Those wind turbines endlessly turning on the hill near your home tell of a changing world. So do the fields of solar panels sprouting from the deserts of California to the plains of Germany. But the world is not changing fast enough, says the latest report from the UN Intergovernmental Panel on Climate Change (IPCC).
The 2,000-page study of how to head off climate change, released in Berlin on Sunday, calls for a tripling of the share of global energy generated by low-carbon energy sources. Electricity generation will have to go from its current 30 percent use of low-carbon sources to 80 percent by 2050, the report says. And with today's main low-carbon sources - nuclear and hydropower - unlikely to grow much, that requires a vastly bigger plug-in to the newcomers, wind and solar.
Only that way, says the IPCC, can the world have a better-than-even chance of keeping below the two degrees of warming widely regarded as the danger level.
Crazy? Some believe an industrial world powered by sun and wind is an expensive green dream that is destined to fail. But maybe not. For one thing, the report says, prices of wind and solar energy are falling fast. So the damaging impact of such a transformation on the global economy would be very small - provided we get moving soon.
But for another, we have already gotten started. Only six days before the IPCC report, a little-noticed study emerged from the UN system. The UN Environment Programme revealed that almost half of all new generating capacity added to grids around the world last year was from renewable energy sources, overwhelmingly wind and solar. UNEP's latest annual assessment of investment in renewables found that global installed solar capacity jumped 26 percent during 2013.
The headline-grabbing new IPCC report, published after a final round of drafting involving governments as well as scientists, is the last of three major assessments by the panel of the state of climate change. The first, in September covered how we are influencing planetary climate processes. The second, in March, investigated likely impacts and how we can adapt. The third, issued on Sunday, concentrates on "mitigation" - how to stop it.
The report analyzes 1,200 possible technological, climatic and economic futures published by 31 different research groups. It finds that after two decades of dithering about how to deal with climate change, we are in dire straits. Carbon dioxide emissions from human activity continue to accelerate. They grew by an average of 2.2 percent a year during the first decade of the new century, faster than the 1.3 percent annual average of the previous three decades. Almost half of total anthropogenic emissions of CO2 since 1750 have taken place since 1970.
The reason for the surge is mostly economic growth. As recently as the 1990s, half of the emissions growth was attributable to rising human population. But between 2000 and 2010, notwithstanding the international economic crisis, rising per-capita GDP was almost twice as important. Another factor, the report says, is the growing share of energy provided by coal, the dirtiest of the mainstream fuels. It is now up to a 30 percent share, its highest level since 1969.
The main countervailing factor is the reduced energy intensity of economies. Improving energy efficiency and the declining role of manufacturing mean we need less energy to produce every dollar of GDP. But that is not enough. On current trends, the IPCC finds, emissions will continue to soar and global average temperatures will rise between 2.5 and 7.8 degrees Celsius before the century is out, depending on the pace of economic growth and the sensitivity of the climate system to CO2.
"We need to move away from business as usual," says the co-chair of the IPCC working group behind the mitigation report, Ottmar Edenhofer of the Potsdam Institute for Climate Impact Research.
There is some uncertainty, but the report says that to cap warming at two degrees may require keeping the concentration of CO2 in the atmosphere below 450 parts per million (ppm) in 2100. With levels up from pre-industrial 280 ppm to 400 ppm today, time is short. The big switch to low-carbon energy has to be largely completed by mid-century, the report says, with CO2 emissions brought to between 40 and 70 percent lower than 2010 levels by 2050, then keeping on a downward trend.
By 2050, the report says, virtually all burning of coal must end, unless the resulting CO2 emissions can be captured as they go up the stack and buried underground - a technology not yet developed at scale. The report gives natural gas, including shale gas, a partial exemption in the medium term as a substitute for coal, because it only emits half as much CO2. But eventually its emissions too must be captured, it says.