Two ends to Climate Change debate; Experts vary on impact on rain, cyclones

The topic has always been contentious, with radical movements like Extinction Rebellion at one end, and leaders like Donald Trump and Brazil's Bolsonaro, who say climate change theory is a hoax at the

Barely a fortnight after Cyclone Amphan struck the eastern and Cyclone Nisarga the western coast of India, a study by London-based Global Warming Policy Foundation (GWPF) on impact of climate change has downplayed the impact of climate change over a 100-year period saying that overall rains, drought and cyclones have not seen much deviations. Experts on climate science and climate change, however, do not agree with this approach and say evening out trends for large heterogeneous geographical area like India will not give a correct picture.

“The scientific evidence simply does not support the idea of any link between drought and climate change. The IPCC (the Intergovernment Panel on Climate Change) was right to express low confidence in any global-scale observed trend,” GWPF said in a study, Weather Extremes: Are They Caused by Global Warming, authored by Ralph B Alexander.

Impact of climate change on global environment has been one of the biggest debates with extreme political and activist positions being taken. While there has been birth of radical movements like Extinction Rebellion, at the other end there are political leaders, like United States President Donald Trump and Brazilian President Jair Bolsonaro, who have labelled climate change theory a hoax. This, even as the Amazon forest in Brazil and forests in Australia burnt past one year to World Environment Day on Friday.

The GWPF study cited two different drought indices during the period 1910–2010 for India, a country subject to parching summer heat followed by drenching monsoonal rains. The two indices—Palmer Drought Severity Index (PDSI) which represents both rainfall and temperature, and the Standardized Precipitation Index (SPI) that relies on rainfall data only.

Negative values in the indices denote drought and positive values wetness. “While both indices are useful, the SPI is better suited to making comparisons between different regions. We see the SPI in India shows no particular trend towards either dryness or wetness over the 100-year period, although there are 20-year intervals exhibiting one of the two conditions; show negative values that denote drought and positive values wetness,” said the study.

The apparent trend of the PDSI towards drought since 1990 is an artefact of the index. “Similar records for other countries around the globe all show the same pattern – no drying of the planet as a whole over more than 100 years,” it asserted.

Jagdish Krishnaswamy, senior fellow, Suri Sehgal Centre for Biodiversity and Conservation, at Ashoka Trust for Research in Ecology and the Environment (ATREE), however, said this approach was not correct for a large country like India especially since the monsoon was a complex phenomenon with South West Monsoon, North East Monsoon and Cyclones affecting rainfall in the country. “The Indian Monsoon is highly variable but has shown a small to moderate decline in annual rainfall since the 1950s even though frequency of more intense rains have increased in some regions. Central India, for instance, has lot of hot spots where intense rain has been witnessed,” he added. 

Krishnaswamy cites the examples of intense rains of Chennai in 2015 and of Mumbai in 2005. If the overall volume of rains remains the same but there are days of intense rains, then that means there are days of no rains or meteorological drought, he argued.  

On tropical cyclones, the GWPF report quotes both the 2012 and 2013 studies of IPCC that expressed only ‘low’ confidence that cyclone activity was increasing over the long term, and that global changes in cyclone activity could be attributed to any particular cause. This assertion was repeated again in the 2019 Special Report on the Global Ocean and Cryosphere, in which the IPCC said, “The lack of confident climate change detection for most tropical cyclone metrics continues to limit confidence in both future projections and in the attribution of past changes and tropical cyclone events.”

The GWPF report also said the frequency of tropical cyclones overall is diminishing. “However, though the number of major hurricanes (cyclone) of Category 2, 3, 4 or 5 strength seems to show a slight increase over the period (100 years), the trend has been ascribed to improvements in observational capabilities, rather than warming oceans that provide the fuel for cyclones.” In fact, it said the frequency of landfalling hurricanes of any categories 1-5 has not changed in the nearly 50 years since 1970 – during a time when the globe warmed by approximately 0.6°C (1.1°F). So the strongest hurricanes today are no more extreme or devastating than those in the past. “If anything, major landfalling hurricanes in the US are tied to La Niña cycles in the Pacific Ocean, not to global warming.”