29 October 2012

Connecting the dots between 'Frankenstorm' and global warming as extreme weather becomes the new norm

Courtesy: AP
“It's a freakish and unprecedented monster,” says Associated Press science writer Seth Borenstein of a super storm heading towards the US east coast “threatening 60 million Americans in the eastern third of the nation in just a couple of days with high winds, drenching rains, extreme tides, flooding and probably snow.”
     As Hurricane Sandy heads towards the east coast, it is likely to merge with an Arctic jet steam cold front to transform into an “unprecedented” “super storm”, the likes of which has not been seen over the eastern US in many decades, with sea surges of 1 to 2 metres.
     This storm is dangerous and unusual because it comes at the tail end of hurricane season and beginning of winter storm season, "so it's kind of taking something from both — part hurricane, part nor'easter, all trouble," says Jeff Masters of Weather Underground.
     Nicknamed "Frankenstorm", there is a climate change component to this story. Dr Kevin Trenberth of the US National Center for Atmospheric Research says it’s not a matter of attributing this or that particular storm to global warming but recognising there is a systematic influence on weather events:
It’s not the right question to ask if this storm or that storm is due to global warming, or is it natural variability. Nowadays, there’s always an element of both... there is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapour lurking around in the atmosphere than there used to be say 30 years ago.
Four uncontroversial facts help put Hurricane Sandy in context:
  • The Atlantic Ocean, over which the hurricane is now travelling, is 5 degrees F (3 C) warmer than average, and warmer water increases the likelihood of stronger storms further north. September had the second highest global ocean temperatures on record.
  • Global warming puts more energy into storms. The warmer the ocean surface temperature, the more evaporation and heavier rains. [This was the case with the very heavy rains across Australia in 2010 and 2011, associated with record high sea surface temperatures across northern Australian waters at the time.] Each 1C rise in temperature on average increases atmospheric water vapour content by seven per cent. 2010 and 2011 globally (and in Australia) were the two wettest years on land on record.
  • Storm surges now ride on sea levels that have risen over the last century due to global warming, amplifying flooding losses where the surge strikes. In the Northeast United States, sea levels are rising up to four times faster than the global average, making this area more vulnerable to storm surge and flooding. Multiple high tides may help drive flooding fuelled by a triple climate whammy: storm surge from a storm kept alive due to elevated sea surface temperatures; sea level rise driven by global warming; and extra heavy rains due to the extra rainfall loaded into the storm by climate change.
  • There may be an Arctic sea-ice melt influence on this event, due to the stalled cold front component of the “super storm”. There is evidence connecting sea-ice loss to the more severe and extreme weather patterns in Europe and north America, consistent with research from the US National Oceanic and Atmospheric Administration (NOAA). As Arctic melting and warming destabilize the jet stream and making it more "wavy", it allows frigid air to plunge farther south. As the jet stream waves become larger, they slow down or even stall at times, leading to a significant increase in so-called blocking events, such as the current stalled cold front. These cause extreme weather simply because they lead to unusually prolonged conditions of one type or another. The recent prolonged heatwave, drought and wildfires in the USA are one example of what can happen; another is the cool, dull and extremely wet first half of summer 2012 in the UK and other parts of Eurasia.
More extremes

The past few years have been marked by unusually severe extreme weather characteristic of climate change. A new study by Munich Re shows that North America has been most affected by weather-related extreme events in recent decades. "Severe weather in North America" analyzes all kinds of weather perils and their trends. It reports and shows that the continent has experienced the largest increases in weather-related loss events.
     Previously the NOAA had reported on the stream of extreme weather in the USA In 2011, when  new records were set in the US for tornadoes, drought, wind, floods, and wildfires. Heat records were set in every state. At one time in the 2011 summer, nearly half of the country’s population was under a heat advisory or heat warning. In late November, hurricane-force winds hit parts of Wyoming, Utah, Nevada, Arizona, New Mexico, and California, with winds reaching 97 mph in Pasaden. The number of events that produced on the order of $1 billion or more in damages in 2011 is the largest since tracking of that statistic began in 1980, even after damages are adjusted for inflation. NOAA estimates that there were at least 14 such events in 2011. (The previous record was nine, set in 2008; an average year would see three or four.) Collectively, the 14 events resulted in approximately $55 billion in damage. Furthermore, many events produced less than $1 billion in damage, but are not included in the tally, although they collectively represent additional significant financial losses.Weather- and climate-related disasters in the US claimed more than 1000 lives in 2011, almost double the yearly average.
     “Climate is what you expect; weather is what you get,” says Dr Jeff Masters, Weather Underground director of meteorology and former hurricane hunter.
     Connecting the dots between extreme weather and global warming, Masters told Climate Progress in February this year:
 I like to think of the weather as a game of dice. Mother Nature rolls the dice each day to determine the weather, and the rolls fall within the boundaries of what the climate will allow. The extreme events that happen at the boundaries of what are possible are what people tend to notice the most. When the climate changes, those boundaries change. Thus, the main way people will tend to notice climate change is through a change in the extreme events that occur at the boundaries of what is possible.
     The natural weather rhythms I’ve grown used to during my 30 years as a meteorologist have become disrupted over the past few years. Many of Earth’s major atmospheric circulation patterns have seen significant shifts and unprecedented behavior; new patterns that were unknown have emerged; extreme weather events were incredibly intense and numerous during 2010 – 2011. The laws of physics demand that the huge amount of heat-trapping gases humans are pumping into the atmosphere must be significantly altering the fundamental large-scale circulation pattern of the atmosphere. Unprecedented behavior like we’ve witnessed in the configuration of the winter jet stream over North America–with the four most extreme years since 1865 occurring since 2006–could very well be due to human-caused climate change.
Masters’ concludes that: “Something is definitely up with the weather, and it is clear to me that over the past two years, the climate has shifted to a new state capable of delivering rare and unprecedented weather events. Human emissions of heat-trapping gases like carbon dioxide are the most likely cause of such a shift in the climate.”

Sources: AP, Climate Progress,Connecting the Dots, Climate Signals, 350.org