A warming Arctic

Human-caused Arctic warming overtakes 2,000 years of natural cooling, “seminal” study finds:
[Via Climate Progress]

A Hockey Stick in Melting Ice

figure

Arctic temperatures in the 1990s reached their warmest level of any decade in at least 2,000 years, new research indicates. The study, which incorporates geologic records and computer simulations, provides new evidence that the Arctic would be cooling if not for greenhouse gas emissions that are overpowering natural climate patterns.

So reports the National Center for Atmospheric Research (NCAR), which coauthored the study to be published in Science Friday. [I’ll put the link up when it’s posted.] The Washington Post story notes:

The analysis, based on more than a dozen lake sediment cores as well as glacier ice and tree ring records from the Arctic, provides one of the broadest pictures to date of how industrial emissions have shifted the Arctic’s long-standing natural climate patterns. Coupled with a separate report on the region issued Wednesday by the World Wildlife Fund, the studies suggest human-induced changes could transform not only the Arctic but climate conditions across the globe.

It’s basically saying the greenhouse gas emissions are overwhelming the system,” said David Schneider, a visiting scientist at the National Center for Atmospheric Research and one of the Science article’s co-authors.

[More]

Nice hockey stick there. I figure the deniers will be pouring over this paper trying to figure out, once again, why facts just do not fit their reality.

The huge change in just the last 100 years or so is quite startling. It obliterates the 2000 year (maybe even 7000 year) trend.The blue line, which is the reconstruction of 2000 years worth of temperatures derived from over 20 well spread out sites using ice cores, lake bed sediments and tree rings, fits quire well with the red line, which shows the actual warming based on direct measurements.

The cooling trend looks to be due to the precession of the Earth’s axis. These
Milankovitch cycles describe changes in the axis of rotation with respect to the sun. Sometimes the Northern axis points towards the sun when the Earth is closest to the sun and other times it points away from the sun at its closest approach to the sun. This results in a 26,000 year cycle of changing intensities of solar irradiation during summer in the Arctic.

So sometimes the Arctic is cooler in summer than other times, simply because of the precession of the Earth’s axis.

The Arctic has been emerging from a hot point in this cycle and has been cooling for the last 7000 years. The trend seen above matches very closely the rate of the cooling trend seen since the end of the Halocene Thermal Maximum. At least until the last century or so.

In fact, in a short 100 years or so, the temperature of the Arctic has not only reversed the trend of the last 7000 years but may now be very close to the HTM temperatures seen then.

This sort of reversal is another point to support anthropogenic causes.

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