory:

Red: The actual rise of atmospheric CO2 from 1966 to 2006
Pink: The actual rise of human emissions within that 40 year timeframe (starting point at 321 ppm for comparison)
Blue: Human emissions multiplied by 24.41 to parallel atmospheric CO2 growth
Black: The human emissions slope as it would be if CO2 had stagnated in the atmosphere
Gray line: Accumulating atmospheric human emissions with a yearly retention rate of 0.56 — meaning that 44% is absorbed yearly, which contradicts the assertion that CO2 remains in the atmosphere for hundreds or thousands of years.

Alan Siddons
Holden, Massachusetts

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Data sources are from the US government’s Carbon Dioxide Information Analysis Center (CDIAC):
http://cdiac.ornl.gov/ftp/trends/co2/maunaloa.co2
http://cdiac.ornl.gov/ftp/ndp030/global.1751_2004.ems

But here’s the trick: How do you convert gigatons of carbon into ppm so you can compare the human and atmospheric trend? Well, CDIAC informs you: Divide gigatons by 2.13.
http://cdiac.ornl.gov/faq.html#Q6

I’ve been having some discussions with a colleague who has never thought too hard about anthropogenic global warming.

Anyway, he says there must be some work/some research results that have been published in reputable scientific journals that:

1. examine the causal link between anthropogenic carbon dioxide and warming, and

2. quantify the extent of the warming from anthropogenic carbon dioxide.

What he really want is links to research papers or citations to research papers.

Cameron Stewart writing in today’s The Australian makes reference to the influence of internet bloggers in succeeding in highlighting that measuring climate change is an evolving science. But, goes on to suggest that “their success has been at the margins only” because we have apparently failed to “prove that these discrepancies negate the broader core arguments about the trends of global warming.”

The article is entitled ‘Key degrees of difference’ and it begins:

“Has global warming stopped? The question alone is enough to provoke scorn from the mainstream scientific community and from the Government, which says the earth has never been hotter. But tell that to a new army of sceptics who have mushroomed on internet blog sites and elsewhere in recent months to challenge some of the most basic assumptions and claims of climate change science…

Read more here: http://www.theaustralian.news.com.au/story/0,25197,24148862-11949,00.html

This is at least the second time in the last two weeks that internet bloggers have been identified by the mainstream Australian media as relevant to the debate on climate change. The earlier story was on ABC Lateline, you can watch the video clip: http://www.abc.net.au/news/video/2008/07/29/2318074.htm . I comment on the Lateline report in an associated blog post here: https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/archives/003290.html.