A recent scientific paper says the changing rainfall pattern in India is more due to natural variation in sunlight than human-induced climate change, but other scientists do not agree
Rainfall patterns in India are changing due to natural variation in the amount of sunlight received at the top of the earth’s atmosphere rather than climate change, says a scientist at the National Physical Laboratory (NPL) in Delhi.
As many as a third of the world’s people depend on the monsoons. During US President Barack Obama’s recent visit to India, it was decided that the two countries would collaborate on scientific research on Indian monsoon rainfall. The work is currently underway aboard the American research vessel JOIDES Resolution in the Bay of Bengal.
In a presentation on the variability of the Indian monsoons in the era of global warming at a session on climate change – the first ever – at the recent Indian Science Congress in Mumbai, Rajesh Agnihotri of the radio and atmospheric division of NPL stressed that such “natural variability” could impact rainfall either positively or negatively.
He and his co-authors of a 2011 paper have shown how between 1880, when rainfall measuring stations were first set up in India, and 2000, the “total solar irradiance” or TSI – the total amount of sunlight received at the top of the atmosphere, causing fluctuating temperatures – closely corresponds with rainfall variations each decade during the main summer monsoon months.
The authors write, “Though often overall impacts of these dry periods are also manmade (mismanagement of resources, wrong economic policies etc.), it is important to address the natural (e.g. external solar forcing) cause behind these abrupt climate anomalies.”
The scientists compiled records of drought over the past 300 years in the Indian subcontinent and compared them with TSI factors. The major droughts corresponded with episodes of high temperatures and records of famines where more than a million lives were lost and there were crop failures.
Agnihotri told indiaclimatedialogue.net, “The authors propose that the temporal changes in TSI influence sea surface temperatures and thereby the temperature gradient between land and sea in the Indian and Western Pacific oceans. This effect can reinforce or provide positive feedback to teleconnections (climate anomalies related to each other over thousands of kilometres) between the North Atlantic climate and those of Indian and East Asian monsoon regions.”
Most of the dry periods occurred within a decade when solar heat was at its highest. Out of 12 episodes when the records showed a high TSI, seven were accompanied by extreme drought events. In 1899, for example, when TSI rose and rainfall dipped, as many as 4.5 million died in a famine. The radical American writer and scholar Mike Davis dubbed this “a late Victorian holocaust”.
Closer to the present, Maharashtra suffered a crippling drought from 1970 to 1973 which, again, coincided with fluctuations in both parameters.
The converse has also been found true. In 2010, researchers M. Lockwood, S.K. Solanki, director of the Max Planck Institute for Solar System Research in Germany, and others found that cold winters in Europe were associated with low solar activity.
In his science congress presentation, Agnihotri cited how the south-west monsoon could be strengthened by stronger atmospheric circulation or increasing divergence between land and ocean temperatures, thereby raising the moisture content in the atmosphere.
It could be weakened by manmade causes, such as increased airborne particles or dispersion of moisture from major cloud-productive areas, resulting in abnormal rainfall events and irregular distribution of rain regionally.
However, he believes that “the recognition, quantification and incorporation of the natural variability component of monsoonal/climate change in climate models is very important because the natural rhythm of climate/monsoon variability may determine net climate forcing.” Thus, it might react either positively or negatively to manmade factors.
Recent variation in monsoon patterns
According to Agnihotri, there is a marked regional variation in monsoon patterns after 1990. In the earlier months from May to June, rainfall is increasing over the north-western Himalaya.
This has been recorded by rainfall measurement by the month in Mukteshwar, Uttarakhand by the India Meteorological Department and confirmed by data from the Global Precipitation Climatology Project in the UK which has worldwide records from 1901 to 2009.
The surest indication of this shift was the cloudburst in Uttarakhand in June 2013 which claimed 5,500 lives and caused major damage to homes and property.
During the later monsoon period from June to September, rainfall in the north-east was significantly lower than in the past, leading – once again – to weather stations in Meghalaya, once witnessing the highest rainfall in the world, recording declines.
Jharkhand, Chhattisgarh and Kerala also showed shortfalls, as did Marathwada in eastern Maharashtra, which has seen a spate of farmers’ suicides.
Agnihotri told the congress, “Marathwada needs more attention. The government needs to do something extraordinary.”
Other regions like Gangetic West Bengal, Jammu and Kashmir, Konkan and Goa witnessed heavier monsoons.
As a countrywide trend between 1961 and 2004, Agnihotri found rainfall per decade between May and June increasing, while it was below normal between July and August.
“Though there is no significant departure in monsoon at an all-India level attributable to an anthropogenic (manmade) cause, two observations are of concern: increase in number of extreme events and strengthening of early monsoon activity at the expense of that during June-September,” he said.
However, Roxy Mathew Koll of the Indian Institute of Tropical Meteorology in Pune told indiaclimatedialogue.net, “The use of all-India summer rainfall is not meaningful and can be misleading. It does not represent the rainfall mean, variability and trends across the country. Just like the rainfall, the effect of climate drivers – El Niño Summer Oscillation (ENSO), global warming, solar activity, etc. – also would be different for different regions of India.”
Agnihotri said, “Hypothetically, even if man stopped industrial activity, stopped using cars and stopped using air-conditioners, monsoon patterns would still change. Natural forces like solar intensity appear to be dominating monsoons to a greater extent than manmade climate change.”
IPCC does not agree
However, as the UK-based website Responding to Climate Change pointed out while reporting Agnihotri’s remarks, headlined “Climate sceptics gain platform at Indian Science Congress”, the UN Intergovernmental Panel on Climate Change (IPCC) 2013 science report stated that “all models and all scenarios project an increase in both the mean and extreme precipitation in the Indian summer monsoon.”
IPCC scientists acknowledged that the natural variability of the earth has some impact on the climate, but they estimated that this has caused 0.1 degree Celsius at most of the 0.6 to 0.7 degree Celsius warming observed between 1951 and 2010. It was “extremely likely” that manmade emissions have been responsible for more than half the impact.
Raghu Murtugudde of the University of Maryland at Madison told indiaclimatedialogue.net, “There was a correlation between sunspot cycles and the Indian monsoon and some mechanistic hypothesis has been proposed. But the percentage of explained variance does not permit the discarding of climate change effects.”
“If the monsoon is heavier in the earlier part of the season than later, it needs to be understood. Other groups are also looking at the shifts in monsoon onset. Disasters such as the Uttarakhand landslide were a combination of cloudbursts and unregulated and unsafe construction on slopes combined with deforestation and other human-induced land use change that exacerbate runoff and landslides.”
Murtugudde added, “It is dangerous to mix our personal views with scientific investigations. India and its neighbours are highly vulnerable to climate change impacts and these can quickly escalate into national security issues. We are better served and our country is better served by focusing on robust scientific investigations that are objective.”