According to a new study the window of opportunity for humanity to cap global warming by slashing greenhouse gases is closing faster than previously thought.
Earlier estimates of the world’s “carbon budget”, the amount of heat-trapping carbon dioxide (CO2) we can still put into the atmosphere without warming Earth by more than two degrees Celsius have ranged from 590 billion to 2.4 trillion tonnes.
“We have figured out that this budget is at the low end of what studies indicated before,” said lead author Dr Joeri Rogelj, a climate scientist at the International Institute for Applied Systems Analysis in Austria.
“If we don’t start reducing our emissions immediately, we will blow it in a few decades.”
The goal of holding the rise in surface temperature to 2.0°C, widely seen at the time as the threshold for dangerous warming, was first agreed by the world’s nations in 2010.
With an increase so far of almost 1.0°C over pre-Industrial Revolution levels, the world has already seen climate-boosted droughts, floods and mega-storms.
As a result, the Paris Agreement, adopted by the United Nations sponsored climate summit in December last year, embraced a more ambitious target of “well below 2.0°C,” while pledging to strive for a 1.5°C cap if possible.
AFP reports CO2 emissions were about 40 billion tonnes in 2015, and are projected to continue climbing over the next decade, even taking into account the carbon-cutting pledges submitted by nearly 190 nations as part of the Paris Agreement.
If current emission rates were held steady, the 2.0°C carbon budget would be spent in about 15 to 30 years, according to the new calculations.
For a 1.5°C target, the carbon budget “would be exhausted in about one decade,” Dr Rogelj told AFP.
“It is beyond doubt that ambition thus needs to be increased radically from anything we have experienced to stabilise warming at either 1.5°C or 2.0°C, or even higher temperature levels,” he said by email.
Dr Rogelj and half-a-dozen colleagues sought to understand why previous estimates of the carbon budget vary so widely.
Part of the gap stems from different methods and scenarios that project trends into the future.
Carbon dioxide accounts for more than 80 per cent of global warming.
“Neglecting the warming from other greenhouse gases leads to larger carbon budgets,” Dr Rogelj explained.
“In our proposed carbon budget range, we take into account warming by all human emissions, and thus shave of the top-end of studies that looked at CO2 only.”