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 Nations (UN) panel on climate science said yesterday.
The fourth and final volume of the Intergovernmental Panel on Climate Change's (IPCC) giant climate assessment offered no surprises, nor was it expected to, since it combined the findings of three reports released in the past 13 months.
But it 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.
The IPCC didn't say exactly what such a world would look like, but it would likely require a massive shift to renewable sources to power homes, cars and industries combined with new technologies to suck greenhouse gases from the atmosphere.
The report warned that failure to reduce emissions could lock the world on a trajectory with "irreversible" impacts on people and the environment. Some impacts already being observed included 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 said the tools are there to set the world on a low-emissions path and break the addiction to burning oil, coal and gas which pollute the atmosphere with heat-trapping CO2, the chief greenhouse gas.
"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," IPCC Chairman Rajendra Pachauri said.
The IPCC was set up in 1988 to assess global warming and its impacts. The report released yesterday caps its latest assessment, a mega-review of 30,000 climate change studies that establishes with 95 per cent certainty that most of the warming seen since the 1950s is man-made. The IPCC's best estimate is that just about all of it is man-made, but it can't say that with the same degree of certainty.
HUMANS TO BLAME
Today, only a small minority of scientists challenge the mainstream conclusion that climate change is linked to human activity.
Global Climate Change, a NASA website, says 97 per cent of climate scientists agree that warming trends over the past century are very likely due to human activities.
The American public isn't as convinced. A year-old survey by Pew Research showed 67 per cent of Americans believed global warming is occurring and 44 per cent said the earth is warming mostly because of human activity. More recently, a New York Times poll said 42 per cent of Republicans say global warming won't have a serious impact, a view held by 12 per cent of Democrats and 22 per cent of independents.
Sleep-deprived delegates approved the final documents Saturday after a weeklong line-by-line review that underscored that the IPCC process is not just about science. The reports must be approved both by scientists and governments, which means political issues from UN climate negotiations, which are nearing a 2015 deadline for a global agreement, inevitably affect the outcome.
The rift between developed and developing countries in the UN talks opened up in Copenhagen over a passage on what levels of warming could be considered dangerous. After a protracted battle, the text was dropped from a key summary for policymakers - to the disappointment of some scientists.
"If the governments are going to expect the IPCC to do their job," said Princeton professor Michael Oppenheimer, a lead author of the IPCC's second report, they shouldn't "get caught up in fights that have nothing to do with the IPCC".
The omission meant the word 'dangerous' disappeared from the summary altogether. It appeared only twice in a longer underlying report compared to seven times in a draft produced before the Copenhagen session. The less loaded word 'risk' was mentioned 65 times in the final 40-page summary.
"Rising rates and magnitudes of warming and other changes in the climate system, accompanied by ocean acidification, increase the risk of severe, pervasive, and in some cases irreversible detrimental impacts," the report said.