TCS Daily

Greenland and Global Warming

By Willie Soon - June 10, 2004 12:00 AM

Recent popular media coverage of climate change issues has presented a scary scenario in which human-induced global warming will give rise to a new ice age. Indeed, this is the scenario sketched out in the climate disaster movie "The Day After Tomorrow." It sounds counterintuitive, so let's explain the science behind the scare scenario, such as it is.

Popular media of climate change has warned that increased man-made CO2 emissions will raise temperatures and thus melt the Greenland ice sheet, filling the Atlantic Ocean with excess fresh water. This will have the unintended effect of shutting down the North Atlantic Thermohaline Circulation or the North Atlantic oceanic heat conveyor belt. This would mean the possible discontinuation of the flow of heat from the tropics to the north pole through the North Atlantic Gulf Stream. The New York Times's Andrew Revkin emphasized in a June 8 article that "a big outflow of water from Greenland could take the system to a tipping point."

Will It Happen?

But such a threat, as predicted from current computer climate models, is most likely an exaggerated hype. In a letter for the April 8 issue of the journal Nature, Professor Carl Wunsch of MIT explained that:

"Real questions exist about conceivable changes in the ocean circulation and its climate consequences. However, such discussions are not helped by hyperbole and alarmism. The occurrence of a climate state without the Gulf Stream any time soon -- within tens of millions of years -- has a probability of little more than zero....

"European readers should be reassured that the Gulf Stream's existence is a consequence of the large-scale wind system over the North Atlantic Ocean, and of the nature of fluid motions on a rotating planet. The only way to produce an ocean circulation without a Gulf Stream is either to turn off the wind system, or to stop the Earth's rotation, or both."

OK, so a warming planet might not shut down the Gulf Stream. But what of the concern that a warming planet will result in a melting of the Greenland ice sheet? After all, a mere 15-pages after Professor Wunsch's caution in the April 8 issue of Nature, a team of European climate modelers on page 616 offers new concerns of their own, claiming the Greenland ice sheet could be wiped out:

"The Greenland ice-sheet would melt faster in a warmer climate and is likely to be eliminated -- except for residual glaciers in the mountains -- if the annual average temperature in Greenland increases by more than about 3°C. This could raise the global average sea-level by 7 metres over a period of 1,000 years or more. We show here that concentrations of greenhouse gases will probably have reached levels before the year 2100 that are sufficient to raise the temperature past this warming threshold. Without the ice-sheet, the climate of Greenland would be much warmer because the land surface would be a lower altitude and reflect less sunlight. This conclusion can be drawn without detailed modeling. Even if atmospheric composition and the global climate were to return to pre-industrial conditions, the ice-sheet might not be regenerated, which implies that sea-level rise could be irreversible."

Figure 1, located below, shows the proof offered for such a disastrous Greenland warming scenario. In it both the annual mean and summer warming in Greenland goes above the critical 2.7°C warming threshold level in which summer ice melting exceeds winter snow accumulation so that Greenland will continue to melt away under a persistent warming. According to Figure 1, that "no return" threshold of a final meltdown of Greenland will occur anytime from 2030 to 2200 for at least 70% of the UN IPCC scenarios (some of which are considered to be realistic by those IPCC authors).

Figure 1-Annual-mean and summer warming in Greenland under five different scenarios of atmospheric CO2 stabilization (450 ppm-purple; 550 ppm-light blue; 650 ppm-green; 750 ppm-yellow; 1000 ppm-red curves) as sketched by the UN Intergovernmental Panel on Climate Change. Dark horizontal dashed line indicates the 2.7ºC warming threshold in which" melting will outweigh the increase in snowfall." According to the authors of this paper, at least 70% of the Greenland warming scenarios will warm above this threshold and thus "threatened loss of the Greenland Ice-Sheet." [Adapted from Gregory et al., 2004, Nature, vol. 428, 616]

Irreversible Developments?

