The momentum of global warming caused by the build-up of greenhouse gases is likely to overwhelm natural cooling processes within decades, according to research by the University of NSW.
Global temperatures have largely plateaued during the past 15 years as natural variability – including oceans absorbing more heat and volcanic activity – have acted to stall warming at the planet's surface.
However, such "hiatuses" are increasingly unlikely if carbon emissions continue on their present trajectory, and will be "a thing of the past" by the century's end, according to a paper published in Geophysical Research Letters.
"From about 2030, it's highly unlikely that we will get one of these cooling decades," said Nicola Maher, a UNSW PhD-candidate and lead author of the paper. "When it does cool, it will not be enough to overcome the warming."
The researchers used about 30 models to simulate different events, including volcanic eruptions of the size of Krakatau, the Indonesian island that erupted in 1883 with an explosion so loud it was heard almost 5000 kilometres away.
By 2100, assuming greenhouse emissions continue to build at the present rate, "even a big volcano like Krakatau is very unlikely to cause a hiatus", Ms Maher said.
While the oceans have absorbed much of the extra heat trapped over the past decade, the process can also go in reverse, quickening warming.
El Nino events, for instance, see the Pacific going from a heat sink to giving up warmth. The Bureau of Meteorology on Tuesday said the chance of an El Nino in 2014 remains above 50 per cent.
The threats posed by global warming were also raised by the World Bank on Wednesday.
Rachel Kyte, a vice-president of the bank and its special envoy for climate change, told a Canberra meeting the world is headed "down a dangerous path" with disruption of the food system possible as nations struggle to feed themselves.
Rising urban populations are contributing to soaring demand for meat, adding to nutrition shortages for the world's poor. Increased greenhouse gas emissions from livestock as well as land clearing will make farming more marginal in many regions, especially in developing nations, Professor Kyte said.
"The challenges from waste to warming, spurred on by a growing population with a rising middle-class hunger for meat, are leading us down a dangerous path," Professor Kyte said. "Unless we chart a new course, we will find ourselves staring volatility and disruption in the food system in the face, not in 2050, not in 2040, but potentially within the next decade."
Agriculture and land-use change currently account for about 30 per cent of greenhouse gas emissions. Feed quality can be so low in arid parts of Africa, where livestock typically graze on marginal land and crop residues, that every kilo of protein produced can contribute the equivalent of 1 tonne of carbon dioxide – or 100 times more than in developed nations, Professor Kyte said.
A two-degree warmer world – which may occur by the 2030s on current emissions trajectories – could cut cereal yields by one-fifth globally and by one-half in Africa, she said.
