McKibben's friend and colleague, James Hansen, believes just as emphatically that climate change can't be defeated without greatly expanding nuclear power. In his book, Storms of My Grandchildren, NASA's chief climatologist wrote, "for the foreseeable future, renewable energies will not be a sufficient source of electric power."
The Intergovernmental Panel on Climate Change (IPCC), the preeminent international scientific body on climate change, is more sanguine about renewable energy. In its authoritative Special Report on Renewable Energy Source and Climate Change Mitigation, IPCC scientists concluded in 2011 that, "close to 80 percent of the world's energy supply could be met by renewables," by 2050, while cutting greenhouse gas emissions by a third.
Dr. Susanne Kadner, a researcher at the Potsdam Institute for Climate Impact Research, was a key author of the IPCC report. In April, I met Kadner at Café Einstein, a coffee house favored by Berlin's cultural and political elite. Located on Berlin's grand Unter den Linden Boulevard, halfway between the Brandenburg Gate and Humboldt University (where Albert Einstein and 28 other Nobel Prize recipients taught) the café is a place to see and be seen. The real joy of the place for her, Kadner said cheerily as we settled into our table in the large and bright back room, is that "you can read your newspaper and have coffee and stay for hours and hours."
In fact, we talked for a good hour and a half, with only hot drinks and a single croissant (mine), without waiters hovering and pointedly looking at their watches.
Although the IPCC's renewables report broke ground in several areas, Kadner seemed especially proud of one achievement—a comprehensive "lifecycle analysis" establishing how much CO2 each energy source produces from manufacturing to disposal. Using the largest data set ever compiled, researchers determined that, compared to fossil fuels, renewables sources such as wind and solar power released 10 to 100 times less CO2 per unit of energy.
In practical terms, Kadner said, "What we found was that if you want to mitigate climate change, first, renewable energies can play a role. And second, they have to play a role."
Kadner and her colleagues calculated that of the 300 gigawatts of new electrical generating capacity built throughout the world between 2008 and 2009, 140 gigawatts—nearly half the total—came from renewables. (An average size nuclear reactor produces one gigawatt of electricity)
Even the Energiewende's most ardent supporters admit that, for all its progress, it must still clear some rather tall hurdles. In the short run, Baake said, Germany needs to build more peaking plants—natural gas turbines that ramp up and down quickly to smooth out the intermittent power of renewables. The electrical grid also needs to be expanded (an expensive proposition) and connected to a wider European system (an expensive and politically challenging proposition). In the long term, viable ways must be found to store surplus wind and solar energy.
Baake is confident that, in time, each of these obstacles will be surmounted. After rattling off that daunting list of challenges, he said something that reminded me of my conversation with Hans-Josef Fell, the member of parliament who created the framework for the Energiewende. When I asked Fell about the storage problem, he responded immediately, "It is not a problem. It is a task."
Now it was Baake's turn to demonstrate the pragmatic optimism that powers the Energiewende.
"The tasks ahead are solvable," he said. "Now we have to tackle them."
Funding for Clean Break was provided by the Heinrich Böll Foundation, through a Climate Media Fellowship, and by the Rockefeller Brothers Fund.