These European authors gained further confidence in their conclusion from a separate climate modeling experiment published earlier this year (January 2004) in the Journal of Climate. Instead of showing us that the Greenland ice-sheet will melt away completely in their climate models, these authors first artificially removed all the ice in Greenland and asked if their climate models would regenerate the Greenland ice sheet when they set their model atmosphere at the pre-industrial level of greenhouse gas concentrations. They failed to have any net accumulation of snow after crunching their computer climate model for some 70 years.

Their conclusion is that "the removal of the Greenland ice sheet due to prolonged climatic warming would be irreversible. Overall, the modified Greenland climate is not very different from that of some forested areas such as in eastern Siberia." But these authors also admitted that their modeling result "does depend on the sensitivity of the GCM to orography and on the assumed heat transport across the stably stratified boundary layer [the layer of turbulent air between the surface and free troposphere with a few hundred meters in thickness] over Greenland in winter and in spring."

Extremely Unlikely

So what can one expect for Greenland under the UN IPCC's global warming scenarios (which predict a disproportionately larger warming over Greenland)? Will a fully reforested Greenland with a marshy environment emerge once annual average CO2 warming at Greenland gets above 2.7°C? Or will we find the opposite extreme of an icy-cold Greenland with an ever expanding and larger ice-sheet if the North Atlantic Thermohaline Circulation is shut down?

While both extremes have been offered up by climate experts over the last few months through the popular media, I suggest that neither extreme will prevail because reality is simply far too complex to even consider these modeled extremes as legitimate climate predictions. The available climatic data for Greenland and over the North Atlantic simply do not give us confidence in the currently available modeled scenarios of Greenland.

Let's start with the raw evidence for our current inability to model climatic change with any degree of confidence. Here one need not go too far to find that region by region modeling of both the complete melting and regeneration of the Greenland ice sheet is indeed largely a matter of faith rather than any actual science.

In the aforementioned April 8 issue of Nature, on page 593, one learned from a top climate modeler that "If you don't believe in the value of global climate model then there's no point in down scaling them [to get regional pattern of change as in Greenland.]"

Figure 2-The drastic differences in the predicted winter surface temperature change in sophisticated computer climate model under two slightly different schemes for the parameterization of its heat transfer efficiency within the atmospheric boundary layer. Such a result illustrates the extreme sensitivity of transfer and exchange of heat and moisture between surface and the free troposphere. One may note the large 2 to 10°C temperature differences calculated for Greenland for the case of weak versus stronger mixing parameterization scheme. [Adapted from Viterbo et al., 1999, Q. J. Roy. Meteorological Society, vol. 125, 2401-2426]

Figure 2, located above, shows one reason I do not "believe in the value of global climate model." This chart shows the extreme sensitivity of surface winter temperature change on local and regional scales to how a model represents the physics of the boundary layer. This boundary layer is critical to how both heat and moisture are exchanged between the surface and the free atmosphere, especially during winters and springs over Greenland as noted earlier by those European modelers that successfully produced a permanently bare Greenland. But the authors of Figure 2 clearly show that with only a slight change or tuning of how heat is being exchanged or mixed, the model differences of the winter surface temperature can be as large as 2 to 10°C -- some of these intra-model temperature differences are certainly as large as those being claimed for CO2-global warming scenarios studied in Figure 1.

Next, the above model experiments for Greenland and large temperature warming in Figure 1 had clearly failed to recognize several contradictory facts from the available temperature data in Greenland. Petr Chylek of the Los Alamos National Laboratory and colleagues, in their paper published in the journal Climatic Change March 2004, found that:

"The Greenland surface air temperature trends over the past 50 years do not show persistent warming, in contrast to global average surface air temperatures. The Greenland coastal stations temperature trends over the second half of the past century generally exhibit a cooling tendency with superimposed decadal scale oscillations related to the NAO [i.e., the dynamic of North Atlantic Oscillation atmospheric circulation]. At the Greenland ice sheet summit, the temperature record shows a decrease in the summer average temperature at the rate of about 2.2°C/decade, suggesting that the Greenland ice sheet at high elevations does not follow global warming trend either. A significant and rapid temperature increase was observed at all Greenland stations between 1920 and 1930. The average annual temperature rose between 2 and 4°C in less than ten years. Since the change in anthropogenic production of greenhouse gases at that time was considerably lower than today, this rapid temperature increase suggests a large natural variability of the regional climate."

