Nature acknowledges warming hiatus, but does not explain continued declines in Arctic sea ice

“Although there have been jumps and dips, average atmospheric temperatures have risen little since 1998, in seeming defiance of projections of climate models and the ever-increasing emissions of greenhouse gases.” Jeff Tollefson, January 15, 2014, Nature. [open access]

The eminent science journal Nature has finally acknowledged that global average temperatures have not behaved as predicted by climate models over the last 16 years. [h/t A. Watts]

Note that predictions of future sea ice declines and associated predictions of future polar bear declines are totally dependent on these climate models.

Here’s my question: if global temperatures have basically flat-lined since 1998, why has Arctic sea ice continued to decline?

If average global temperatures govern Arctic sea ice behavior, why was 1998 (or the year after) not the lowest September sea ice extent reached over the last 30 years? Oddly, 2012 was the lowest September extent (see graphs below, from NSIDC).

Paradoxically, not only has sea ice continued to decline since 1998 – despite the hiatus in global warming – but since 1998, all but one polar bear populations have either increased in size, not declined, or are doing very well by other measures (see previous summary post, “Polar bears have not been harmed by sea ice declines“).

Sea ice extent graphs for September (which all the hysteria is about) compared to selected months from March, June and November. Ranges given are approximate; note the differences in scale for each graph. NSIDC graphs, colored labels added.

In the graphic that accompanied the Tollefson article (below), note the cool Arctic Ocean temperatures associated with the “cold” phase of the Pacific Decadal Oscillation (PDO):

Here are some more quotes from the Tollefson article:

“The biggest mystery in climate science today may have begun, unbeknownst to anybody at the time, with a subtle weakening of the tropical trade winds blowing across the Pacific Ocean in late 1997. These winds normally push sun-baked water towards Indonesia. When they slackened, the warm water sloshed back towards South America, resulting in a spectacular example of a phenomenon known as El Niño. Average global temperatures hit a record high in 1998 — and then the warming stalled.

For several years, scientists wrote off the stall as noise in the climate system: the natural variations in the atmosphere, oceans and biosphere that drive warm or cool spells around the globe. But the pause has persisted, sparking a minor crisis of confidence in the field. Although there have been jumps and dips, average atmospheric temperatures have risen little since 1998, in seeming defiance of projections of climate models and the ever-increasing emissions of greenhouse gases. Climate sceptics have seized on the temperature trends as evidence that global warming has ground to a halt. Climate scientists, meanwhile, know that heat must still be building up somewhere in the climate system, but they have struggled to explain where it is going, if not into the atmosphere.
Some have begun to wonder whether there is something amiss in their models.

Now, as the global-warming hiatus enters its sixteenth year, scientists are at last making headway in the case of the missing heat. Some have pointed to the Sun, volcanoes and even pollution from China as potential culprits, but recent studies suggest that the oceans are key to explaining the anomaly. The latest suspect is the El Niño of 1997–98, which pumped prodigious quantities of heat out of the oceans and into the atmosphere — perhaps enough to tip the equatorial Pacific into a prolonged cold state that has suppressed global temperatures ever since.

“The 1997 to ’98 El Niño event was a trigger for the changes in the Pacific, and I think that’s very probably the beginning of the hiatus,” says Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. According to this theory, the tropical Pacific should snap out of its prolonged cold spell in the coming years.“Eventually,” Trenberth says, “it will switch back in the other direction.”

…

The simplest explanation for both the hiatus and the discrepancy in the models is natural variability. Much like the swings between warm and cold in day-to-day weather, chaotic climate fluctuations can knock global temperatures up or down from year to year and decade to decade. Records of past climate show some long-lasting global heatwaves and cold snaps, and climate models suggest that either of these can occur as the world warms under the influence of greenhouse gases.

…

“I believe the evidence is pretty clear,” says Mark Cane, a climatologist at Columbia University in New York. “It’s not about aerosols or stratospheric water vapour; it’s about having had a decade of cooler temperatures in the eastern equatorial Pacific.” [my bold]

References
Tollefson, J. 2014. Climate change: The case of the missing heat. Nature 505 (7483):276-278. (open access) doi:10.1038/505276a

See also the related Editorial [Nature 505, 261–262 (16 January 2014) doi:10.1038/505261b “Cool heads needed. As cold weather rages, it is easy to forget the difference between weather and climate.”