Paul

Any reader not familiar with Milankovitch can read the Wiki write up here.

I’d already considered posting this interesting new Nature paper entitled ‘Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years,’ so when Luke Walker also drew my attention to it, I decided to give it a go.

The first paragraph summarises the paper:

The Milankovitch theory of climate change proposes that glacial–interglacial cycles are driven by changes in summer insolation at high northern latitudes. The timing of climate change in the Southern Hemisphere at glacial–interglacial transitions (which are known as terminations) relative to variations in summer insolation in the Northern Hemisphere is an important test of this hypothesis. So far, it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined. Here we present a new chronology of Antarctic climate change over the past 360,000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the Dome Fuji and Vostok ice cores. This ratio is a proxy for local summer insolation, and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter. The accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation. Our results indicate that orbital-scale Antarctic climate change lags Northern Hemisphere insolation by a few millennia, and that the increases in Antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of Northern Hemisphere summer insolation. These results support the Milankovitch theory that Northern Hemisphere summer insolation triggered the last four deglaciations.

The paper states, “contrary to hypotheses ascribing the trigger of glacial terminations to CO2, obliquity (axial-tilt), or southern summer insolation, our chronology implicates northern summer insolation as the primary trigger.”

“In summary, the mean phasing of Antarctic climate, as well as the timing of the last four terminations and three post-interglacial coolings, are consistent with the hypothesis that high northern latitude summer insolation is the trigger of glacial–interglacial cycles. The role of CO2 as conveyor and amplifier of the orbital input should be quantified with climate models run using our new timescale; this quantification is important for future climate change predictions. Our timescale should be validated further with new radiometric age markers, as well as by process studies for complete understanding of the physical link between O2/N2 and local insolation. With future O2/N2 measurements, it may be possible to apply this method to the Dome Fuji and Dome C cores for termination V and older terminations, to investigate the phasing of climate and atmospheric composition with respect to orbital forcing further back in time.”

Fortunately, there is a write up here which makes it easier to understand compared with the original article:

“Strong Evidence Points to Earth’s Proximity to Sun as Ice age trigger”

A question unresolved for more than a century may have an answer Scripps Institution of Oceanography/UC San Diego

When do ice ages begin? In June, of course.

Analysis of Antarctic ice cores led by Kenji Kawamura, a visiting scientist at Scripps Institution of Oceanography, UC San Diego, shows that the last four great ice age cycles began when Earth’s distance from the sun during its annual orbit became great enough to prevent summertime melts of glacial ice. The absence of those melts allowed buildups of the ice over periods of time that would become characterized as glacial periods.

Results of the study appear in the Aug. 23 edition of the journal Nature.

Jeff Severinghaus, a Scripps geoscientist and co-author of the paper, said the finding validates a theory formalized in the 1940s but first postulated in the 19th Century. The work also helps clarify the role of carbon dioxide in global warming and cooling episodes past and present, he said.

“This is a significant finding because people have been asking for 100 years the question of why are there ice ages,” Severinghaus said.

A premise advanced in the 1940s known as the Milankovitch theory, named after the Serbian geophysicist Milutin Milankovitch, proposed that ice ages start and end in connection with changes in summer insolation, or exposure to sunlight, in the high latitudes of the Northern Hemisphere. To test it, Kawamura used ice core samples taken thousands of miles to the south in Antarctica at a station known as Dome Fuji.

Scientists studying paleoclimate often use gases trapped in ice cores to reconstruct climatic conditions from hundreds of thousands of years in the past, digging thousands of meters deep into ice sheets. By measuring the ratio of oxygen and nitrogen in the cores, Kawamura’s team was able to show that the ice cores record how much sunlight fell on Antarctica in summers going back 360,000 years. The team’s method enabled the researchers to use precise astronomical calculations to compare the timing of climate change with sunshine intensity at any spot on the planet.

Kawamura, a former postdoctoral researcher at Scripps, used the oxygen-nitrogen ratio data to create a climate timeline that was used to validate the calculations Milankovitch had created decades earlier. The team found a correlation between ice age onsets and terminations, and variations in the season of Earth’s closest approach to the sun. Earth’s closest pass, or perihelion, happens to fall in June about every 23,000 years. When the shape of Earth’s orbit did not allow it to approach as closely to the sun in that month, the relatively cold summer on Earth encouraged the spread of ice sheets on the Northern Hemisphere’s land surface. Periods in which Earth passed relatively close in Northern Hemisphere summer accelerated melt and brought an end to ice ages…………

…..The team found that the changes in Earth’s orbit that terminate ice ages amplify their own effect on climate through a series of steps that leads to more carbon dioxide being released from the oceans into the air. This secondary effect, or feedback, has accounted for as much as 30 percent of the warming seen as ice ages of the past have come to an end…..

For the first time a globally coherent solar cycle response to the surface temperature has been established. Charles Camp and Ka Kit Tung report in Geophysical Research Letters (DOI: 10.1029/2007GL030207) that global temperatures oscillated by 0.2C during the high and low points of the cycle. The research uses satellite solar radiation and surface temperature gridded data from the last 50 years over four and a half solar cycles.

The authors’ analysis also shows greater warming in the polar regions in common with climate model predictions.

In a yet unpublished but submitted paper, Tung and Camp undertake another analysis, without resorting to climate models, that give a climate sensitivity for doubling CO2 between 2.3 and 4.1C as a 95% confidence interval.

