A new report from the Intergovernmental Panel on Climate Change (IPCC), released in Japan today, says that climate change is threatening food and water security, human health, livelihoods and economies.

The IPCC ---- an international body of scientists tasked with assessing how heat-trapping greenhouse gases are changing the planet ---- has reaffirmed that climate change is intensifying heat waves, floods and droughts, melting glaciers and raising sea levels.

However, the report has also examined in greater detail than ever before how the impacts can be reduced through adaptation and mitigation.

Calcutta, Mumbai, Dhaka, Guangzhou and Ho Chi Minh City are among Asian cities that will by 2070 have the largest populations vulnerable to climate change-induced coastal flooding, the report says.

India’s eastern coast has clusters of districts with poor infrastructure and demographic development that are, the report cautions, also the regions of maximum vulnerability where extreme events such as cyclones could have catastrophic effects.

The report is intended to accelerate international efforts to curb greenhouse gas emissions to limit global warming to no more than 2 degrees Celsius, a target that more than 190 countries have embraced through UN-mediated negotiations.

“If the world fails to achieve the target, it’s because it didn’t make the right choices in time,” said Aromar Revi, director of the Indian Institute of Human Settlements and a coordinating lead author of the report. “Not because we didn’t know what to do.”

According to the IPCC, climate change has already affected agriculture, human health, water supplies and ecosystems.

“Societies and ecosystems around the world are vulnerable, but with different vulnerability in different places,” Chris Field, a senior scientist at the Stanford Woods Institute for the Environment in the US, who chaired the IPCC working group that produced today’s report, said in a media release from the IPCC.

Several scientific studies reviewed by the IPCC show that climate change is likely to cause a reduction in the yields of rice, wheat and maize ---- the world’s staple crops ---- in most tropical and temperate regions although the yield may actually rise in some locations.

The combination of floods, droughts and weather changes --- including a higher frequency of extreme weather events --- could decrease productivity and hurt economic growth, said Surendra Kumar, professor of business economics at the University of Delhi South Campus and the lead author of the report.

“But there have been limited studies: the magnitude of the impact on economy needs to be better understood,” Kumar said.

Citing a 2010 study, the report says that beach tourism would be hit the hardest in India and the least in Cyprus. The poor condition of India’s existing coastal infrastructure could contribute to this vulnerability, Kumar said.

Climate experts not associated with the IPCC report said the document reflects both the exponential growth in climate science research over the past five years and the urgent need to accelerate global action to curb greenhouse gas emissions.

“What we do now will determine the risks associated with climate change through the 21st century,” Kelly Levin, a climate science and policy analyst with the World Resources Institute in Washington DC, told The Telegraph.

Climate scientists believe that the world’s greenhouse gas emissions should peak by about 2020 and then decrease for the average rise in global temperature to remain below 2 degrees Celsius.

Among the observed impacts of climate change, the IPCC report has cited heat waves, changing rain patterns, altered abundance of plants, movements of animals, shifts in the distribution of fish species, and new patterns of diseases such as malaria.

Revi said a key component of the efforts to reduce the vulnerability of populations would be to abandon maladaptive practices.

“Construction along floodplains, extensive deforestation, and farmers’ indebtedness are all examples of maladaptive processes,” he said.

“Yet there are also examples of adaptation already being practised here and there. Some farmers are trying to shift from traditional cereals (such as rice and wheat) to millet and fishermen are adapting to new catch as distribution of fish changes.”