3 August 2012

New Peer Reviewed Science Indicates Arctic Melt is Mainly Due to Humans

Posted by Dan Satterfield

While the main stream media has focused on a study that has yet to be peer-reviewed ( and really just confirms a dozen others), the present weather continues to be nothing less than amazing. The records from the dust bowl that most meteorologists (me included ) looked at with awe are tumbling daily. Tulsa, in Oklahoma, ( my hometown by the way) may approach it’s all time high this week. The max temperature reached 109° (43°C) there today, and they also set an all time record high minimum.

The hottest temp. ever in Tulsa was 116 (46.7°C) in 1936. My grandmother remembered that day well! She told me that her Dad directed them to take their beds outside and they all slept there until the heat eased up. Their neighbors quickly followed suit! A little dust bowl history for you from expat Okie!

In Related News

The Arctic sea ice is running at all record lows as well and the 2007 record low is certainly in jeopardy. There is a new study in Enviro. Research Letters that makes a good case that about at least 70% of the Arctic ice loss is due to anthropogenic causes. The paper is open access, and well worth a read.

In general they found that there is a connection between the Atlantic Multidecadal Oscillation (AMO) and Arctic Sea, ice but that correlation can only explain a small amount of the drop we are now seeing. They also found that other ocean atmosphere oscillations have little effect on the ice. They used climate models run with pre-industrial atmospheric conditions to discern how widely the natural oscillations in the ice might be. They found that at most 30% of the loss per decade could be attributed to the AMO.

No time to read the paper? Here is the main part of the conclusion:

We find little evidence for a relationship between the
AO and September SIE in either the observations or the
five models. Further, from modelling we find that over short
periods (58 years) there will be apparently significant
correlations between the AO and SIE purely by chance,
indicating the need for long term observations. However,
missing physical processes in the GCMs may cause a lack of
sensitivity to changes in atmospheric circulation.
In agreement with Mahajan et al (2011), we find that a
significant correlation between the annual AMO index and
SIE and is a robust feature of the five models. Correlation
between the AMOC and SIE is also a consistent feature
of all 5 pre-industrial simulations, except for September
in GFDL-CM2.1. In the models considered variations in
the AMO and AMOC are associated with variations in the
North Atlantic heat transported to the Arctic, it is through
this mechanism that North Atlantic variability impacts SIE.
However, the lag time which maximizes the correlation
between AMOC and SIE differs between models. The lack of
long term, century scale monthly sea ice or AMOC estimates
does not allow us to robustly infer this relationship from
The method used here shows that for the period
1979–2010, 0:5–3:1%=decade of the observed decline of
5Environ. Res. Lett. 7 (2012) 034011 J J Day et al
10:1%=decade is associated with the natural cycle of the
AMO, consistent with Kay et al (2011). During this period
the AMO has moved from a negative phase, associated with
anomalously cold North Atlantic SSTs, to a positive phase,
associated with anomalously warm SSTs. The effect of the
AMO over the extended observational period 1953–2010 is
much smaller since the record both begins and ends in a
negative AMO state. This suggests that despite increased
observational uncertainty in the pre-satellite era, the trend in
SIE over this longer period is more likely to be representative
of the anthropogenically forced component.

Another Paper Says The Same

There is another paper in Geophysical Research Letters (AGU) by lead author Dirk Notz that says something very similar. Press release is here. A quote form the conclusions:

If this radiation is increased because of increasing CO2 concentrations, a decreasing sea-ice extent would be a direct consequence.

[29] The fact that we (a) have strong physical arguments for a possible causal relationship between CO2 and Arctic

sea-ice extent, and that we (b) find a pronounced correlation between the two in the observational record is very suggestive

of a causal relationship between the observed increase in atmospheric CO2 concentration and the decreasing Arctic

sea-ice extent. We are not aware of a similarly large and physically plausible correlation between sea-ice extent and

any other external driver. Such correlation would require a strong trend in the external driver consistent with the

observed sea-ice decrease. However, a strong trend is not found in the other external drivers discussed before, nor has

it been observed, for example, in cosmic rays [Chowdhuryet al., 2010], volcanic eruptions [Ammann et al., 2003], or

poleward oceanic heat transport [Schauer and Beszczynska- Möller, 2009].

[30] Hence, unless there is some external driver with a strong trend that we have not considered, we can conclude

that the most likely explanation of the downward linear trend in sea-ice extent is the increase in atmospheric CO2


Note: the UK Guardian has a nice piece on this as well, along with the obligatory Polar Bear pic.