Climate change a fact, and it’s our fault

Climate change is happening, it's almost entirely man's fault and limiting its impacts may require reducing greenhouse gas emissions to zero this century, the United Nation's panel on climate science said Sunday.

The fourth and final volume of the Intergovernmental Panel on Climate Change's giant climate assessment underlined the scope of the climate challenge in stark terms.

Emissions, mainly from the burning of fossil fuels, may need to drop to zero by the end of this century for the world to have a decent chance of keeping the temperature rise below a level that many consider dangerous.

Failure to do so, which could require deployment of technologies that suck greenhouse gases out of the atmosphere, could lock the world on a trajectory with an "irreversible" impact on people and the environment, the report said.

Some impact is already being observed, including on rising sea levels, a warmer and more acidic ocean, melting glaciers and Arctic sea ice and more frequent and intense heat waves.

"Science has spoken. There is no ambiguity in their message. Leaders must act. Time is not on our side," UN Secretary-General Ban Ki-moon said at the report's launch in Copenhagen.

Amid its grim projections, the report also offered hope. The tools needed to set the world on a low-emissions path are there; it just has to break its addiction to the oil, coal and gas that power the global energy system while polluting the atmosphere with heat-trapping CO2, the chief greenhouse gas.

"We have the means to limit climate change," IPCC Chairman Rajendra Pachauri said. "All we need is the will to change, which we trust will be motivated by knowledge and an understanding of the science of climate change."

The IPCC was set up in 1988 to assess global warming and its impacts. Yesterday's report caps its latest assessment, a mega-review of 30,000 climate change studies that establishes with 95 percent certainty that nearly all warming since the 1950s is man-made.

Today, only a small minority of scientists challenge the mainstream conclusion that climate change is linked to human activity.

World governments in 2009 set a goal of keeping the temperature rise below 2 degrees Celsius compared to before the industrial revolution. Temperatures have gone up about 0.8 degrees since the 19th century.

Meanwhile, emissions have risen so fast in recent years that the world has already used up two-thirds of its carbon budget, the maximum amount of CO2 that can be emitted to have a likely chance of avoiding 2 degrees of warming, the IPCC report said.

"This report makes it clear that if you are serious about the 2-degree goal, there is nowhere to hide," said Alden Meyer of the Union of Concerned Scientists.

Pointing to the solution, the IPCC said the costs associated with mitigation action such as shifting the energy system to solar and wind power and other renewable sources and improving energy efficiency would reduce economic growth by just 0.06 percent a year.

The report is meant as a scientific roadmap for the UN climate negotiations, which continue next month in Lima, Peru. That's the last major conference before a summit in Paris next year, where a global agreement on climate action is supposed to be adopted.

"Lima should be the place where we put the pieces together so we can move toward success" in Paris, said Peruvian Environment Minister Manuel Pulgar-Vidal.

The biggest hurdle is deciding who should do what, with rich countries calling China and other developing countries to take on ambitious targets, and developing countries saying the rich have a responsibility to lead the fight and to help poorer nations cope.