What's more, in a study of sea ice conditions and its historical changes around the Fram Strait (i.e., located northeast of Greenland) and ice flows around the coast of southwestern Greenland published last year in the Journal of Climate, Torben Schmith and Carsten Hansen of the Danish Meteorological Institute found that the annual export of ice through the Fram Strait is strongly correlated with the see-saw pattern of winter atmospheric circulation in the North Atlantic during the 1980-1990 interval called the North Atlantic Oscillation. Simultaneously, they also found a similar relationship suggesting the importance of atmospheric wind flow on the export of sea ice through the Fram Strait for earlier intervals around 1930-1950 and 1840-1860. This fact allows Schmith and Hansen to conclude that "this casts doubt on the hypothesis of enhanced greenhouse effect being the cause for the recent increase in correlation coefficient [during 1980-1990]." In addition, this sea ice study independently confirms the conclusion by Chlek and colleagues that large natural variability of climatic and environmental variables around Greenland is the norm rather than the exception to be expected strictly from man-made greenhouse gases.

Finally, it has long been known that the Greenland ice sheet probably originated some 2.4 million years ago. It is further deduced from geological records that the Greenland ice sheet is most likely the only Northern Hemisphere ice sheet to have survived the last Interglacial warm period around 130 to 115 thousand years ago (also roughly known as the Eemian warm period through terrestrial records from Europe). It must be emphasized that observed climatic and environmental changes during the last interglacial around the North Atlantic region are indeed dramatic. For example, tall mixed hardwood forests with a closed canopy covered much of Europe during the peak warm period and after about 115 thousand years ago, open vegetation replaced the mixed forests in northwestern Europe.

Professor Svend Funder[1] of the Geological Museum at the University of Copenhagen and his colleagues described the climatic and environmental conditions around Central and East Greenland [see the two marked locations in Figure 2] during the Eemian warm period as follows[2]:

"During the [Eemian warm period], Jameson Land had a different appearance from the present, and also from what it had during the Holocene climatic optimum [i.e., about 5 to 9 thousand years ago]. At present, the optimal type of vegetation is dwarf shrub heath, during the [Eemian warm period] there were copses of birch and alder on sheltered sites, and the heaths contained several plant, moss, and insect species which today only live in the warmer west Greenland. Bennike and Bocher (1994) concluded that summer temperatures were 5º [C] higher than at present, and ca. 3º-4º higher than during the Holocene climatic optimum. Also the marine faunas contain a number of subarctic species which are now absent from the East Greenland coast. These include Mytilus edulis and Chlamys islandica [i.e., species of mollusks with shells consisting of twin valves including mussels and clams], which lived in the area for some millennia during the Holocene climatic optimum, while Lacuna divaricata, Buccinum undatum, and Boreotrophon truncatus [i.e., species of gastropods or mollusks with single piece of straight or spiral shells like snails, limpets or with no shells like slugs, etc.] are restricted to West Greenland, and have not been recorded before in East Greenland. Finally, the gastropod Solariella varicosa has not been found earlier in Greenland. These subarctic species require warm Atlantic water to maintain their reproduction, and show that more Atlantic water was advected into the Nordic Sea and the Arctic in general than during the Holocene. Some oceanic species which are now restricted to the open coasts, also extended into the fjord system and show that water exchange between the ocean and the fjord system was more vigorous in agreement with marine geological results from the continental shelf. In summary, summer temperatures were already ca. 5º higher than at present and the oceanic circulation more vigorous with a large influx of Atlantic water than in the Holocene, at the time when the coast of Jameson Land was deglaciated. These conditions lasted longer than 3500 years."

