Media Releases

Unprecedented Arctic ozone loss occurred last winter:

October 5, 2011

U of T physicists play key role in international study

TORONTO, ON – A NASA-led study has doc­u­ment­ed an unprece­dent­ed deple­tion of the Earth’s pro­tec­tive ozone lay­er above the Arc­tic last win­ter and spring that was caused by an unusu­al­ly pro­longed peri­od of extreme­ly low tem­per­a­tures in the stratos­phere.  Uni­ver­si­ty of Toron­to physi­cist Kaley Walk­er was part of the inter­na­tion­al team behind the study to be pub­lished online Sun­day, Octo­ber 2 in Nature.

The researchers found the amount of ozone destroyed in the Arc­tic in 2011 was com­pa­ra­ble to that seen in some years in the Antarc­tic, where an ozone “hole” has formed each spring since the mid 1980s. The stratos­pher­ic ozone lay­er, extend­ing from about 15 to 35 kilo­me­tres above the sur­face, pro­tects life on Earth from the sun’s harm­ful ultra­vi­o­let rays.

The sci­en­tists found that at some alti­tudes, the cold peri­od in the Arc­tic last­ed more than 30 days longer in 2011 than in any pre­vi­ous­ly stud­ied Arc­tic win­ter, lead­ing to the unprece­dent­ed ozone loss. Fur­ther stud­ies are need­ed to deter­mine what fac­tors caused the cold peri­od to last so long.

The Antarc­tic ozone hole forms when extreme­ly cold con­di­tions, com­mon in the win­ter Antarc­tic stratos­phere, trig­ger reac­tions that con­vert atmos­pher­ic chlo­rine from human-pro­duced chem­i­cals into forms that destroy ozone. While the same ozone-loss process­es occur each win­ter in the Arc­tic, the gen­er­al­ly warmer stratos­pher­ic con­di­tions there lim­it the area affect­ed and the time frame dur­ing which the chem­i­cal reac­tions occur.  This means there is gen­er­al­ly far less ozone loss in most years in the Arc­tic than in the Antarc­tic.

To inves­ti­gate the 2011 Arc­tic ozone loss, Walk­er and sci­en­tists from 18 oth­er insti­tu­tions in nine coun­tries (Unit­ed States, Ger­many, The Nether­lands, Rus­sia, Fin­land, Den­mark, Japan and Spain) ana­lyzed a com­pre­hen­sive set of mea­sure­ments. These includ­ed dai­ly glob­al obser­va­tions of trace gas­es and clouds from NASA’s Aura and CALIPSO space­craft; ozone mea­sured by instru­ment­ed bal­loons; mete­o­ro­log­i­cal data and atmos­pher­ic mod­els.  The Uni­ver­si­ty of Toron­to team con­tributed to the bal­loon-borne data with mea­sure­ments from Eure­ka, Nunavut, locat­ed at 80 ºN (1,100 km from the North Pole).  The team was par­tic­i­pat­ing in a Cana­di­an Space Agency-fund­ed project mak­ing spring­time mea­sure­ments to ver­i­fy the per­for­mance of a Cana­di­an satel­lite called the Atmos­pher­ic Chem­istry Exper­i­ment (ACE).

“In the 2010-11 Arc­tic win­ter, we did not have tem­per­a­tures that were low­er than in the pre­vi­ous cold Arc­tic win­ters,” said Walk­er.  “What was dif­fer­ent about this year was that the tem­per­a­tures were low enough to gen­er­ate ozone-deplet­ing forms of chlo­rine for a much longer peri­od of time.  Arc­tic ozone loss events such as those observed this year could become more fre­quent if win­ter Arc­tic stratos­pher­ic tem­per­a­tures decrease in future as the Earth’s cli­mate changes.

The 2011 Arc­tic ozone loss occurred over an area con­sid­er­ably small­er than that of the Antarc­tic ozone holes. This is because the Arc­tic polar vor­tex, a per­sis­tent large-scale cyclone with­in which the ozone loss takes place, was about 40 per­cent small­er than a typ­i­cal Antarc­tic vor­tex. While small­er and short­er-lived than its Antarc­tic coun­ter­part, the Arc­tic polar vor­tex is more mobile, often mov­ing over dense­ly-pop­u­lat­ed north­ern regions. Decreas­es in over­head ozone lead to increas­es in sur­face ultra­vi­o­let radi­a­tion, which are known to have adverse effects on humans and oth­er life forms.

Although the total amount of Arc­tic ozone mea­sured was much more than twice that typ­i­cal­ly seen in an Antarc­tic spring, the amount destroyed was com­pa­ra­ble to that in some pre­vi­ous Antarc­tic ozone holes. This is because ozone lev­els at the begin­ning of Arc­tic win­ter are typ­i­cal­ly much greater than those at the begin­ning of Antarc­tic win­ter.

The sci­en­tists not­ed that with­out the 1989 Mon­tre­al Pro­to­col, an inter­na­tion­al treaty lim­it­ing pro­duc­tion of ozone-deplet­ing sub­stances, chlo­rine lev­els already would be so high that an Arc­tic ozone hole would form every spring. The long atmos­pher­ic life­times of ozone-deplet­ing chem­i­cals already in the atmos­phere mean that Antarc­tic ozone holes, and the pos­si­bil­i­ty of future severe Arc­tic ozone loss, will con­tin­ue for decades.

“Each of the bal­loon and satel­lite mea­sure­ments includ­ed in this study were absolute­ly nec­es­sary to under­stand the ozone deple­tion we observed this past win­ter,” Walk­er said.  “To be able to pre­dict future Arc­tic ozone loss reli­ably in a chang­ing cli­mate, it is cru­cial that we main­tain our atmos­pher­ic mea­sure­ment capa­bil­i­ties.”


For more infor­ma­tion, please con­tact:

Prof. Kaley A. Walk­er
Depart­ment of Physics
Uni­ver­si­ty of Toron­to
416 ‑978‑8218

Kim Luke
Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to