Heat released from the Arctic in ice free areas and areas with thin ice has changed wind patterns, driving cold Arctic air towards Japan.

Last January I explained December, 2009's bizarre weather.



Negative phase of the Arctic Oscillation These regional contrasts in temperature anomalies resulted from a strongly negative phase of the Arctic Oscillation (AO). The AO is a natural pattern of climate variability. It consists of opposing patterns of atmospheric pressure between the polar regions and middle latitudes. The positive phase of the AO exists when pressures are lower than normal over the Arctic, and higher than normal in middle latitude. In the negative phase, the opposite is true; pressures are higher than normal over the Arctic and lower than normal in middle latitudes. The negative and positive phases of the AO set up opposing temperature patterns. With the AO in its negative phase this season, the Arctic is warmer than average, while parts of the middle latitudes are colder than normal. The phase of the AO also affects patterns of precipitation, especially over Europe. The phase of the AO is described in terms of an index value. In December 2009 the AO index value was -3.41, the most negative value since at least 1950, according to data from the NOAA Climate Prediction Center.

A number of climate scientists think that a tipping point was passed in 2005.

The changes in the Arctic are now irreversible, he (Overland) said. "This is a very big change for the entire planet," said David Barber, an Arctic climatologist at the University of Manitoba in Canada. The planet's cold polar regions are crucial drivers of Earth's weather and climate.

...... The winter of 2005-6 was the coldest in 50 years in Japan and eastern Eurasia, reported Meiji Honda, a senior scientist with the Climate Diagnosis Group at Japan's Agency for Marine-Earth Science and Technology. Honda's studies show that the air over the Arctic was quite warm in the fall of 2005, which altered normal wind patterns, pushing the jet stream further south and bringing arctic cold to much of Eurasia and Japan. He also documented the same mechanism for the colder winters of 2007-8 and 2009-10, he told participants. In eastern North America, the same conditions of 2007-8 produced increased precipitation and colder temperatures in the winter. As the sea ice declines, big impacts are likely to be seen in this region, said Sara Strey of the University of Illinois.

Reduced sea ice this fall warmed the Arctic, weakening the Arctic's atmospheric circulation. The warming may explain this December's record low Arctic Oscillation (AO) index. Note that before the recent strong decline in sea ice levels beginning in 2005, AO index levels were high.

The Arctic Oscillation (AO) is based on seal level pressure differences (now measured by satellite for the 1000 mb height). (See: http://www.cpc.noaa.gov/... ) "The AO index describes the relative intensity of a semipermanent low-pressure center over the North Pole. A band of upper-level winds circulates around this center, forming a vortex. When the AO index is positive and the vortex intense, the winds tighten like a noose around the North Pole, locking cold air in place. A negative AO and weak vortex ... allow intrusions of cold air to plunge southward into North America, Europe, and Asia.

Sea surface temperature changes over 58 years show that reduced sea ice in the Arctic is associated with increased flow of warm water into the Labrador sea and Arctic ocean. It appears that the Gulf Stream and the global thermohaline circulation is being enhanced by increased overturning of dense salty water in the Labrador sea and the far north Atlantic.

Linear trend in sea surface temperature based on the December–January–February (DJF) seasonal mean for the 1950–2008 period. Units are in Deg C/58-years.



Increasing sea surface temperatures are increasing in the tropical Indian ocean and western Pacific while the eastern Pacific is cooling because of increased upwelling of cool midlevel water.

It's well established that weaker high pressure in the mid-Atlantic (the Azores high) is associated with warmer water temperatures in the tropical Atlantic. This spring's weak Azores high is one of the factors in Klotzbach and Gray's forecast of an intense hurricane season this year.

Another factor in our forecast increase is the weaker-than-normal Azores High that prevailed during April-May. Weaker high pressure typically results in weaker trade winds that are commonly associated with more active hurricane seasons.

Anomalous low-level wind (ms-1) observed during April-May 2010. Westerly anomalies were observed over the tropical Atlantic, indicating a reduction in the easterly trade winds. Weaker trades typically warm the tropical Atlantic.

