Countries with the lowest historical emissions experienced three to four times higher than seasonal temperatures this June-August days than G20 countries, according to an analysis conducted by an independent US-based group of scientists using a metric called the Climate Shift Index (CSI).

The three-month June-August 2023 season was the warmest on record globally and the analysis by Climate Central indicates that human-caused climate change made the unprecedented heat far more likely across the globe.

CSI measures how often and how much temperatures have shifted from the historical average. A higher index indicates more dramatic changes compared to the past.

The CSI levels above 1 indicate climate change, while levels between 2 and 5 mean that climate change made those temperatures between two to five times more likely.

During the June-August period, nearly half (48 per cent) of the world's population experienced at least 30 days with a CSI level 3 or higher, Climate Central said in a report released on Thursday.

"On each day in June-August, between 1.5 and 4.2 billion people felt a very strong influence of climate change (CSI level 3 or higher). Heat at CSI level 3 or higher persisted for at least half the June-August period in 79 countries throughout Central America, the Caribbean, the Arabian Peninsula, and parts of Africa," it said.

The scientists found countries with the lowest historical emissions experienced three to four times more June-August days with CSI level 3 or higher than G20 countries (the world's largest economies).

At least half of all June-August days were a CSI level 3 or higher in 11 Indian states and Union territories: Kerala, Puducherry, Andaman and Nicobar, Meghalaya, Goa, Karnataka, Mizoram, Manipur, Tripura, Nagaland and Tamil Nadu.

Kerala, Puducherry, Andaman and Nicobar experienced more than 60 days at CSI level 3 or higher.

"Virtually no one on Earth escaped the influence of global warming during the past three months," Andrew Pershing, Climate Central's vice president for science, said.

"In every country we could analyse, including the southern hemisphere where this is the coolest time of year, we saw temperatures that would be difficult - and in some cases nearly impossible - without human-caused climate change. Carbon pollution is clearly responsible for this season's record-setting heat," he said.

According to the European Union-funded Copernicus Climate Change Service (C3S), earth just had its hottest three months (June-August) on record. It was the hottest August on record - by a large margin - and the second hottest ever month after July 2023.

The year so far (January to August) is the second warmest on record behind 2016, when there was a powerful warming El Nino event.

Climate Central researchers had earlier found that a three-day extreme heat event over Uttar Pradesh from June 14-16 was made at least two times more likely by human-caused climate change.

According to them, extreme temperatures coupled with high humidity contributed to the severity of the event.

Earth's global surface temperature has risen by around 1.15 degrees Celsius. The CO2 spewed mostly by the developed countries into the atmosphere since the start of the industrial revolution is closely tied to it.

In the business-as-usual scenario, the world is heading for a temperature rise of around 3 degrees Celsius by the end of the century.

Climate science says the world must halve emissions by 2030 from the 2009 levels to limit global average temperature rise to 1.5 degrees Celsius as compared to the pre-industrial levels to avoid extreme, destructive and likely irreversible effects of climate change.

Developing countries argue that wealthier nations should take greater responsibility for emission reductions, given their massive historical emissions, and provide the necessary means of implementation, including finance and technology, to assist developing and vulnerable nations in transitioning to clean energy and adapting to climate change.

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