US-China pact to curb emissions not enough, CSIRO scientist Pep Canadell says China and the US will have to do more to curb emissions, CSIRO's Dr Canadell says. The US-China pact to curb greenhouse gas emissions is "unprecedented" but won't be enough to prevent dangerous climate change, said Pep Canadell, the head of CSIRO's Global Carbon Project. The world's carbon budget is about 300 billion tonnes of carbon by 2100 if it is to have a two-in-three chance of limiting the temperature increase to less than the internationally agreed 2-degree level, Dr Canadell said. "At the current rate of emissions - of about 10 billion tonnes of carbon a year - we have less than 30 years to fully decarbonise," he said. Each tonne equates to about 3.66 tonnes of carbon dioxide, the major greenhouse gas blamed for global warming. Instead of rising at the current rate of 2-3 per cent, carbon emissions will need to peak globally by about 2020 and then start falling about 3 per cent annually for decades, Dr Canadell said. China and the US are the world's two biggest emitters, contributing about 42 per cent of the global total in 2013. Dr Canadell comments follow Wednesday's climate accord agreed in Beijing between the US and China that would commit the US to reducing greenhouse-gas emissions by 26-28 per cent below 2005 levels by 2025. The reduction amounts to about a doubling of the annual pace of 1.2 per cent of US cuts planned for 2005-2020. China's pledge is less clear, offering only to cap total emissions before 2030 while also increasing the share of renewable energy to 20 per cent. "Both commitments don't seem to be too consistent with the goal to remain under a 2-degree increase," Dr Canadell said. The Sino-US agreement, while "extraordinary and unprecedented," can only serve as a starting point of negotiations ahead of the 2015 UN climate summit in Paris, he said. "Stronger and bigger pledges will have to come over the next two years," said Dr Canadell. We'd expect the two super powers to do more. Environment Minister Greg Hunt defended Australia's target - to cut emissions by 5 per cent from 2000 levels by 2020 - as "almost exactly the same" as US actions over the 30-year period to 2020. "If you look at the current US base from 2005 to 2020, the US is minus-17 [per cent] and if you use the same base for Australia, we'd be minus-12 per cent, so actually we're in the same ballpark," Mr Hunt told reporters in Sydney. Australia contributes about 1.5 per cent of global emissions, and the Abbott government will make "an appropriate, relevant, and proportionate response" to other nations' post-2020 positions in the first half of 2015, Foreign Minister Julie Bishop said at the same media event. The International Energy Agency, a body representing 29 rich nations, on Wednesday said current efforts to cut carbon emissions were insufficient to prevent a 2-degree increase on pre-industrial age levels. On the current trajectory, carbon emissions will rise 20 per cent on 2012 levels by 2040, exhausting the carbon budget need to keep within the 2-degree warming target. Temperatures would climb by 3.6 degrees by 2100 or even 4 degrees if melting permafrost and other feedback mechanisms were triggered. "With 4 degrees warming, severe and widespread changes are expected in human and natural systems, including substantial species extinction and large risks to global and regional food security," the IEA said in its World Energy Outlook 2014 report.