Because Atlantic hurricane activity is highly variable while the scientific record of hurricanes is short, the relationship between climate change and Atlantic basin hurricane activity has been hotly debated by hurricane experts and climatologists. Professor Michael Mann has examined geologic evidence of hurricane overwash in the sedimentary record to supplement the short historical record.

Atlantic tropical cyclone activity, as measured by annual storm counts, reached anomalous levels over the past decade. The short nature of the historical record and potential issues with its reliability in earlier decades, however, has prompted an ongoing debate regarding the reality and significance of the recent rise. Here we place recent activity in a longer-term context by comparing two independent estimates of tropical cyclone activity over the past 1,500 years. The first estimate is based on a composite of regional sedimentary evidence of landfalling hurricanes, while the second estimate uses a previously published statistical model of Atlantic tropical cyclone activity driven by proxy reconstructions of past climate changes. Both approaches yield consistent evidence of a peak in Atlantic tropical cyclone activity during medieval times (around AD 1000) followed by a subsequent lull in activity. The statistical model indicates that the medieval peak, which rivals or even exceeds (within uncertainties) recent levels of activity, results from the reinforcing effects of La-Nin˜a-like climate conditions and relative tropical Atlantic warmth.

Note that increasing warmth in the tropical Atlantic and La Nina like cooling in the eastern Pacific is exactly what has been observed over the past 58 years. The same tropical sea surface pattern that caused the increase in Atlantic hurricane activity in the Medieval warm period is being observed today.

In a related paper in 2007 Sabetelli and Mann analyzed how 3 climate state variables affect the number of hurricanes in the north Atlantic.



Time Series (1870-2004) of (a) annual Atlantic TC counts, (b) MDR ASO SST time series,

(c) Nin˜o3.4 DJF SST index, and (d) NAO DJFM SLP index. Red (blue) indicates positive (negative) anomalies in TC counts and Hurricane-favorable (unfavorable) conditions in the three indices (MDR SST, Nin˜o3.4 and NAO). Note that year convention applies to the ‘D’ in DJF and DJFM for both ‘c’ and ‘d’.

They found that the variables El Nin˜o/Southern Oscillation (ENSO) in August-October, Sea Surface Temperatures (SST) over the main development region (‘MDR’: 6-18N, 20-60W), and the North Atlantic Oscillation(NAO) accounted for virtually all non random correlations with hurricane counts.

The Arctic oscillation is directly positively correlated with the NAO. Some climate scientists consider the AO and the NAO to be the same thing.

If the loss of Arctic sea ice caused this winter's extremely low AO levels it is also contributed to warming the tropical Atlantic by reducing the strength of the Azores high, weakening the trade winds and making the NAO strongly negative.

Based on the statistical methods developed in the 2007 paper Mann is predicting a near record hurricane season this year.

The prediction is for 23.4 +/- 4.8 total named storms, which corresponds to between 19 and 28 storms with a best estimate of 23 named storms. This prediction was made using the statistical model of Sabbatelli and Mann (2007, see PDF here), including the corrections for the historical undercount of events (Mann et al., 2007, see PDF here). The basis of this forecast is the assumption that the current extremely warm sea surface temperature (SST) anomaly (1.34 C from NOAA’s Coral Reef Watch),(Today's SST anomalies inserted by author)

in the Main Development Region (MDR) in the North Atlantic will persist throughout the 2010 hurricane season. It also takes into account current model predictions of near-neutral or slight La Nina conditions during boreal Fall/Winter 2010 (see ENSO predictions here). Climatological mean conditions are assumed for the North Atlantic Oscillation (NAO) in Fall/Winter 2010.

If the Arctic climate scientists quoted in this post are correct, then both this winters heavy east coast snows and this summer's forecast intense hurricane season are related to changes in atmospheric circulation patterns caused by the melting of Arctic sea ice.



Sea ice is now so thin in much of the Arctic ocean that it is allowing much more heat to escape to the Atmosphere than it did 10 or 20 years ago.

The increasing amount of heat escaping from the Arctic ocean is changing atmospheric circulation patterns (causing the strongly negative Arctic Oscillation index) leading to harsher snowy east coast winters and more intense Atlantic basin hurricane seasons.