I have often commented on the often seemingly contradictory predictions revolving around anthropogenic global warming (AGW). On the surface, these can seem a bit humorous. We have seen forecast of more hurricanes and less hurricanes, warmer weather and colder weather, more drought as well as more floods. It would seem as if the prognosticators are trying to cover all the bases, so that no matter what happens, it can be blamed on AGW.
One of the more interesting contradictions is the fact that many areas of the globe are experiencing harsher winters (we have had our share during the 3 years prior to this Winter), even though most data indicates the average temperature of the globe is very slowly rising. The one thing to remember is that even if there is a harsh (cold and snowy) Winter, the rest of the year might end up enough above normal that when the final annual average is calculated, the temperature could still end up above normal.
A recent study which focused on the eastern U.S., southern Canada, and northern Eurasia, found that the harsh Winters were linked to warmer Summers. What?! The nascent theory is that warmer Summers lead to warmer water temps, which lead to more moisture in the air, which leads to more snow in the Winter, which leads to colder temps. The aggregate snow cover has a big impact on temps over large geographical regions. During Winter when the entire Midwest is covered in snow, temps will not warm up much even when warm winds blow into the area. Of course, the snow also reflects a lot of sunlight away from the ground preventing much warming. Snow-less ground absorbs a lot more sunlight and warms up.
This got me to wondering about positive feedback loops. During the course of studying many research results throughout the years, the “positive feedback loop” is often mentioned in climate forecasts. One example: less ice in the arctic leads to more warming in the ocean, which leads to less ice, which leads to more warming, ad infinitum (or so it seems). Almost every feedback loop that has been proposed is theorized to enhance AGW (in what seems like classic group-think). Hardly anyone has suggested feedback loops that work against AGW, even though the atmosphere is non-linear and has seen historical extremes at both the cold and warm end of the spectrum.
Something eventually tips the balance of temps toward colder weather as evidenced by the glacial periods. Could increased snowfall tip the scales and counteract some of the warming of recent decades? It certainly does in the Winter as found by the recent study. But what would it take to affect temps on a global scale during other seasons of the year? A humongous amount of snow. If the Winter snow was deep enough in certain areas of the globe, it would last longer into the Spring (or even Summer in far northern latitudes). If the cryosphere (ice and snow covered areas of the globe) increased because of very heavy snowfall in the Winter, it could lead to a feedback loop that eventually creates a cooling trend. I don’t know how much snow we are talking about here, but it is part of the process that drove the past ice ages. Check the current state of the cryospere here.
For more on the reasons for past ice ages check out this recent report adding to the evidence that changes in the earth’s orbit and tilt drove the cycles between glacial and interglacial periods.
Have a pleasant Wednesday! Meteorologist Justin Loew.
This post was written by jloew on January 18, 2012