So it is clear that the Greenland ice sheet did not simply melt away despite rather extreme climatic conditions and swings during the last interglacial. In addition, it is equally important to note that during the persistent warmth of the Eemian Interglacial, there were no signs of a weakening or a total shut down of the North Atlantic thermohaline circulation in climatic records around the North Atlantic-Greenland region despite the distinct possibility for excessive freshening of the North Atlantic ocean from enhanced rainfall and melting of Greenland's coastal ice.

Furthermore it may also be possible to rule out the computer scenario that suggests that the bare Greenland could not regenerate and re-support its ice sheet simply because a net accumulation of local snow was not possible in their model run after 70 years. Today, the ice thickness is over 3000 meters at Summit, Central Greenland (see the location marked in Figure 2), the site of the Greenland Ice Core Project (GRIP). From the work of Professor Roland Souchez[3] at the Université de Bruxelles, it is known that the gas contents of the basal silty ice (at depths between 3023 and 3029 meters) from the GRIP core at Summit, Greenland have enormously high levels of CO2 from about 30,000 ppm to 130,000 ppm and CH4 from about 1,000 to 6,000 ppm, while the 1980s-1990s atmospheric levels of CO2 and CH4 are about 360-370 ppm and 1.5-1.85 ppm, respectively.

Professor Souchez reasoned that the most probable scenario that could explain this observation[4] is that:

"such [basal] ice was developed probably within a peat deposit in a permafrost environment [when Central Greenland was bare without the giant ice sheet]. This local ice was subsequently intimately mixed with glacier ice from an advancing ice sheet progressing on this site. This is in agreement with the 'highland origin and windward growth' hypothesis for ice sheet development, not for an in situ or regional growth from snowbanks. The basal ice from the GRIP core possibly dates back to the original buildup of the Greenland Ice Sheet 2.4 million years ago. [Also] as suggested by a recent comparison of the isotopic profiles of GISP 2 [Greenland Ice Core Project 2] and of the GRIP cores, the ice sheet was developed in the Summit region during the Eemian [i.e., the last interglacials] ... It can be [further] assumed that the Greenland Ice Sheet was developed during the interglacials preceding the Eemian since the climate during these periods was less warm than that of the Eemian. The basal ice thus possibly represents the original build-up of the Greenland Ice Sheet."

In other words, the Greenland Ice Sheet has a long history of being stable for the past 2.4 million years enduring all extremes of warm and dry conditions most likely dwarfing even what is being emphasized by the UN IPCC CO2 global warming scenarios. Furthermore, it is clear that the Greenland Ice Sheet was not built by local deposition and accumulation of snow year after year as simplistically evaluated in the current computer models. As Souchez concluded:

"The preservation at the base of GRIP core of ice of local origin, formed most probably within a peat deposit in a permafrost environment, mixed with glacier ice from an ice sheet, is in itself a strong argument against in situ growth of the Greenland Ice Sheet."

[1] Funder et al. (1998), Quaternary Science Reviews, vol. 17, 77-123.

[2] Note that I have removed all the scientific references cited in this quote for the convenience of reading and the references are available upon request. My apology to Professor Svend Funder and colleagues for the potentially rude treatment of the scientific details in their paper.

[3] Souchez (1997), Journal of Geophysical Research, vol. 102, 26317-26323.

[4] Note that Professor Souchez was able to rule out the possibility that the high levels of CO2 may be produced through diffusion of highly concentrated CO2 from the subglacial ground because it was estimated that over the 2.4 million years of the original build up of the Greenland ice sheet, any trapped CO2 in the subglacial ground is only expected to slowly travel over a distance of 2 meters of the known 800 meters of relatively flat bedrock beneath the silty ice at the GRIP drill site.


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