Experts vary on whether cyclones, rain are signs of climate change
Barely a fortnight after Cyclone Amphan struck the eastern coast and Cyclone Nisarga the western coast of India, a study by the London-based Global Warming Policy Foundation (GWPF) has downplayed the impact of climate change over a 100 -year period, saying that overall rain, drought, and cyclones have not seen much deviation.
Experts on climate science and climate change, however, do not agree with this approach and say evening out trends for large heterogeneous geographical areas 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,” the GWPF said in a study called Weather Extremes: Are They Caused by Global Warming, authored by Ralph B Alexander.
The impact of climate change on the global environment has been one of the biggest debates with extreme political and activist positions being taken. While there has been the 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 forests in Brazil and forests in Australia burnt for the 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 monsoon rain. The two indices — the Palmer Drought Severity Index (PDSI), which represents both rainfall and temperature, and the Standardized Precipitation Index (SPI), which 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, 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 rain 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 rain in Chennai in 2015 and Mumbai in 2005. If the overall volume of rain remains the same but there are days of intense rain, 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 the 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 was diminishing.