IPCC´s PREDICTIONS HOLD TRUE?
According to satellite measurements, the present level of
rise is about 3 mm per year. In hundred years, this will amount to 30
cm. So, when the IPCC predicts a sea level rise of about 30 cm during
the 21st century, they actually say that the present rate of rising
will continue unchanged. And when they have a lower boundary saying 18
cm, this means that they keep the possibility open that the rate of sea
level rise will decrease.This is problematic, because up to now, the
rate of sea level rise is faster than what IPCC is able to explain by
summing up the known contributions.
In the most recent (fourth) IPCC assessment from
2007, the scientists have utilised information that was available since
the third assessment in 2001, but they have not utilised the very
newest information, because they had to go through a time-consuming
review process and did not have the opportunity to include the latest
evidence. For instance, their predictions about the extent of
melting of the polar sea ice during the arctic summer are already
outdated - the extent of melting in 2006 and 2007 has been much larger
than predicted by IPCC.
Another point where IPCC may have underestimated the
rate of melting, is the melting of land ice on Greenland and
Antarctica. In their calculations, they have included the increased ice
flow from Greenland and Antarctica at the rates observed for 1993-2003,
but they have not included the further increases in the ice flow
observed after 2003.
The processes governing the rate of discharge of
land ice via glaciers into the sea are not fully understood.
Information obtained in recent years is that melt water on the surface
of the ice may form socalled `moulins´, that is vertical holes
through which the water runs to the bottom of the glacier, where it
forms a lubricating layer which allows the glacier to slide faster
towards the sea. The effect is similar to what is seen in those
glaciers whose bottom is below sea level, which means that during
periods of high sea water level (tides), the bottom of the glacier is
lifted up, which accelerates the outward movement of the glacier ice.
During recent years, much new information has been
gathered on the movements of certain glaciers on Greenland, which are
outlets for about 10 % of the total inland ice there. In the Jakobshavn
glacier in west Greenland, the velocity of ice movement increased from
1996 to 2000, and increased further from 2000 to 2005. The extent of
melting hit a new record in 2007, and altogether the rate of melting
during the latest decade was almost twice that of the preceding decade,
link. In glaciers in
mid east Greenland (Helheim and Kangerdlugssuaq) the volocity of ice
movement has increased only after 2000. In the latter glacier, the
velocity of ice flow has tripled from 2000 to 2005 (data in an article
by Rignot and Kanagaratnam, see this
link and also this).
flow have not yet happened further
north in Greenland, but may come if temperatures continue to increase.
The point is that IPCC has not foreseen these
events, and not included them in their projections. This means that the
projected net losses of ice from Greenland and Antarctica are already
lower than the actual losses (see this lecture
Bindschadler). IPCC has considered the possibility that melt
water may increase ice flow by lubricating the glacier bottoms, but
they do not include this effect in their sea level projections,
and only notice that this effect may probably give an extra increase of
0.1 to 0.2 m over the century.
The point is that you may calculate what will happen
if ice discharge into the sea grows linearly with temperature rise. But
the sudden drastic accelerations in ice flow that have been observed in
Greenland after 2000 cannot be incorporated into the
mathematical models. One paper has calculated that the contribution to
sea level rise from melting Greenland ice has increased from about 0.23
mm per year in 1996 to 0.57 mm per year in 2005 (Rignot
Kanagaratman), but after proper reductions due to snow
accumulation in the centre of Greenland, the net contribution to sea
level rise is maybe more correctly estimated at about 0.04 mm in
2000 and 0.23 mm in 2005. Some others arrive at a contribution of 0.28
mm per year for 2003-2005 (Luthcke et al. 2006), and still others reach
estimates of up to 0.7 mm per year for this period (Chen, Wilson &
Tapley 2006; references in Cool it).
Altogether, what happens when the ice on Greenland
starts to melt is so complicated that it cannot be simulated properly
by mathematical models. This means that nobody knows for sure what will
happen. Important facts are 1) that the system does not behave linearly
- we see sudden accelerations in ice discharge. 2) The rate of ice loss
from Greenland (and Antarctica) seems already to be larger than
projected by the linear models of IPCC. The recent
acceleration of ice discharge is more than just a random fluctuation
due to unusual weather for a few years, but we do not know if it will
last - maybe it stops again when the
affected outlet glaciers have retreated from the coast line. However, a
continued acceleration of ice flow
is a definite possibility.
An important question is if the projected
atmospheric levels of CO2 will cause a temperature rise
that is sufficient to destabilise the whole inland ice on Greenland and
parts of Antarctica. Existing computer models show that a partial or
full deglaciation of Greenland may be triggered by even quite modest
future increases in CO2 (see this
link).Another important question is, if
it happens, will we have sufficient time to react? Time passes from the
point when greenhouse gases have increased in the atmosphere till the
full effect on melting of Greenland ice is seen. And from the time when
this is seen, further time passes until the political system wakes up
and reacts. The crucial question is if the effects of greenhouse gas
reductions appear soon enough to revert the unwanted melting effects.
Lomborg is sure that we have time enough to react,
should this be necessary. Others are not so sure.
Comments to pages 74 - 78 in Cool it.
Page 75: " . . . we are engaging in a reckless drive-by drowning . . .