The authors add that due to ocean lag effects these numbers are likely to be underestimates.

The work, bound to be controversial, puts more complexity back into the game coming hot on the heels of the Smith et al internal variability paper.

But reader beware, these papers are serious science not rambling quasi-political anecdotes.

A recent paper by IPCC lead author Kevin Trenberth and Aiguo Dai:
Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering

suggests that there would be adverse effects, including drought, as a result of the use of geoengineering in order to offset greenhouse warming:

Abstract
The problem of global warming arises from the buildup of greenhouse gases such as carbon dioxide from burning of fossil fuels and other human activities that change the composition of the atmosphere and alter outgoing longwave radiation (OLR). One geoengineering solution being proposed is to reduce the incoming sunshine by emulating a volcanic eruption. In between the incoming solar radiation and the OLR is the entire weather and climate system and the hydrological cycle. The precipitation and streamflow records from 1950 to 2004 are examined for the effects of volcanic eruptions from El Chichón in March 1982 and Pinatubo in June 1991, taking into account changes from El Niño-Southern Oscillation. Following the eruption of Mount Pinatubo in June 1991 there was a substantial decrease in precipitation over land and a record decrease in runoff and river discharge into the ocean from October 1991–September 1992. The results suggest that major adverse effects, including drought, could arise from geoengineering solutions.

As Hurricane Dean works its way through Mexico, we are reminded of the debate between those who link Hurricanes with global warming, and those who don’t. Scientists Chris Landsea of NOAA and Greg Holland of UCAR find themselves on opposite sides of the debate. Holland has recently claimed that tropical storms have doubled due to global warming in a new paper with Peter Webster. Landsea has also published a recent paper entitled Counting Atlantic Tropical Cyclones Back to 1900. Holland is quoted as saying, “….my sense is that we shall see a stabilization in frequencies for a while, followed by potentially another upward swing if global warming continues unabated.” Landsea’s response was to call Holland’s research “sloppy science.”

Roger Pileke Jr, who has several publications on Hurricanes co-authored with Chris Landsea, waded into the debate by asking Webster for his data. Webster told him in no uncertain terms to recreate it himself, so he did.

The storm data set used is divided into halves, each 51 years long:

1905-1955 (51 years) and 1956-2006 (51 years).

The official HURDAT data looks like this:

1905-1955 = 366
1956-2006 = 458

Holland/Webster 2007 looks like this using their storm-count underestimate correction:

1905-1955 = 417
1956-2006 = 458

Landsea also uses a storm-count underestimate correction:

1905-1955 = 529
1956-2006 = 527

It all comes down to which correction is correct.

William Gray has his say here.

From Benny Pieser’s CCNet:

Mistreatment of the economic impacts of extreme events in the Stern Review Report on the Economics of Climate Change

Abstract

The Stern Review on the Economics of Climate Change has focused debate on the costs and benefits of alternative courses of action on climate change. This refocusing has helped to move debate away from science of the climate system and on to issues of policy. However, a careful examination of the Stern Review’s treatment of the economics of extreme events in developed countries, such as floods and tropical cyclones, shows that the report is selective in its presentation of relevant impact studies and repeats a common error in impacts studies by confusing sensitivity analyses with projections of future impacts. The Stern Review’s treatment of extreme events is misleading because it overestimates the future costs of extreme weather events in developed countries by an order of magnitude. Because the Stern Report extends these findings globally, the overestimate propagates through the report’s estimate of future global losses. When extreme events are viewed more comprehensively the resulting perspective can be used to expand the scope of choice available to decision makers seeking to grapple with future disasters in the context of climate change. In particular, a more comprehensive analysis underscores the importance of adaptation in any comprehensive portfolio of responses to climate change.

Roger Pielke Jr

Center for Science and Technology Policy Research, University of Colorado, 1333 Grandview Ave, Campus Box 488 boulder, Co 80309-0488, USA
Received 5 March 2007; revised 21 May 2007; accepted 22 May 2007. Available online 15 August 2007.

Global Environmental Change

“In its Chapter 5 the Stern Review concludes, “The costs of climate change for developed countries could reach several percent of GDP as higher temperatures lead to a sharp increase in extreme weather events and large-scale changes.” (Stern, 2007, p. 137). This conclusion cannot be supported by the Review’s own analysis and references to literature. One error is a serious misrepresentation of the scientific literature, and the second is more subtle, but no less significant. The serious misrepresentation takes the form of inaccurately presenting the conclusions of an unpublished paper on trends in disaster losses. The second error is more complex and involves conflating an analysis of the sensitivity of society to future changes in extreme events, assuming that society does not change, with a projection of how extreme event impacts will increase in the future under the integrated conditions of climatic and societal change. The result of the errors in the Stern Review is a significant overstatement of the future costs of extreme climate events not simply in the developed world, but globally-by an order of magnitude.

In light of these errors if the Stern Review is to be viewed as a means of supporting a particular political agenda, then it undercuts its own credibility and this risks its effectiveness. If instead the Stern Review is to be viewed as a policy analysis of the costs and benefits of alternative courses of actions on climate change, then at least in the case of extreme events it has missed an opportunity to clarify the scope of such actions and their possible consequences, and arguably misdirects attention away from those actions most likely to be effective with respect to future catastrophe losses. In either case, on the issue of extreme events and climate change, the Stern Review must be judged a failure. This short paper documents these errors and suggests how an alternative approach might have been structured.”