Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

Archives for August 12, 2008

Two New Papers Examining the Hurricane-Climate Link

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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.

Causal Linkage between Carbon Dioxide and Global Warming (Part 3): Causal Criteria Still Wanting

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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

Conflict of Interest for Chairman of UK Environment Committee

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Tim Yeo used his casting vote as chairman of the all-party Environmental Audit Select Committee to push through a report, published last week, which backed the decision by Alistair Darling, the Chancellor, that new, higher rates of vehicle excise duty (VED) rates should apply to previously-purchased cars.

The committee had been evenly split, with three Labour MPs supporting the Government line while three Tory and Lib Dem MPs opposed it, arguing that the move amounted to retrospective taxation. Mr Yeo broke the deadlock by siding with the Labour MPs.

He is paid £40,000 a year as non-executive chairman of Eco City Vehicles Plc, a company which plans to market a hybrid car which would qualify for low rates of VED under the new tax regime, due to its low carbon emissions.

Telegraph.co.uk: Tory MP Tim Yeo in conflict-of-interest row over car tax report

A spoonful of enviro-sugar helps the atmospheric medicine go down

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In her 16th July 2008 media release, GREEN PAPER ON CARBON POLLUTION REDUCTION SCHEME RELEASED, Senator, the Hon. Penny Wong, Minister for Climate Change and Water, stated that:

“Climate change threatens … icons like the Great Barrier Reef, the Kakadu wetlands and the multi billion dollar tourism industries they support.”

The selection and juxtaposition of these two icons is, at the very least, strategically interesting. The Great Barrier Reef is widely celebrated as one of the natural wonders of the world, epitomising environmental importance for Australians. Kakadu, in a similar vein, is resplendent with fauna and flora and resounds of antiquity and Aboriginal spirituality. It is a logical companion to the Reef and particularly if the Minister’s intention was to capture the breadth and diversity of Australia’s environmental concerns.

However, the Reef is thought to be around a half-million years old and quite obviously has endured temperature variations throughout this period. With an even greater perseverance, Kakadu is believed to have formed around 140 million years ago, with the prominent escarpment wall forming sea cliffs and the Arnhem Land plateau a flat land above the sea.

Yet, despite these environmental assets enduring against the ravages of turbulent climate variation, their imminent environmental collapse is foreshadowed alongside the devastating implication of multi-billion dollar economic losses, unless dramatic changes are implemented as outlined in the Federal Government’s draft Carbon Pollution Reduction Scheme.

But what of other environmental icons, like the World Heritage-listed Daintree Rainforest? Surely it is even more vulnerable to these forecast catastrophic climate changes? Being coastal, it is more proximal to inundation than Kakadu, it is more primitive, has a far richer biodiversity and endemism and attracts more than twice the annual visitation and expenditure.

Perhaps its ecological interaction with the contiguous Great Barrier Reef is spatially less inclusive of the broader environmental diversity between the Reef and Kakadu. Nevertheless, localised carbon pollution should be more of a concern in the Daintree rainforest with its greater vulnerabilities and visitation, as well as its more abundant income-earning performance. Not that Kakadu should be under-valued, but it seems entirely incongruous that for all the urgency for this necessary intervention, that nothing is being done to protect the Daintree rainforest from carbon pollution emitted from hundreds of concurrently running engine generators.

It has been conservatively estimated that the federal government will raise ten billion dollars in 2010 from the sale of permits to emit greenhouse gases. Every cent of this estimated bounty will purportedly be used to help Australian households and businesses adjust to the emissions trading scheme and to invest in clean energy options.

Perhaps the federal Government might be persuaded to embrace the Daintree World Heritage rainforest as a priority pilot project to remove the unnecessary emissions of so many generators.