An increase in heat waves is almost certain, while heavier rainfall, more floods, stronger cyclones, landslides and more intense droughts are likely across the globe this century as the Earth’s climate warms, UN scientists say.
In a report released in Uganda last week, the UN Intergovernmental Panel on Climate Change (IPCC) urged countries to make disaster management plans to adapt to the growing risk of extreme weather linked to human-induced climate change.
The report gives differing probabilities for weather events based on future greenhouse gas emissions scenarios, but the thrust is that extreme weather is likely to increase and that the likely cause is humans.
The IPCC defines “likely” as a 66-100 per cent probability, while “virtually certain” is 99-100 per cent.
“It is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes … will occur in the 21st century on the global scale,” the IPCC report said.
A 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the 21st century in most regions.
“It is very likely that the length, frequency and/or intensity of … heat waves will increase,” it added.
“A 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the 21st century in most regions,” under one emissions scenario.
An exception is in very high latitudes, it said. Heat waves would likely get hotter by 1-3 degrees Celsius by mid-21st century and by 2-5 degrees by late-21st century, depending on region and emissions scenario, it said.
Delegates from nearly 200 countries will meet in South Africa from November 28 for climate talks with the most likely outcome being modest steps towards a broader deal to cut greenhouse gas emissions to fight climate change.
The IPCC report found human emissions have “likely” caused more extreme heat waves and sea surges, but is less sure about the link between man-made climate change and worse floods.
“There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases,” it said.
CARBON EMISSIONS UP
The risks posed by increasingly erratic weather have been highlighted by a spate of disasters in recent years, such as flooding in Thailand and Australia, droughts in east Africa and Russia and hurricanes in the Caribbean.
The United Nations, the International Energy Agency and others say global pledges to curb emissions of CO2 and other greenhouse gases are not enough to prevent the planet heating up beyond 2 degrees Celsius, a threshold scientists say risks an unstable climate in which weather extremes are common.
Global carbon emissions rose by a record amount last year, rebounding on the heels of recession.
The report did not address this, but recommended that action is taken now to shore up the defences of vulnerable states, including early warning systems, better land use planning, restoring ecosystems that act as buffers, enforcing building codes and weather-proofing infrastructure.
“The clear message from this report is that there are a lot of smart things we can do now that reduce the risk of losses in disasters,” co-author Chris Fields said.
“It is likely the frequency of heavy precipitation … will increase in the 21st century over many areas,” the report said, especially in “high latitudes and tropical regions”.
There was “medium confidence” this would lead to “increases in local flooding in some regions”, but this could not be determined for river floods, whose causes are complicated.
Tropical cyclones were likely to become less frequent or stay stable, but those that do form are likely to get nastier.
That, coupled with rising sea levels were a concern for small island states, the report said.
DROUGHTS AND DOUBTS
Droughts, perhaps the biggest worry for a world with a surging population to feed, were also expected to worsen.
The global population reached 7 billion last month and is expected to reach 9 billion by 2050, according to UN figures.
“There is medium confidence that droughts will intensify in the 21st century … due to reduced precipitation and/or increased evapotranspiration,” in “the Mediterranean … central Europe, central North America, Central America and Mexico, north-east Brazil and southern Africa,” the report said.
There was a high chance that landslides would be triggered by shrinking glaciers and permafrost linked to climate change.
“Today’s IPCC report brings home the inescapable fact: that climate change is … causing an escalation in impacts … most of which are increasingly being borne by the developing world,” Greenpeace climate policy coordinator Maria Ryding said.
Sceptics have questioned the models the IPCC uses to make its climate predictions, but Fields defended the science: “There are many cases in which just from observations, we’ve seen a change,” he said.
“Climate models are only some of the tools used to make future projections. Some … are based on projecting historical data forward or what we know about the physics of the system. Lots of observations are built-in for us to test how they work.”