With much attention on the effects of global warming on the climate system, the recent severe winter weather has heightened global warming scepticism among the general public. Analysis of the most recent observational and modelling data supports links between strong regional cooling trends in the winter and warming trends in the prior seasons
Mumbai and several parts of the country are reeling under the cold and chilly weather. Some think it is the extended winter. However, the sudden drops in minimum temperatures (between 2°C to 4°C) at many places are not because of just random variations, but in fact are side effects of the global warming phenomenon. According to researchers and scientists, the global warming might be causing more cooling and snow in many parts of the world.
In an article published in Environmental Research Letters, a team led by Judah L Cohen of Atmospheric and Environmental Research (http://iopscience.iop.org/1748-9326/7/1/014007), wrote that, “Evidence suggests that summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover. And that dynamically induces large-scale wintertime cooling.”
Rajan Alexander, who keeps a track of various things through his blog, reported that earlier this week, the Sahara desert witnessed snowfall. A 24-hour cold spell brought snow and rain to the Bechar province in western Algeria. Bechar is located in the northern Sahara, about 36 miles south of the Moroccan border. Similarly, the Gulf countries are facing extreme cold waves, Mr Alexander wrote. According to the National Centre of Meteorology and Seismology (NCMS) forecast for Tuesday, minimum temperatures were set to dip to 0°C in the United Arab Emirates’ (UAE) mountainous regions while internal areas could see temperatures dipping to a nippy 5°C and coastal areas could see minimum temperatures of 13°C.
Back home, Leh in the Ladakh region recorded its coldest night at minus 21.8°C of the season with Kargil recording a minus 21°C was the second coldest place in India on Tuesday. The harsh cold weather, on 17 January 2012, broke records in many places, with Madikeri (Karnataka) registering its lowest in 132 years at 4.8 degrees Celsius, Mysore’s coldest day in 120 years was at 7.7 degrees Celsius and Bangalore’s coldest day of January in the past 19 years with minimum temperature dropping to 12 degrees Celsius.
Many climatologists believe that the Arctic Oscillation (AO) affects the probability of certain weather events occurring in certain places. However, the heightened chance of a phenomenon by no means assures it, nor does the lessened likelihood exclude it. When the AO index is positive, surface pressure is low in the polar region. This helps the middle latitude jet stream to blow strongly and consistently from west to east, thus keeping cold Arctic air locked in the polar region. When the AO index is negative, there tends to be high pressure in the polar region, weaker zonal winds, and greater movement of frigid polar air into middle latitudes.
The AO fluctuates stochastically between negative and positive values on daily, monthly, seasonal and annual time scales and despite its stochastic nature, meteorologists have attained high levels of predictive accuracy in recent times, at least for the shorter term forecasts.
While the AO may not have much effect on Indian-sub continent, it’s the North Atlantic Oscillation (NAO), which may have some co-relation with Indian monsoon. A study, “Interannual and long-term variability in the North Atlantic Oscillation and Indian summer monsoon rainfall” was done by Dugam, Kakade and Verma of the Indian Institute of Tropical Meteorology (http://cat.inist.fr/?aModele=afficheN&cpsidt=2068184) to investigate the co-relation based on data of over 108 years.
The study found that: “The decadal scale analysis reveals that the NAO during winter (December-January-February) and spring (March-April-May) has a statistically significant inverse relationship with the summer monsoon rainfall of Northwest India, Peninsular India and the whole of India. The highest correlation is observed with the winter NAO. The NAO and Northwest India rainfall relationship is stronger than that for the Peninsular and whole of India rainfall on climatological and sub-climatological scales.”
In short, fluctuations in the AO and NAO caused due to global warming can be blamed for the cold, chilly and extended winter across the globe. According to the article published in the Environmental Research Letters, the Arctic is warming more strongly than other parts of the globe and also sees more sea ice melt all the way into late summer and early fall.
It said, “The warmer conditions over open Arctic waters (remember, dark waters absorb heat from sunlight while light-coloured ice reflects it) lead to higher moisture levels in the air. More moisture means more clouds that can bring on more precipitation. Over Siberia, where it’s still cold enough for snow instead of rain, those additional clouds and moisture mean more snow than normal, especially in the fall.”
“Increased autumn snow cover in Siberia can help bring on the winter phase of what’s called the AO, a variation in surface atmospheric pressure patterns. That can affect the jet stream and other prevailing wind patterns, bringing blasts of Arctic air deep into lower latitudes, especially in the eastern United States, southern Canada and northern Eurasia,” the article added.
Here is the anomaly in temperatures provided by WXMaps.org and published by Steven Goddard in his blog real-science.com. The graph and pattern shows all heat trapped is causing temperatures 10°C below normal across the northern hemisphere.
So what is in store for India in next week? According to WXMaps.org report, the temperatures may go back to their normal averages at most places. However, places like northern India and south India would continue to see temperatures 2°C to 6°C below their normal range during this season. Some parts in central India is likely to be little warmer. See the image below…
1. Rajan Alexander from http://devconsultancygroup.blogspot.com/