Two degrees no longer seen as global warming guardrail
PARIS — Limiting global warming to 2C will not prevent destructive and deadly climate impacts, as once hoped, dozens of experts concluded in a score of scientific studies released on Monday.
A world that heats up by 2C — long regarded as the temperature ceiling for a climate-safe planet — could see mass displacement due to rising seas, a drop in per capita income, regional shortages of food and fresh water, and the loss of animal and plant species at an accelerated speed.
Poor and emerging countries of Asia, Africa and Latin America will get hit hardest, according to the studies in the British Royal Society’s Philosophical Transactions A.
“We are detecting large changes in climate impacts for a 2C world, and so should take steps to avoid this,” said lead editor Dann Mitchell, an assistant professor at the University of Bristol.
The 197-nation Paris climate treaty, inked in 2015, vows to halt warming at “well under” 2C compared to mid-19th century levels, and “pursue efforts” to cap the rise at 1.5C.
UN Secretary-General Antonio Guterres on Thursday said climate change was “the most systemic threat to humankind”.
With only one degree of warming so far, Earth has seen a crescendo of droughts, heat waves, and storms ramped up by rising seas.
Voluntary national pledges made under the Paris pact to cut CO2 emissions, if fulfilled, would yield a 3C world at best.
The treaty also requires that — by the end of the century — humanity stop adding more greenhouse gases to the atmosphere than oceans and forests can absorb, a threshold known as “net zero emissions”.
“How fast we get to a 2C world” is critical, Mitchell said.
“If it only takes a couple of decades, we will be in trouble because we won’t have time to adapt to the climate.”
Researchers led by Felix Pretis, an economist at the University of Oxford, predict that two degrees of global warming will see GDP per person drop, on average, 13 percent by 2100, once costly climate change impacts are factored in.
Under a 2C scenario, oceans rise about half a meter over the course of the 21st century, but well over a meter by 2300, another study found.
“When the planet warms, it takes the ocean hundreds, if not thousands, of years to fully respond,” lead author Rober Nicholls, a professor of coastal engineering at the University of Southampton, said.
That’s bad news for 500 million people living in “highly vulnerable” low-lying deltas, mainly in Asia, along with some 400 million people in coastal cities, many of which are already sinking due overconstruction or collapsing water tables.
Even in a 2C world, the number of people affected year by flooding could approach 200 million by 2300, the study calculated.