At 2 degree Celsius warming, Kolkata could see deadly heatwaves: IPCC report

India could witness deadly heatwaves if the planet's temperature goes up by two degrees Celsius, according to a report released on Monday by the UN's Intergovernmental Panel for Climate Change (IPCC).

Avoiding global climate chaos will require a major transformation of society and the world economy that is "unprecedented in scale", the IPCC said in the landmark report that warns time is running out to avert disaster.

"At +1.5 degrees Celsius, twice as many megacities as present such as Lagos in Nigeria and Shanghai in China are likely to become heat stressed, potentially exposing more than 350 million more people to deadly heat stress by 2050.

"At +2 degrees Celsius warming, Karachi (Pakistan) and Kolkata (India) could expect annual conditions equivalent to their deadly 2015 heatwaves (medium confidence)," the report said.

The report said regionally differentiated multi-sector risks are already apparent at 1.5 degrees Celsius warming, being more prevalent (where) vulnerable people live, predominantly in South Asia -- mostly Pakistan, India, and China, but these spread to sub-Saharan Africa, the Middle East and East Asia as temperature rises, with the world's poorest disproportionately impacted by 2?C.

The report said that although warming is projected to be the highest in the Northern Hemisphere under 1.5 degrees Celsius or 2 degrees Celsius of global warming, regions in the tropics and Southern Hemisphere subtropics that are projected to experience the largest impacts on economic growth.

Despite the uncertainties associated with climate change projections and econometrics, it is more likely than not that there will be large differences in economic growth under 1.5 degrees Celsius and 2 degrees Celsius of global warming for developing versus developed countries.

"Statistically significant reductions in Gross Domestic Product (GDP) per capita growth are projected across much of the African continent, southeast Asia, India, Brazil and Mexico," the report said.

Coastal flooding by the sea is likely to cost thousands on billions of USD annually, with damage costs under constant protection 0.3-5.0 per cent of global GDP in 2100, it said.

Risks are projected to be highest in south and south-east Asia, assuming there is no upgrade to present protection levels, for all temperatures of climate warming.

"Countries where at least 50 million people exposed to SLR (sea level rise)...Include China, Bangladesh, Egypt, India, Indonesia, Japan, Philippines, United States and Vietnam," it said.

The report said recent projections of the potential impacts of climate change on malaria globally and for Asia, Africa, and South America confirm that weather and climate are among the drivers of the geographic range, intensity of transmission, and seasonality of malaria, and that the relationships are not necessarily linear, resulting in complex patterns of changes in risk with additional warming.

"Projections suggest the burden of malaria could increase with climate change because of a greater geographic range of the anopheles vector, longer season, and increase in the number of people at risk, with larger burdens with greater amounts of warming, with regionally variable patterns."

Vector populations are projected to shift with climate change, with expansions and reductions depending on the degree of local warming, the ecology of the mosquito vector, and other factors, it said.

"Aedes (mosquito vector for dengue fever, chikungunya, yellow fever, and Zika virus) - projections of the geographic distribution of Aedes aegypti and Ae. Albopictus (principal vectors) or of the prevalence of dengue fever generally conclude there will be an increase in the number of mosquitos and a larger geographic range at 2 degrees Celsius than at 1.5 degrees Celsius and beyond than at present, and suggest more individuals at risk of dengue fever, with regional differences," the report stated.

Earth's surface has warmed one degree Celsius -- enough to lift oceans and unleash a crescendo of deadly storms, floods and droughts -- and is on track toward an unliveable 3C or 4C rise, the report said.

The IPCC report, however, shows that global warming impacts have come sooner and hit harder than predicted.

The IPCC report was timed to feed into the December UN climate summit in Katowice, Poland, where world leaders will be under pressure to ramp up national carbon-cutting pledges which -- even if fulfilled -- would yield a 3C world.