SINGAPORE - Human activities such as the burning of fossil fuels are warming the planet, causing societies to reel from impacts that will only worsen if actions to deal with the crisis are not immediately taken, the United Nations' top climate science body said in a major report released on Monday (Feb 28).

Rising temperatures, changing rainfall patterns and extreme weather events have cascading impacts on human society, said the Intergovernmental Panel on Climate Change (IPCC), pointing to food and water shortages, and the loss of lives, infrastructure and biodiversity.

"The extent and magnitude of climate change impacts are larger than estimated in previous assessments," said the IPCC.

"They are causing severe and widespread disruption in nature and in society - reducing our ability to grow nutritious food or provide enough clean drinking water, thus affecting people's health and well-being and damaging livelihoods."

The IPCC's message is clear: The impacts of climate change go beyond environmental indicators - they are affecting billions of people in many different ways.

As climate change impacts are expected to intensify with every additional degree of warming, things could get worse if action is not taken to mitigate climate change by cutting the amount of planet-warming emissions being released, as well as help vulnerable communities cope with impacts that are now unavoidable, such as sea-level rise.

The burning of fossil fuels and deforestation are key human activities driving global warming, as these processes release plenty of planet-warming emissions that get trapped in the atmosphere. The excess heat throws Earth's systems out of whack, driving climate change, symptoms of which include rising temperatures and sea levels, as well as more frequent extreme weather events.

In climate change discourse, there are two key prongs of climate action.

Mitigation refers to efforts to reduce emissions, such as initiatives to boost energy efficiency or switch to renewable energy sources, while adaptation strategies are geared at helping communities cope with impacts. This could include building sea walls to keep out the rising sea levels, or developing drainage infrastructure to prevent flooding from bouts of more intense rain.

But the latest IPCC report - which involved more than 200 authors from different countries, including Singapore - noted that progress on adaptation is uneven, pointing to increasing gaps between action taken and what is needed to deal with the increasing risks.

These gaps are largest among lower-income populations, it said.

IPCC chairman Hoesung Lee said the latest report - the second of three major ones that will collectively make up the IPCC's sixth assessment report (AR6) - is a dire warning about the consequences of inaction.

He said: "It shows that climate change is a grave and mounting threat to our well-being and a healthy planet. Our actions today will shape how people adapt and nature responds to increasing climate risks."

Climate change manifestations

The IPCC carries out assessment reports, or reviews of the latest research on climate science, every six or seven years on behalf of governments. The first assessment report was published in 1990, while the fifth one was published in 2014.

The assessment reports comprise updates from three working groups of the IPCC - Working Group 1 synthesises the latest on the basic science of climate change, Working Group 2 looks at how these impacts translate to impacts on societies, while Working Group 3 focuses on actions to reduce the amount of planet-warming greenhouse gases in the atmosphere.

The Working Group 1 report of the AR6 was released last August and focused on indicators of the problem, such as temperatures and rate of sea-level increase. That report had found, among other things, that climate change is widespread, rapid and intensifying with some impacts, such as sea-level rise, now irreversible over hundreds to thousands of years.

The latest Working Group 2 report highlights the implications of these indicators on societies.

"This report recognises the interdependence of climate, biodiversity and people and integrates natural, social and economic sciences more strongly than earlier IPCC assessments," said the IPCC's Dr Lee. "It emphasises the urgency of immediate and more ambitious action to address climate risks. Half-measures are no longer an option."

For example, it found that increasing heat and extreme weather are driving wildlife towards the poles, higher latitudes or deeper ocean waters.

This has repercussions on food security for many communities. For example, the IPCC noted that many Pacific island countries could see their maximum fish catch potential drop by at least 50 per cent by 2100 compared with the period from 1980 to 2000, even if the world makes drastic cuts in the amount of emissions released.

Changes in temperature, rainfall, and extreme weather have also increased the frequency and spread of diseases in wildlife, agriculture, and people.

In Asia, the IPCC Working Group 2 said that increased frequency of hazards such as heatwaves, floods or drought could increase vector-borne and water-borne diseases, undernutrition, mental disorders and allergic diseases. Higher temperatures could also drive higher infant mortality in the region, it said.

Water shortages, which already plague half the world's population at some point in a year, could become worse due to erratic rainfall patterns, or extreme events such as floods or droughts.

Such dry conditions could negatively affect agriculture and energy production from hydroelectric power plants, said the report.

Nature as a solution

Despite the dire outlook, the report said mankind can still reduce the magnitude of climate impacts on societies by harnessing nature.

Climate change interacts with other global trends, said the scientists, citing the unsustainable use of natural resources, growing urbanisation, social inequalities, losses and damage from extreme events and a pandemic.

IPCC Working Group 2 co-chairman Hans-Otto Portner said healthy ecosystems are more resilient to climate change and provide life-critical services such as food and clean water.

"By restoring degraded ecosystems and effectively and equitably conserving 30 to 50 per cent of Earth's land, freshwater and ocean habitats, society can benefit from nature's capacity to absorb and store carbon, and we can accelerate progress towards sustainable development," he said.

But there must be adequate finance and political support to achieve this, he added.

Well-planned cities can also reduce risks of urbanisation and climate change.

IPCC Working Group 2 co-chairman Debra Roberts said cities provide opportunities for climate action in the form of green buildings, reliable supplies of clean water and renewable energy, and sustainable transport systems that connect urban and rural areas.

She added: "Our assessment clearly shows that tackling all these different challenges involves everyone - governments, the private sector, civil society - working together to prioritise risk reduction, as well as equity and justice, in decision-making and investment."