The impeding disaster: Global warming is fuelling tropical cyclones at an unprecedented rate

By Asma Rashid
Awareness regarding climate change and its economic and social impacts is one of the dire needs of the hour considering the ever-mounting phenomenon of global warming. Tropical cyclones, which bring in their wake huge devastation to life and property, is the area where people need to be educated beforehand, particularly at a time when global climate change has every likelihood to enhance their frequency and intensity with the passage of time.

Among the most consequential effects of global climate change is a probability of change in tropical cyclone activity. Hurricanes, severe cyclonic storms or typhoons are region-specific names of intense tropical storms of sustained winds of 74 miles per hour and greater. The recent past has witnessed unprecedented manifestations of cyclone occurrences. The period between June 1 and November 30, 2005, witnessed the most active and robust hurricane activity in the Atlantic Ocean in the recorded history. Seven hurricanes were formed in the Atlantic during this time, wrecking property of over $120 billion and claiming more than 2,000 lives.

Similarly, the 2007 cyclone season in the Indian Ocean happened to be very active and distinctive in the known history. Tropical cyclone Gonu and tropical storm Yemyin developed in the northern Indian Ocean in the space of just two week, during June 2007, a unique happening for the basin. Moreover, Gonu (a Category-5 cyclone in the Arabian Sea) and Sidr (a Category-4 cyclone in Bay of Bengal) were the unprecedented high-intensity cyclones formed in 2007 in the Indian Ocean. Scientists speculate that the increase in intensity, number and associated destructive potential of tropical cyclones is due to the rising ocean surface temperatures associated with global warming.

Tropical cyclones do not form till certain conditions are met. A sea surface temperature usually higher than 26 degrees Celsius, associated with high humidity and low wind shear, provides conducive circumstances for the formation of a tropical cyclone. Some recent scientific articles have reported 40 percent increase in tropical cyclone energy, numbers and wind-speeds in some regions during the last few decades. An increase in ocean temperature and water vapours contributes to more intense tropical cyclones.

The world's oceans have absorbed about 20 times as much heat as the atmosphere over the past half-century, leading to higher temperatures not only in surface waters (depth of less than 100 feet) but also down to substantial depths, with the most severe warming occurring in the first 1,500 feet below the surface. In addition, observations of atmospheric humidity over the oceans show that water vapour content has increased four percent since 1970. The Intergovernmental Panel on Climate Change (IPCC), in its Fourth Assessment Report, speaks of the evidences of increased cyclone activity since the 1970s.

In August 2005, a study by Emanuel was published in weekly scientific journal Nature claiming that the power dissipated by tropical cyclones in the Atlantic and Pacific Ocean has approximately doubled since the 1950s, with most of the increase occurring over the past three decades. Another article by PJ Webster, published in weekly journal Science in September 2005, revealed that the percentage of hurricanes of Category-4 or -5 intensities has increased over the same period in all six tropical storm basins: North-western Pacific Ocean, North-eastern Pacific Ocean, North-central Pacific Ocean, Northern Atlantic Ocean, Northern Indian Ocean and South-eastern Indian Ocean. The findings from both studies correlate with the rise in sea surface temperatures in regions where tropical cyclones typically originate.

A study by Knutson and Tuleya, published in Journal of Climate in September 2004, shows that a one percent annual increase of atmospheric Carbon dioxide concentrations over the next 80 years would produce more intense storms, and rainfall would increase at an average of 18 percent compared with the present day conditions. The World Meteorological Organisation projects a 3-5 percent increase in wind-speed per degree Celsius increase of tropical sea surface temperatures. Water vapour in the lower troposphere (0-3 kilometres) will increase about 6 percent for every 1 degree Celsius of warming.

Rising sea levels resulting from climate change also contribute to the damage caused by cyclones. The inflow of water from polar and glacial ice, melting due to increasing atmospheric temperature, raised global sea level at an average rate of 1.8 (1.3 to 2.3) millimetres per year from 1961 to 2003. The rate was even faster between 1993 and 2003: about 3.1 (2.4 to 3.8) millimetres per year, according to the IPCC Fourth Assessment Report published in 2007. A rising sea level means higher storm surges, even from relatively minor storms, which increases coastal flooding and subsequent storm damage along coasts. In addition, the associated heavy rains can extend hundreds of miles inland, further increasing the risk of flooding.

The increased cyclone activities around the globe pose serious threat to Pakistan also. It is a bi-modal phenomenon in the Indian Ocean: tropical cyclones occur in the months before and after the monsoon season. The 1,050 kilometre-long coastline of Pakistan along the Arabian Sea, with 800 kilometres of it belonging to Balochistan and the remaining 250 kilometres to Sindh, renders the areas highly vulnerable to destruction by cyclones.

Development of tropical cyclone Gonu and tropical storm Yemyin in the Indian Ocean in June 2007 was an unprecedented spectacle of cyclonic activity in such quick succession. The cyclone Gonu was the strongest tropical cyclone on record in the northern Indian Ocean. Fortunately, it did not make landfall on Pakistan's coast. However, cyclone Yemyin did made its landfall along the Makran coast and ravaged the southern parts of Balochistan.

According to government sources, 250,000 people were rendered homeless in Balochistan by the cyclone and the ensuing heavy rains and flash floods. On the whole, the disaster affected 2.5 million people in Balochistan and Sindh, destroying habitats, as well as social and physical infrastructure. The disaster has been deemed by the UN disaster prevention official, Salvano Briceno, as an "indication of what might happen more frequently and severely due to global warming."

Keeping in view the economic pulse of Karachi and Gwadar ports, the need to attend the adverse impacts of climate change and global warming on coastal areas of Pakistan is a must. Research efforts on cyclone activity in the Arabian Sea are sparse despite the critical economic significance of the area. As a matter of fact, a research-guided approach to mitigation and adaptation needs to be adopted to address the losses not only to the coastal communities of Pakistan, but also in the larger economic interest of the country.

(The author is Scientific information Officer at Global Change Impact Studies Centre, Islamabad.Email: asma.ras@gmail.com)
Source The News International on Sunday