China, the world’s top source of the toxic gases blamed for global warming, said Thursday it was “not very optimistic” that its efforts to slash emissions were working.

Beijing issued a similar warning a month ago, prompting speculation that it could miss its emissions reduction targets.

The country’s vice minister for environmental protection, Zhang Lijun, told a press conference that sulphur dioxide emissions had risen by 1.2 percent year-on-year in the first quarter of 2010 – the first jump since 2007.

“This sounded the alarm for our emissions reduction work and showed that the prospects of emissions cuts are not very optimistic,” Zhang said.

He said a severe drought in southwestern China, increases in the output of high-emissions industries and the “slack mentality” of local governments and firms were complicating China’s efforts to slash emissions.

Beijing has pledged to reduce its carbon intensity – the measure of greenhouse-gas emissions per unit of gross domestic product – by 40 to 45 percent by 2020 based on 2005 levels.

Last month, Premier Wen Jiabao laid out a series of measures to help tackle the situation, including punishing local authorities that did not achieve their targets.

“Areas that achieve their energy-saving targets must be rewarded, those that haven’t must make their main leaders and relevant leaders accountable, and they will be punished accordingly, and might even be dismissed,” he said.

The government has already said it will spend 83 billion yuan (12 billion dollars) on promoting emissions cuts in 2010.