The quote is correct (see here)
cited out of context. "The rest of the planet" means sites outside
USA. McKibben is not talking about floods of many meters, but just
flooding of very low-lying lands like Tuvalu and Bagladesh.
Page 76 top: "Nonetheless, when using the more than 1,800 tide gauge
stations . . ".
Figure 20 is based on data from 1,023 tide gauge stations. Data from
old time periods are sparse. There are useful data from only 70
stations in 1900, and only 5 in 1850.
Page 76 top: "we get the longest data series for sea levelse, as shown
in Figure 20."
It is no advantage to have a very long time series, because the oldest
records are associated with great uncertainty. Before 1870, the
uncertainty on the figures is so large that they are nearly useless.
Page 76 bottom, note 376: "This is consistent with IPCC, 2007b ch. 5
and generally in the same range as Church & White (2006). . "
This is a strange formulation. Lomborg´s data are the same as
those in the IPCC report, which are based on the papers cited by
Lomborg, such as Church & White (2006).
Page 76 bottom, Figure 20 and note 377
The reader who checks the note gets the impression that the sea level
curve is the same as depicted by IPCC, only adjusted vertically. But
this is not so. The part of the curve that is
before 2000 is taken from Jevrejeva et al. (2006), and only the
projection is taken from the recent IPCC report. The IPCC concludes
that data from before 1870 are too unreliable to be illustrated,
whereas Jeverejeva et al. do a greater effort to include as many tide
gauge stations as possible, by using certain corrections. The inclusion
of more tide gauge stations causes the curve to diverge from the IPCC
curve for the period before about 1930. It has a greater upward slope
than the IPCC curve. As to the course before 1870, Jevrejeva et al.
stress the large uncertainty by indicating a very broad confidence
interval (range of uncertainty), and they write specifically that "the
large acceleration in sea level 1850 - 1870 coincides with a few new
stations becoming active, and is probably not statistically
significant." So the temprary drop around 1860 is probably a
statistical artifact, which means that the documented rise in sea level
is about 20 cm, from the late 19th century to 2000. The rise of 29 cm
since 1860 is not reliable, which is stated clearly in Lomborg´s
Lomborg presents a confidence interval (light grey
shade) for future values, but omits the confidence interval for the
oldest values that are also very uncertain. Instead, he presents a very
detailed curve with many ups and downs, which suggest to the reader
that the underlying data are very exact and reliable. They are not.
This is therefore a deliberately misleading
See also the article on sea level rise
Page 77 top: " . . it is back at around 2.4 mm per year"
This is a biased presentation of the information available. The figure
of 2.4 mm is taken from Jeverejeva et al. and is based on data from
tide gauges, where the compensation for vertical movements of land
masses is incomplete. Satellite measurements, such as those referred to
by Lomborg in his note 376, demonstrate a sea level rise of about 3
mm/year for the period 1993-2003. Thus, Lomborg has cherrypicked those
values that make sea level rise look smallest. A longer time series of
satellite data, covering the period 1993-2008, gives a steady rate of
sea level rise of 3.2 mm rise per year, with some ups and downs, but no
clear change of the rate (source: this
link). Lomborg conceals that the rate of sea level rise is larger
than ever before, and his text is therefore very
Page 77 top: "In its 2007
report, the UN estimates that sea levels will rise about 29 cm over the
rest of the century . . "
The average for the six scenarios is 34.5 cm. Only the B1 scenario has
a central estimate of about 29 cm. It is not acceptable that Lomborg
uses just that, because this scenario has the lowest CO2 emission,
whereas Lomborg advocates for nearly no restricitons on
CO2 emissions, which would rather correspond to the A1FI scenario with
a sea level rise of about 42 cm. As Lomborg should know, the actual
development of CO2 emissions is close to the A1FI scenario, or even a
Page 77 top: " . . it is certainly not outside the historical
This is not true. Allison et al. (2009):
21 (5): 413-426 write: "At about 2000 years before
present (BP), sea level rise had almost ceased and, from 1000 yrs BP to
the late 19th century, sea level variation was confined within a range
of about 0.2m."
Page 77: "In its 2007 report, the UN estimates that sea levels will
rise about 29 cm . . "
This is a biased statement. The report presents projections for six
different scenarios, in which the central estimates range from 28 cm to
42.5 cm. Only one has a figure below 30 cm. In addition,
the text in section 10.6.5. says explicitly that because not all of the
observed sea level rise can be explained up to now, the projections are
likely to be underestimates. The report mentions a
extra contribution of up to 20 cm sea level rise due to melt
water lubricating ice flow; this is omitted by Lomborg. Considering
that recent information indicates that such lubrication of glacier flow
does indeed occur to a hitherho unexpected extent, it is fair to say
that the data in the report indicate a sea level rise of probably 50 cm
Page 77: "It is also important to realize that the new prediction is
lower than the previous IPCC estimates."
is not true. IPCC WGI paragraph 10.6.5 states that the appraent
difference has two reasons: First, the new projections are for
2090-2099, whereas the previous were for 2100. Second, the previous
included some small constant additional contributions to sea level rise
which are omitted now. . . The previous report would have had similar
ranges to those shown now if it had treated the uncertainties in the
Page 77 and note 380: "This
continues a declining trend from the nineties . . . "
which is also evident from the note.